Overheating at cutoff switch from battery bank to inverter

[chuckpfaff]

Hi there.

I am experiencing high temperatures at the cutoff switch when my system is under load.

I have a 13.2 kWh 24VDC battery bank and 4000 Watt 24VDC Giandel Pure Sine Inverter
https://www.amazon.com/gp/product/B07D1LRKY5

The cutoff switch is a Blue Sea 9003e rated at 350 amps continuous.
https://www.amazon.com/dp/B0844QCXK6

I am using 1/0 gauge wire with very short length cables, most under 1ft, longest run is 3 feet from battery bank to the bus. All lugs are are soldered to the wire.

When then inverter is providing about 1.65kW AC the temperature at the cutoff switch gets up to 130 degrees Fahrenheit after 30 minutes.

If I take the cutoff switch out of the system it doesn't heat up nearly as much.

I have noticed a voltage drop of less than .5 volts at the cutoff switch when it is under load.
No noticeable voltage drop when using less than 800w AC.

Temperature of the wire is much cooler everywhere else in the chain.

Any suggestions would be greatly appreciated, I am at my wits end.

I have attached a picture of the system.

Thanks,
Chuck Pfaff

 

[John Frum]

4000 ac watts / .85 conversion factor / 24 volts low cutoff = 196.078431373 service amps

196.078431373 / .8 fuse headroom = 245.098039216 fault amps.

245 fault amps is the absolute limit for 1/0 awg pure copper with 105C rated insulation.

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Those busbars look like the cheap brass ones from amazon or similar.
Brass is significantly less conductive than copper.

Considering the above, if the disconnect switch is the acute hot spot on that current path I would check the crimps on the compression lugs going into and out of the switch.

An IR thermometer would help with this task.

 

[chuckpfaff]

Thanks very much for the reply. The lugs are soldered to the 1/0 and I measure no resistance on the wires into and out of the cutoff switch. I also tried a bar instead of wire and still overheated.

 

[Bud Martin]

"I have noticed a voltage drop of less than .5 volts at the cutoff switch when it is under load."
So at 4000W, the dcA = 196dcA,
0.5Vdc drops x 196dcA = 98W of power dissipation on the switch!

1.65KW load/0.85/24Vdc = 80dcA, so switch power dissipation = 0.5V x 80dcA = 40W of power dissipation on the switch.

What is the contact resistance spec of the switch?
Are you sure the connections are really tight and clean and no washer between the switch terminal and the wire terminal?