Melted wires between BMS and cells!

[WorldwideDave]

I created 2/0 AWG sized conductors with 1/4” tinned copper lug on one end and 3/8” on the other end using my temco hydraulic crimper. I replaced the conductors coming off the BMS and heading to the Victron smart shunt. On the positive side I replaced the 2 in 1 silicone wire that came with my battery also with 2/0 AWG. I have been having zero issues.

Today I decided to turn off my PV disconnects and a/c to D/c charger and see what max amps I could pull. I was able to get between 150-160A load no problem with pool pump on max speed. I’ve done this test a few times. I figured it would take about an hour and 25 minutes to drain my 200 amp power battery to the point where the inverter was shut off the load. I set an alarm for an hour and 15 minutes, and walked away.

At the end of my alarm, I came back to the pool only to find that the pump isn’t running I looked around and I could see that the inverter was shut off. I won’t get an alert if that happens from VRM because it is a non-Victron device.

And then open VictronConnect and I could see the shunt state of charge was 52%. I thought that was strange. I’ve never seen that before. I then looked at some of the reports, and it appeared that the load had stopped going through the shunt about 40 minutes before.

I then looked inside Overkill Solar app and it also showed around the same state of charge. I looked for errors inside the BMS or over on VRM and I saw no alerts. I wondered if maybe the inverter saw that it was at its 2000 W limit for too long of a period, and just quit. I push the button to turn on the inverter which it did just fine. The pool then started up no problem. I decided I would sit around and try to see what happened.

I started to smell something funny. It smelled electrical. I got out my temp gun and immediately started reading temperatures and everything looked fine. The temperature is on the battery also looked great.

I looked down at the battery, and I could see some slight smoke color coming off the battery bank. Battery is wrapped up inside that yellow plastic materials, so then I started to open it. The top of the BMS was 109°C. The conductor is coming off of the battery to the BMS for 107°C.

I turned off the load and started to rip open the battery to help it vent. That is when I noticed some scorched, yellow plastic, and then ultimately the two wires that run from the negative battery post to the battery negative on the BMS had me melted.

My BMS is rated for 300 A. My cells appear to be fine. But as you can see in the photos below, the wires did not hold up.

This was a very close call. I’m glad I was home. I could see what was happening.

The wires which came from the battery, to the BMS, which I was told multiple times could handle the load, did not.

This was one of those wire adapter cables that come with an inverter or are usually inside the Chinese made batteries. It is a 15 mm² wire, but there are two of them. I believe a single one can support up to 35 A, and is roughly equivalent to a 6 AWG gauge. I was told that with two of them would be equivalent to 0/2 AWG, but I believe that was wrong information… I think it’s only rated or the equivalent of 2 AWG. I believe the wire was only rated to about 120 A. I was pushing 160 A. The wire coating says that it is rated to 105°C. My readings were 107°C.

I believe that the “Y” cable was a bottleneck for the electrons and it caused it to generate heat.

One thing I saw in my BMS before I unplugged it safely Why is that it showed sell one voltage at around 2.6 while the rest of the cells were at 3.2.

My theory is that the wires were melting and shorting out, and that may be caused it to draw more current from the first cell in the battery pack.

Either way I’ve ordered a 15 pack of new lugs and will create my own cables between the BMS and the battery negative post.

Since I have the battery out anyway, what are some things that I can do to test things?

Because the inverter was off and I presume that is because it dropped below 11 V, also the Overkill Solar BMS tool did not show any errors logged, which leads me to believe that no conditions were met that would’ve turned off the VMS. No short circuit event, no over temperature event, no voltage drop below 10 V so so it was the inverter that decided to stop working due to 11v low voltage shutdown. My inverter does not have any logic in it. It says when the voltage goes up to start up the inverter again.

Any other speculation as to what it might be?

 

[Skypower]

I’d like to see what the crimp looks like under that heat shrink. Looks like a point of high resistance.

 

[fnnwizard]

The connection (wire to lug crimp is not good enough for the current) and yes, 2awg equivalent is only good for around 100A in that enclosed space.

