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Model Forum / Radio Controlled / Air Models / September 2006How low is "low" TX voltage?
I have a Futaba TX that has a digital readout for the battery voltage (T6XAS). As far as I know, it doesn't have a low voltage indicator (I'm a little short on documentation, I got it used). How low should I let the volatge get before I worry about recharging it? I don't mind operating conservatively, I just don't want to unnecessarily charge it all the time. Has anyone put a meter on a TX to see how much current it draws when it's on? Thanks, Steve > I have a Futaba TX that has a digital readout for the battery >voltage (T6XAS). As far as I know, it doesn't have a low voltage [quoted text clipped - 8 lines] >Thanks, >Steve Here's the 6XAS manual: http://www.futaba-rc.com/manuals/6xas-hs-manual.pdf According to the manual, your tx has a low voltage warning that trips at 8.5V. /daytripper >Here's the 6XAS manual: > >http://www.futaba-rc.com/manuals/6xas-hs-manual.pdf > >According to the manual, your tx has a low voltage warning that trips at 8.5V. That's another advantage of a 'computer' radio. We had a pilot lose his Twist at the field the other week because his transmitter battery went dead. It was a basic 4 channel unit with a 'needle' meter. He claimed he put a good charge on it the night before. Oh well...  SignatureDavid - WD4JKH Valid email: no-spam0879@mindspring.com > Here's the 6XAS manual: > > http://www.futaba-rc.com/manuals/6xas-hs-manual.pdf > > According to the manual, your tx has a low voltage warning that trips at 8.5V. Thanks for the link, I had searched but missed it.... Thank you, Steve >> Here's the 6XAS manual: >> [quoted text clipped - 6 lines] >Thank you, >Steve No problem. If you go through the corporate futaba.com site you'd likely never find it... /daytripper | I have a Futaba TX that has a digital readout for the battery | voltage (T6XAS). As far as I know, it doesn't have a low voltage | indicator I have one. It does have a low voltage alarm -- it starts beeping very loudly and insistantly. | How low should I let the volatge get before I worry about recharging | it? I don't mind operating conservatively, I just don't want to | unnecessarily charge it all the time. When it gets down to 1.2 volts per cell, or 9.6 volts, perhaps 70% of your charge is gone. when it's down to 1.1 volts per cell (8.8 volts), you're running on fumes. | Has anyone put a meter on a TX to see how much current it draws when | it's on? Not this specific radio, I seem to recall my 9C (a fancier radio, granted) drawing around 215 mA with the stock module. More specific results here -- http://groups.google.com/group/rec.models.rc.air/msg/5a0063936df977d3 SignatureDoug McLaren, dougmc@frenzied.us Sleep is just a bad substitute for coffee ... If you have NiMh batteries in it, don't let it get below 9v. These batteries can drop off in seconds. CM > I have a Futaba TX that has a digital readout for the battery > voltage (T6XAS). As far as I know, it doesn't have a low voltage [quoted text clipped - 8 lines] > Thanks, > Steve | If you have NiMh batteries in it, don't let it get below 9v. These batteries | can drop off in seconds. They don't really drop off signifigantly faster than NiCds, but you probably don't want to let your NiCds drop below 9v either. And once you get below 9.2 volts or so, the voltage drop really speeds up. If that low battery alarm (at 8.5 volts) starts beeping, it's time to land NOW -- you may only have two or three minutes, NiCd or NiMH, before it stops working entirely. SignatureDoug McLaren, dougmc@frenzied.us `Every man has his price. Mine is $3.95.' Doug McLaren Wrote: > They don't really drop off signifigantly faster than NiCds, but you > probably don't want to let your NiCds drop below 9v either. And once > you get below 9.2 volts or so, the voltage drop really speeds up. That's what I used to think, until I cycled NiCds and NiMhs down with CBA analyzer. The NiCds dropped as expected when they hit the 'knee', but the NiM drop-off curve wasn't a curve, it was a cliff. I'd be real money that if your