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Model Forum / Radio Controlled / Helicopters / March 2005Electric Heli Voltage question
How do the number of volts used (battery volts) effect the electronics of an all electric heli? What does 7.2 volts do compared to 11.1 volts for example? I'm thinking about buying an 11.1 volt 2200mah li-poly battery for my Humminngbird V2 but am worried about burning it up in the process! LOL! If you can shed any light on this stuff please let me know.... Century has a disclaimer on their website stating that any battery greater than 8.4 volts are used at customers risk, which made me wonder. Thanks! - Michael the problem is the amount of power the BEC & other circuits have to cope with at 7.2 volts it has to drop the receiver and servo volts down to 4.8 or 6 volts and running at 11.1volts it increases the watts the bec is running at by 50% > How do the number of volts used (battery volts) effect the electronics of > an all electric heli? [quoted text clipped - 8 lines] > > - Michael Ok but which is good and which is bad, Kevin? I'm a computer scientist not an electrical engineer! LOL! - Michael > the problem is the amount of power the BEC & other circuits have to cope > with at 7.2 volts it has to drop the receiver and servo volts down to 4.8 [quoted text clipped - 12 lines] >> >> - Michael a circuit designed for 7.2 volts with no tolerance for running a higher voltage could be damaged or its life shortened think of it like running a 7.2 volt bulb at 12 volts it will work and it will be brighter but its life will be shortened it all depends on what the speed controller and bec circuits were designed for > Ok but which is good and which is bad, Kevin? I'm a computer scientist not > an electrical engineer! LOL! [quoted text clipped - 17 lines] >>> >>> - Michael Ok then I guess 11.1 volts would be bad connected to a Hummingboard designed more for an 8.4 volt battery? :-\ Seems most of the Li-poly batts are 11.1 volts though dangit. :-| I'm open to suggestions if anybody's got 'em. Thanks! - Michael >a circuit designed for 7.2 volts with no tolerance for running a higher >voltage could be damaged or its life shortened think of it like running a [quoted text clipped - 22 lines] >>>> >>>> - Michael possibly but I have a honey bee that is sold on either 8.4 or 11.1 so it depends on the design > Ok then I guess 11.1 volts would be bad connected to a Hummingboard > designed more for an 8.4 volt battery? :-\ [quoted text clipped - 32 lines] >>>>> >>>>> - Michael Not true. There's 2s LiPo's out there, they only have 7.4 volts (which is fine for your bird) J > Ok then I guess 11.1 volts would be bad connected to a Hummingboard designed > more for an 8.4 volt battery? :-\ [quoted text clipped - 33 lines] >>>>> >>>>>- Michael Jennifer I didn't mean it as a *fact*, only that 11.1 was all I've been seen so far. :-p Since the Century "birdseed" batteries are 8.4 volts, have you seen any Li-poly's anywhere that are 8.4 volts? Thanks! - Michael > Not true. There's 2s LiPo's out there, they only have 7.4 volts (which is > fine for your bird) [quoted text clipped - 39 lines] >>>>>> >>>>>>- Michael Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH too), and it seem to work fine. You could possibly go ahead and plug in a 11.1v LiPo and use a circuit board to regulate it down to 8.4v - I think they're available at many electronics stores, and not heavy either. J > Jennifer I didn't mean it as a *fact*, only that 11.1 was all I've been seen > so far. :-p [quoted text clipped - 47 lines] >>>>>>> >>>>>>>- Michael > Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH > too), and it seem to work fine. You could possibly go ahead and plug in a > 11.1v LiPo and use a circuit board to regulate it down to 8.4v - I think > they're available at many electronics stores, and not heavy either. Confused, I ask the following question. If you're running a 7.4v Li-pol and Mike is running an 8.4v Li-pol, what exactly is the voltage of a single cell Li-pol?  SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >>Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH >>too), and it seem to work fine. You could possibly go ahead and plug in a [quoted text clipped - 4 lines] > Mike is running an 8.4v Li-pol, what exactly is the voltage of a single cell > Li-pol? He's running an 8.4v NiMH - not a LiPo. Since 7.4v LiPo is a 2S (2 cells in serial) each single cell would have 3.7v. J Hey Jennifer, what do you think about this one? http://www.heli-world.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MX-2LI 2200&Category_Code=Batt 2200mAH! I may have to order one of these critters. >:-) - Michael >>>Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH >>>too), and it seem to work fine. You could possibly go ahead and plug in a [quoted text clipped - 9 lines] > > J I've got a LiPo, this is a LiIon. Mine gives me easily 30 minutes flight time. For some more technical information about LiIon batteries (most of it applies to LiPos too): http://en.wikipedia.org/wiki/Lithium_ion_battery J > Hey Jennifer, what do you think about this one? > http://www.heli-world.