DIY Charger for 7S/29.4V ?

tjobapuerh

tjobapuerh

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Feb 10, 2021
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Hey guys!

I am about to assemble a battery I've been planning for a while, that was supposed to be 7S 24V li-ion.
The project has been infinitely delayed because of crazy shipping times due to the whole covid situation, obviously.

My problem now, is that I don't have a charger that would work for 7S.
I was too quick in my planning/ordering, because I had originally planned for 3/4S set-up.

Now I'm stuck with a 7S BMS and an iMax b6 charger that can only charge up to 6S.

I was wondering if it's possible to leave out one of the wires from the BMS, effectively making it 6S?

OR

I have a step-up step-down converter of 4v to 35v, and 0.1a to 5a. Could I fiddle with that to make my own custom 29.4V out of some laptop charger, or something like that? If yes, I believe my BMS would also take care of the balancing at charging (DALY BMS).


Thanks!
 
I would consider just purchasing a 7s charger, it is cheaper and less messing around than a DIY job for this bit.

You would need to build a CC/CV charge circuit to work with the BMS. When I was looking at this, it was far cheaper for me to purchase an electric scooter charger which uses CC/CV and then cut the end off and put my own connector on.
There are also some cheap modules you can buy online to manage CC/CV charging but worked out around the same price as a complete scooter charger.

You should not leave out the wire from the BMS. I am not sure (as I can't find a reference to one) that Daly has a 6/7s BMS, they make either one or the other.

Your alternative if you want to have a 6S cell is just to have it as a 6S cell, and use the iMax charger to charge and balance the battery pack.
 
deswong said:
I would consider just purchasing a 7s charger, it is cheaper and less messing around than a DIY job for this bit.

You would need to build a CC/CV charge circuit to work with the BMS. When I was looking at this, it was far cheaper for me to purchase an electric scooter charger which uses CC/CV and then cut the end off and put my own connector on.
There are also some cheap modules you can buy online to manage CC/CV charging but worked out around the same price as a complete scooter charger.

You should not leave out the wire from the BMS. I am not sure (as I can't find a reference to one) that Daly has a 6/7s BMS, they make either one or the other.

Your alternative if you want to have a 6S cell is just to have it as a 6S cell, and use the iMax charger to charge and balance the battery pack.
Click to expand...
Thanks man for your feedback! I will do as you suggest, I've located a local dealer for electrical scooters that sell a 29.4v (7s) charger at 3a. I guess that'll do the job -- because if I understand correctly the BMS should do the balancing during charge.

The 6S iMax alternative would mean operating w/o a BMS, and keeping an eye on the voltage manually during operation, correct?
 
The iCharger would be great as well - there is a really big debate on *cough* another forum where they are telling people to not use a BMS or anything else there and just use a voltage meter with a charger such as the iCharger, to do the charge/balance.

I would agree with OffGridInTheCity and have some sort of low/cut-off protection if you already don't have a charger and want to have something simple and have a general purpose tool.

I already have a few 6s chargers around, so for me it was easier for what I was doing (rebuilding a mobility scooter pack) to have a single 7s charger and BMS setup internally in the scooter.

Now I will have to add the iCharger to my shopping list :) I haven't had a need previously as most of my R/C stuff is up to 6s but the iChargers look nice and I haven't bought a charger in almost a decade!
 
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