model was flying when the NiMhs reache the end of the discharge 'plateau', you wouldn't have enough charg left to land unless you were about to touch down anyway -- the-plumbe The discharge curve depends somewhat on the age of the battery. Newer ones seem to have a sharper cut off than old cells that have built up more internal resistance as the carbonates form from oxidation of the separator. Regardless of all this technical discussion, flying them much below 9.4 is asking for trouble - unless you really love to build. SignatureRed S. Red's R/C Battery Clinic http://www.rcbatteryclinic.com Check us out for "revolting" information. > Doug McLaren Wrote: >> [quoted text clipped - 11 lines] > the end of the discharge 'plateau', you wouldn't have enough charge > left to land unless you were about to touch down anyway. > The discharge curve depends somewhat on the age of the battery. Newer ones > seem to have a sharper cut off than old cells that have built up more [quoted text clipped - 3 lines] > Regardless of all this technical discussion, flying them much below 9.4 is > asking for trouble - unless you really love to build. This is interesting. I was under the impression (no empirical data) that NiMH batteries were more gradual in their decline than NiCads. Glad to learn the truth. Ed Cregger > Red's R/C Battery Clinic > http://www.rcbatteryclinic.com [quoted text clipped - 15 lines] >> the end of the discharge 'plateau', you wouldn't have enough charge >> left to land unless you were about to touch down anyway. > > The discharge curve depends somewhat on the age of the battery. Newer ones > > seem to have a sharper cut off than old cells that have built up more [quoted text clipped - 9 lines] > > Ed Cregger Now we have CENTER posting? As if top-posting weren't bad enough... Anyway, NiMH ARE more gradual in the voltage drop. They give nearly full voltage MUCH longer than NiCads... UNTIL they hit a certain point. Then the voltage drops dramatically (the "cliff" mentioned earlier). So, over the length of useful voltage, the NiMH will have more sustained voltage than NiCad, with less drop, and a longer useful life per charge. SignatureEvaluating all GUIs by the example of Windows is like evaluating all cars by the example of Yugos. Here are some curves from Sanyo specs. that give you a pretty good idea of how they compare. Ni-Mh http://sanyo.wslogic.com/pdf/pdfs/HR-3U-1700.pdf Ni-Cd http://sanyo.wslogic.com/pdf/pdfs/KR-1100AAU.pdf Red S >> The discharge curve depends somewhat on the age of the battery. Newer >> ones seem to have a sharper cut off than old cells that have built up [quoted text clipped - 7 lines] > NiMH batteries were more gradual in their decline than NiCads. Glad to > learn the truth. > Doug McLaren Wrote: >> [quoted text clipped - 11 lines] > the end of the discharge 'plateau', you wouldn't have enough charge > left to land unless you were about to touch down anyway. hah. Funny that just as I was reading this, I went out to fly a little model on my no 2 TX (futaba FF6, NiCd cells)...and it started out at 9.6v. Withing 30 seconds the tranny was beeping and showing 8.2v. 30 seconds later it was 8.1v.. The model which was being tested after repairs, came in OK...and the tranny is now on charge. It got a ten minute flight a week ago and now its flat, Nicads won't keep charge at all..unlike LIPOS. I want LIPOS in may transmitters PLEASE Mr Futaba. The Natural Philosopher <a@b.c> wrote in news:1157390024.27829.0 @proxy02.news.clara.net: > hah. Funny that just as I was reading this, I went out to fly a little > model on my no 2 TX (futaba FF6, NiCd cells)...and it started out at [quoted text clipped - 4 lines] > tranny is now on charge. It got a ten minute flight a week ago and now > its flat, NiCd has a pretty hefty self-discharge, but not *that* hefty. If it was fully charged a week ago, it should have been fine today. There's something seriously wrong with that pack; I'm guessing at least 1 bad cell and maybe 2. > Nicads won't keep charge at all..unlike LIPOS. I want LIPOS in may > transmitters PLEASE Mr Futaba. If they include the regulation circuitry