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?
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