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Lynx BMS Overheating while charging

Lynx Smart BMS is overheating with 12V 300A charge from alternators for 30 minutes.

I'm getting a BMS internal temperature too high alarm via bluetooth in Victron App. I have 2x 250A alternators regulated to a max of 150A each. Clamp amp meter confirms 300 Amps headed to a 600ah battery setup. In theory, I should be able to get pretty close to charging 50% of capacity in 1 hour. In reality, the BMS is overheating in about 25 minutes.

1) Has anyone upgraded heat dissipation? I'm thinking of adding a heat sink, or possibly using a PC computer's liquid cool system to transfer heat away from bms installation.

2) Does anyone know the temperature at which the BMS internal heat alarm signals? I will test with laser thermometer next time, but would love to know the spec, which isn't in the published manuals.

lynx bmsTemperature Alarm
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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ commented ·

Are there consumers that discharge the battery at the same time (adds to the total current that flows through the contactor)?

Have you checked if the internal fan is running?

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pommesfrites avatar image pommesfrites Stefanie (Victron Energy Staff) ♦♦ commented ·

No, The consumers are on the right side of the BMS, along with the alternators. So, any of that current would be direct alternator->battery protect->consumers, and not be going through the contactor. The fans are running.

The current running through the contactor is 300A. I can't actually get the current measuring clamp around it, but given that each of the three batteries measures at 100amps inbound current, and no consumers are on the left side of the lynx, it's seems very unlikely that more charge is diverting through the contactor. Furthermore, the shunt measures ~295 amps, which is within 1% of my independent measurement.

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klim8skeptic avatar image klim8skeptic ♦ pommesfrites commented ·
Is the fan in the BMS running?
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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ pommesfrites commented ·

Ok, then I'm curious about the measured temperatures, ambient and also that of the PCB and the busbar (check they are properly flush) inside the Lynx Smart BMS. I'll try to find out the threshold for the high temperature alarm.

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oldchubbyknuckle avatar image oldchubbyknuckle commented ·

Any update on this? Was it poor connections on the bus bar or lugs?

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1 Answer
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pommesfrites answered ·

I tested this this thoroughly, and become convinced it was not fasteners or cable crimps. I used a laser thermometer and carefully checked the temps on either side of each connection, looking for a delta. I could find none.


In the end, I decided that it must have been some unknown combination of the ambient temperature, a loose connection, or undersized alternator cabling. I rewired the alternators with 000 cables, and moved the batteries and bms to another location. I created all the new cable lugs and precisely torqued the fasteners.


Some combination of those solutions solved the problem. The bms doesn’t heat up past 40c, even when charging at 300 amps for an hour.

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Related Resources

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LED indications, warnings, alarm and error codes

Lynx Smart BMS product page

Lynx Smart BMS online manual

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