best voltage/cell arrangement for maximum capacity? DIY 18650 pack

Thread Starter

bigjoncoop

Joined Feb 1, 2019
60
hey fellas,
im currently using a 4s6p 18650 pack I made to run a rc/lipo charger to charge lipo's in the feild. the pack was working fine powering my older charger that pulled a max of 6amps.

I just purchased a new charger that can pull up to 15amps. If I set it to use 10amps or so, with in 5min the chargers low voltage input alarm goes off which is set to 13v...

I just purchased 40 more 18650 batterys to add to my pack. So my question is what is the best cell arrangement in order to get the maximum amperage and capacity out of the pack? the highest voltage battery I use this charger for is 4s. (16.8v)

My charger specs:
Specification:

Input Voltage: DC 10-30V
Output Voltage: 0-30V
Charge Current: 0.1-15A

Am i better off making my battery pack 5s or 6s or keeping it at 4s and just add the 40 new cells in parallel and make a 4s16p pack?

Thx
 

Alec_t

Joined Sep 17, 2013
10,607
If the chemistry of the cells in your pack is the same as that of the cells you want to charge then a 4S pack is inadequate. The pack voltage must be higher than 16.8V to give the charger some headroom so that it can charge the cells fully.
 

Chris65536

Joined Nov 11, 2019
139
Input Voltage: DC 10-30V
Output Voltage: 0-30V
Charge Current: 0.1-15A

Am i better off making my battery pack 5s or 6s or keeping it at 4s and just add the 40 new cells in parallel and make a 4s16p pack?
Higher voltage might help, but it depends. Does the charger have a DC-DC switching converter? What is the voltage of the Lipo batteries you are charging?
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
60
Hey guys thanks for your quick responses. The lipos I am charging are 4S packs.

And the charger must have buck-boost capability because it can take anywhere from 11 to 30 volts and charge any pack up to 8s.

Now before I got my newer charger my older charger also had buck-boost capability but was only capable of delivering 6 amps or 80 watts. And my 18 650 pack in my charging case would last for quite a while. It's just now that I am trying to charge at over 6a usually around 10a, my 18 650 pack seems to die fairly quickly. A lot faster than it was with only pulling 6 amps from it.

Here is the PDF of my new charger I'm trying to power. Rctoolkit m8 "badass MA'AMA JAmma

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.toolkitrc.com/filedownload/61003&ved=2ahUKEwiZm87B3JrmAhVaHTQIHRc1Bf8QFjAJegQIBhAB&usg=AOvVaw1t0GsjHVxtD4n28MkOP8ye


So basically should I keep my 18 650 pack at 4S and just add the other 40 cell I just got in parallel or would it be wise to raise the voltage of the pack. Here's the breakdown of the cells that I have.

Currently I have 24cells around 1300mah in a 4s6p config.

Just got 40 more cells that are also 1300mah.

Using this pack to charge 4s 1500mah lipos. Normally at 10amps into 3 lipos in parallel. My goal is to charge as many lipos as possible from my fully charged 18 650 pack.

Thx
 

Chris65536

Joined Nov 11, 2019
139
And the charger must have buck-boost capability because it can take anywhere from 11 to 30 volts and charge any pack up to 8s.
Higher voltage would mean lower amps, and less voltage drop. If it really is a buck converter, that is. Can you measure the voltage drop while it's charging? What size conductors connect the 18650 pack to the charger?
 

oz93666

Joined Sep 7, 2010
701
Beyond doubt go up to 6s the input voltage of charger is 30V so it's perfectly fine this will definitely solve the problem
 
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