How to charge two batteries.

[shawnd816]

Ok I took two scooter batteries each 36v ran them together to get 72v. Each one has it's own BMS. Each bms has to be bypass to work. I did that. Now when I charge them should I unplug them from each other and charge each battery by itself,or is there a safe way to change them while they still plugged into each other

 

[E-HP]

Ok I took two scooter batteries each 36v ran them together to get 72v. Each one has it's own BMS. Each bms has to be bypass to work. I did that. Now when I charge them should I unplug them from each other and charge each battery by itself,or is there a safe way to change them while they still plugged into each other

What type of BMSs do the packs use? Are they single port? Why did they need to be bypassed to work and how did you do it?

 

[fill]

How much extra hassle is it to pull and charge the batteries separately?

Have you considered adding plugs and sockets to your batteries to facilitate easy disconnection for separate charging.

 

[shawnd816]

They came off a bird rental scooter. The only way for me to get the 36v output was to bypass BMS. From my understanding even know it's bypassed it still charges it correctly.

 

[freesty]

When the BMS is bypassed it's not safe to charge/discharge.

 

[docw009]

When the BMS is bypassed it's not safe to charge/discharge.

I killed a new 48V battery that way, bypassing the BMS and putting on a load I thought would self-shut off at 40V, but when I came back, it was at 21V. If you're doing a scooter, the controller should shut off around 60V , but it would be wise to stop around 30% SOC,

If the batteries can still charge from their regular charge port, the safe way to recharge is to disconnect the series connection, and charge each battery separately.

 

[E-HP]

They came off a bird rental scooter. The only way for me to get the 36v output was to bypass BMS. From my understanding even know it's bypassed it still charges it correctly.

Neither battery is safe to charge or use.

 

[Tony01]

DO NOT BYPASS BATTERIES.

With BMSs: You will be fine charging them connected as 72v. The only difference between a stock 72v and this is that you now have a custom battery with a separate bms for each half. The batteries don’t know or care what configuration they’re run in.

 

[amberwolf]

The only difference between a stock 72v and this is that you now have a custom battery with a separate bms for each half.

If he had a BMS, that would be true, but he doesn't, because he bypassed them.

 

[fill]

If the default bms boards are locked due to f/w and not being able to handshake etc replace them. you could then source a 72v bms and wire up the cell groups from both packs for a complete solution**. It might cost $30? more and be a pita to wire up, but at least its a proven solution with no experimental features..

 

[Tony01]

If he had a BMS, that would be true, but he doesn't, because he bypassed them.

With a brief ES background check I see guys new.

OP you are too new to this stuff to be bypassing batteries and rigging them up. There are too many things you don’t know about how to safe handling batts, how they perform when having problems…

I suggest you put the BMSs back on and get a new 72v off amazon. They really aren’t that expensive. Batteries are NOT safe to be worked on in general so pros take lots of special precautions. I don’t know if you have ever blown up batteries but I have, a few… it is NOT a fire you can put out with water or fire extinguisher, or even get within 1m of…