Do all BMSs "waste" the energy of overvoltage modules?

I have tried to research this topic, but without a definitive answer, so far:

From what I have seen/read, Battery Management Systems that balance the modules/packsin a battery (I'll use 'module' to refer to each set of parallel cells in the rest of my post), do so by lowering the voltage of any modulesthat are at a higher voltage - reducing them to the voltage of the lower (lowest?) modulein the battery. They do this, if I am correct in my thinking, by discharging some of the energy stored in the higher voltage modulethrough high-wattage resistors.

My question is this: This seems a big 'waste' of energy. Are there any BMSs around (either in design stage or as physical products) that use this energy to charge the lower/lowest voltage modulesso that all of the modulesreach the same voltage and are truly BALANCED as opposed to reducing them all to the lowest voltage?

If my thinking here is way off the mark, then I would appreciate being directed to a good read about BMSs, by the way!

Thanks in advance for any and allresponses from the community.

There are active balance units that transfer between cells:
One of the better ones is "QNBBM 1s active balancers":
https://www.aliexpress.com/item/lit...oltage-difference-within-10mV/1768384410.html
https://secondlifestorage.com/t-QNBBM-balancers
They do work but you still need other BMS functions & a bad heater may pull your whole pack down.

It also depends on how tight your power budget is - if every watt counts & you can't add more solar, then maybe this is for you vs resistive balancers.

Yes what you're looking for are active balancers. I use an active balancer as well. Now the question is how much waste it is vs passive. After using my packs for a year I find that properly balanced packs don't require much balancing at all. My balancer will balance at most 1A, but I suspect it's closer to 200-500ma continuous. I also don't charge to the maximum voltage (4.2V) or the lowest voltage (2.8V). If I do that I know my packs will start to deviate faster as it approaches the max, just because the curve of the charge at it's peak or bottom is almost flat. By keeping at between 4.05v to 3.6v on my system and with properly balanced packs I haven't had any issues deviating by more than 20ma. My active balancer only turns 'on' when there's a deviation of 30ma or greater. So most of the time it's sitting idle. The same thing will happen for a passive balancer, as you only require it to drain when you hit a certain criteria, like if you do top balancing, ie. only balance when it hits a certain high voltage or state of charge.

not2bme said:

Yes what you're looking for are active balancers. I use an active balancer as well. Now the question is how much waste it is vs passive. After using my packs for a year I find that properly balanced packs don't require much balancing at all. My balancer will balance at most 1A, but I suspect it's closer to 200-500ma continuous. I also don't charge to the maximum voltage (4.2V) or the lowest voltage (2.8V). If I do that I know my packs will start to deviate faster as it approaches the max, just because the curve of the charge at it's peak or bottom is almost flat. By keeping at between 4.05v to 3.6v on my system and with properly balanced packs I haven't had any issues deviating by more than 20ma. My active balancer only turns 'on' when there's a deviation of 30ma or greater. So most of the time it's sitting idle. The same thing will happen for a passive balancer, as you only require it to drain when you hit a certain criteria, like if you do top balancing, ie. only balance when it hits a certain high voltage or state of charge.

Click to expand...

What active balancer are you using?

bogptrsn said:

What active balancer are you using?

Click to expand...

https://www.aliexpress.com/item/4-2...-multi-channel-equalizer-BMS/32816488046.html

Nothing special balancer, doesn't allow any customization. But it has a serial lcd output that I use to put the info into grafana. You can see some test on my build:
https://secondlifestorage.com/t-The-Outhouse-Powerwall?pid=35023#pid35023

I use these active balancers I just connect to the balance connectors, they balance during charging/discharging at up to 6 amps. Its connected to my 4s 220 ah lifepo4 battery that had balancing problems. After a year in use have worked quite well. The 4s balancers cost me about 92 dollars when bought a year and half ago, price is higher now. They can be use on lifepo4 or li-ion and they have for all series of batterys. I bought from electriccarpartscompany. Without these balancers one of the cells(modules) shown in picturewould be reading 3.55 volts and would trigger the bms to stop charging before the battery was even fully charge. These you just connect to battery, no programming needed, they work in the background.

If you are burning too much power with a passive balancer, you really need to build better matched packs. Active balancers do have the advantage of generating less heat.

That said, given there are some reasonably priced options out there, I would be worth going for active balancing. However, without logging, such as what Batrium offers, it can mask problems with your packs.