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how about this instead of a bms?

Posted: Oct 22 2017 11:05pm
by Hummina Shadeeba

Re: how about this instead of a bms?

Posted: Oct 22 2017 11:13pm
by Ykick
Balance only not for protection.

Re: how about this instead of a bms?

Posted: Oct 25 2017 10:53am
by Hummina Shadeeba
it will not protect against over-discharge but assuming it's working right it should protect against over-charge which is the real danger anyway, no? I got a couple of these and plan to use them. I will monitor cells periodically but unless someone can convince me this isn't safe enough it seems so to me. I'll charge somewhere safe just incase.

Re: how about this instead of a bms?

Posted: Oct 25 2017 11:10am
by Addy
Hummina Shadeeba wrote:it will not protect against over-discharge but assuming it's working right it should protect against over-charge which is the real danger anyway, no? I got a couple of these and plan to use them. I will monitor cells periodically but unless someone can convince me this isn't safe enough it seems so to me. I'll charge somewhere safe just incase.
From the ebay page it says "Operating Current:68mA". This means it's balancing by draining individual cells at 68 mA to bring them into balance with the other cells. I'm sure your charger can charge at a much higher current than that, which means your charger could still overcharge a cell and this balance board will be too weak to stop it.

They even say on the ebay page "This balanced board has no function of charging or discharging,and it cannot replace the protection board."

Re: how about this instead of a bms?

Posted: Oct 25 2017 12:18pm
by Hummina Shadeeba
and that's what I thought, that the current it could burn off while balancing would be too little, but people told me that if the cells were equally matched it wouldn't be an issue. Yea if the cells were way off or ended up way off then when getting towards full charge there could be a bum cell that could be charged faster than it can discharge and could potentially go way over a safe voltage. We will see

but tell me would the balance function only be happening while charging? I think so and then the risk is as stated, but if it balances all the time then not an issue.

Re: how about this instead of a bms?

Posted: Oct 25 2017 12:33pm
by Addy
Hummina Shadeeba wrote:and that's what I thought, that the current it could burn off while balancing would be too little, but people told me that if the cells were equally matched it wouldn't be an issue. Yea if the cells were way off or ended up way off then when getting towards full charge there could be a bum cell that could be charged faster than it can discharge and could potentially go way over a safe voltage. We will see

but tell me would the balance function only be happening while charging? I think so and then the risk is as stated, but if it balances all the time then not an issue.
This board wouldn't know when you're charging, so it should be balancing all the time.

Even if you had this thing balancing all the time it won't cure bad cells. For example if you discharged your pack and your cells were at 3.3V each, the balancer would be happy because all the cells are at the same voltage. However, if the cells are unmatched and you charge the pack, some cells will charge up faster and they might get overcharged. Just having the voltages balanced before charging doesn't protect you.

Re: how about this instead of a bms?

Posted: Oct 25 2017 12:44pm
by Hummina Shadeeba
aha. thank you. i'll monitor the cells and see. I've heard of people replacing the resistors so as to be able to discharge more.

if cells are always balancing with this thing or a bms, and it's using resistors to drop the higher cell's voltage, then the energy storage would be only as good as the weakest cell as every other cell will be pulled down to it in the balancing no?

Re: how about this instead of a bms?

Posted: Oct 25 2017 6:56pm
by Voltron
Sort of, but not the way you're thinking. It bleeds off the high ones, but then they go back up as the low one catches up. So each group ends up fully charged, not with a few artificially low to match a weak group.
But you still have a problem, as a weak group that goes low quicker than the others is still limiting your pack power to the capacity of the weakest group, and its going to need lots of balancing. so you still end up with a weaker battery, but not because of bleeding off high groups. That is, in my mind ,the main reason to run a BMS... I can manually monitor the top balancing, but I've killed several batteries by having a group go to super low voltage during hard running that didn't get noticed in time, and something automatically protecting against that would have saved some hassles.