Lipo Capacity Readings

[westyguesty]

I'm new to lipo's after getting back into rc cars again. I have purchased a few second hand sets that seem to perform OK.
I'm charging them with a Core UAC50, balance leads and the right setting for each pack.

I wanted to test the capacity of them, so hooked them up to my old Ice Deltapeak Charger as it will discharge up to 10 amps, as looks like the Core will only discharge at 1 amp.

The lipos are ok makes, reedy, lrp, speedpower. I have set the cut off to 6v.

I'm getting the following readings,

5300 cells 4072 capacity
4200 cells 2522 capacity
4200 cells 2804 capacity

Am I doing something wrong, or are these lipo's jsut past their best ?

Thanks

[RudolfXC]

I've tested brand new 5000mAh cells that have only stored 4500mAh.

Anyway, you'll probably never use more than 2500mAh in a 5 minute race.

[mattybucks]

Where as with NIMH's we would discharge them, with Lipo's it's bad to take the voltage to low. Most new Esc's have a cut off at around 3v per cell.

So back to your answer, I've never discharged them. Just charge, use, charge, use. I have two packs but usually just top the same pack up on a club night.

If they last a race they should be fine, even if the are past there best.

[mdb_75]

You're not discharging your lipo's right down are you? They're only meant to go down to 3 volts per cell (6 volts for a stick pack as they're made up of two cells) at the most or you will damage them. Mine never go any lower than around 3.5 volts per cell.

[westyguesty]

I have taken them down to 6v to test the capacity. As soon as they finish, the voltage rises to around 7v on their own. I then put them back on the core charger and charge them using the storage option.

[mdb_75]

Those Mah capacitys you've got are from a fully charged 8.4 volts down to 6 volts, what does each pack take to get back up to 8.4 volts, fully charged again?

You will never get back every Mah that you put in whan you discharge them, but Lipos are better that nicads/nimh's used to be.

Looking at your figures though they don't look too healthy..

[lardy37]

as far as i know when you charge a lipo in storage mode they do not charge right up they might go to 8.4 volts but that doesnt mean they are full as when you charge normally my charger will say 8.4 but still charge for a while after until the amps drop down. storage charge normally only half charges a battery hence storage mode so if you want to test them to there max set you speedo cut out to 6v run the car untill it cuts out then charge propely (but its not good to run them flat)

[westyguesty]

The core charger is putting in around 500-600 for storage mode.

To charge from cut off to full on the core charger are virtually the same figures as the discharge figures above.

[badger5]

When you charge a Lipo with the charger in storage mode it only takes it to approx 60% capacity. To test the capacity as you are doing balance charge each pack at 1C, the end voltage should be 8.4V and then discharge. If you have been doing that and those are the capacity readings you are getting then I would say that those cells don't look too healthy.
With Lipo's there isn't much capacity left once the individual cell voltage drops to 3V.
To get a better understanding of the type of test your trying to do have a read of the bigsquidrc Lipo shootout 4 article here; http://www.bigsquidrc.com/lipo-batte...0-mah-edition/
The capacity of your cells should be a lot closer to the amount they are rated at.