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Model Forum / General / Models / September 2008motor starting and reversing.
I bet this appears twice now. it seems to be in limbo, so reposting... got cheap on ebay a box with forward reverse stop buttons, but that's all it is, the box and contactors under the buttons. The start buttons have push-to-make switches and the stop one has push-to-break. So... can I make it drive the single-phase motor on the lathe, forward and reverse, and if so what else does it need. I already have stop-start-overload switch thing, but that only goes one way. It's also not no-volt release, which is not ideal. currently, reversing is done with a pair of SPDT switches, which is far from ideal, especially as they're only just big enough current rating.  SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > I bet this appears twice now. it seems to be in limbo, so reposting... > [quoted text clipped - 9 lines] > currently, reversing is done with a pair of SPDT switches, which is far from > ideal, especially as they're only just big enough current rating. Dis you see my reply Austin? Bob >> I bet this appears twice now. it seems to be in limbo, so reposting... >> [quoted text clipped - 12 lines] > >Bob nope. whole thread seems to be AWOL. unless it was by email, in which case, you need to fix the address, or it goes into a rarely-checked spambin. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >>> I bet this appears twice now. it seems to be in limbo, so reposting... >>> [quoted text clipped - 15 lines] > nope. whole thread seems to be AWOL. unless it was by email, in which > case, you need to fix the address, or it goes into a rarely-checked spambin. I replied usenet thus: "Use your existing stop start overload as the NVR and starter and wire the new box as a latching forward/reverse switch. Bob " >>>> I bet this appears twice now. it seems to be in limbo, so reposting... >>>> [quoted text clipped - 20 lines] >the new box as a latching forward/reverse switch. >Bob " ah, right. Hmmm. the swtiches in the new box are not latching though. They're just push-to-make. I get the impression it's intended to control something else. Also, the current switch is not NVR (although that too was cheap), and I'd prefer it if it was. I may have to hunt a proper one... SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >>I replied usenet thus: >> [quoted text clipped - 11 lines] > >I may have to hunt a proper one... Get thee to your nearest electrical wholesaler, plumbing shop or larger DIY shed and get a DPST or DPDT relay with base, if needed. Use the start button to energise the coil. One pair of NO contacts to also energise the coil, giving the latching function and the stop switch in series with those contacts. The other contacts are now latching on, no-volt release. Total cost about £5-£8. Use a contactor with auxiliary contacts if the current demands it. Mark Rand RTFM >>>>> I bet this appears twice now. it seems to be in limbo, so reposting... >>>>> [quoted text clipped - 29 lines] > > I may have to hunt a proper one... Hi Austin, Sorry I had made too many assumptions 1 that your existing switch was NVR 2 that the new box had some contactors in behind the buttons Mark is pointing you in the right direction for the NVR bit but you will need a second relay wired to latch the reversing AND most importantly, to lockout any change of direction when the motor is running. Single phase motors MUST be configured as forward or reverse before starting them. Once started, trying to change direction will have no effect. You might want to consider two start buttons, one for each direction and a common stop button. Just make sure you can't operate both start buttons at the same time. HTH Bob >Sorry I had made too many assumptions >1 that your existing switch was NVR [quoted text clipped - 12 lines] > >Bob It might be that I'm not being as precise as I could, either. The new box has 3 buttons, 2 green and a red in the middle, and it's designed to be a controller for forward-stop-reverse. Each button has a non-latching switch beneath it. The 2 greens have NO (push-to-make) and the red in the middle has NC (push-to-break). If I follow Mark's post right, I can use a DPST relay, with 1 pair of contacts supplying the motor and self-feeding the coil through the stop button, while the other terminals switch the motor neutral. Energise the coil using start button 1, once energised it will stay energised until the stop is hit, breaking the coil circuit and motor circuit both. Lack of supply volts will also release the relay which won't re-energise by itself until power is supplied by the start button. All that's good for one direction. The same circuit wired differently would make the motor go the opposite way - so either 2 DPST relays or one DPDT provided it has 2 coils, and an "off" state with nothing connected by default. The motor could be run from a single giant DPDT switch, provided it was on-off-on, but this would lack overload and NVR. Hmmm. The existing switch can do the overload bit, and has no NVR. Might feed the relays alluded to above from that. Does that sound right? nothing so far prevents pressing the "start reverse" button while the motor's running forward. Unless a DPDT relay can only have 1 coil energised at a time? SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >It might be that I'm not being as precise as I could, either. [snip stuff] this is more or less what I have: http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3 308521 although naturally at a fraction of the price. Is what I'm looking for called a "contactor"? I see plenty of such things, although I've yet to find a DPDT. However, I can, AFAICT, do the job with 2 single-way ones. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >> It might be that I'm not being as precise as I could, either. > [quoted text clipped - 9 lines] > although I've yet to find a DPDT. However, I can, AFAICT, do the job with 2 > single-way ones. Unless the motor is a big bugger then relays ought to do the job and these are readily available as change over types. You will need two poles to do the main switching and at least one extra pole on each to do the 'logic' of the latching and interlock. Bob >>> It might be that I'm not being as precise as I could, either. >> [quoted text clipped - 15 lines] > >Bob In addition to that, if you wire an NC contact pair of the forward relay in series with the coil of the reverse relay and vice-versa, then you will avoid the possibility of both being on at once, with resultant loss of magic smoke. With a bit of thought and a lot of sketching, it should be possible to do this with the double pole(or auxiliary pole on contactors) relays, without needing the rarity of triple pole devices. Contactors are basically relays with more robust contacts, usually with a bar that joins two separate contacts. a bit better for breaking higher currents, but not necessarily needed for manually operated switching of a domestic lathe. Mark Rand RTFM > >>> It might be that I'm not being as