 

[WorldwideDave]

I’d like to see what the crimp looks like under that heat shrink. Looks like a point of high resistance.

Of course - right now I have it disconnected at the battery side and cooling down along with the BMS. So for now the two wires are still connected to the BMS side, but not the cell side. I'll remove it tonight or tomorrow. 107C is equal to 225 F - not going to touch that and get burned.

 

[WorldwideDave]

The connection (wire to lug crimp is not good enough for the current) and yes, 2awg equivalent is only good for around 100A in that enclosed space.

I think it is important to not take everyone's word as fact here on the forums. If someone had said 2 AWG wouldn't be good enough, I would not have left it there. Also there are some who claim the Y cable is not that bad, but clearly that is my weakest link. If someone knew that the two of those 15mm2 wires were not equal to the 0/2 I was putting on the rest of the upgraded BMS, I wish they would have spoke up.

discharging at 150A is not common. But need to test at that load for the rare exception it does.

 

[Brucey]

The wires which came from the battery, to the BMS, which I was told multiple times could handle the load, did not.

This was one of those wire adapter cables that come with an inverter or are usually inside the Chinese made batteries. It is a 15 mm² wire, but there are two of them. I believe a single one can support up to 35 A, and is roughly equivalent to a 6 AWG gauge. I was told that with two of them would be equivalent to 0/2 AWG, but I believe that was wrong information… I think it’s only rated or the equivalent of 2 AWG. I believe the wire was only rated to about 120 A. I was pushing 160 A. The wire coating says that it is rated to 105°C. My readings were 107°C.

So you replaced the cables going from bms output to system negative with a 2/0 cable you made, and then some random factory y cables on the bms to battery cell negative?

What battery did that cable come from? It doesnt look like it was properly crimped. Need to use 200C rated silicon cable if you are doing y cables like that. My jk bms came with two 7AWG silicon wires rated for 200C.

 

[Brucey]

I think it is important to not take everyone's word as fact here on the forums. If someone had said 2 AWG wouldn't be good enough, I would not have left it there. Also there are some who claim the Y cable is not that bad, but clearly that is my weakest link. If someone knew that the two of those 15mm2 wires were not equal to the 0/2 I was putting on the rest of the upgraded BMS, I wish they would have spoke up.

discharging at 150A is not common. But need to test at that load for the rare exception it does.

I was following along very generally and saw you were going with 2/0 to 1/4" lugs, so never thought you'd leave some kind of absolute garbage on the other side. When you make one side of things very efficient sometimes the weaker side can fail spectacularly.

 

[WorldwideDave]

So you replaced the cables going from bms output to system negative with a 2/0 cable you made

Yes.
I also replaced the positive ones.
The two cables coming off the BMS to the shunt I replaced, not the Y cable between the BMS and the cells.

, and then some random factory y cables on the bms to battery cell negative?

The factory Y cable came from the CHINS battery I cut open.
Note the BMS is not the factory BMS - JBD BMS now with bluetooth.

What battery did that cable come from?

CHINS

It doesnt look like it was properly crimped.

Not my fault. Will cut it open.

Need to use 200C rated silicon cable if you are doing y cables like that.

Again, I didn't make it.

My jk bms came with two 7AWG silicon wires rated for 200C.

That's cool when they come with the right cables. Mine obliviously did not.
Bought more wire, lugs, and shrink wrap to do those last 2 cables. That will be a tomorrow project.

 

[Brucey]

Yes.
I also replaced the positive ones.
The two cables coming off the BMS to the shunt I replaced, not the Y cable between the BMS and the cells.

The factory Y cable came from the CHINS battery I cut open.
Note the BMS is not the factory BMS - JBD BMS now with bluetooth.

CHINS

Not my fault. Will cut it open.

Again, I didn't make it.


That's cool when they come with the right cables. Mine obliviously did not.
Bought more wire, lugs, and shrink wrap to do those last 2 cables. That will be a tomorrow project.

Ultimately you took a working chins battey opened it up replaced bms and some of the wiring and had a close call to meltdown.

