Chargers Quick questions about battery maintenance

[callsign4223]

Didn't see a battery section Tony so the charger section seemed like the next best spot.

Question number 1: How do you measure the voltage of individual cells? Whenever I put a multimeter on the first and second pins of the balance plug I get a number that looks like 1 cell voltage, i.e. 3.7, but when I put it on pins 1 and 3 I get a number like 2 cells i.e. 7.2 and so on. Do I just write down each value and subtract the first cell value from the second value and that is it, or am I doing it wrong somehow?

Question number 2: How damaging is it really to leave a lipo at full charge for extended periods of time, like a month or more? With my Thunder AC6 it takes a full evening to charge all my 3S lipos and with the wind in Oklahoma I never know when I might actually get a chance to fly. If I don't leave them charged I stand a good chance of missing a nice flying day.

Question number 3: Are there any good sub $100 charger/powersupply combos that will show internal resistance? I have looked on my AC6 and it doesn't appear to do it.

 

[Lee]

1) Get a lipo battery voltage checker. It will show all the individual cell voltages.
2) If they are at 4.2V and the temp goes up, then they can go over that and damage them. Charge them to just below, say 4V and then you can just top them up when you need to go flying.
3) Don't know any cheap chargers that show resistance.
Hope this helps.

 

[callsign4223]

So the real danger is if they go over temp and then over charge? What about keeping them in the fridge/freezer then and letting them warm up on the way to the field, or would that damage them as well? I think my AC6 has a way to do custom programs, so I think I could set it up to charge to 4V without too much difficulty.

 

[Derek]

To easily check your batteries cell voltage, you may consider getting one of these

http://www.horizonhobby.com/products/li-po-cell-voltage-checker-EFLA111

I have basically the same thing, just a different brand name. You plug this into your lipo's balance port and it will tell you the voltage of each individual cell as well as the total voltage of all cells, up to 6S. It's a handy little investment and it doesnt take up much space at all in a field box or just put it in your pocket.

After buying this lil tool, I know that I can get one more flight from my plane before I need to call it a day.

 

[pvolcko]

If you can measure each pin against pin 1 then you can measure pin 2 to 3, 3 to 4 to get the other cell voltages without having to do the subtraction.