precise as I could, either. > [quoted text clipped - 33 lines] > > - Show quoted text - Actually, I should never have attempted to describe the wiring so late at night. Mia Culpa. There's an error. You need to connect the NO1/NC2 junction to the junction of the Start relay contact and Motor Run winding. NOT directly to Main L. That way, the Start winding is not energised continuously, but only when the Start relay is operated. In addition. You can use 2off DPDT relays for the reversing function with the coils connected in parallel. That gives you 4off Change-over contacts. Wire the remaing NO contacts across the Start Switch and you then have single button operation. Viz. Press Start (now renamed Forward) - Motor runs forward. Press Reverse - Motor Runs Reverse. Mark. Wrote "In addition to that, if you wire an NC contact pair of the forward relay in series with the coil of the reverse relay and vice-versa, then you will avoid the possibility of both being on at once, with resultant loss of magic smoke." Not only does that need additional contact sets, but it doesn't matter if you push the Reverse button as well as the Start. No smoke will appear. The circuit is safe. In addition, the reverse relay, as I describe it (modified connexions as above), would de-actuate the start relay if one of its NC contacts was in series with the start relay coil, so the motor wouldn't run. I have the circuitry for using contactors, but you still need additional relays to do the interlocking - it's still necessary to swap the conexion of the two ends of the Start Winding wrt the Run Winding and you can't do that with two DPST contactors. BTW, the Interlocking relays also provides the safety operation from covers and guards micro-switches. Regards Andy [mucho snippage, will study it all later] >Regards >Andy It's too bloody invovled. Why doesn't someone just sell a box with forward-stop-reverse buttons and switchgear in it? It's a piece of piss to get stop-start boxes... The forward and reverse on this motor is just a case of connecting it the other way around, and it can be done with a single DPDT switch. But finding them, in sufficient current range, is far from trivial. I did find 30A relays somewhere for a good sounding price, so that will be the way to go. I'll have a think about the circuit. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > [mucho snippage, will study it all later] > [quoted text clipped - 18 lines] > >> http://www.schlockmercenary.com/ << \ ...and Kill them. > a webcartoon by Howard Tayler; I like it, maybe you will too! I suppose that the reason for the scarcity of Fwd-Rev-Stop control gear for single-phase motors is that, in general, industry uses 3- phase motors and control-gear and manufacturers/suppliers must, ecconomically, serve the bigger market. I'm a little worried by your statement, "The forward and reverse on this motor is just a case of connecting it the other way around, and it can be done with a single DPDT switch." If this is a single-phase (induction) motor - as you appear to say in your first posting - reversing requires the "Start Winding" to be reversed relative to the "Run Winding" - not the whole motor connexion reversed wrt Mains. This is a single-phase induction motor we're talking about and not some other type ? If it's a brushed - so called universal - motor, it would still not reverse if the live and neutral were swapped. >> [mucho snippage, will study it all later] >> [quoted text clipped - 35 lines] >If it's a brushed - so called universal - motor, it would still not >reverse if the live and neutral were swapped. sorry, too little info again. The motor has a 4-terminal block and 2 links - live and neutral to opposite corners, and then it's "links vertical" makes it go one way and "links horizontal" the other. I presume that does indeed alter the direction of the start winding. However, it's possible to arrange a DPDT switch to do the same job as the aforementioned links. At the moment, it's got 2 SPDT switches which have to be switched in unison, 'cos I failed to find a fat enough DPDT. The ones on it are only just high enough rating. Hence wanting a better solution. I reckon though that I can replace that pair of SPDT switches with 30A relays; the existing stop-start switch can stay to supply the reversing part and provide overload trip. The existing switch doesn't have NVR, but I can arrange that in the relays for forward reverse. In normal operation, the main switch will stay on and the stop start buttons and relays will do the starting and stopping, and NVR. I just need to get me head around the circuit. Just thought. the relays need to default to "disconnect", and only contact one way or the other when energised. I don't know if you can get such things. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >I just need to get me head around the circuit. > >Just thought. the relays need to default to "disconnect", and only contact >one way or the other when energised. I don't know if you can get such >things. 'k, a quick search reveals no such thing. However, I reckon this: http://www.roman-road.co.uk/temp/PICT0373.JPG should do it using either 2 DPNO or 2 DPDT (as shown) relays. Wire the relays as discussed upthread for NVR effect. Now, someone tell me why it won't work. The only thing it doesn't do is prevent you pressing the reverse button while it's running forwards, but that's not something I'd be inclined to do anyway, I don't think the machine is designed for instant-reverse. Actually, (albeit crudely) it does do that: energising both relays simultaneously will connect a live direct to a neutral, and that will take out a breaker somewhere, provided the relays are fat enough that the breaker opens before the relays burn out... The supply is via an overload switch (set to about 11A ISTR) and the whole workshop is on a 40A breaker on the distribution board... also there's a 13A fuse in the supply to the lathe, 'cos it's plugged into a socket. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! On Aug 21, 12:01 pm, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: > >I just need to get me head around the circuit. > [quoted text clipped - 29 lines] > >> http://www.schlockmercenary.com/ << \ ...and Kill them. > a webcartoon by Howard Tayler; I like it, maybe you will too! If you have DPDT relays as shown, why not just use one for reversing. If you wire relay B contacts (reading from top) to the motor tags 3,2,2,3 in that order, the motor would run Fwd when the relay wasn't energised and reverse when it was (as per my description of the wiring in an earlier posting) You could then use the other relay for the NVR Start function. The problem you would have with only two DPDT relays is that you wouldn't get a latching (remaining on) when the Reverse button was released. You'd need an extra DPDT relay on the reverse to do that. Using a single DPDT relay to swap the motor Start winding means you can't connect Mains L to Mains N in any way. Even if you press Start and Rev simultaneously. If I had a simple way of posting a circuit diagram, all would be clear and a lot easier than it sounds. >On Aug 21, 12:01 pm, Austin Shackles ><austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: [quoted text clipped - 46 lines] >can't connect Mains L to Mains N in any way. Even if you press Start >and Rev simultaneously. yeah, that would be a possibility, now you mention it. As I said, it only takes 1 DPDT to do the reversing bit. If I could find a relay which was the equivalent of an on-off-on switch then it'd only need one. In fact, the DPDTs in my circuit could be DPNOs, since only 1 contact pair on each is being used, although that doesn't have any gain in safety. Hmmm. could interlock it, it just needs an extra pole in the relays so that the forward relay, once energised, breaks the circuit for the reverse button and vice versa. In fact, might be able to run it through the live terminals in the DPDT. I shall study it some more. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >Hmmm. could interlock it, it just needs an extra pole in the relays so that >the forward relay, once energised, breaks the circuit for the reverse button >and vice versa. In fact, might be able to run it through the live terminals >in the DPDT. I shall study it some more. A bit more thought and several more bits of paper and I reckon this circuit does it. http://www.roman-road.co.uk/temp/DSC00200.JPG shown in the off state. The forward start button is fed from the reverse relay and the reverse start is fed from the forward relay, so that either will work from rest. Once it's running forwards, it self-excites through the stop button, so it latches, and the supply to the reverse start button is interrupted. Pressing the forward button again has no effect, just connects live to live. The only thing this one doesn't do is prevent pressing forward and reverse at *exactly* the same instant. However, you'd need to be clever as the relay operating speed is pretty fast. Just one fly in the ointment now: the box as supplied only has one set of terminals in the stop button, and my circuit requires 2. However, there's scope to add another set if I can get hold of the right one. Considering the price, if the bloke has more of them, I could just buy another box and rob the switch from it. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! On Aug 22, 9:24 am, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: > >Hmmm. could interlock it, it just needs an extra pole in the relays so that > >the forward relay, once energised, breaks the circuit for the reverse button [quoted text clipped - 29 lines] > >> http://www.schlockmercenary.com/ << \ ...and Kill them. > a webcartoon by Howard Tayler; I like it, maybe you will too! Yes. That circuit would work. I'm just a bit worried by the fact that applying mains to the motor terminals 1&4 when the circuit, as you posted it last, is in the "at rest" (ie Off state). By this means you could cook the motor as it will not rotate until either the FWD or REV button is pushed. Similarly, you'll have to be quick to hit the main switch as pushing the STOP button will have no effect if the motor is running. Not, IMHO, a very safe way of controlling the motor. BTW. What wattage/hp is this motor ? >On Aug 22, 9:24 am, Austin Shackles ><austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: [quoted text clipped - 6 lines] >main switch as pushing the STOP button will have no effect if the >motor is running. hmmm. that's a point. The reversing switch on it now does the same as the setup in the latest drawing but is downstream of the main supply switch (with the overload cut-out), so there are no volts anywhere when the supply is off. Ideally, I need to get the start buttons to control the main switch as well, then. Or perhaps I need another relay to make the L and N lines into the motor 1 and 4 pins. >Not, IMHO, a very safe way of controlling the motor. yeah, needs more work... It'd be a damned sight easier if I could just buy the necessary box. >BTW. What wattage/hp is this motor ? 2HP high starting torque. I've got 30A relays on order... SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >>On Aug 22, 9:24 am, Austin Shackles >><austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: [quoted text clipped - 24 lines] > >2HP high starting torque. I've got 30A relays on order... When I wired up my CNC mill the contactors had switches added to the sides which are used to prevent both forward and reverse contactors from being energised at the same time. The coil from one contactor is wired through the NC switch on the other contactor. When a contactor is energised the switch turns off so that even if the control tries to turn it on it can't because no power will flow. Why can't you do this with relays with moltiple contacts? To make the scheme work the motor will need to be turned off first which is fine for your situation because your single phase motor will not plug reverse. If you want I can make a sketch, scan it, and post it to metalworking.com. Or e-mail it to you. Maybe this has already been discussed and rejected. If so then of course just ignore this post. Eric On Aug 22, 11:35 am, e...@whidbey.com wrote: > > When I wired up my CNC mill the contactors had switches added to the > sides which are used to prevent both forward and reverse contactors [quoted text clipped - 11 lines] > > - Show quoted text - Yes. That would work as well. Ideally, you'd need two 4-pole ST contactors each with Aux C/O contacts. You could get away with two 3- pole ST contactors with Aux C/O contacts if you wired one side of the motor run-winding permanently to Main N. Andy David P wrote:- "The type of motor that does what he describes is a sp induction motor with separate forward and reverse start windings. They can be switched by spdt switch and separate main contactor. Better to use dpdt with centre off position, then you can control the contactor to give forward-off-reverse control. Usually cheaper to do it this way than some relay switching to reverse one winding. Nothing special needed for the switch, I use toggle switches as the contactor does all the power stuff." Yes. I'm aware of the type of motor that Austin has. I was thrown by his remark in an earlier posting viz:- "The forward and reverse on this motor is just a case of connecting it the other way around, and it can be done with a single DPDT switch." That appeared to say that the complete feed to the motor was connected the other way giving reverse whereas, after I checked by asking, Austin clarified matters with a circuit diagram and words. As his motor is 2hp (1.5kW), I doubt you would find a DPDT, centre off toggle-switch capable of taking the starting current. Austin was also asking how to use the Fwd-Stop-Rev pish-button set he'd sourced from e- bay and the only way of doing that is to use relays or contactors. Besides which, I cannot see how you'd control a single contactor with a DPDT, centre off toggle-switch to give Fwd-Off-Rev as you suggest, so I'd be interested to see the wiring diagram. BTW. Many of the Taiwanese lathes sold in Anerica (and some sold here with