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MX-2LI 2200&Category_Code=Batt [quoted text clipped - 16 lines] >> >>J Michael, Three things worry me about this one though I accept that my concern may be unfounded because they are based on the lack of information. (i) Li-Ion - not as good as LiPo - poor relation in terms of capacity per gramme and in terms of discharge capability (ii) No dimensions and weight - given Li-Ion are quite heavy and its large capacity and the fact that it is packed in a tube rather than the foil envelope this could be heavier than the birdseed. (iii) No indication of discharge capacity. I reckon you need at least 8A to power your hummer - so this would have to be a 4C or greater. I got mine from http://www.rcflying.biz/PipsElectricPlanes.htm in Singapore - cost me £16 ($29) including postage to the UK. This may not be such a great deal in the US but for the UK its is quite a saving. Cheers, Nigel > Hey Jennifer, what do you think about this one? > http://www.heli-world.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MX-2LI 2200&Category_Code=Batt [quoted text clipped - 17 lines] >> >> J > Michael, > [quoted text clipped - 16 lines] > > Nigel Good points, and thanks for the link :) I'm always collecting links... pack rat that I am ;) J So everyone agrees that the 7.4 V Lipo will work correctly on th Hummingbird? I'm in the same bost as everyone else and don't want t upgrade mine to a $500+ bird but want more flying time -- SkyCaptia > So everyone agrees that the 7.4 V Lipo will work correctly on the > Hummingbird? I'm in the same bost as everyone else and don't want to > upgrade mine to a $500+ bird but want more flying time. It works for me anyway. I don't have a Hummingbird, I have one of the Dragonfly clones - but these birds are pretty much all the same. The battery I'm using is a 2s Thunder Tiger 2200mAh, and I can easily fly for >30 minutes. The only thing I am a little worried about is that the main motor gets very, very hot (so hot that I cannot touch it) and there's no room for a heatsink. It's cheap though, so I'll see what happens :) J >>>Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH >>>too), and it seem to work fine. You could possibly go ahead and plug in a [quoted text clipped - 6 lines] > > He's running an 8.4v NiMH - not a LiPo. Back to the reading lessons for me then :-) Since 7.4v LiPo is a 2S (2 cells > in serial) each single cell would have 3.7v. Indeed it would, but if he used three (coz 2 wouldn't be enough), at 11.1v he'd be well over the capabilities of his current speed controller/motor combo I'd hazard. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) >>>>Nope :) I'm using a 7.4v Lipo in my bird (which came with an 8.4v NiMH >>>>too), and it seem to work fine. You could possibly go ahead and plug in [quoted text clipped - 16 lines] > he'd be well over the capabilities of his current speed controller/motor > combo I'd hazard. Agreed, although I don't know what the tolerances on these circuits are. I sure won't try :) J >> Indeed it would, but if he used three (coz 2 wouldn't be enough), at >> 11.1v [quoted text clipped - 3 lines] > Agreed, although I don't know what the tolerances on these circuits are. I > sure won't try :) Neither would eye. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) What would be the result if I took 2 of these 2s 7.4 packs and tied them together in parrallel? The voltage would remain the same being in parrallel, but the mah would be nearly doubled and they'd provide much better usable ballast wouldn't they? - Michael > What would be the result if I took 2 of these 2s 7.4 packs and tied them > together in parrallel? The voltage would remain the same being in parrallel, > but the mah would be nearly doubled and they'd provide much better usable > ballast wouldn't they? > > - Michael Theoretically correct. You will have to be careful that the packs are exactly the same charge though, else you'll have an imbalance which might have some "interesting" side effects. In theory the batteries should balance themselves, but I've heard because of the specific properties of LiPos they don't do that. J Second what Jennifer says - but it is really important with LiPos - they need to be precisely balanced - you really need to buy a balancing circuit to run LiPos in parallel - this technique is used by plank fliers who need big AMPs for their motors. If LiPos are mistreated (charged incorrectly, discharged too much, run unbalanced) they can catch fire and because the chemical reaction generates its own oxygen, a LiPo fire is very difficult to extinguish. LiPo fires are nowhere near as common as the alarmists make out but at the same time you shouldn't take un-necessary risks. Cheers, Nigel >> What would be the result if I took 2 of these 2s 7.4 packs and tied them >> together in parrallel? The voltage would remain the same being in [quoted text clipped - 11 lines] > > J > Ok but which is good and which is bad, Kevin? I'm a computer scientist not > an electrical engineer! LOL! What'd happen to a CPU designed to run at 1.4v if you shoved 2.8v up it's arse? I have a feeling something would become useless pretty quickly. Same thing with ANYTHING electrical. Most RC equipment will handle voltages in excess of their quoted number, but there's a limit. I suspect your spped controller would get fried. SignatureBeav Reply to "beavis dot original at ntlworld dot com" (with the obvious changes) Michael, Voltage is the measure of the potential to drive current through a circuit. The higher the voltage for the same resistive load the higher the current and the higher the power delivered into the circuit. If the circuit is an electric motor (or two) then they will probably generate more mechanical power within the restrictions of their design. Many people fly Hummingbirds with 3 Cell Lipos and most will say that