Emergency 100A DC fuse

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rhills
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Emergency 100A DC fuse

Post by rhills »

Hi All,

I have a mate who, for his sins, is currently cruising on his yacht in the Indonesian Islands. He has a 12VDC anchor winch which has a 100A fuse on it that blew up the other day under load. He has now discovered that the spare that he thought he had isn't actually there.

He has various gauges of wire on board (most rated in Amps eg 5A, 10A, 20A) and called me to ask if I knew what was the best way to fashion a replacement fuse that will get him back to Australia (he's planning to be back in Darwin in a few weeks. He said he tried some 10A wire "with a few strands removed" but that blew with a moderate load.

Leaving aside for the moment questions about why his anchor winch blew the fuse in the first place, is there any guidance I can give him about making an emergency fuse using ordinary wire?

Thanks in advance for any tips,
Rob Hills
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Johny
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Emergency 100A DC fuse

Post by Johny »

Hi Rob. Having seen no anwers to you yet, I'll dive in.
The fuses main job is to stop his wiring going up in smoke and to a lesser extant stop motor burnout - assuming no electric control of the motor (current limit).

For any "non-calibrated fuse product" he must keep an eye on the motor (some current monitoring would be helpful - does he have an ampmeter in the cabin?).

Anyway - my take on it is to use some wire that is clearly of lighter gauge than the wiring going to/from the fuse holder. If the damage to the fuse holder isn't going to be too signficant he could work up gradually in wire thickness until he gets one that will do the job. Strip the insulation off the wire so that, if it does go when he is not looking, at least the insulation won't start a fire.

As always in boats, ensure that a wire getting red hot isn't going to light fumes in the bilge. Doing the above could be dangerous stuff - especially as you pointed out, he doesn't know why the 100A blew.
rhills
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Emergency 100A DC fuse

Post by rhills »

Hi Johnny, thanks for the reply.

I've swapped a few SMS with him and have a bit more detail. He actually had a 100A circuit breaker in place, but it blew up because of "operator error" - the anchor control has separate buttons for up and down and someone pressed both together Image

He tried a bit of 10A wire with the insulation stripped and "a few strands removed" but it blew with only modest work by the anchor winch. He's inspected the motor and wiring and there's no visible sign of any problem.

He's reluctant to replace the fuse with a nail for obvious reasons. He'd prefer to be a little more scientific if possible as it's not easy to test load up the winch to the sorts of loads it may be called on to pull in "stressful moments" and obviously he'd prefer not to have an improvised fuse blow out on him during the same "stressful moments"!

Is there somewhere I can find some specs on what kind of resistance one would find in 100A fuse wire and then find a gauge of copper wire with a similar resistance? I've been Googling without success, but I'm probably searching for the wrong terms.
Rob Hills
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CometBoy
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Emergency 100A DC fuse

Post by CometBoy »

This might help you?

Fusing Currents for Wire

I’ve used Litz wire from these guys in repairing fluxgate compasses used in auto helms but they have a good section on fusing currents with an example close to yours. Obviously it is not the best Idea and not that accurate but better then taking out the wiring on the boat should a fault be present. Not sure if currents mentioned are DC or AC but so many variables in practice, probably not important anyway....


Cheers and good luck!

I guess he could SMS Jessica Watson..... Image

Bruce

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Johny
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Emergency 100A DC fuse

Post by Johny »

That's great Bruce.
The table tend to suggest 16 AWG wire will melt just above 100A.
16 AWG is considered OK for 22A loads with a single conductor and high temp insulation so the 20A wire he has, with insulation stripped off, sounds about right.
Again though - make sure that he understands that the fuse wire must be lighter gauge than the wiring it is protecting.
rhills
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Emergency 100A DC fuse

Post by rhills »

Hi guys,

Thanks for the information. The guy is an ex-RAN submariner who serviced and maintained the diesel-electric systems so he's got a reasonable tech background and understands the issues pretty well I think. I suspect that, like me, he understands the fundamentals, but doesn't have the detail to get him close.

I'll suggest that he try a stripped 20A wire and see how he goes with that. Hopefully it will be the right ballpark and he can experiment from there.

Many thanks,
Rob Hills
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2014 Mitsubishi Outlander Aspire PHEV
Petrol Usage to last refill: Jul 2014 - Oct 2020
Total Petrol: 756.3L
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rhills
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Emergency 100A DC fuse

Post by rhills »

BTW, my mate will be in Kupang by 30 May and I expect he'll do his darndest to source 2 or 3 replacement 100A Circuit Breakers there. I was in Kupang last month and it's amazing the range of gear you can buy there, just so long as you can find someone who understands what you're looking for, or else your own Indonesian is good enough.

Anyone know the Indonesian for "100A Circuit Breaker" (says he, high-tailing off to Google Translate).
Rob Hills
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Petrol Usage to last refill: Jul 2014 - Oct 2020
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CometBoy
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Emergency 100A DC fuse

Post by CometBoy »

A few Bintangs at Teddy's Bar upon arrival should sort that out!
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