control transformers) use 110v relays to do the interlocking, NVR and hold functions which then switch 110v coil contactors switching mains to the 220v (240v) motor. Jet and Grissly (sold in USA) lathes have 3-wire single-phase motors switched by two three-pole contactors. This type of motor has a 110v start winding connected to the centre-tap of the 220v run winding. The run winding connexions are, usually, U1 & U2 and the motor is reversed by connecting the free end of the start winding (Z1) to either U1 ot U2. With a three pole contactor you can connect the run-winding to 220v and Z1 to, say, U1. Then, with the other 3-pole contactor, connect run-winding to 220v and Z1 to U2. For the motor that Austin has - usual separate run and start winding (ie 4 connexions) - you'd need two 4-pole contactors (assuming you interlocked, etc, using relays as per Jet/Gris). I proposed a design using 3off DPDT relays, which provides interlocking, NVR and reversing from Austin's push-buttons. You could use a DPST, NVR/Overload contactor - with C/O Aux contacts - to do the main switching, but you'd still need two DPDT relays for the reversing (one to do the motor switching, one for the interlock) OR 1-off QPDT relay. >I proposed a design using 3off DPDT relays, which provides >interlocking, NVR and reversing from Austin's push-buttons. You could >use a DPST, NVR/Overload contactor - with C/O Aux contacts - to do the >main switching, but you'd still need two DPDT relays for the reversing >(one to do the motor switching, one for the interlock) OR 1-off QPDT >relay. OK, nother rethink (and annoyingly, I just ordered 2 relays - might be able to add to the order if they haven't dispatched it) http://www.roman-road.co.uk/temp/DSC00201.JPG I reckon this one works. Assuming that 240V ac relay coils work the same regardless of L/N connection, and I can't see how they don't. does that equate to the design you proposed, out of interest? it doesn't make the main relay 'til after the forward/reverse, but I don't see that as an issue, it's only a few milliseconds. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! In article <37938fb7-c68e-4173-9282-79acc4b98582@a1g2000hsb.googlegroups.com>, houstonceng <andrew@houstonceng.co.uk> in uk.rec.models.engineering wrote: >David P wrote:- >"The type of motor that does what he describes is a sp induction motor [quoted text clipped - 18 lines] >As his motor is 2hp (1.5kW), I doubt you would find a DPDT, centre off >toggle-switch capable of taking the starting current. It doesn't need to take the starting current, that flows thro' the main winding (and is switched by the contactor). All the switch is doing is, on one pole, selecting which starting field is to be used, and on the other pole, taking the coil current of the contactor. If it's for a battleship, RS 316-642 is 15A, @240VAC A. (Making capacity not specified) . Or, as Austin almost says, a conventional motor p/b starter with all the trimmings and a separate dpdt switch to reverse the start winding. I like KISS! Must admit, it was somewhat confusing as to exactly what he had and what he was doing. >Austin was also >asking how to use the Fwd-Stop-Rev pish-button set he'd sourced from e- >bay and the only way of doing that is to use relays or contactors. Yes, you need to memorise the states of the p/bs. >Besides which, I cannot see how you'd control a single contactor with >a DPDT, centre off toggle-switch to give Fwd-Off-Rev as you suggest, >so I'd be interested to see the wiring diagram. Any clearer now? Obviously some misunderstanding when you refer to the switch taking starting current. >BTW. Many of the Taiwanese lathes sold in Anerica (and some sold here >with control transformers) use 110v relays to do the interlocking, NVR [quoted text clipped - 8 lines] >Then, with the other 3-pole contactor, connect run-winding to 220v and >Z1 to U2. Same basic idea, consider the two starting coils to be a single, centre tapped coil. Or feed a single start winding from one side of a 240/240-0-240 transformer. We can choose to reverse either the start or the run windings. I'd choose the one with the lower current demand every time. (Unless it's a DC motor.) >For the motor that Austin has - usual separate run and start winding >(ie 4 connexions) - you'd need two 4-pole contactors (assuming you [quoted text clipped - 6 lines] >(one to do the motor switching, one for the interlock) OR 1-off QPDT >relay. Depends on what you want. Provided it's a machine under operator control, emulation of ye olde forward/stop/reverse gear lever is ok by me. I like to see what's selected. Don't see much need for interlocking forward and reverse, except via the switch. Worst that can happen is that the switch is flipped too quickly and it carries on in the same direction. No NVR release either. Not suitable for (say) a remote suck/blow fan in ductwork. Oh! Almost forgot,and just to placate the elf'n'safety stazi, a stayput emergency stop p/b in series with the contactor overload. Regards, David P. > In article > <37938fb7-c68e-4173-9282-79acc4b98...@a1g2000hsb.googlegroups.com>, > houstonceng <and...@houstonceng.co.uk> in uk.rec.models.engineering > wrote: Big SNIP Sorry David. It's the "English usage" in your explanation that threw me, viz :- "They can be switched by spdt switch and separate main contactor. Better to use dpdt with centre off position, then you can control the contactor to give forward-off-reverse control." The way it read was that the motor could be switched by the SPDT switch (between forward and reverse) with only the need for a main contactor. You then went on to mention that a DPDT switch could control the contactor to give Fwd-Stop-Rev, so I assumed that the contactor referred to was the "main contactor", so I was interested to see how you could do that with it. My mistake. Shouldn't have read it the way it looked. You then said :- "Usually cheaper to do it this way than some relay switching to reverse one winding." Which implied that you used the DPDT switch to reverse one winding since, if you were using two contactors (One Main, One Reversing), that's exactly what the contactors would do - reverse one winding (ie the same as using two relays). So it also seemed that you were using a DPDT, switch to carry Start or Run winding current. You reinforced the implication with :- "Nothing special needed for the switch, I use toggle switches as the contactor does all he power stuff." See my confusion with your explanation ? "The Contactor" instead of "Contactors" and the implication (incorrectly inferred) that a contactor and DPDT switch were all that is needed. Since you also said :- "Same basic idea, consider the two starting coils to be a single, centre tapped coil. Or feed a single start winding from one side of a 240/240-0-240 transformer. We can choose to reverse either the start or the run windings. I'd choose the one with the lower current demand every time. (Unless it's a DC motor.)" I think you should re-read what I said about 220v, 3 wire, 1-phase motors in USA on Jet and Griss lathes. 