Replacing a BMS in a bottle battery

[Thamosy]

Hello, I have a Battery problem - thought to be its BMS.

I have a bottle battery that fell onto a stone floor. It is now not working properly and I can only think its BMS is now faulty.

I bought a new BMS identical to the one fitted but I'm worried about the correct order in which to connect it up. A year or so back I replaced a BMS incorrectly (ruined the BMS) and had to repeat the exercise. Second time it was fine.

I don't particularly want to go through the rigmarole of individually connecting balance wires in the correct order and wonder if I can simply take out the balance wire plugs from the old BMS and put those plugs into the new one.

In terms of the wiring order, could I first connect B- then simply plug in the collection of balance wires already connected to the battery, then finish by connecting P- and C-?

Would that wreck the new BMS?

In terms of why I want to replace the BMS, these are the symptoms.

All cells are okay and have held the charge for several months whilst I've been pondering the problem. The battery charges okay and cuts off when at the right voltage. When out riding it seems fine for several miles when not put under load, but as soon as put under maximum load it cuts out and the battery then appears to be totally dead.But it isn't, when the case is opened the cells and charge are fine and simply taking it from the case seems to rejuvenate it!

On the second occasion this happened the supposedly dead battery (left in a corner for a few weeks) suddenly regained a working state. Any ideas why this should happen (if not the BMS) would be gratefully received!

 

[Nealh]

If the bms is identical you can wire up the new one and use the old jst balance plug/wires. Just double check that B0+ etc are in the same order on both bms's.

In terms of wiring order I connect B +, P+ & C+ first.
Then as you have said B+, Sense wires , P- & C-.

Disconnect bms in reverse order.

A bms either works or it doesn't, it should perform equally as well whether it is under load or not.

Having dropped the battery thoroughly check all cell welds ( in case of a false/intermittent contact ) by gently trying to see if any lift by using a non metallic object.
Try a continuity check on all wiring end to end and wiggle them a little in case of a wire break or loose solder joint, if the beep is broken then there will lay an issue.

When cutting out under load either the cells are poor or one or two in the parallel connection aren't receiving a full charge and are unbalanced. If any welds are intermittent then this will cause an issue.

With all cells connected in parallel the group as a whole will appear fine giving the same reading as it's neighbour but an individual cell can be low but won't show up. The only way of checking cell voltage is individually and not connected in parallel as this will only give a false reading.

 

[KirstinS]

I’ve broken welds when the battery jumped off the bike and down the hillside

My fault for forgetting to lock them on mind!


Sent from my iPhone using Tapatalk

 

[Nealh]

Finished repairing a 3s cell pack I put in series with a 10s pack, after my last ride over the S/Down's. 3s pack failed and although reading 12v and my 10s reading 40v, when in series I got a very funny voltage reading.
The jarring/bumpy terrain over/on the Down's caused four welds to fail, now repaired all appears well.

Note to my self,
Need a bit more foam for packs to sit on in my top bag to help with cushioning.

 

[KirstinS]

Finished repairing a 3s cell pack I put in series with a 10s pack, after my last ride over the S/Down's. 3s pack failed and although reading 12v and my 10s reading 40v, when in series I got a very funny voltage reading.
The jarring/bumpy terrain over/on the Down's caused four welds to fail, now repaired all appears well.

Note to my self,
Need a bit more foam for packs to sit on in my top bag to help with cushioning.

Do I recall you built a welder ?


Sent from my iPhone using Tapatalk

 

[Thamosy]

I've taken a long time getting around to replacing my BMS, and many thanks for the advice. I did check all the cells and they seemed okay so I decided the dent in the aluminium pack was probably a good indication the tripping BMS was the problem. So far so good, I've not yet had the new BMS trip out. Fingers crossed.

But I've another problem with the battery on my sister's bike and maybe I should start a new thread for this, but I'll ask anyway on the offchance ....

This problem is a bottle battery where the switch has gone soft and refuses to switch off (good that the battery is still useable, but it can't be left like that). I opened it up with the intention of replacing the switch, but find that it's wired with no fuse and no way I can disconnect the wiring. (I've no idea how it was put together) but my plan of action is to cut the positive and negative wires so as to disconnect everything and replace the switch with a new one. I'll then fit a Deans connector to the positive/negative wires when putting it back together.
Help! The wires are live and is there likely to be a problem cutting them? Is this likely to damage the BMS? And which wire should I cut first? etc, etc. Any advice would be truly wonderful.

 

[Nealh]

I've taken a long time getting around to replacing my BMS, and many thanks for the advice. I did check all the cells and they seemed okay so I decided the dent in the aluminium pack was probably a good indication the tripping BMS was the problem. So far so good, I've not yet had the new BMS trip out. Fingers crossed.

But I've another problem with the battery on my sister's bike and maybe I should start a new thread for this, but I'll ask anyway on the offchance ....

