Data Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports

[davecrash]

Originally Posted by AirChime

Hi Dave - thanks for the info. How does a Watt meter hook up to the system? Also, a 1300mah lipo at 20C would be 1.3 x 20 = 26 amps max discharge (right?), however are there any negative results that could be associated with using a battery that has a max amp draw that's way higher than what the system requires?

That is correct for the 20C. The higher C rating will actually give you a little more power out of your system and the liPo will be a little heavier too. I have deans plugs on my Watts up and it goes between the battery and ESC. just plug it in and run it up. It will tell you the amps, watts, mah and voltage. I test all my setups this way on the bench before the first flight. If my system wants 20 amps then I look for a battery capable of at least 25amps.

[AirChime]

Originally Posted by davecrash

That is correct for the 20C. The higher C rating will actually give you a little more power out of your system and the liPo will be a little heavier too. I have deans plugs on my Watts up and it goes between the battery and ESC. just plug it in and run it up. It will tell you the amps, watts, mah and voltage. I test all my setups this way on the bench before the first flight. If my system wants 20 amps then I look for a battery capable of at least 25amps.

Sounds like I need to get a Watts Up. Too bad they're out of stock! So a higher C rating could damage my ESC if it can't handle the extra amps?

[davecrash]

Originally Posted by AirChime

Sounds like I need to get a Watts Up. Too bad they're out of stock! So a higher C rating could damage my ESC if it can't handle the extra amps?

Everything has an amp rating that you have to stay within. Your currant setup should be fine, I assume this was a manufacture motor ESC combo? The higher "C" battery shouldn't be any problem. the higher C battery will just give your setup a little more umpth and only draw another amp or 2. Can you tell me what you have right now? Motor, Esc, Fan, etc. Send me a PM, were taking this thread off topic.

[carlsoti]

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[AirChime]

How does one calculate the max amp draw of a Lipo from the C rating and the mAh rating? I read another post that said it's not quite as simple as multiplying the C rating by the mAh... Something about degrading the C rating by 30%? Say I have a 20C 2200mah Lipo. Would that mean it's 14C x 2.2Ah = 30.8 max amp draw? If I were to calculate 1C of this, would I use the rated C value of 20C or the degraded value of 14C?

Thanks!

[carlsoti]

Your max calculation is correct. People use 70-80% to help promote long battery life. That battery may, in fact, put out 40+ amps, but doing so for any length of time may reduce the # of cycles you get out of it.

If you're trying to determine 1C rates for charging, I think you should be safe using the full 20C rate, which would be 2.2A.

Keep in mind, I've only been doing this just short of 1 year, so others may chime in and correct the info I've provided.

[williec30]

this seems like a silly question given all the great info here... maybe i am just missing it.

should i be discharging my lipos after every use? if no, how often should it be done?

and checking my math, i have a turnigy 2200mAh 3cell 11.1v : 30-40C discharge. so, 2.2mah x 30c = max 66 amps

thanks in advance...

[hoppy]

Originally Posted by williec30

this seems like a silly question given all the great info here... maybe i am just missing it.

should i be discharging my lipos after every use? if no, how often should it be done?

and checking my math, i have a turnigy 2200mAh 3cell 11.1v : 30-40C discharge. so, 2.2mah x 30c = max 66 amps

thanks in advance...

Discharge after every use? Absolutely not. If you used the "discharge no more than 80% of the packs capacity just leave it uncharged till the next week(s) flying.
If you used almost all of the packs capacity, charge it to 3.7-4V/cell and finish charging just before flying next time.
If you didn't use the pack, you can either discharge to 3.8-4V/cell or just keep it till next week.

The idea is to store the pack at something other then fully empty or fully charged. For long term storage, put them at 3.8-3.9V/cell.

Your math is correct. 2.2Ah x 30C = 66A
The real question is: "Is the manufacturers C rating accurate or inflated for sales purposes?" I like to plan on only using 50-70% of what the manufacturer claims it can do.

[williec30]

thanks hoppy...

so, the discharge feature on chargers/balancers is only used when needing to bring batteries down for storage purposes?

[hoppy]

Originally Posted by williec30

thanks hoppy...

so, the discharge feature on chargers/balancers is only used when needing to bring batteries down for storage purposes?

Maybe, maybe not....
Most older chargers with a discharge function that discharges the lipos down to 3V/cell which is good for determining the capacity of the lipo but not for storage. You might want to check capacity once or twice a year to see how the packs are aging.
Some newer chargers have a storage discharge capability which puts the pack voltage at 3.85V/cell.

So it depends on what features your charger has if it can be used for storage discharge.

Of course, the packs can be put into storage condition during either discharge or charge by simply watching the voltage and stopping at 3.85V/cell.

[AirChime]

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