220v is supplied (via two poles of a contactor) across the centre-tapped (110v - 0v - 110v) RUN winding and the motor direction is dictated by connecting the free end of the (110v) START winding to one end of the RUN winding - using the 3rd pole of the contactor (the other end is connected to the centre- rap of the RUN winding. The reversing circuit uses a second 3-pole contactor to connect the RUN winding to 220v as before and the free end of the START winding to the other end of the RUN winding. To ensure that the two contactors are not operated simultaneously, to provide NVR and guard interlocking, additional relays are used to provide the logic and hold functions. In any case, suggesting that "ye olde forward/stop/reverse gear lever is ok", isn't a solution to Austin's request for a "how-to" using his Push-buttons, that Bob, Mark and I are trying to provide. Andy Austin, Andy (houstonceng) and I have been pooling our thoughts, off- group, on a the design for a 3 button reversing starter which has been finalised (until somebody reports an error). Circuits and notes can be seen at: http://chainganger.co.uk/Page1/PDF/Reverser.pdf Comments are welcomed. Bob >Austin, Andy (houstonceng) and I have been pooling our thoughts, off- >group, on a the design for a 3 button reversing starter which has been [quoted text clipped - 6 lines] > >Bob A bit late but may still be of interest The circuits all look OK but you've chosen to to switch BOTH the live and the neutral lines of the single phase input (in the off position neutral is no longer connected to the motor or the relay sequence). In single phase systems it's only necessary to isolate the live line - the neutral line can always remain connected . Using live line switching and permanently connected neutral the control complement can be simplified and reduced to two, three phase motor control relays fitted with 240V coils. These are fitted with three heavy duty MAKE contacts and two light duty contacts. One light duty contact is normally OFF the second is normally ON. The construction guarantees "BREAK before MAKE" One relay is used to switch the motor to forward, the second relay is used for reverse. The light duty contacts are interconneced to provide no volt release and to interlock the forward and reverse functions. When forward or reverse is selected the other button is disabled. If both are accidentally pressed "simultaneously" whichever button actually makes contact first takes over and disables the other. The snag is that I don't know of a retail supplier of the necessary relays - my own are all rescued from scrap machinery!. These are fairly easy to find but may not have the right combination of light duty MAKE and BREAK (twin MAKE is common). However,in the ones I have played with, MAKE or BREAK operation is determined by the way the contacts are assembled into the bakelite housing. It's pretty easy to open the housing and reassemble with the contacts moved to the desired locations. Alternatively, any pair of three phase contactors can be augmented with a separate pair of light duty relays. The light duty MAKE and BREAK function must be on the same relay and the contact arrangement should be of BREAK before MAKE design (most small relays fitted with a pair of changeover contacts work this way) . The system will still function correctly if the incorrect MAKE before BREAK relay type are used but the both button pressed protection is lost. If Forward and Reverse are are pressed simultaneously there is a small chance (dependent on relative time delays) of a catastrophic supply short circuit. However it's still an OK system if the Forward and Reverse buttons are arranged so that it is physically impossible to press both at once. I've posted the circuit and also JPG of a typical three phase contactor in the xs.to image hosting site :- http://xs.to/xs.php?h=xs231&d=08365&f=motor_reverse933.jpg http://xs.to/xs.php?h=xs231&d=08365&f=three_phase_contactor931.jpg jim > When forward or reverse is selected the other button is >disabled. If both are accidentally pressed "simultaneously" >whichever button actually makes contact first takes over and >disables the other. provided, of course, that the relay action times allow this. Relays are quick but not instant, ditto contactors. OK, not likely, but we are trying to deal with sod's law as well, to an extent, and sod's law dictates that if someone's daft enough to press both fwd and rev at the same time, the contacts will make sufficiently close together as to cause a problem if the possibility exists. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! >> When forward or reverse is selected the other button is >>disabled. If both are accidentally pressed "simultaneously" [quoted text clipped - 8 lines] >fwd and rev at the same time, the contacts will make sufficiently close >together as to cause a problem if the possibility exists. Then I suggest that you use a mechanical interlock between contactors. I would not use relays in such an application. -- Richard Email address is valid but remove burrs before sending! On 6 Sep, 10:22, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol- las.net> wrote: > OK, not likely, but we are trying to deal with sod's law as well, to an > extent, and sod's law dictates that if someone's daft enough to press both > fwd and rev at the same time, the contacts will make sufficiently close > together as to cause a problem if the possibility exists. > -- > Austin Shackles. So cross wire the fwd / rev buttons thru the aux contacts on the opposite relay. Whilst fwd is running there is no feed to the rev button. Then put a big stop button between the two so you need two hands. Failing that have a two position switch to select fwd / rev and a start stop button. The advantages of this on single phase is that you can switch from fwd to rev whilst running ready to hit stop then start like at the end of a thread. John S. I had this system on my Myford for years with just one mains relay swapping wires. >On 6 Sep, 10:22, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol- >las.net> wrote: [quoted text clipped - 10 lines] >Whilst fwd is running there is no feed to the rev button. >Then put a big stop button between the two so you need two hands. that (the cross-wiring) is what the circuit we ended up with does. >The advantages of this on single phase is that you can switch from fwd >to rev whilst running ready to hit stop then start like at the end of >a thread. Not sure the motor would like that, more to the point, not all the machines will stand that sort of instant reversing. Some will, some won't. In particular, any lathe with a screwed-on chuck will undo it's chuck. Which could of course be handy :-) SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > >The advantages of this on single phase is that you can switch from fwd > >to rev whilst running ready to hit stop then start like at the end of [quoted text clipped - 4 lines] > -- > Austin Shackles. I was referring to the typical single phase motor with centrifugal start as fitted to the Myford. Until the motor stops and the switch