BMS for every cell?

[imginit]

Is this helpful or is this just redundant?

I am setting up my batteries 4 x 10s1p instead of 10s4p.

I am worried that if a cell degrades to a lower capacity and lower voltage over time that it would create a dangerous situation where the parallel cells would rapidly charge the lower voltage cell.

 

[riba2233]

You don't have to worry about that, just connect bms normally.

 

[dmwahl]

If the individual strings are paralleled only at the end then yes you would need a BMS for each string. But if all the cells in each string are connected with the corresponding cells in the other strings, then they act as a single cell and only need a single BMS. That's the way to do it. Many people use parallel boards to connect cells together using the balance connectors commonly included with prebuilt packs.

 

[fellow]

Choose the safe "idiot-proof" cell chemistry tested for 12V overvoltage, and 0V abuse (Panasonic NCR18650pf or better for example), or some of the other high quality 18650 cells with built in protection circuits. That means no extrernal wires that can short because of the vibration, no BMS that can draw half the pack to zero when not used and so on. Best built in circuits are about 10A per cell. Those pictures are illustrating it:

Pay attention that not all protective circuits do protect from the undervoltage abuse, and some are 5A rated only.

I'm using 2 x 13s config without problems (no external BMS at all, idiot proof NCR18650PF cells. They love being abused due to their mazo nature, PTC built-in-elements, safe chemistry and safety layers...).

 

[riba2233]

Cells with built-in protection boards are not suitable for building larger packs.

 

[major]

Choose the safe "idiot-proof" cell chemistry tested for 12V overvoltage, and 0V abuse (Panasonic NCR18650pf or better for example), or some of the other high quality 18650 cells with built in protection circuits. That means no extrernal wires that can short because of the vibration, no BMS that can draw half the pack to zero when not used and so on. Best built in circuits are about 10A per cell. Those pictures are illustrating it:

Pay attention that not all protective circuits do protect from the undervoltage abuse, and some are 5A rated only.

I'm using 2 x 13s config without problems (no external BMS at all, idiot proof NCR18650PF cells. They love being abused due to their mazo nature, PTC built-in-elements, safe chemistry and safety layers...).

What does this circuit do? Does it actually do anything beneficial when using a single cell in an application?

 

[riba2233]

Of course it does, why else would it be there?

It provides over-voltage, under-voltage, and over-current protection by disconnecting cell from the load.


And please don't quote pictures, you're making topic hard to read.

 

[Ypedal]

Protected cells are good for flashlights.. not ebikes.

 

[major]

Of course it does, why else would it be there?

It provides over-voltage, under-voltage, and over-current protection by disconnecting cell from the load.


And please don't quote pictures, you're making topic hard to read.

Sorry about quoting the photos, but I have experience where the quoted post is deleted leaving my response without reference.

Anyway, thanks for your response. And to Ypedal, yes I know. I wanted to use it on a single cell application for a screwdriver. So riba, how does it disconnect the load or charger? I see the 2 connection ribbons. Where is the third?

 

[riba2233]

Third is between the PCB and the cell negative. PCB has a tiny mosfet that turns off.

Here is some more info:

http://www.lygte-info.dk/info/battery%20protection%20UK.html

 

[major]

Third is between the PCB and the cell negative. PCB has a tiny mosfet that turns off.

Here is some more info:

http://www.lygte-info.dk/info/battery%20protection%20UK.html

There are 2 ribbons. One is B+ and the other is B-. The third terminal is the circular plate on the back of the round pc board, right? It is connected to the charger and load, right? Having instructions helps. I got a couple of these things for like a buck apiece shipped from China, but no instructions. I've been trying to figure out how to use them. Thanks for the link. Do you have a link where to buy the ones pictured there? They look to be better than the cheap ones I got.

 

[riba2233]

Yeah, that's right!

I don't know where to buy those PCBs from the link, but you can search on aliexpress maybe.

 

[Hummina Shadeeba]

How big a pack can be made with those cells with built in protection? It sounds like a bms wouldn't be necessary using them. How bout a 10ah pack?

 

[riba2233]

Nope, they are only for single cell, or maybe up to two cells in series.