Is this dangerous to do? Need help

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ebike11

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Hi guys

I have a 20 cell lipo pack that I plan to use. It has no BMS only a 20pin JST-type connector wired to the battery. There is no BMS unit plugged into it and goes from
B20+ ~ B1+

Roughly sketched pic below

Its a long 20 pin connector so my idea is to break it up into smaller JST plugs to use as cell checking and balancing whenever needed. I will manually monitor the cells and main voltage while riding.

I use the Q6 Pro so the largest JST it accepts to do balancing is 6 cells which need a 7 pin plug when including the Negative wire.

If I use 3 or 4 smaller JST plugs...can I wire all 3 connectors Negative pins (The first one on each connector) together ?

If so, can I tap into the packs main Negative and run each JST Neg. from that single wire?

Hope it doesnt sound too confusing!
Thanks

https://ibb.co/4FMV8sd
 
If you connect ANY cells that are already in series into a parallel connection, you short across the cells, which is VERY BAD.

Smoke, fire, etc.
 
Don't do that! Multiple shorts in that proposal. Look at it again and see the many short circuits created, loop after loop. :flame:
 
amberwolf said:
If you connect ANY cells that are already in series into a parallel connection, you short across the cells, which is VERY BAD.

Smoke, fire, etc.
Click to expand...

Ok thanks a lot for the warning!

What would u recommend me to do in order to be able to check and balance the cells when needed?
Most cell checkers and balancers dont do 20S.
How could I split it up to be able to do that?
Thanks!
 
https://ibb.co/YhKs73q

Is this any better?? In order to use the smaller JST plugs on cell checker etc.
 
NO! Many shorts! Each one of those negative wires (except the most negative one) is creating a dead short across the set of cells between it and the negative end of the pack.

The correct way to do this is by connecting the negative of each set to the positive of the previous one. Since you're dividing 20 cells into 4 parts you might as well go with all 5S "subpacks", so 4x 6 pin JSTs.

Right now you should have 21 wires coming out to the existing connector, so you'd connect

Subpack #1 - Wires 1 to 6
Subpack #2 - Wires 6 to 11
Subpack #3 - Wires 11 to 16
Subpack #4 - Wires 16 to 21

Of course being aware of polarity throughout. Negative end of the JST goes to the most negative end of the subpack, not the entire pack.
 
dustNbone said:
NO! Many shorts! Each one of those negative wires (except the most negative one) is creating a dead short across the set of cells between it and the negative end of the pack.

The correct way to do this is by connecting the negative of each set to the positive of the previous one. Since you're dividing 20 cells into 4 parts you might as well go with all 5S "subpacks", so 4x 6 pin JSTs.

Right now you should have 21 wires coming out to the existing connector, so you'd connect

Subpack #1 - Wires 1 to 6
Subpack #2 - Wires 6 to 11
Subpack #3 - Wires 11 to 16
Subpack #4 - Wires 16 to 21

Of course being aware of polarity throughout. Negative end of the JST goes to the most negative end of the subpack, not the entire pack.
Click to expand...

Thanks for your helpful advice!!
However the problem is there is only 20 wires not 21 wires coming out of the battery. Its a 20s pack with just 20 pin JST connector
Have you seen this before?
 
It means the BMS is taking (most likely) the first negative from it's terminal connection to the battery.

So the first wire on the cable is 1st cells negative/2nd cells positive. Probably. Check with your DMM first.
 
What dustnbone said is mostly correct, but he's counting cells starting from the positive end?. I count from the negative end, so the small bms wire one is cell one positive. The main negative is the cell one negative. Like he said, the DVM will confirm. Put the negative of the DVM on the main negative leave it there, and then each bms wire should be 4.2v, then 8.4v, and so on.

If you have twenty cells, you have 21 wires. one on each end, the main positive and main negative wires. Then there are 19 wires that loop from the positive of one cell to the negative of the other. Each of those 19 loops is potentially both a positive and a negative. Each of those loops has a bms wire soldered into that loop. And likely there is a bms wire attached to the main positive wire. So the main neg, and 20 bms wires make 21.

Good idea to break it into 5s plugs. So starting with the negative wire of the whole pack, that is the negative wire of the 5s plug. This is usually called cell 0, on a cellog. The negative end cell is cell one, and its positive end of that cell is 1 positve.

Each loop from one cell to the next is the next wire on the plug, and has a bms wire attached. The last wire on the 5s plug is the wire between cell 5 and cell 6. This wire will be the positive end of the first 5s plug, AND it will also be the negative end of the next 5s plug.

So as you wire it up, the loops between cell 5 and 6, 10 and 11, 15 and 16, will all be a y connection now, with two wires. One wire is the positive wire of the last plug, and other is the negative wire of the next plug down the line. So you will need to have three places where you add a y connection to the existing bms wire. This way you don't make any shorts.

Make sense? Once you have 4- 5s plugs wired up, there will be a total of 24 wires connected to the cells.