As you said good thing you were there. When doing high load testing its always good practice to remain there to monitor. Don't just turn it on and walk away.

 

[fnnwizard]

I think it is important to not take everyone's word as fact here on the forums. If someone had said 2 AWG wouldn't be good enough, I would not have left it there. Also there are some who claim the Y cable is not that bad, but clearly that is my weakest link. If someone knew that the two of those 15mm2 wires were not equal to the 0/2 I was putting on the rest of the upgraded BMS, I wish they would have spoke up.

discharging at 150A is not common. But need to test at that load for the rare exception it does.

Slit the heat shrink so we can see how it was crimped.
The yellow stuff is likely FR4, takes a lot of heat to scorch it like that.

The lug looks non optimal also, shows there was air (dirst, oils etc) in between it and bus bar = not 100% contact = added resistance = added heat generation on top of crimp. PVC melts at around 150C.

So yea, lucky you stayed and watched.

 

[Skypower]

The way I see it is 15mm2 is close to a #6awg
So in an enclosed area with safety margin I’d think that 50amp would be max per cable. So 100 amps for two cables with a good crimp in a welded barrel lug sound about right?

 

[Backyard]

My chart shows 15mm2 is close to about 6.5 AWG and would take 4.5 of them to equal one 2/0 in copper area

 

[Skypower]

My jk bms came with two 7AWG silicon wires rated for 200C.

Yup, and that’s just another reason why I derate my 200 amp JKs to 100 amps. Those Two silly 7AWG cables are the choke point of my whole battery.

 

[WorldwideDave]

Ultimately you took a working chins battey opened it up replaced bms and some of the wiring and had a close call to meltdown.

I took a non-working chins - it was overheating at the negative battery post, and BMS couldn't be connected to via bluetooth, and it was advertized as a 100A bms that could not handle more than 42A. So I fixed it.

As you said good thing you were there. When doing high load testing its always good practice to remain there to monitor. Don't just turn it on and walk away.

I had done this same test probably 20 times. The difference was that it was drawing closer to 162 A vs the normal 155 A because I left the MPPTs off hoping not so much to raise the amp draw, but get it to zero percent SOC faster. (90 minutes instead of 2 hours).
In past tests I had just sat there. There was a medical situation I had to take care of, which is why I was called away. I can't always sit in the sun for 90+ minutes waiting for something to go bad given it had worked fine the past 20 times.
I replaced the shunt from a 500A to a 1000A, which gives me two mounting points for the negative conductors, which I like vs. doing a Y cable. I replaced that on March 16. I have done it 5 times since then. Chart shows current - notice they get to 150 A on many of those days, even with the MPPTs on.
I stopped the fast discharge testing and let the battery get to a higher SOC over the past few days, reaching 100% SOC 2 days ago. I was waiting until the weather was super sunny to do a full 100A+ charge test. That day was today, but I never got to the charge test because during the discharging phase to prepare the battery the cable melted :-/

 

[WorldwideDave]

So yea, lucky you stayed and watched.

I started the test, left for an hour, came back and nothing was running. Then the second try to discharge battery melted that cable (unless it had melted and stopped). But yes, thankful I was home and paying attention during this phase.

 

[WorldwideDave]

The way I see it is 15mm2 is close to a #6awg
So in an enclosed area with safety margin I’d think that 50amp would be max per cable. So 100 amps for two cables with a good crimp in a welded barrel lug sound about right?

doesn't matter to me now - not going to use that Y cable, nor will I ever recommend anyone else does.

 

[WorldwideDave]

Yup, and that’s just another reason why I derate my 200 amp JKs to 100 amps. Those Two silly 7AWG cables are the choke point of my whole battery.

This needs to be explained in a video to people. I know that Will discusses oversizing, like 4/0 on things that need AWG 2, but the 'choke point' concept needs to be explained, graphically, to people to avoid what I went through.

 

[Brucey]

I took a non-working chins - it was overheating at the negative battery post, and BMS couldn't be connected to via bluetooth, and it was advertized as a 100A bms that could not handle more than 42A. So I fixed it.

