High Power 10s Lipo Battery Pack with BMS

So I can also leave it on and it will do the magic? I guess it wouldn’t damage cells - current will be very low at the stage of trimming and balancing. I was under impression BMS is a full package and won’t have to be disconnected and connected again after full charge.

How would I know when cells are balanced ( BMS doesn’t have any LEDs) since charge will have green light on even before balancing is finished?

I use a lab power supply to charge my batteries. It starts in CC mode and continues to raise the voltage keeping it just enough above the battery’s voltage for the electrons to flow into the battery. Once the power supply reaches the max voltage that I set (42v) it then switches to CV mode. At this point the battery is usually around 41.5v Then as the voltage in the battery becomes more and more equal to the voltage from the power supply the flow of electrons (current) gradually decreases until the voltage (pressure) in the battery is equal to the voltage(pressure) coming from the power supply. I can’t say if a $12 charger works the same way or not. It would be easy to find out with a volt meter on the output of the charger while charging the battery

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You’ll know the battery is balanced when the total voltage stops dropping

Yes, it can “feel” it, if you want to put it like that. During CC mode, the voltage will rise as the battery voltage rises, linearly. Check this page out, third graph. https://endless-sphere.com/w/index.php/Charging_Lithium_Polymer_batteries

How can I tell it is balanced by using “Brick” 42V 5A charger with LED? It doesn’t display voltage … Well I have voltage meter attached to the board … but I guess I would have to look at it for some time so catch voltage drop. I guess I can’t just rely on Green LED on the brick right?

Thanks guys …

So in princip. I could charge my 10s pack without a BMS, and my Charger would still show green LED, when the pack have reached 42v (given that without my BMS, the cells would not be in ballance to each other)

I have latching LED switch which I would like to disconnect it from Vedder anti spark and connect it to built in Bestech BMS switch to save on space in my enclosure. Here are the schematics of this model.

Based on above is my below connection diagram correct? Switch is rated for 6/12/24 V and max of 3A so might be slightly dimmer than at 6V ( I will bench test it later). I want it to light up when pressed.

I think it looks fine @SilentException… what do you think?

Yes but you don’t want that. Why? Well let’s say one parallel group or cell in the series pack is “bad” and it is out of balance. Example of 3S pack: 4.0V 3.8V 4.0V Charger will charge until pack gets at 12.6V and at this point the pack will be something like: 4.3V 4.0V 4.3V = 12.6V Some of the cells will be overcharged, not a good idea.

Momentary switch…not going to work :slight_smile: You need latching one.

I’m sorry, it is latching switch. Not sure why I wrote momentary. It must have been 12hrs shift I have just finished at work :slight_smile: Would wiring be correct?

I know. I would never do that. It was just to help me understand how the Charger Works, and how it ‘sees’ the battery. I got it now…

God, no. I think you might burn something using those connections. Just use a switch part as a switch and LED part as a LED. Simple :slight_smile:

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@SilentException Ohh silly me. So + and - on the latching switch are for LED voltage and NO ( normally open) and C ( common) are for the switch! Makes sense :slight_smile:

I guess resistor won’t be needed - LED can take 3A max and 5V on Vesc is I think 1A max. Thanks!

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This sounds very implausible to me. You might be looking at switch rating and not the LED.

Green and blue to E-switch Red and black to open channel on receiver for 5v

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Here is example if charging with CC/CV power supply and bms.

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Sorry for the late reply. It would be best to balance the packs before assembling them but if you don’t have a hobby charger, then you can get around that as long as all packs are close to the same charge. I once experienced a problem when I had to replace a pack who’s main power cable came loose inside the case. the new battery was at storage charge and the rest of the pack was somewhere over 4.0v per cell. In that case the charger stopped before the total pack voltage could reach 42v so the bms balancing was not triggered. I had to go in and charge the new pack separately to equalize it with the rest of the battery. After that everything was fine. Frankly, I don’t know of any BMS that can balance cells as well as a good hobby charger can.

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Thanks for your response! What margin would be acceptable for the cells? What voltage is common for ‘storage charge’?

according to my hobby charger, 3.8v per cell is storage charge. as far as the maximum acceptable margin for the bms, I really don’t have any hard numbers for sure but my best guess is no more than 0.1v per cell.

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Ok I’ll have a look at my batteries when I get them in. If any doubt I’ll contact you here in this topic with my measurements, maybe then we can see what is ok as a margin! Thanks! This is a really nice topic full of very useful information

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