it is the only way to go if you want to turn your heli into something that performs well. There are a couple of provisos though ... (i) The Battery Eliminator Circuit (BEC) needs to be able to handle it without buring out - it must be able to receive 11.1V rather than the designed 8.4V and deliver 4.8V for to the servos and receiver. Basicly it has to be able to handle a power equal to the current delivered to the RX and Servos multiplied by (11.1V - 4.8V) - normally the volatge drop would be (8.4 - 4.8) - in other words it must be able to disspipate an extra 75% power (heat). (ii) The Electronic Speed Controller (ESC) must be able to handle 11.1V rather than 8.4V although this isn't usually a problem as most ESCs simply pass through the source voltage without any voltage drop. (iii) The motors must be able to handle it - they will be receiving 11.1V rather than 8.4V (i.e. an 32% electrical power increase). This will result in higher revolutions and torque leading to more mechanical power but will also generate more heat and strain on the motors. Okay theory over, where does that leave you. Well in short, (i) BEC If your electrics are seperate (RX, Gyro, ESC/BEC are three sepearte components) then you stand a good chance of being okay. If you have a one of the all-in-one boards there is more risk. The Hummingbird ones seem better than most and remember than Century sell a 3 cell LiPo as an upgrade. The cheaper units you get in Dragonflies, Jabos, Aerohawks etc have a history of burning out on 11.1V. (ii) ESC Should be okay as a good ESC simply passes voltage on and therefore doesn't have to disipate much power (iii) Motors Your main motor should be okay but probably won't last as long. If you have a 480 rather than a 400 then so much the better. The stock tail motor won't last long on 11.1V - Century sell a more powerful upgrade especially for this but be aware that this is heavier and since you have a lighter battery up front the heli becomes more challenging to balance. I fly my HB with a 1300 2 Cell LiPo (7.4V). I wasn't sure what to expect because it delivers less instaneous power than the birdseed. But in reality it is superb. The loss of about 40g of weight more than makes up for the lower voltage. Also the way in which LiPos deliver power is much more smoother - they maintain the power until the battery is used, unlike the Birdseed which delivers good power initially but then falls off quickly. My HB literally leaps into the air with the 7.4 LiPo compared with the birdseed and is much easier to fly as a result. One thing though - I hinted above about Centre of Gravity. The LiPos are much lighter and so place the LiPo in the same place as the birdseed will leave it really tail-heavy. It's bad practice to add ballest to any aircraft so you have two options - move the battery forward or get a heavier battery. With a very light LiPo you will have to move it so far forward that you will not be able to fit the canopy (even with a heavier LiPo this is a challenge). So my advice would be not to go for a really light LiPo - get a 1500mAh minimum (maybe even a 2100mAh) so that the ballest earns its keep. Wow that went on a bit, but I hope it helps. Cheers, Nigel Thanks for shedding so much light on this subject, Nigel! That was very informative. So going for lower voltage (7.2V) and greater mAH sounds like the best way to go then, correct? - Michael Depends on what you want to do. But if you just want it to fly a little better and for longer then I would go for a 2 Cell large capacity. The guys who fly 3 cell are virtually all running with brushless set ups and upgrades than have turned their little HB into a $600 machine. I went for a 1300mAh GWS 2 Cell. It weighs 54g compared with 90g for the birdseed. It fits reasonably neatly but I have seperates and have everybit moved up to the front. Even then the canopy won't fit as designed so I have it velcro'ed to the battery. Looks okay but it is about 5mm forward so won't clip onto the rear post. With this hindsight I would have gone for a larger capacity - a 1500mAh or higher. Make sure you get LiPo and LiOn - LiOn are the poor relation. Also make sure you get a discharge rate of at least 6C so you can comforatably get power to the motors. Cheers, Nigel > Thanks for shedding so much light on this subject, Nigel! That was very > informative. [quoted text clipped - 3 lines] > > - Michael > How do the number of volts used (battery volts) effect the electronics of an > all electric heli? > > What does 7.2 volts do compared to 11.1 volts for example? > > I'm thinking about buying an 11.1 volt 2200mah li-poly battery for my > Humminngbird V2 but am worried about burning it up in the process! LOL! If > you can shed any light on this stuff please let me know.... Century has a > disclaimer on their website stating that any battery greater than 8.4 volts > are used at customers risk, which made me wonder. Thanks! > > - Michael 11.1V 2200mah is too powerful for your Hummingbird V2, I think the Hummingbird V2 only use the 8.2V battery, right?? If that is correct, you only need the 7.4V li-ion battery ONLY. 7.4V 1800mah Li-ion battery reference: http://www.hobbyjapan2000.com/store/proddetail.php?prod=LIPOBATC don't use your bec system anymore, and use a smaller pinion gear greatings A.Redert > How do the number of volts used (battery volts) effect the electronics of > an all electric heli? [quoted text clipped - 8 lines] > > - Michael |
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