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Rewiring battery, starter, alternator high current wiring?
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rcx822



Joined: 31 Dec 2010
Posts: 112

PostPosted: Tue Jul 15, 2014 8:17 am    Post subject: Rewiring battery, starter, alternator high current wiring? Reply with quote

I'm fitting a high output alternator and 190A winch to my 1990's Suzuki jeep. It has 110 A output. The original alternator was 70A.

The primary fuse is 60A, meaning that no more than 60A charge from the alternator can go to the battery. If I'm fitting a larger alternator then I guess this means I should fit a higher capacity primary fuse and fusebox holder.

I've seen these mega fuses which go upto 500A. Should I take the opportunity to fuse the starter motor? Presently the starter is unfused.

The winch comes with a circuit breaker which allows unlimited time draw at 100A, 20 min at 150A, 10 min at 200 A etc. But the winch instructions do not specify fitting a fuse. But maybe this is sensible in addition to the circuit breaker?

If I do fuse the winch and starter, then seperate fuse for each one, or should I just use a big 400A primary fuse and wire the starter, winch, and distribution box off that?
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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Tue Jul 15, 2014 11:07 am    Post subject: Reply with quote

In my opinion there is no need to fit any of the fuses that you propose. The 60 amp fuse you talk about will be a fuse-able link and it's primary purpose is to protect the wiring harness. As to fitting a 110 amp alternator, you will get a higher output yes, but only at higher revs. You lose the advantage of a higher output at low engine speed. I don't see any need to fit a fuse to the starter. If it was needed the manufactures would have fitted one. What sort of work will the winch be doing? If it is sustained high load work then you should fit a bigger battery as well. This will help to 'cushion' the load on the alternator.

That's my tu'pence worth

Art
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rcx822



Joined: 31 Dec 2010
Posts: 112

PostPosted: Tue Jul 15, 2014 11:11 am    Post subject: Reply with quote

47Jag wrote:
The 60 amp fuse you talk about will be a fuse-able link and it's primary purpose is to protect the wiring harness.


The primary fuse lies between the alternator and battery, so won't it get blown if the alternator supplies more than 60A?

47Jag wrote:

As to fitting a 110 amp alternator, you will get a higher output yes, but only at higher revs. You lose the advantage of a higher output at low engine speed.


I've looked at an output chart showing RPM vs max alternator output, and the higher rated alternator has way higher potential output even at idle.
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rcx822



Joined: 31 Dec 2010
Posts: 112

PostPosted: Tue Jul 15, 2014 11:50 am    Post subject: Reply with quote

Here's the current wiring setup. I imagine that at least the fuse box needs to be upgraded and I should check that the current wire between the alternator and battery is capable of safely working at 110 A.

As you can see, the primary fuse (60 A) will limit the new alternator, won't it?

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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Tue Jul 15, 2014 10:11 pm    Post subject: Reply with quote

In the circuit as described the fuse would be under most stress when the winch was operating at load assuming that the winch is powered straight from the battery.
My comments about reduced low speed output is based on older Delco alternators, so it would seem that technology has solved that problem.
If the fuse is like the older BMW style where the metal link was replaceable (just as well as they cracked and left the car powerless) you could fit two links to double the current rating.
I don't think that you need to worry about the battery handling a high current charge. It has to deliver a high current discharge every time you start the engine.

Art
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Wed Jul 16, 2014 7:33 am    Post subject: Reply with quote

I would expect there is a chart somewhere, that shows alternator output versus RPM, and that a big alternator, even at tick over delivers no more appreciable charge rate than a smaller one, the effective rate is when the alternator is spinning. Alternators have a maximum safe rotation speed, I did read somewhere this is quite high, around 20,000rpm, so for me, leave the fuses alone, fit a hand throttle to up the tick over speed when winching, use a bigger battery to steady out the dips, and look closely at the rotation speed of the alternator, aiming for a higher speed, therefore charging rate at lower engine speed, achieved through alternator pulley diameter.
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KA

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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Wed Jul 16, 2014 8:30 am    Post subject: Reply with quote

The fuse is there amongst other things to protect the wiring, if you are planning to increase the capacity of the fuse, the wiring between the alternator and battery would also need to be upgraded.

Dave
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rcx822



Joined: 31 Dec 2010
Posts: 112

PostPosted: Wed Jul 16, 2014 10:02 am    Post subject: Reply with quote

Idle up sounds like a great idea, saves someone sitting in the cabin with the gas on.

I'm still waiting for a chart for my exact alternator, but here's a sample from a modern alternator. Remember that this is showing alternator RPM, which is a lot higher than engine RPM. And even between the 108 A and 140 A alternators shown in this chart there are huge gains at low RPM.



So what's the final concensus because I'm not clear? Do I uprate the fuse box, primary fuse and cable from the alternator to battery? Considering that the fuse is between the alternator and battery and the alternator has been upgraded from 70 A to 110 A (and the original fuse is 60A).
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Thu Jul 17, 2014 6:43 am    Post subject: Reply with quote

Wedge on the throttle pedal to hold engine at 2000rpm looks good to me, and a lot cheaper!
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KA

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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Thu Jul 17, 2014 9:32 am    Post subject: Reply with quote

ka wrote:
Wedge on the throttle pedal to hold engine at 2000rpm looks good to me, and a lot cheaper!


Wedge? Luxury! We always made do with an old brick... Laughing
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