Newbie question re. using a balance-charger in combination with a BMS

Joined
Jul 15, 2022
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Building my first e-bike pack, I plan to have a BMS and a bulk charger wired to the BMS, but I also want to be able to use a balance-charger periodically to monitor and fine-tune the state of the in-series groups. The question is how to connect the balance charger to the pack? Should I unplug the balance wires connector from the BMS and plug it into the balance charger or add a 2nd set of balance wires just for the latter? And how do I connect the balancer-charger's power cable? Through the pack discharge cable mounted on the BMS? Or should that be connected directly to the pack terminals by-passing the BMS altogether?

In short, would having a BMS in-place interfere with the normal operation of a balance-charger?
 
Yes.

The core battery should be bare cells no circuitry hardwired.

Balance leads available without breaking open the pack, for:

Per cell/group voltage check independent of BMS

BMS when desired, easily replaceable

Balance charger.

Maybe a dedicated active balancer if / when a higher balance rate becomes a good idea as the cells wear.

Getting a protective-only BMS no balancing function would simplify things, most just suck at that anyway.

HVC will be handled by the charger anyway, low temp cutoff can be manual, short / OCP can be a good fuse

If you are not implementing LVC in use, or the controller handles that, maybe go without a BMS while riding, just monitor voltages.


 
john61ct said:
Yes.

The core battery should be bare cells no circuitry hardwired.

Balance leads available without breaking open the pack, for:

Per cell/group voltage check independent of BMS

BMS when desired, easily replaceable

Balance charger.

Maybe a dedicated active balancer if / when a higher balance rate becomes a good idea as the cells wear.

Getting a protective-only BMS no balancing function would simplify things, most just suck at that anyway.

HVC will be handled by the charger anyway, low temp cutoff can be manual, short / OCP can be a good fuse

If you are not implementing LVC in use, or the controller handles that, maybe go without a BMS while riding, just monitor voltages.

Thanks for your reply. So let's say I already have a battery pack with a BMS that I want to balance-charge with an iCharger. Are you saying I can't use the existing battery output lead (from the BMS)? Are you sure of this? How inconvenient!
 
Not if you disable the BMS balancing function, or if a bad design not allowing that, keep the termination voltage below its start-balance setpoint.

But you now have a system that is an inherently bad design, exponentially more complex, thus much more likely to wrong, and more opaque to troubleshooting.

 
theabsurdman said:
Are you saying I can't use the existing battery output lead (from the BMS)?
None of the above has anything to do with discharging.

IF your BMS is separate input/output, then charging happens in the input side only

 
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