question

JedTheFed avatar image
JedTheFed asked

I keep blowing 400 amp t-fuses when charging at 240 amps

Hello everyone,

Scenario

10 KW onan generator

cerbo gx set to accept 50 amps

800 amps renogy batteries

2 multiplus 3000 wires in split phase.

400 amp t fuse

I set both inverters to charge at 120 amps the 400 amp t-fuse blows. If I set them both to 100 amps charging it seems ok. Why is this happening?

I thought it was because my solar charger was on at the same time when the first fuse blew, but it is still happening. I was bringing the power up from 62% charge and it got as far as 71% before the last fuse blew. This time it even melted the fuse holder.

Can I not use the full 240 amps charging? It seems I could do this before but can not do it recently without the fuse blowing.

Why is 200 amps charging blowing a 400 amp fuse?

Gary





fuses
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jefffay avatar image jefffay commented ·

Did you ever get this figured out? I have the same setup and I'm having the same problem. I switched to a 500 amp fuse (Lynx Shunt) and the fuse still gets really hot, as does the bus bar.


I should add that I'm only charging at 160 amps...

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3 Answers
wkirby avatar image
wkirby answered ·

It sounds to me like the fuse is overheating or not getting enough ventilation to keep it cool. When a large amount of current flows through a fuse it will warm up, When a large amount of continuous current flows through a fuse it will continue to warm up exponentially if it is not kept cool.
The hotter it gets, the more its resistance increases and so the hotter it gets in a vicious circle. A hot fuse will then have a lower rating than what it would be at ambient temperature.
It's becomes a nightmare.

You did not mention which type of fuse holder you are using or how well cooled it is when its running with such high currents. Are they mounted in a small enclosure?

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JedTheFed avatar image JedTheFed commented ·

Hi wkirby,

That sounds very logical, It is in an eclosed bay with the batteries, solar controller and inverters. Also when I was ok with charging at 240 before I was in a much cooler climate and had not installed the solar controller yet.

I have been told it could have been the solar charger and inverters charging at the same time. But I don't know why that would matter except for the added heat as you pointed out.

Gary

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dtcassist avatar image
dtcassist answered ·

Some more detail of your setup would be helpful - what voltage battery bank? What type of batteries? How much solar?

Is the solar charge controller wired to pass through the same fuse? If solar is incoming through the same fuse as the inverters then yes that would absolutely increase the current passing through.

A basic schematic of what you have would be very telling to help understand.

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dwmarine avatar image
dwmarine answered ·

Do you have a picture of your fuse holder? I wonder if the heat melted the fuse?

The most common melting problem we find is that the fuse and cable lug are not bolted directly together in the fuse holder, but with a spacer washer in between. The extra resistance from the washer causes excessive heat and possible subsequent melting.

The stainless steel washers commonly used in the marine industry are the worst, the nickel plated brass washers aren't so bad.

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