Once you get it properly wired up, you can very easily monitor the cells. Use a main pack voltmeter as you ride, and stop at a conservative low voltage. Then check each cell before you charge. Check again as it gets full. If one cell is lower than the others, and it gets full first, there you have your low capacity cell. Now you need only watch that cell, or any others that act the same. When its empty, you can't use the whole pack anymore till you charge it. When its full, the pack has all the capacity it can hold. To balance, charge the whole pack, then discharge that cell that got full first a bit, with a light bulb or something, then charge the whole pack again. Repeat till all cells are holding all they can, and you are now balanced.

Shouldn't have to balance every ride, because that one cell will always be fuller when charged, and emptier when empty. Just keep it within .1v of the others.
 
dustNbone said:
It means the BMS is taking (most likely) the first negative from it's terminal connection to the battery.

So the first wire on the cable is 1st cells negative/2nd cells positive. Probably. Check with your DMM first.
Click to expand...

Thx for the reply!
Yes Im pretty sure the main pack negative is the neg. for the 1st bms wire coz there are only 20 on the jst plug
 
dogman dan said:
What dustnbone said is mostly correct, but he's counting cells starting from the positive end?. I count from the negative end, so the small bms wire one is cell one positive. The main negative is the cell one negative. Like he said, the DVM will confirm. Put the negative of the DVM on the main negative leave it there, and then each bms wire should be 4.2v, then 8.4v, and so on.

If you have twenty cells, you have 21 wires. one on each end, the main positive and main negative wires. Then there are 19 wires that loop from the positive of one cell to the negative of the other. Each of those 19 loops is potentially both a positive and a negative. Each of those loops has a bms wire soldered into that loop. And likely there is a bms wire attached to the main positive wire. So the main neg, and 20 bms wires make 21.

Good idea to break it into 5s plugs. So starting with the negative wire of the whole pack, that is the negative wire of the 5s plug. This is usually called cell 0, on a cellog. The negative end cell is cell one, and its positive end of that cell is 1 positve.

Each loop from one cell to the next is the next wire on the plug, and has a bms wire attached. The last wire on the 5s plug is the wire between cell 5 and cell 6. This wire will be the positive end of the first 5s plug, AND it will also be the negative end of the next 5s plug.

So as you wire it up, the loops between cell 5 and 6, 10 and 11, 15 and 16, will all be a y connection now, with two wires. One wire is the positive wire of the last plug, and other is the negative wire of the next plug down the line. So you will need to have three places where you add a y connection to the existing bms wire. This way you don't make any shorts.

Make sense? Once you have 4- 5s plugs wired up, there will be a total of 24 wires connected to the cells.

Once you get it properly wired up, you can very easily monitor the cells. Use a main pack voltmeter as you ride, and stop at a conservative low voltage. Then check each cell before you charge. Check again as it gets full. If one cell is lower than the others, and it gets full first, there you have your low capacity cell. Now you need only watch that cell, or any others that act the same. When its empty, you can't use the whole pack anymore till you charge it. When its full, the pack has all the capacity it can hold. To balance, charge the whole pack, then discharge that cell that got full first a bit, with a light bulb or something, then charge the whole pack again. Repeat till all cells are holding all they can, and you are now balanced.

Shouldn't have to balance every ride, because that one cell will always be fuller when charged, and emptier when empty. Just keep it within .1v of the others.
Click to expand...

Thanks so much for your lengrhy reply!
The plug itself has just 20 small bms wires on so Im assuming the main pack negative is the negative for the first bms wire.
However i see no small wires coming from the main pack negative. Should i splice into the pack negative with a jst wire to put that on my first pin slot as the negative?
 
There is multiple shorts in that arrangement

To be honest I would just add a bluetooth bms and use that for balancing and logging, and i would wire it in based on this diagram like so

https://imgur.com/a/EN9vbvw
 
tolkaNo said:
There is multiple shorts in that arrangement

To be honest I would just add a bluetooth bms and use that for balancing and logging, and i would wire it in based on this diagram like so

https://imgur.com/a/EN9vbvw
Click to expand...

Hi yes I wont be doing it that way.
Actually it better for me not to use any bms. I prefer manually checking. Its more work but less wiring etc. I just gotta do the balance wires for monitoring
 
ebike11 said:
Actually it better for me not to use any bms. I prefer manually checking. Its more work but less wiring etc. I just gotta do the balance wires for monitoring
Click to expand...
There are MORE wires to use a few monitor units than for a BMS.

Plus teh BMS wiring is all just within the pack. Monitor wiring has to exit the pack for you to access and is susceptible to damage, weather, shorting (which can destroy your pack, cause a fire, etc).
 
Yes. to wire up your jst plugs for monitoring, add one more small wire to the pack negative.

Look at pictures of lipo packs to see which end of the jst plug is the negative end. Then the pack checker/ warning alarm you use will work right with it.

Best approach, keep the bms, but still have the jst plugs to check on what the bms is doing.

I have been telling Jason to get his battery manufactures to add this diagnostic port to the batteries. So a bike shop guy could test a battery easy, and report back to the company for warranty. Right now, its kind of guessing if a new battery is needed, or just a charger. The industry in china is kind of like, warranty? :lol:
 
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