is closed the changes can't take effect. > In particular, any lathe with a screwed-on chuck will undo it's chuck. Which > could of course be handy :-) Will ?? you read too many horror stories, but if it worries you that much stuff a centre in the end of the work and it can't unscrew as it has nowhere to go. Incidentally in the 24 odd years I owned two Myfords I only ever had the chuck come loose twice, note loose not unscrewed. both times I was pushing the machine more than it was capable of, in fact in retrospect that was for the whole of the 24 years. Yes in theory they can come unscrewed and someone always has heard of a brother / co-worker / maiden aunt / escaped prisoner [ delete as required ] who had this happen to them. After mixing with people who uses machine tools seriously for a living none have ever had this happen to them. John S. >I was referring to the typical single phase motor with centrifugal >start as fitted to the Myford. >Until the motor stops and the switch is closed the changes can't take >effect. when does the switch close though? It stays in circuit during start up until the motor is up to speed, but does it actually come to a halt before the switch re-makes? and do ALL such motors do so? The one that the circuit is intended for is a 2HP capacitor start/capacitor run with 2 caps on it. Without studying it in detail, I'd prefer to play safe. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > >I was referring to the typical single phase motor with centrifugal > >start as fitted to the Myford. [quoted text clipped - 6 lines] > > and do ALL such motors do so? But the centrifugal switch doesn't close until the motor slows down - and it doesn't do that until the power is off. The start/reverse switch changes the direction of the starting coil - the main switch still controls the power - so it'll be fine unless you try and start it in the other direction before it's stopped. My previous lathe was wired like this. It's a good system and is much cheaper than Dewhurst type reversing switches. Russell > But the centrifugal switch doesn't close until the motor slows down - > and it doesn't do that until the power is off. The start/reverse switch [quoted text clipped - 6 lines] > > Russell If you try and start it in the other direction before it's stopped nothing will happen as it has forward momentum and will carry on, like a bad motor you rope start. It needs the centrifugal switch to be closed before it can start in reverse and this happens at low speed anyway so if you are that quick with the start button as soon as you hear it click then it will instantly reverse but only from a few revs. This won't harm the motor as there are many standard 3 phase motors in industry that are designed to plug reverse and do so all day long. John S. > If you try and start it in the other direction before it's stopped > nothing will happen as it has forward momentum and will carry on, like > a bad motor you rope start. So long as the centrifugal switch hasn't remade. > It needs the centrifugal switch to be closed before it can start in > reverse and this happens at low speed anyway so if you are that quick > with the start button as soon as you hear it click then it will > instantly reverse but only from a few revs. But it won't do the motor much good if you do this too often. Besides which, if it's a Capacitor Start & Run motor it may not have a centrifugal switch ! > This won't harm the motor as there are many standard 3 phase motors in > industry that are designed to plug reverse and do so all day long. But three-phase motors start and run using an entirely different principle to single phase motors - so you're not comparing like-with- like. > John S. Andy On 7 Sep, 11:45, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol- las.net> wrote: > >I was referring to the typical single phase motor with centrifugal > >start as fitted to the Myford. [quoted text clipped - 4 lines] > until the motor is up to speed, but does it actually come to a halt before > the switch re-makes? It doesn't come to a halt before closing but , normally, it's not far off. Just try running the motor without any load connected, switch it off and listen for the switch to close. I think that there's a very strong chance that, if you press the reverse direction button just at the point the switch has closed then the motor will reverse OK. > and do ALL such motors do so? No. The secondary winding of Permanent Split Capacitor (PSC) and Cap start/Cap run (CSCR) motors is normally called the Auxiliary winding, instead of Start winding, because it is always energised at the same time as the main winding and uses a heavier gauge wire. If you reverse the connection to the Aux winding (plus its series capacitor) it will probably try to decellerate it and eventually reverse it but a lot of heat is generated and there will be a large current spike, particularly if the reverse connection occurs at, or near, a peak of the AC cycle. Single phase motors and controllers are made using this principle to stop them (known as plugging) but I wouldn't want to do it with a bog-standard motor. Just because a motor has a centrifugal switch doesn't mean that you can switch it into reverse without it having any effect when the motor is running. CSCR motors have a centrifugal switch (although some have a timer instead) but that simply switches out the start capacitor; it still leaves the aux winding and its capacitor energised when the main winding is. > The one that the circuit is intended for is a 2HP capacitor start/capacitor > run with 2 caps on it. Without studying it in detail, I'd prefer to play > safe. As it's a CSCR I'm sure that that's the wise way to go, Bob >> When forward or reverse is selected the other button is >>disabled. If both are accidentally pressed "simultaneously" [quoted text clipped - 8 lines] >fwd and rev at the same time, the contacts will make sufficiently close >together as to cause a problem if the possibility exists. Fair comment but sod has to be particularly vindictive to to cause a problem. This is of course a setup that I have used for many years without problem but,since I'm not addicted to simultaneously pressing Forward and Reverse buttons, this is not useful evidence. There's no doubt that the Break before Make sequencing logic works fine if there's a significant time difference in the "simultaneous" pressing of the two buttons, What is less clear, as you have pointed out, is the behaviour if the relay closures are truly simultaneous. To test this I disconnected the motor load (to avoid overheating from frequent stop starts) and proceeded to repeatedly press first Stop, then both Forward and Reverse buttons at the same time. Behaviour was as expected with correct closure by either of the two contactors in apparently random order. All went well for 50 successive attempts but at the 57th try the supply fuse blew! This clearly justifies your comments but also gives some idea of the extent of the problem. Accidental simultaneous pressing of both buttons is, in itself, a pretty rare event but