like cell phones & laptop computers, then yes. But if I have to put my Tx in an ammo box whenever I want to charge it, and closely monitor it for fear that it will burst into flames . . . well, my Tx isn't weight-critical ly my planes are. Tx LiPos aren't a priority for me. Signature"Whatever will have been, will have been." - Douglas Adams, "Life, The Universe, and Everything" | > Doug McLaren Wrote: | > | > The NiCds dropped as expected when they hit the 'knee', but the NiMh | > drop-off curve wasn't a curve, it was a cliff. Strange. NiCd looks pretty `cliff-like' too once you get below 1.1 v/cell. | > I'd be real money that if your model was flying when the NiMhs reached | > the end of the discharge 'plateau', you wouldn't have enough charge | > left to land unless you were about to touch down anyway. Well, the problem with this bet is that `plateau' isn't very well defined. But either way, let it go down to 8.5 volts (when the alarm goes off), you don't have much time left, NiCd or NiMH. The two spec sheets Red gave for AA NiCd and NiMH cells give relatively similar discharge charts for around 300 mA discharge rates once you take into account the different scales in the graphs. (And it's important to consider similar discharge rates ... things look different at higher discharge rates.) | hah. Funny that just as I was reading this, I went out to fly a little | model on my no 2 TX (futaba FF6, NiCd cells)...and it started out at | 9.6v. It should have started out at around 11.0 volts. Either it wasn't charged properly, or one of your cells has shorted out. Or both. | Withing 30 seconds the tranny was beeping and showing 8.2v. 30 | seconds later it was 8.1v.. [quoted text clipped - 5 lines] | Nicads won't keep charge at all..unlike LIPOS. I want LIPOS in may | transmitters PLEASE Mr Futaba. The 14MZ comes with a LiPo or Li-ion battery. And yet it still only lasts a few hours, since it uses so much power. NiMH cells do self-discharge a good deal faster than NiCd cells. But even with NiMH cells, a week or two of idleness after a full charge should still leave you with plenty of juice for flying. Beyond that, I'd strongly suggest charging. (And I always charge RX packs at most a day or two before flying -- you don't have a nice gauge or warning bell to tell you when it gets low ...) SignatureDoug McLaren, dougmc@frenzied.us It's hard to be nostalgic when you can't remember anything. --Unknown Steve, According to your tx's spec sheet in the manual, current draw is reported to be 250ma......... as noted here already, the Low Voltage warning trips on at 8.5VDC. Nominal Nicad voltage is 9.6VDC. Personally, I would not fly it below 9.4VDC, as the "dump" curve on the battery below this point is rapid... Cheers, Bill > I have a Futaba TX that has a digital readout for the battery > voltage (T6XAS). As far as I know, it doesn't have a low voltage [quoted text clipped - 8 lines] > Thanks, > Steve Thank you everyone for all the info, I learned a lot from it all. I learned that the Futaba site is very difficult to use and just because I can't find something on it doesn't mean it's not there. That my batteries can stand a bit more discharge than I've been giving them even though they've got some mileage on them, but also that a new pack (with much higher capacity) is well under $15. And, finally, if you ask a question someone will certainly give you an answer, and the whole thing may well spin off in to something that's actually interesting to read (and, at times, even related to the topic at hand...). Thanks, Steve > Thank you everyone for all the info, I learned a lot from it all. I > learned that the Futaba site is very difficult to use and just because [quoted text clipped - 5 lines] > thing may well spin off in to something that's actually interesting to > read (and, at times, even related to the topic at hand...). Just to add my 5 cents, I had a 6XAS and on the odd occasion the low bat signal went off, I was often able (had) to continue flying for a couple of minutes until the strip was clear and never had a problem. |
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