First battery built, confusion re capacity, charge in.

[mctubster]

Hi all,

Thanks you all for the great info here.

I built my first LiPo battery from new drone batteries (Xiro Xplorer 11.1V 5200mAh) making a 10S4P battery pack.
(the drone batteries were 3S2P and a bargain at $15 each)

According to my calculations this is a 37V x 10.4Ah = 384Wh battery.

When I charged from 35V (resting) monitored the charge with a Mooshimeter (logged the voltage and current every 1 minute).
At charge termination (2A charger) ... when I calculate the charge in I recorded 431Wh.

Should I be concerned?

Battery is not warm during charging, has a BMS attached. Are the batteries that over spec'd?
I calculated the charge in by summing per minute Volts*Amps/60. Is this wrong? I figured it would be closed enough as the rate of change of voltage and current is minimal per 1 minute period.

Thanks!

 

[dustNbone]

If you made a 10S4P pack of 5200mAh cells, you should have a 20.8Ah battery, which at 37V would be a bit over 750Wh.

 

[e-beach]

Hi all,

Thanks you all for the great info here.

I built my first LiPo battery from new drone batteries (Xiro Xplorer 11.1V 5200mAh) making a 10S4P battery pack.
(the drone batteries were 3S2P and a bargain at $15 each)

According to my calculations this is a 37V x 10.4Ah = 384Wh battery.

When I charged from 35V (resting) monitored the charge with a Mooshimeter (logged the voltage and current every 1 minute).
At charge termination (2A charger) ... when I calculate the charge in I recorded 431Wh.

Should I be concerned?

You need to be a bit more clear on what you built. Did you build a 10s2p battery or a 10s4p battery?
If you built a 10s4p battery it goes like this.


10s4p=769wh nominal.

This is a ball park rule of thumb, but it goes like this.
3.7v x 10 cells in series = 37v nominal. (It is nominal because the a full charge is 4.2v but that 4.2v drops to 3.7v soon after the battery's are used.)

5200mAh x 4 strings of 10 cells in series = 20800mAh divided by 1000 = 20.8 Ah.

So, 20.8Ah x 37v = 769 watt hours nominal.

IF you charge to 4.2v per cell, you might even get more then 769 watt hours of usage.

Double check your total capacity and review how to safely charge your new battery pack so you don't do something wrong, like accidentally burn your house down.

 

[mctubster]

You need to be a bit more clear on what you built. Did you build a 10s2p battery or a 10s4p battery?
If you built a 10s4p battery it goes like this.

Sorry I was ambiguous. Each cell is 2600mAh so yes 10s4p = 10400mAh.

I confused the issue because the each drone battery was 3s2p which I thought was unusual.

Let me rephrase ... is a battery pack likely to be 10-12% under-specified in capacity? Seems like a lot.

 

[e-beach]

Sorry I was ambiguous. Each cell is 2600mAh so yes 10s4p = 10400mAh.

I confused the issue because the each drone battery was 3s2p which I thought was unusual.

Let me rephrase ... is a battery pack likely to be 10-12% under-specified in capacity? Seems like a lot.

Some battery manufactures and sellers round up from what they really have. Instead of rating from say 3.7v they rate from the full charge of 4.2v.

So they say 10 x 4.2v = 42v x 10.4ah = 436.8 watt hours or something like it.

So, if your are charging to 4.2v per cell, you should have around 436 Wh at you disposal. If you are charging to less then 4.2v then you will get less watt hours to use.

 

[dogman dan]

Brand new lipo can be a bit bigger than the spec. Not always the case, but sometimes 10% bigger than they call them happens.

I would not worry, that 10% more wont last all that long. ALL that matters, is don't overcharge much. If you need more capacity, you can charge them a tiny bit higher than 4.2v per cell. If I end up with a few cells charged to 4.25v, I don't panic, I just discharge them back to at least 4.2v asap.

If your charger is not taking them over 4.2v, absolutely fine, even if capacity in is a lot higher than expected.

Lastly, even if not warm, some watt hours were lost along the wires, connections, the bms functioning at top of charge, and slight heating of the cell. So you should always put in a tad more than you think should be able to come out. With a bms involved, or a balancing RC charger, you have a high charged cell discharging down a few times, making a lot of heat at the bms.