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-   -   Safe lipo voltage?? (https://www.wattflyer.com/forums/showthread.php?t=39087)

Reckless_Meanie 09-16-2008 01:23 PM

Safe lipo voltage??
 
Hello,
I've got 5 11.1v lipo packs. I always check them with a volt meter when I'm done using them. I never run them down low enough for the esc to cut off the power. My charger carges them to 12.6 volts and I uasually run them down to about 11.2-11.4 volts and that gives me 12-25 minutes of flight depending on how I fly. I know lipos are finicky (and expensive) and I don't want to ruin them. How low can I run the voltage. I've heard 9.0 volts 9.6 volts etc. but I'm not sure? What's best for the batteries? I store them at 11.4 volts. Is that correct?

Thanks
Travis

soar-ne 09-16-2008 02:52 PM

RM
Im with you on this one. I never run to ESC kick-out. I have read that Lipos are basically "dead" at the nominal voltage of 3.7v per cell in the percentage of energy left, so that where I stop also. I also overbuy on capacity and am sceptical of manufactures C rating and ussually figure a 20C battery is probably really a 15C so I figure my amp draw accordingly. I have never had a temperature problem or a puffing problem. OK, I puffed a small lipo onetime by shorting it out but that was my fault and not the batteries. I have some smaller Lipos (750ma) that are 4-5 years old and are starting to get a little anemic but still flyable. I believe if you buy a good product, use them conservativly they last a good long time!!!!!!!!

Happy Flying
Bob

coro 09-16-2008 04:50 PM

Everything is right.
There is a big difference between voltage under load, and voltage after load is removed, perhaps after few minutes of rest.. So that is the reason why You are not certain, probably.
Rest voltage should be at least 3.6V per cell (=flat empty), or much better around 3.7V (cca 20 percend left unused, the most recommended point to stop discharge).

Voltage under load depends on pack "C" rating, momentary load current, temperature and so on, so, it is not certain. 3.0V per cell is considered minimum, but with new, better and better cells, we are actualy at 3.2V per cell minimum, and there is nothing wrong if You set 3.3V cutoff if load is not that high and ESC will not prematurely cut the throttle.

However, You have mentioned overall pack voltage only. Be sure that in full state of charge, each cell has equal voltage that is at or below 4.20V (well balanced pack when fully charged), and You can verify also, after flight, that no cell get empty much sooner than others and fall way too deep. Do not try to balance discharged pack, do not be afraid if cell voltages will not be exactly equal after discharge.

Reckless_Meanie 09-16-2008 05:01 PM

So are you saying that at rest (a few minutes after a flight) an 11.1 volt battery should not be below 10.8 volts or 11.1 volts?

flydiver 09-16-2008 05:14 PM

Here's a chart I got off the forum (credit to who ever the author was). It gives you an approximate idea of RESTING voltage, which is no where nearly as accurate as voltage under load.
4.20v = 100% 12.6v
4.03v = 76% 12.09v
3.86v = 52% 11.58v
3.83v = 42% 11.49v
3.79v = 30% 11.37v
3.70v = 11% 11.1v
3.6?v = 0% 10.8v


Many, if not most, ESC have a LVC that is too low in my opinion. From the reading I've done I'm going with trying to leave a minimum of 20% left.

I think there a other reasons than crummy lipos we see so many unhappy people with dead/puffed ones.





Condre'2000 09-18-2008 09:06 PM

For some time I've noticed that some of my 3s lipos charge to 12.7 volts. Should I be concerned? That is slightly higher 12.6 that's often cited as the proper maximum voltage.


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