OK it makes sense now. The battery was designed for a 100A bms. Internal Y cable wiring also designed for 100A load.

You then put a higher current bms in there, and replaced half of the bms current carrying wiring with upsized wire. You left the original y cabling from bms to battery cells in place. You then consistently pulled nearly 150A from the pack.

This is absolutely a failure on your part and not a defect in the CHINS.

You claimed someone told you the original CHINS y cables would be sufficient for 150+ amps? Which post and who told you that?

 

[Brucey]

This was one of those wire adapter cables that come with an inverter or are usually inside the Chinese made batteries. It is a 15 mm² wire, but there are two of them. I believe a single one can support up to 35 A, and is roughly equivalent to a 6 AWG gauge. I was told that with two of them would be equivalent to 0/2 AWG, but I believe that was wrong information… I think it’s only rated or the equivalent of 2 AWG. I believe the wire was only rated to about 120 A. I was pushing 160 A. The wire coating says that it is rated to 105°C. My readings were 107°C.

If someone did say that they probably also said to use 200C silicon insulated wire. Not 105C rated wire.

 

[WorldwideDave]

OK it makes sense now. The battery was designed for a 100A bms. Internal Y cable wiring also designed for 100A load.

I think the early first edition ones with no bluetooth it was 50A continuous, 100A burst, but I couldn't do 42A continuous without it overheating - I have the emails posted in the other older thread about that from Chins providing evidence. Its in the past, I've moved on.

You then put a higher current bms in there, and replaced half of the bms current carrying wiring with upsized wire. You left the original y cabling from bms to battery cells in place. You then consistently pulled nearly 150A from the pack.

yes

This is absolutely a failure on your part and not a defect in the CHINS.

Victim blaming? Easy now...no, the CHINS bms was not working at 50A continuous...was a bad BMS from them. Not the only one to experience this. it's in the past.

You claimed someone told you the original CHINS y cables would be sufficient for 150+ amps? Which post and who told you that?

I did not say they felt it would support 150A. I said they said it was 0/2 and not 2 AMG when you add the 15MM together. It's fine, its in the past, I've learned. Not every piece of advice given by folks here is right.
Please don't kick me while I'm already down, amigo.

 

[WorldwideDave]

If someone did say that they probably also said to use 200C silicon insulated wire. Not 105C rated wire.

because I never shared the wire rating with anyone that I can recall - the print is so hard to read - I don't know that this fact ever came up. You're saying that at 15mm2 if it has a 200C rating and is in silicon, it would have been fine? Even if that were true, I was going off the statement that someone made where AWG 0/2 was the same as 15mm2 when doubled up.
I don't care at this point who said what. I caught the problem before a fire happened.
I think that should be celebrated.

 

[Brucey]

because I never shared the wire rating with anyone that I can recall - the print is so hard to read - I don't know that this fact ever came up. You're saying that at 15mm2 if it has a 200C rating and is in silicon, it would have been fine? Even if that were true, I was going off the statement that someone made where AWG 0/2 was the same as 15mm2 when doubled up.
I don't care at this point who said what. I caught the problem before a fire happened.
I think that should be celebrated.

Nobody is kicking you while you are down but you've accused someone of claiming that dual 15mm2 is equivalent to 70mm2. I'd like to see that to understand the context of that statement.

 

[WorldwideDave]

The fact is simple - I did not fact check something I saw on this forum, and it almost caused a fire. I'm good now - lesson learned - moved on.
You should too.

 

[Brucey]

Please don't kick me while I'm already down, amigo.

I think it is an important lesson to all. If you are going to take an off the shelf battery and replace the bms with a higher capacity one than factory rating, you need replace to all the wiring, not just part of it.

 

[WorldwideDave]

I think it is an important lesson to all. If you are going to take an off the shelf battery and replace the bms witha higher capacity one than factory rating, you need replace all the wiring, not just part of it.

Yes...even if a forum member tells you that what you currently have will suffice.