Battery fuse blew?

[JonL]

The fuse that goes from my battery positive to my bus bar positive blew. In fact it melted the container the plastic fuse was in, but the metal piece between the fuse did not break?
I’m wondering if the 300 amp fuse was the right size? Anybody have an idea if I was using the right type of fuse. ?
Anyway I have eight battle born batteries. Hundred amp hour 12 V batteries wired in series parallel for 24 V. Everything in my system is 24 V.
Thanks, Jon

 

[Diysolar123]

that picture seems to show more "melting" (which means heat) on one side.
With the fuse intact that looks more like, this is a guess, that end was either not tightened down enough or somehow became a higher resistance connection. A high resistance conneciton of just 20amps going thru it would melt plastic. The melting point of plastic is wayyyyy lower than what it would take to blow that strip of fuse metal hehe

 

[JonL]

that picture seems to show more "melting" (which means heat) on one side.
With the fuse intact that looks more like, this is a guess, that end was either not tightened down enough or somehow became a higher resistance connection. A high resistance conneciton of just 20amps going thru it would melt plastic. The melting point of plastic is wayyyyy lower than what it would take to blow that strip of fuse metal hehe

The side that melted was going to the bus bar. Still not sure if the 300 amp fuse is the right size?

 

[Ampster]

I can't tell clearly from the picture what the wire size is but the fuse should be sized to protect the wire. I agree with @Diysolar123 that the cause of the heat should also be investigated.

 

[JonL]

I can't tell clearly from the picture what the wire size is but the fuse should be sized to protect the wire. I agree with @Diysolar123 that the cause of the heat should also be investigated.

Thanks. The wire size was 1/0. I was running a 1800 W AC heater for over a half an hour. I did notice that the wires were hot. But nothing that seemed to concerning? Perhaps my system isn’t big enough for that. I don’t think I’ll run that heater again. Although the microwave is 1800 W also. ?
Victron 3000/24 V inverter.

 

[Freep]

Yeah but the MW won't run for 30 minutes, right?

 

[JonL]

Yeah but the MW won't run for 30 minutes, right?

Got me? I’m also wondering if the fuse holder being plastic was the real problem. As the wire didn’t seem but slightly burned and the fuse didn’t crack, just turned darker. Perhaps I shouldn’t use a plastic fuse holder?

 

[Whinny]

My thoughts are that type of screw in connection with stranded wire is not suitable for high amperage-crimp connections only....

 

[JonL]

My thoughts are that type of screw in connection for stranded wire is not suitable for high amperage-crimp connections only....

Probably right thanks. ?? I’ll look for a different type next time.

 

[Ampster]

The wire size was 1/0

That load was less than 100 Amps and that wire should be good for more than that so I would suspect a crimp or lug connection was creating the heat. Some of those ANL fuses and holders can be flimsy. Did I understand correctly that the fuse did NOT actually blow?

 

[JonL]

That load was less than 100 Amps and that wire should be good for more than that so I would suspect a crimp or lug connection was creating the heat. Some of those ANL fuses and holders can be flimsy. Did I understand correctly that the fuse did NOT actually blow?

As far as I can tell the fuse didn’t blow, just turned a bit darker - like a little burned singe. at least that’s the way it looks to me, it’s not broken anywhere. Thanks

 

[Ampster]

My thoughts are that type of screw in connection for stranded wire is not suitable for high amperage-crimp connections only....

And it may be aluminum in which case you may need to use Noalox for the Copper to Aluminum interface and torque it down pretty hard to get past the Aluminum oxide.

 

[John Frum]

The side that melted was going to the bus bar. Still not sure if the 300 amp fuse is the right size?

What is the maximum continous design current for the system.
Usually its the inverter continous ac watts. / .85 conversion factor / 24 volts low cutoff = dc amps

 

[JonL]

And it may be aluminum in which case you may need to use Noalox for the Copper to Aluminum interface and torque it down pretty hard to get past the Aluminum oxide.

Thanks, this time I ordered a blue sea fuse holder, as this is the type I have for everything else.

 

[JonL]

What is the maximum continous design current for the system.
Usually its the inverter continous ac watts. / .85 conversion factor / 24 volts low cutoff = dc amps

The inverter is a 3000/24 V 70 amp

 

[Ampster]

The inverter is a 3000/24 V 70 amp

I would also downsize the fuse to protect the wire. Check to tables but my guess is 150 Amps is close.

 

[JonL]

I would also downsize the fuse to protect the wire. Check to tables but my guess is 150 Amps is close.

Thanks, but I don’t know where to find these charts. Or really how to read them. Wish somebody made an app on your phone for this. Plus battle born batteries told me to try 300 amp fuse. My inverter is a 300 amp fuse.

 

[John Frum]

The inverter is a 3000/24 V 70 amp

3000 ac watts / .85 conversion factor / 24 volts = 147 dc amps
147 dc amps / .8 fuse headroom = 183 amps.
You want a fuse in the vicinity of 185 amps and wire with insulation that won't melt at 185 amps.
Also please don't buy your fuse block and/or fuse from amazon or similar.
Littlefuse and Eaton bussman are trusted names.

 

[JonL]

3000 ac watts / .85 conversion factor / 24 volts = 147 dc amps
147 dc amps / .8 fuse headroom = 183 amps.
You want a fuse in the vicinity of 185 amps and wire with insulation that won't melt at 185 amps.
Also please don't buy your fuse block and/or fuse from amazon or similar.
Littlefuse and Eaton bussman are trusted names.

Cool, thanks ??
i’m sure you can tell I don’t do this for a living! ?

 

[John Frum]

Cool, thanks ??
i’m sure you can tell I don’t do this for a living! ?

Oh, I see its a Victron.
Those are low frequency with significant surge capacity.
Have a look at the doco and see what the 90second surge rating is.
That can change the math I did.