4/0 cables & 250ANL fuse heating

[Texas-Mark]

Remember the RV fire
Always fuse both legs

Only if you have a poor design.

 

[chrisski]

I'm not sure what you mean by both legs? Positive and Negative? Each of two Batteries independently? Every leg off a busbar?

 

[Texas-Mark]

I'm not sure what you mean by both legs? Positive and Negative? Each of two Batteries independently? Every leg off a busbar?

If you want overkill, a fuse would be right off the battery bank on both the positive and negative terminals of the compete bank (not each battery). But IMO fusing both is not necessary in a properly set up system. The RV fire posted above appears to have been caused because the positive terminal was too close to the grounded frame and things fried when it came loose and came into contact with it.

 

[DerpsyDoodler]

If you want overkill, a fuse would be right off the battery bank on both the positive and negative terminals of the compete bank (not each battery). But IMO fusing both is not necessary in a properly set up system. The RV fire posted above appears to have been caused because the positive terminal was too close to the grounded frame and things fried when it came loose and came into contact with it.

ehhh, I disagree. i have 2x 24v DIY LFE batteries operating in parallel. Each battery is fused on the positive line before the bus bar. Each battery also has a BMS controlled contactor, before the fuse. Any wire leaving the positive busbar is also fused. The inverter and battery wire fuses are 350 and 200 amp class-t fuses respectively. The smaller wires have ceramic fuses. Even smaller ones just have fast blow glass fuses. I didnt want a problem with one battery to potentially kill the other. Perhaps this is overdone.

What does a fuse on both the negative and positive lines achieve?

If it was an SLA bank I wouldnt be so concerned with fusing each battery.

 

[Texas-Mark]

What does a fuse on both the negative and positive lines achieve?

Nothing, unless you have a poor design as I mentioned. The RV fire had an issue because the positive terminal shorted to the frame which was grounded to the negative. A fuse on the negative terminal would have blown before any serious damage was done.

I personally think fusing each battery is overkill, but I guess it does no harm unless it upsets the balance if one of them develops some resistance.

 

[kenryan]

Have we even established how hot things are getting? Hot or warm? Can you grab it and hold on?

 

[Texas-Mark]

Have we even established how hot things are getting? Hot or warm? Can you grab it and hold on?

I really think moving the washers and cleaning the connections will solve the problem for the most part. Or at least try that first before looking into other possibilities.

 

[solarstuff]

I'll move the washers and sand the metal as suggested and get back to you. Thanks for the feedback, all!

 

[mrzed001]

Fuses has multiple purposes.
- Protect your cable (less A than cable allowed)
- protect your battery (less A than battery can charge/discharge)
- protect your equipment (less A than equipment can max use/make)
- ....

For example you have a 4p battery system, and some inverters (bigger system)
Where do you put and what size fuses ?



- Fuse 1 to 4 sized based on battery. 280Ah battery should not charge/discharge over 1C: 300A
- Even with 3 battery strings out of order the inverters will work and can use up to 300A from remaining 1 battery. Also they can not overuse it.
- Fuse 0 based on inverters. Like 3x 8kW inverter can use 500A (x1,5 peak): 700A

And now for the questions:
- Why do I need a fuse on both leg? Because a short can occur in the unprotected leg. And that gets around your only fuse and that is like you did not have it at all.
- Why disconnect both leg? To completely remove the battery from the circuit. To make it easy to service.
- Why an extra fuse before the inverters? Because F1+F2+F3+F4 together will allow too much: 1200A (and not 700A).
- Why bother with that lot of fuses? I am handy, never dropped a tool. I am certain I will not make a short! Good boy But you know sometimes accidents happen. Sometimes years later. Sometimes outside forces you can not control.

These are the principles how I design the fuses on a bigger system.
Some will say overkill. I will say safety and foresight.

 

[Texas-Mark]

Why do I need a fuse on both leg? Because a short can occur in the unprotected leg. And that gets around your only fuse and that is like you did not have it at all.

If the positive is properly fused at the source, it is unlikely the negative leg is going get around the fuse. I'm not saying not to do it, but just not seeing the need in a properly set up system. IMO people would be better off routing cables properly and fusing in the correct places, rather than adding more fuses (and more potential points of failure). Just my $.02