even if it does happen there's something like a 50:1 on chance that the setup will still behave correctly. If it does fail, the supply fuses blows. This is the result of the short circuit across the motor terminals - there is no possibilty that this will damage the motor. It's a simple and very convenient setup if you have have the right contactors and I will certainly continue to use mine. However it doesn't provide total protection against simultaneous selection of Forward and Reverse. Jim >>> When forward or reverse is selected the other button is >>>disabled. If both are accidentally pressed "simultaneously" [quoted text clipped - 22 lines] >as you have pointed out, is the behaviour if the relay closures >are truly simultaneous. Use decent industrial p/bs, the ones that you would find in clunky old relay control stuff. Usually 1n/o, 1n/c contacts which can be assembled as break before make or v.v. Interlock the p/bs and it doesn't matter what the relays do. > To test this I disconnected the motor load (to avoid >overheating from frequent stop starts) and proceeded to [quoted text clipped - 3 lines] >order. All went well for 50 successive attempts but at the 57th >try the supply fuse blew! That's all that should happen! However, in a previous existance I used to specify multi-motor control boards for power station stuff. The contactors for a reversing drive were allways "electrically and mechanically interlocked". Before the elf and safety fools buggered things up you could usually get 3ph reversing starters for a beer token from your local scrappy. Ok, at the worst all you have to do is rewind the coil with 240/415 the number of turns in 415/240 csa wire of the original > This clearly justifies your comments but also gives >some idea of the extent of the problem. [quoted text clipped - 10 lines] >mine. However it doesn't provide total protection against >simultaneous selection of Forward and Reverse. If that's important, use a selector switch, not p/bs. I don't like p/bs for any application where nasties could happen if the wrong selection is made. All too often, reversing is done in auto pilot mode and if you get it wrong you only find out after it's rotating. A forward-off-reverse switch with 45 degree indexing and an arrow shaped operator will give you tactile feedback before you goof. Regards, David P. >If that's important, use a selector switch, not p/bs. I don't like >p/bs for any application where nasties could happen if the wrong >selection is made. All too often, reversing is done in auto pilot >mode and if you get it wrong you only find out after it's rotating. >A forward-off-reverse switch with 45 degree indexing and an arrow >shaped operator will give you tactile feedback before you goof. that's what it might have already, if such a thing and at a suitable rating were even remotely easy to find. All I actually needed was a big DPDT switch, ideally with centre off position. But you try finding one. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! SNIP I used the "snip" is because the intro is getting a bit long. It's not necessary because I believe we are in full agreement on the facts - the issue is really a matter of philosophy which perhaps merits wider discussion. For professional installations and the more luxurious amateur workshops your viewpoint is undoubtedly correct - but this is a Usenet group for MODEL engineers. It is true that there are welcome and extremely helpful inputs from professional engineers but it still remains a group of MODEL engineers many of whom have to do the best they can on a very limited budget. Inevitably, corners are cut and few if any home workshops would pass a professional Health and Safety survey. It helps to try to plug in a few numbers. They won't be very accurate because of the limited data but give an idea of the scale of the problem. I don't believe I've ever simultaneously pressed Forward and Reverse buttons but lets assume that someone is sufficiently ham fisted to do this twice a year. At this rate it will be somewhere near year 2033 before an interlock failure is likely. This "event" would require replacement of the supply fuse! We can compare this with another common home workshop stratagem. Many of us are still using ancient three phase motors which were designed long before VFDs were even thought of. They were never intended to be run significantly above or below their rated speed and the insulation stress distribution was designed on the assumption that the supply waveform would be sinusoidal. We now cheerfully run these machines from modern VFDs over a very wide range of speeds and operating from a VFD output waveform which induces insulation stresses in the windings far beyond the original design limits. By and large this works because of the generous safety factors built into these venerable machines. 100% overspeed is rarely troublesome and the low speed overheating is usally manageable. The voltage stress is more serious because not only are VFD peak voltages higher than the motor rated voltage but the strange nature of the fast switching of the voltage waveform concentrates excessive insulation stress in the first few turns of each winding. VFD rated motors take this into account by using higher standards of insulation and with special attention to the winding starts. Insulation failure results in a burnt out motor and a possible fire risk. Ideally we should all replace our old motors but how many of us will do this? I've not enough information to properly quantify failure rates but I have no doubt that it's higher than once in twenty odd years. It's also a LOT more serious than just replacing a supply fuse! Regards Jim Jim mwrote :- > The circuits all look OK but you've chosen to to switch BOTH > the live and the neutral lines of the single phase input (in the [quoted text clipped - 3 lines] > In single phase systems it's only necessary to isolate the > live line - the neutral line can always remain connected . One of the circuits I shared with Austin and Bob was a two-contactor interlocked system with Aux contacts. Both 3-pole (Switching Line only) and 4-pole (Switching Line & Neutral). Obviously, switching both Line and Neutral on a single-phase system is not absolutely necessary - but is the safest thing to do on a machine tool - Neutral is rarely 0v wrt Earth (sometimes as high as 50v) and a Lathe or Milling Machine is a large lump of earthed metal. BTW. Your circuit is a "No-No" because the stop button is in the Neutral and you should only switch the Line or both Line & Neutral - never Neutral on it's own.. John S wrote :- >The advantages of this on single phase is that you can switch from fwd >to rev whilst running ready to hit stop then start like at the end of >a thread. Not a good idea. In a capacitor Start & Run motor there'd probably be a "bang" and a damaged Cap or Motor - and in an Induction Run Motor (either Split phase or Capacitor Start) the centrifugal switch re- makes before the motor stops, so it'd try to restart in reverse whilst still running - all be it slowly - forward. Andy On 