LiPo Battery and Protection

JimmyB

JimmyB

Now retired - trains and fishing
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When I first started my battery conversions I use Lithium Polymer (LiPo) batteries, these normally come with 2 sets of leads, a positive and negative giving full pack voltage for use with the equipment, and 3/4/5 wire lead depending on if it is 2S/3S/4S for balance charging. These packs do not come with any type of protection, and I am now slowly moving to Lithium Ion (Li-Ion) batteries with Battery Management Systems (BMS) as part of the pack.
My question is, can I add BMS to LiPo batteries by using the charging lead as in input to the BMS, and then utilising the output from the BMS. I hope this is clear, as to what I am asking. TVM :)
 
Are you *sure* there is no protection on you LiPo batteries?

The balance lead is just that, a wire connection to the overall positive and negative of the pack, and a wire from each intermediate cell junction.

The BMS board sits in parallel, across the individual cells.
It is only the overall positive/negative output from the pack, which is via the the full management / protection system.

PhilP
 
PhilP said:
Are you *sure* there is no protection on you LiPo batteries?

The balance lead is just that, a wire connection to the overall positive and negative of the pack, and a wire from each intermediate cell junction.

The BMS board sits in parallel, across the individual cells.
It is only the overall positive/negative output from the pack, which is via the the full management / protection system.

PhilP
Click to expand...
I have bought from a number of sources, and none mention protection of any type, below is the side view showing the cells and there is no sign of any circuit, the "white" at the bottom is Velcro I use to secure the battery pack.

IMG_1688.jpeg

IMG_1689.jpeg
 
Looking at the ultra-high discharge rate (35C) there almost cannot be a protection circuit available... It will do a burst of 65C, i.e. 132 amps!!!

It would be almost impossible to have a circuit to determine the difference between a short and 132 amps for example.

I would agree with Jimmy's assessment that there is no BMS (besides no room in the pictures).

So to try to answer Jimmys question, if you are using BMS for one cell, yes attach one to each cell, charging input to BMS.

Looks like you would be better off with a BMS for 3 cells, but I don't know if they make them.

Greg

p.s. I would be sure to fuse the output at the least, with the high current capability of that pack.
 
Greg Elmassian said:
Looking at the ultra-high discharge rate (35C) there almost cannot be a protection circuit available... It will do a burst of 65C, i.e. 132 amps!!!

It would be almost impossible to have a circuit to determine the difference between a short and 132 amps for example.

I would agree with Jimmy's assessment that there is no BMS (besides no room in the pictures).

So to try to answer Jimmys question, if you are using BMS for one cell, yes attach one to each cell, charging input to BMS.

Looks like you would be better off with a BMS for 3 cells, but I don't know if they make them.

Greg

p.s. I would be sure to fuse the output at the least, with the high current capability of that pack.
Click to expand...
3 Cell BMS is what I was think of, and yes I have a 3 amp fuse, so the battery and equipment are both protected.
 
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3S 10A 2T Balance Li-ion Lithium LiPo Battery BMS Protection Board 12.6V | eBay

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I get 4S and 3S BMS boards from Aliexpress, so no problem with supply. No reason why you can't add one to a LiPo pack with balance leads. Except that you need to know which cell junction each wire is attached to, so I think you will have to remove the shrink wrap cover and take a look. Don't let any of them short circuit! Use masking or similar tape to hold the pack together while you explore.
 
Fred2179G said:
www.ebay.com.au

3S 10A 2T Balance Li-ion Lithium LiPo Battery BMS Protection Board 12.6V | eBay

Find many great new & used options and get the best deals for 3S 10A 2T Balance Li-ion Lithium LiPo Battery BMS Protection Board 12.6V at the best online prices at eBay!
www.ebay.com.au

I get 4S and 3S BMS boards from Aliexpress, so no problem with supply. No reason why you can't add one to a LiPo pack with balance leads. Except that you need to know which cell junction each wire is attached to, so I think you will have to remove the shrink wrap cover and take a look. Don't let any of them short circuit! Use masking or similar tape to hold the pack together while you explore.
Click to expand...
The balance lead is a standard JST-XH, so the leads are easily identified, though of course care is required.
 
Fred2179G said:
I didn't realise that would tell you which cell was on which wire.
Click to expand...
You can measure the voltage across the cells using a multimeter onto the plug.
Black-Red should be full battery voltage then black-white should be individual cell voltage.
 
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