This problem is a bottle battery where the switch has gone soft and refuses to switch off (good that the battery is still useable, but it can't be left like that). I opened it up with the intention of replacing the switch, but find that it's wired with no fuse and no way I can disconnect the wiring. (I've no idea how it was put together) but my plan of action is to cut the positive and negative wires so as to disconnect everything and replace the switch with a new one. I'll then fit a Deans connector to the positive/negative wires when putting it back together.
Help! The wires are live and is there likely to be a problem cutting them? Is this likely to damage the BMS? And which wire should I cut first? etc, etc. Any advice would be truly wonderful.

Cutting the wiring one at a time should be ok just don't let them touch anything insulate each one after cutting or cut one and immediately connect/solder it.

 

[Nealh]

Do I recall you built a welder ?


Sent from my iPhone using Tapatalk

Sorry Kirstin, I missed this one.
No I didn't build one, I paid $80 and got a Boss spot welder from AULAKIRA in Korea which runs off a 65/130c 3s lipo.
Its a great bit of kit approx. 7.5cmx 7.5cm x 10cm.
Totally programmable to get exact weld strength required.

This is the ES thread with some superb how to vid's by Rojitor.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=89076&sid=d5c9d1e2bb6654659fa990cdb3c82366
It can do copper but needs 4s and wasn't designed for copper use so damage may occur to the unit.

Originally I used crappy 3s lipos 3x 25c in parallel, welds were good but they are much better with the 65/130c lipo.

 

[Thamosy]

Cutting the wiring one at a time should be ok just don't let them touch anything insulate each one after cutting or cut one and immediately connect/solder it.

Hello again. Thanks for that reassurance. A couple more questions. First about a replacement switch. The battery is a 36V 15Ah bottle battery and I've just been trying to find a rocker switch replacement. To me, most of the ones I can find on line don't seem man enough for the job, although I guess its never going to be switched on/off when under any load. The best I can do seems to be one rated at 20 amps that looks pretty much the same as the existing one (that has failed), but do you think that would be okay?

My second worry is still about the wiring. On this battery the B+ wire is through the switch to the positive discharge (load) but that side of the switch is also linked to the positive charging port as well. Would it matter that I'll be disconnecting that too? I can't think that disconnecting the P- (the negative discharge/load) will affect the BMS, but I'd be grateful for a confirmation of this.

I'm not worried about the 'careful not to touch live wires' -- I'll instantly insulate anything that's cut and I'll probably be wearing rubber gloves and my wellies too!


Thanks again for the help.

 

[Sturmey]

Hello, I have a Battery problem - thought to be its BMS.

I have a bottle battery that fell onto a stone floor. It is now not working properly and I can only think its BMS is now faulty.

I bought a new BMS identical to the one fitted but I'm worried about the correct order in which to connect it up. A year or so back I replaced a BMS incorrectly (ruined the BMS) and had to repeat the exercise. Second time it was fine.

I don't particularly want to go through the rigmarole of individually connecting balance wires in the correct order and wonder if I can simply take out the balance wire plugs from the old BMS and put those plugs into the new one.

In terms of the wiring order, could I first connect B- then simply plug in the collection of balance wires already connected to the battery, then finish by connecting P- and C-?

Would that wreck the new BMS?

In terms of why I want to replace the BMS, these are the symptoms.

All cells are okay and have held the charge for several months whilst I've been pondering the problem. The battery charges okay and cuts off when at the right voltage. When out riding it seems fine for several miles when not put under load, but as soon as put under maximum load it cuts out and the battery then appears to be totally dead.But it isn't, when the case is opened the cells and charge are fine and simply taking it from the case seems to rejuvenate it!

On the second occasion this happened the supposedly dead battery (left in a corner for a few weeks) suddenly regained a working state. Any ideas why this should happen (if not the BMS) would be gratefully received!

Hi. My battery developed a fault lately (the battery would not even charge) and it looked like a faulty bms. However, after much investigation, I discovered that one of the 10 sense voltages was missing and eventually I found bad soldered connection between nickle strip and separate pcb board where sense wires are collected, (along with four wires from two temperature sensing devices) and feed to bms via ribbon type cable. I also noted that cable sense voltages on my cable are not in sequence and some criss crossing or rewiring of sense voltages would be required if a different type bms was fitted in my case.

From my experience, I think its always worthwhile checking (on the bms board) and noting the sense voltages (both against positive and against negative) before condemning the bms.
PS Also check wiring to temperature sensors if fitted

 

[Nealh]

Remove the jst connection for the sense wires so no damage can be done to the bms as this is where damage may occur. Power for the bms is usually via the jst sense wire connection as this has multiple v+ & a single v- supply and only needs to see low voltage for power.

For the switch disconnect v- then v+ and reconnect v+ then v- last.

Generally you are over thinking the disconnection, the only real issue is a shorting one.

 

[Thamosy]

Remove the jst connection for the sense wires so no damage can be done to the bms as this is where damage may occur. Power for the bms is usually via the jst sense wire connection as this has multiple v+ & a single v- supply and only needs to see low voltage for power.

For the switch disconnect v- then v+ and reconnect v+ then v- last.

Generally you are over thinking the disconnection, the only real issue is a shorting one.

Hi again. Thanks for holding my hand. It all went well and the battery is now switching on and off as it should.