Heat from high draw question ...

[Apacha]

Hello. Just another newb dropping in for a quick sanity check ...

I have the following system just purchased and put together:

- TimeUSB 12v 140ah BT LifePO4 battery, 150amp BMS, M8 bolts
- Alffaa 12v 1500w Inverter
- Bay Marine Supply MRBF Terminal Fuse Block Kit with 175a fuse
- iGreely brand 2ft 2AWG 5/16 lug battery cable, tinned copper

I've tested this setup with a Keurig coffee maker, a dual speed ceramic heater and an electric water kettle. Everything appears to work well, no overloads, but the temps on positive side battery cable and fuse block are concerning.

Last test was running about two minutes with the water kettle which was pulling 1535w and 118amps at battery via Bluetooth app stats and 1252w at Inverter. Using an infrared temp gun, the positive side cable closest to battery was showing 150F, wire slightly melted just below ring terminal and the fuse block itself read 185F just below the fuse. It was only 110F on top of the positive side of battery where fuse is bolted into. It appears most of the heat is originating from the fuse block (?!?)

I went with 2AWG over 4AWG to pull more amps if I need to, but use case for this setup is NOT for continuous 1500w loads. I just wanted to test the max and see how it holds. Battery and inverter runs well, just a bit concerned about the temps here.

Thoughts? Thanks in advance.

 

[robbob2112]

Welcome to the forum,

The wire you are using is 105c pure copper 2awg. This means it is technically capable of 205amp. But to run at 200amps it will be 221F.... The NEC says 2awg THHN is good to 115amps - this is 75c cables.... I am not proposing you use THHN, so keep yer shorts on .... But what I am saying is 2awg cable is 2awg cable and it will get hot when you run 118 amps through it. Just the battery cable sheath can take more heat without melting.

Cable rating tables generally consider a 30c rise the max anticipated - so for 25c (room temp) + 30c = 55c = 131f max --- you are under the max by a touch

Something else to consider is if the fuse block and terminals can take the heat you are generating?

Did you use no-ox-id special A on all the connections? it is a corrosion inhibitor and it will lower the resistance of your connections a bit. Did you use a torque wrench when tightening the connections? This will keep you from stripping them out and also make sure you got them tight enough... 3-squeeks tight like on a car isn't much of a way to measure.

If the cables run cool enough in normal operation then you are probably fine, but getting close to the max.

Anyways, were it me I would bump up to 1/0 or 2/0 cable and so long as your connections are good everything will run cool to the touch at max pull.

 

[Apacha]

Thanks for the reply.
- No on the contact grease; didn't think to need it. I'll look further into this.
- Wrench tight to snug, no torque wrench used
- I can change out cables for thicker gauge, but the heat appears to be coming from the MRBF fuse block or fuse itself.

It appears I'm not alone with heat originating from MRBF fuses at high loads. There are a few threads on Reddit I just found discussing this. I may pull the fuse block off and run the same loads checking heat - at least eliminate this component.

 

[Apacha]

Well ... removed the fuse block/fuse, reattached inverter and ran the same high water kettle load as before. Hottest point was just under the battery terminal ring against the battery terminal and barely reached 100F after two minutes of high load.

Ok good ... let's reattach the fuse block and try again. Hmm .... now that also appears ok. The previous 185F temp on the fuse block is now only 105F max after several minutes. Unsure of this one. Installed in the same orientation as before with the same snug tightness. I suppose there were some contact issues going on previously. I'm going to look further into the contact grease. I'm really surprised by this. Thanks for pointing this out.

 

[robbob2112]

you had a bad connection and cured it when you put it back.... Use grease and buy a torque wrench