BMS balancing and charging only to 4.0v

I tried searching and couldn't find an answer for this.

On the Smart Chinese BMS's such as Aliexpress 7S 30A/40A/60A active bms 2018 new Li-ion smart bms pcm with android Bluetooth app UART wi software (APP) monitor

if I set the top voltage to 4.0v will this unit maintain balance. Looking for as many cells in possible.
Will it shutoff charging if only on cell bank goes high?

Or will the unit charge each bank to 4.0v then stop?


Sorry for the newbie questions.

That's a good question. Not really sure. But, generally speaking, a balancing BMS will allow all cells to charge up. Then when a cell starts to go over a preset voltage, it starts burning off that voltage to keep it low until the rest have caught up. Generally.

Thanks for the quick reply.

Is there a BMS that will charge in Parallel then switch the circuit back to Series? Then they would all be balanced.

Or is there a BMS that independently charges each cell that is series connected thus cutting off charge to each cell bank once desired Voltage is reached?

Seems burning overVoltage is wasteful and more dangerous.

I think you want a active balance bms

Bubba said:

Thanks for the quick reply.

Is there a BMS that will charge in Parallel then switch the circuit back to Series? Then they would all be balanced.

Or is there a BMS that independently charges each cell that is series connected thus cutting off charge to each cell bank once desired Voltage is reached?

Seems burning overVoltage is wasteful and more dangerous.

Click to expand...

The BMS doesn't charge your battery it's your charger, inverter ..., so to charge in parallel you must set a lot of cabling, contactors, relays or whatever that disconnect from your battery, that are in series and recable it in parallel to charge with a different charger that your normal 12V, 24V, 48V. First that imply that you can't use it as battery (won't power your inverter) and second you need a huge 4.2V charger to charge them all in parallel, so for a live solar system that makes no sense.

To the second question, again the same, it is your charger wich charges the whole battery injecting 12V, 24V... to the extrems of the series of packs, you can't disconnect one serie when is charged.

The BMS only can waste some power where this pack reaches the desired voltage, cheaper option but a waste of power or make some kind of isolate power bus that transfer energy from highest voltage packs to the lowest ones, that's call active balancer as Jason said. Of course are more expensive, and normally are only balancer not a complete BMS, even expensive Batrium system is pasive.

I've bought few of these. Used by some friends around here. I already have a BMS that cuts by over current or over/under voltage of whole serie or single packs

https://www.aliexpress.com/item/1pc...2c1f-4642-847d-a29095424c55&priceBeautifyAB=0

So summarizing from the poit of view of charging your packs are a whole voltage system of 12V, 24V, 48V ..., to balance are independent 4.2V packs.

Regards

The onboard balancing on these BMS can only balance at 50 ma, that means you have to charge (with regular charger) the battery pack at less then one amp for it to stay in balance, if you fast charge at high amps the BMS will always trip and stop the charge early.

A balance charger will fast charge until one cell reaches 4.0 volts (you want) then the amps drop to less then 1 amp until all cells reach 4.0. This can take hours if the battery is severely out of balance.

Active balancer like in my picture will transfer amps from high cell to low cells (not bleed/waste any amps) at up to 10 amps, you can fast charge your pack all the way to 4.0 volts and each cell should stay in balance. Those who like to fast charge there batteries, active balancers are the way to go. I notice all my batteries no matter how well balance will drift off a little when fast charge, a little is all it takes to stop the charge early. If one of your cell reads 3.98 volts and all the rest read 3.90 volts, When the BMS stops charging your pack will be closer to 3.90 volts then the 4.0 volts you wanted. Myself I like my lithium fully charge everytime, even if they last less longterm. Even less life will still outlast lead acid.

If proper charger is used the bms will NOT trip the over voltage protection! Ie a charger that have a proper top voltage limit. This of course demands that your cells are in proper balance from start.

Note that a pack does not go out of balance unless something is horrible wrong. Thats why the industry have not needed more than 50mA of balancing current on small packs since start and I bet it wont change!

jonyjoe505: I guess you have calculated how much you loose when the active balancers transfer energy between packs all the time?

I found this active balancer online by accident.

https://www.ebay.com/itm/173387258279?ssPageName=STRK:MEBIDX:IT&fromMakeTrack=true


Could they be using active 'LOOSELY'? And it's actually resistivity burning and not transfering the energy from high cell to low cell?

Any thoughts?

That's a good question. Can't fully tell by the description and they don't give a good view of the devices used. Zooming in on the box doesn't show a good view of them, either. Just different S value boards depending on your need.

It looks like there isn't enough circuitry on those boards to warrant true active balancing. But, they may only be the gateway boards and the real work is done inside the main box.

On theTahmazo T6B Active Balancer, I found that its a cheaper version of the more powerful Tahmazo T6B MaxActive Balancer, the max version handles 10 amps and balances at300ma. The cheaper version handles 6 amps but no where I could find what the balancing current is.

But even if it could balance at 300ma,no way will it keep up with a battery that drifts out of balance during fast charging.

I couldnt find how it actually does the balancing but for the price I suspect it bleeds the high cells like my 10 dollar3in1 balancer. It says in warnings not to block the cooling vents.

Tahmazo T6B MaxActive Balancer

Doesn't look like the Tahmazo one is true active balancing, it's only balancing at 300mA/cell & like said above it's not physically big enough.

The better units are like these:
https://www.aliexpress.com/wholesale?catId=0&SearchText=qnbbm+active+balancer
They can balance at several amps, they continuously balance at all voltages.
They basically transfer energy between connected cells until the voltages are equal, whatever the voltage (has to be above min operating voltage).