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Batt Charger and Fuses


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Hi

I have been having a little trouble with my cranking battery not charging. I have traced this down to a "thermal" fuse. My charger is 30A and the fuse is 40A. It is one of those push in / pull out ones and it wont stay in, even with everthing turned off so I guess it is...broke. The cheapest I can find a new one is £45.00 :o

Therefore I am wondering if there is an alternative I can use, especially as I think I will need two. The cable that goes to the domestic batteries has no fuse at all and I am guessing I should have one.

Whilst tracing cables I also noticed that the eber is powered directly off the cranking battery (via a fuse). As it has a 7 day timer I understand why it is directly powered but why the cranking battery not the domestics?

Many thanks

Wayne

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Wayne, Hi

I don't see why you can't (but I'll probably be contradicted) substitute the thermal fuse with a simple in-line one at very much reduced cost.

No way can I see why the eber is powered by the cranking battery. The cranking battery is designed to do just that (crank) and NOT to power a domestic device...

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especially as I think I will need two. The cable that goes to the domestic batteries has no fuse at all and I am guessing I should have one.

A mains charger/PSU that is capable of charging multiple batteries (or banks) independently on demand doesn't need a separate fuse/breaker for each bank.

The negative connections are common on the charger, so a fuse or breaker can be fitted there, where it will protect the combined output of the charger in one place.

This picture shows the relevant circuit extracted from my sterling installation instructions, from: http://www.sterling-power.com/images/do ... german.pdf

Your charger may be a different make, but the principle should be the same.

I actually use a "midi fuse" and holder, the holders of which are rated up to 200 amps.

post-669-136713792321_thumb.jpg

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Hiya

Yes the negative cable - now that makes sense - thanks.

The stirling charger I have is rated at 30A, I guess that is total regardless of the number of battery circuits I am charging so I just have to put a 40A fuse in the negative - right?

I'll swap the eber to the domestics - It is connected to the back of the Isolator on the battery side so just a matter of swapping to the other isolator.

Many thanks

Wayne

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The stirling charger I have is rated at 30A, I guess that is total regardless of the number of battery circuits I am charging so I just have to put a 40A fuse in the negative - right?

Yes, that's what Sterling recommend.

Also the negative and each of the the positive cables need to be capable of carrying at least 40 amps, to protect against over-current in any single leg.

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Just found a download on Stirling's site - the seem to want a fuse on both the positive AND negative lines???

That's a 'belt and braces' approach Wayne, and if you are going to use the likes of blade fuses in waterproof holders, which aren't expensive, then why not.

I fitted a Sterling Charger in my boat, but have to admit that I only fused the Positive outputs.

Dave

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The only trouble with a "belt and braces" approach with fusing is that it makes maintainability more complicated.

With a single fuse on the negative rail, the unit is completely protected, because the only over-current path is via that single negative connection.

If the unit ever stopped charging, then there's only one fuse to check.

No item of electrical equipment on boats or cars requires fusing on both negative and positive, it would introduce more problems without adding any additional protection.

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