3P Three batteries

[charliehorse]

Hi All
Just a quick question. I swear I am not trying to shortcut without searching for my answer.
Most topics regarding parallel charging relate to Lipo packs with single series'ed cells.
I made up some 3P7S batteries using Sanyo 18650's with balance leads on each cell.
I have a Revolectric Powerlab8 with the balance board.
I have three batteries charging but I am unsure about selecting 3P or 9P
Basically if I have three, 3P batteries charging, does that make 9P as far as the charger can see?
It works ok using 3P or 9P so which is the correct setting?
Just afraid I am charging at too high a current.
I have the PC interface.

 

[icerider]

Basically if I have three, 3P batteries charging, does that make 9P as far as the charger can see?

The current going in will see 7 sets of 9 batteries. So paralleled for charging the composite battery is 7s9p.

BUT... you are really only concerned about the charge current being driven in. Say each of those 18650s is 2000mAh. You have 9 in parallel for a total of 18Ah. So, 18 amps of current going in is 1C.

I don't know what C-rate your batteries will sustain for charging, but many good cell types (e.g. Sony US18650VTC4) are limited to 1C or below. The chargers for most "turn key" ebikes take 4-6 hours to fully charge a depleted battery. Now some of this time is spent in the constant voltage reduced current portion of the charge, but it is clear that they are NOT charging at 2C rate. It is also true that higher c-rates for charging reduce cell life. All of the e-cigarette batteries that advertise high c-rate charging also advertise pretty low cycle life (400-500 cycles). So that is just one more reason to keep the c-rate for charging reasonably low.

I would MEASURE the charge current (in the bulk charge wires at either end of the battery) and would choose settings that keep the charge current well below the 1C 18 amp level and fully charges the battery in 4-6 hours.

 

[charliehorse]

Hi Ice,
Thanks for that. Thought I had posted in the wrong place...
I was unsure how the charger sees multiple batteries attached to the balance board. So it as one battery.
I will choose a charge current setting that gives 1C max to the total batteries on charge.
I assume that the info on the PC interface like IR and fuel figures and graphs
would not be very meaningful with multiples charging on the board.
I was going to use the batteries down to 3.6v and then use the mAh-In figure to set a suitable charge current.
This would find the true capacity of each battery.
I could charge similarly matched capacity batteries together with a current to charge them around 1C.
They are all red Sanyo cells. I see 2600mAh being quoted for new ones.