question

steve-maloney avatar image
steve-maloney asked

Fuse cable heating why?

Hello,

I have a heating issue that I do not understand, My positive lead to the inverter is heating above > 50deg c. (and would go higher if not switched off)

I have 1 x 300Amp battery, with a 12v1200 watt Victron inverter.

When the inverter is near load max output at 1130 watts, I'm finding that my positive lead connecting the battery to the inverter is getting hot between the battery and fuse.
I previously used 25mm pure copper multistrand welders cable, which I have replaced with 35mm cable, my understanding the cable is rated to 290Amps.
I previously used a cheap Amazon ANL 125A fuse, which I've upgraded with a Victron Energy Mega Fuse Holder and a Mega Link Fuses Current Rating: 150A

The constant test load is 106A (240v) ( 1130 watts )
The Battery is good for a consistent load of <150A
The Cable is good for < 290 Amps, and has been created with recommended pure copper lugs.

Even after the "uprating" Its still getting hot, > 45+ deg C

I have now completely removed the fuse by making a new cable straight from battery to inverter (yes I know that's not recommended) and the heat disappears!

Note:

  • All connections are fully tightened.
  • Lugs are good, as same batch and assembly method used on direct connection cable above.
  • Maximum allowed cable (as per manual) used, is 35mm pure copper multistrand welding cable rated to <290Amps


Any idea's please?


thanks
Steve.

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7 Answers
scraggs avatar image
scraggs answered ·

I had this with a setup using an ANL fuse and the heat was coming from the fuse itself and traveling down the cable, is the cable hotter the nearer you get to the fuse ?

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steve-maloney avatar image steve-maloney commented ·

Yes, it is hotter near the fuse. thanks


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semlohnhoj avatar image
semlohnhoj answered ·


Please reconnect the fuse :)

Fuses get warm, they rely on heat to break at the rated current over time. If it's a 150A fuse and you're drawing 106A for a prolonged period of time they will generate heat which will radiate wherever it can, into the air but mainly up the cable because cooper is a good conductor of heat.

That said, I'd check that the fuse holder is of good quality and that there is room around the fuse and cable for air flow to dissipate the heat.




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steve-maloney avatar image steve-maloney commented ·

I changed to what I believe is a good quality fuse and holder:

Victron Energy Mega Fuse Holder and a Mega Link Fuses Current Rating: 150A

As I say above, I still have the problem

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semlohnhoj avatar image
semlohnhoj answered ·

Incidentally, what's your ambient temperature and how long are you running the test?

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steve-maloney avatar image steve-maloney commented ·
ambient temp has been quite low, between 2 and 8 deg C
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semlohnhoj avatar image
semlohnhoj answered ·

For reference, I just ran my inverter at 103A for around 5 minutes and the temperature of the cable at the fuse was above 30 degrees (nearly 36 degrees at it's highest). The same cable run at the isolator was only 22 degrees (see below). The ambient temperature is only around 14 degrees in the room as well. The fuse is a 150A coincidentally.
Fuse:

fuse.jpg


Isolator:

isolator.jpg


fuse.jpg (46.1 KiB)
isolator.jpg (50.1 KiB)
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pyrorider avatar image pyrorider commented ·
Why is there such a temperature difference in the middle of the cable shoe? did you crimp it with proper tools?
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steve-maloney avatar image steve-maloney commented ·
thanks for taking the time to do that.

So is it the case that heat should be expected and is unavoidable and should be accepted ?

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semlohnhoj avatar image semlohnhoj steve-maloney commented ·
You don't want to generate unnecessary heat so joints should be good and cable sizes adequate to keep the resistance to an acceptable level (Victron as well as other sites provide advice on recommended cables sizes). It looks like you've done that.

What you don't want is heat building up that is too high (i.e. outside the specification of the cable/connectors/fuses you are using) and most importantly, it needs to plateau at a level that is acceptable and not reach thermal run away. That is why you need adequate ventilation around anything that generates heat. In theory even small amounts of heating will be dangerous if they can't radiate.

If you are finding it levels off at a reasonable temperature then that's fine.

If it makes you feel any better, I'll be doing a longer test of mine periodically, especially in the summer to see if mine is getting too hot :)

Oh, one other thing, sometimes they have the fuses deliberately connected directly on a chunky bus bar because that is a great way to dissipate heat. Think the Lynx works on this principle (if you've got lots of money!)

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pyrorider avatar image
pyrorider answered ·

Welding cable often has a temperature rating higher than the usual allowed 70 degree C so it can handle more current because it basically allows higher losses.

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steve-maloney avatar image
steve-maloney answered ·

thanks for your inputs, appreciated.

Having learnt / watched Will Prowse videos, I thought it was desirable to have no heat ( heat = lost power ?) however, I'm at a loss how to achieve this.

The only way to avoid the heat seems to not have a fuse at all between the battery and the inverter.

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semlohnhoj avatar image semlohnhoj commented ·
You can't have no heat, and the minimum is the minimum you reasonably want to and can afford to achieve. You could use 200mm cables but that would be a terrible balance of cost versus benefit, and would still generate some heat.
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pyrorider avatar image pyrorider semlohnhoj commented ·
also, you would never even manage to fit a 95mm2 or 120mm2 cable into a multiplus XD
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Alexandra avatar image
Alexandra answered ·

@Steve Maloney

I have always found it funny how we have monster sized cables and then a tiny little wire for a fuse for all the current to pass through. and I agree heat is loss and bad as it changes resistances.

Do you have the 12/1200 multiplus? I thought those used/manual recommended 50mm² cable?

The fuse can be a NH fuse and holder. Heat is less of an issue. Has the advantage of being a disconnect and a fuse. So you can still be safe.

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