22 Aug, 09:24, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: > ............... > [quoted text clipped - 3 lines] > http://www.roman-road.co.uk/temp/DSC00200.JPG > ............. That circuit will probably work but, in the interval between pressing the FWD or REV button and the relevant relay making contact (about 10ms), current flows through both the other relay coils connected in series. Typically, the specified minimum coil operating voltage of a relay is 75% of its nominal voltage but some will work at a much lower voltage so you could have a race condition. During that same interval the button is carrying all the current to the start winding of the motor. Typically start/stop buttons are rated at 3A. If you happen to press the button near the peak of the AC cycle the current through the button will probably be considerably more than its rating which could result in shortened contact life or, even, contact welding. Bob >On 22 Aug, 09:24, Austin Shackles ><austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: [quoted text clipped - 19 lines] >its rating which could result in shortened contact life or, even, >contact welding. There's a new one now, 201.JPG instead of 200.JPG - that circuit, as was pointed out, won't stop again and has the motor permanent live, which I didn't really intend. The buttons don't supply motor current though, start or run. they only feed the relay coils. Well, I suppose they supply current while the relay is switching. That's about 15ms if I recall the spec sheet right. If it causes issues, then it could have a current-limiting resistor in series with the buttons, or something. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! My previous posting was incorrect when I referred to DSC00200.JPG. It was, in fact, regarding DSC00201. I've also spotted another "feature". If the fwd or rev button is held down at the same time as stop then the motor will run in the relevant direction. To an optimist this is the jog function but, to a pessimist, it's a no-no as stop should always override go. You shouldn't discount possible damage to the switches because of the short duration; it's the act of making or breaking contact that does the damage. The holding current of most switches is normally many times greater than their switching capacity. Bob >My previous posting was incorrect when I referred to DSC00200.JPG. It >was, in fact, regarding DSC00201. [quoted text clipped - 8 lines] >the damage. The holding current of most switches is normally many >times greater than their switching capacity. There's another circuit I may use instead, supplied by yon Houstonceng chappie. I shall study it. I don't know the details of the button contacts, but they look quite solid. As for saftey features, it's got to be better than the current setup which has no NVR and dodgy reverse switching. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! In article <3c7830f5-0e8d-47d8-8aa1-98ef26809577@2g2000hsn.googlegroups.com>, houstonceng <andrew@houstonceng.co.uk> in uk.rec.models.engineering wrote: >> [mucho snippage, will study it all later] >> [quoted text clipped - 32 lines] >This is a single-phase induction motor we're talking about and not >some other type ? The type of motor that does what he describes is a sp induction motor with separate forward and reverse start windings. They can be switched by spdt switch and separate main contactor. Better to use dpdt with centre off position, then you can control the contactor to give forward-off-reverse control. Usually cheaper to do it this way than some relay switching to reverse one winding. Nothing special needed for the switch, I use toggle switches as the contactor does all the power stuff. >If it's a brushed - so called universal - motor, it would still not >reverse if the live and neutral were swapped. Regards, David P. On 19 Aug, 19:09, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-las.net> wrote: SNIP > If I follow Mark's post right, I can use a DPST relay, with 1 pair of > contacts supplying the motor and self-feeding the coil through the stop [quoted text clipped - 29 lines] > > - Show quoted text - Austin No. That isn't correct. The neutrals should NOT be switched. OK. Assuming you have obtained two mains coil relays with contacts capable of taking the motor current - remembering that the "start current" will be higher than the run current - and that you've got some form of Overload cut-out/Fuse in the mains supply. For the Start function. Use a double-pole/single-throw (DPST) or doble- pole/double-throw (DPDT) relay. Wire one end of the relay coil and one end of the single-phase motor "Run" winding to Mains Neutral. Wire one side of the NC Stop switch to Mains live and the other side to one side of the Start switch. Wire the other side of the start switch to the - as yet - unconnected side of the Relay coil. Connect one set of the relay NO contacts across the Start button. Test. Relay should pull on and hold on operation of the Start button and drop-out when the Stop button is pressed. Wire one side of a Tripple Pole/Double-Throw (TPDT) or Quadruple pole/ Double-Throw (QPDT) Relay coil to Mains N. You could use a contactor with Main Contacts DPDT and a separate light current "hold contact". Let's assume we have a TPDT relay. Wire one side of the Reverse switch to the junction of the Stop switch and Start switch (previously wired as above) and the other - as yet - unconnected side to the TPDT relay coil. Connect one set of NO contacts of this relay across the Reverse switch. Test as above. Pressing the Reverse button should energise the TPDT relay which will then hold until the Stop button is pressed. OK So far ? Start Relay to Motor. Wire one side of the - as yet - unconnected NO Relay contacts to Main Live. Wire the other to the - as yet - unconnected side of the motor "Run Winding" Reverse Relay to Motor. Let's call the common of the remaining rwo sets of contacts C1 and C2 and the NO/NC Contacts as NO1, NO2 and ditto NC1 & NC2. Dirstly, wire C1 to one side of the Motor "Start winding" and C2 to the other side of same. Connect NO1 ro NC2 and NO2 to NC1. Connect NO1/NC2 junction to Mains Live and NO2/NC1 junction to mains neutral. Operation. For forward rotation, press Start Button only. Stop motor with Stop button. For reverse rotation, press both Reverse and Start button together. Stop as above. Wiring in this way does not require any special circuitry to :- a) Prevent both Start and Reverse buttons being operated simultaneously b) Prevent trying to start the motor in opposite directions simultaneously (Which would probably mean connecting Mains Live to Main N - which not a good thing to attempt with a relay contact !) Downside ? You need to press two buttons sumultaneously to get reverse. So what ? You'll probably only use reverse very occasionally. I hope you can follow this. If not, I can send you a wiring diagram if you can ley me know how to send you a PM with attachments (I'm new to this group and they all use different mechanisms) Andy |
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