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Old 12-05-2013, 17:58   #31
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Re: 2/0 wire being burnt from Alternator

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Originally Posted by Kettlewell View Post
Bill: Is there any reason not to use SS nuts and washers as long as you just use them to supply the clamping pressure on things like the alternator, batteries, or other connections?
Nope. So long as they're just used to apply the clamping pressure, and the actual electrical connection is made between the lug or ring-terminal and the stud, that should be fine.

Note that if you used copper or tin-plated copper or silver-plated or gold-plated hardware instead, you'd have extra protection in that good electrical contact would be made on both sides of the lug or ring terminal, instead of just one side, but for most purposes I think this can be ignored so long as the main connection is a good one with adequate surface area and adequate clamping pressure.

For reference, 304 and 316 stainless has about 40 times more electrical resistivity than does copper or silver or gold.

Bill
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Old 13-05-2013, 09:30   #32
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Re: 2/0 wire being burnt from Alternator

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If you're going to use stainless steel hardware on the alternator output bolt (nut, washers), be sure that they are NOT used between the cable lug and the alternator post. S/S hardware should be used ONLY to compress the cable lug onto the alternator post.

A single s/s washer in the wrong place, for example, is enough to cause overheating.

Also, be sure you use lugs with the proper size holes to fit the stud on the alternator and on the shunt.

Bill
Thanks for the info ! Unfortunately, I used SS for both nuts, but I'll rectify that right now !

So, in conclusion, I have installed a new piece of cable between the alternator post and the shunt. I did use 2/0, mainly because I had some on hand and neither of the stores here had enough of the 1/0. Lugs are the right size holes (different size each end of course !). Shrink wrapped. Despite the twisting and turning I tried, I could not get a coil to fit. However, I made a nice loop, 11" down from the post, then 14" up to the shunt. It just softly quivers when the engine is going.

I started up the engine, and read various temperatures as follows: Cable itself 51F, Alternator=100F (pumping 34 amps) (bit high ?), shunt=51F, 2/0 cable from shunt back to battery =51F. So all seems good so far.

Interestingly enough, I had the boat semi-rewired in Annapolis in 2000 at a professional boat yard. They put down three 2/0 cables going from the engine to the battery box (mid point of boat). First a cable connecting battery -negatives to engine frame; Second a cable to the alternator; Third a cable to the starter. I noticed for years that this latter cable had a loop in it near the actual starter, but the others did not, and wondered why. I think I semi-understand now: the alternator is about 24" from the floor, so initially, before I introduced the shunt, the cable would run from the floor right up to the alternator, thus giving it enough length to vibrate. And the starter being low down would need a loop. But why didn't they put a loop in the ground wire, where it's connected low down ? Is it because you don't have this "hardening" problem with ground wiring ?

At any rate, I would like to sincerely thank everyone for their input. I have learnt a lot and avoided a possible dangerous case of fire onboard.
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Old 13-05-2013, 09:57   #33
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Re: 2/0 wire being burnt from Alternator

"But why didn't they put a loop in the ground wire, where it's connected low down ? Is it because you don't have this "hardening" problem with ground wiring ?"
Ground is no different from positive that way. But since the ground cable was "low down" and the bottom of the engine usually doesn't "swing" on the mounts as much as the top would, they may have just felt there wasn't enough motion to justify it. Or, run out of cable.
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Old 13-05-2013, 10:02   #34
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Old 13-05-2013, 10:04   #35
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Re: 2/0 wire being burnt from Alternator

Dunno which is worse. If your surgeon or your electrician makes a mistake. For 30-40 years running.
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Old 13-05-2013, 10:16   #36
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Re: 2/0 wire being burnt from Alternator

The other thing you can do is get a short length of welding cable and put good ends on it and seal them up. It is far more flexible than battery cable. Finer strand wire is what makes it that way. I've beentold that the electrons actually move best on the surface of the wire, so finer strand is actually a better conductor too. Go to a welding supply shop and see if they sell it by the foot.
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Old 13-05-2013, 10:29   #37
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Re: 2/0 wire being burnt from Alternator

" I've beentold that the electrons actually move best on the surface of the wire, "
I was taught that actually, that's 1950's physics, and that it is not the electrons moving but rather the electron acceptance holes, or some such thing I've long forgotten. That is, the actual flow is the reverse of what we were taught.

But in either case, AC power flows mainly with a "skin effect" on the surface of the conductor. DC flows inside the mass of the metal. So welding cable has many fine fibers, with a great deal of surface area, to optimize it for AC welding power. Not what we want in battery cable, which can carry more power by using thicker strands which also present less surface area to corrode.

But as Chairman Mao said, "Black cat, white cat, all catch mice." You could probably wire up the boat with aluminum foil still on the roll and find a way to make it work.
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Old 13-05-2013, 11:00   #38
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Re: 2/0 wire being burnt from Alternator

Yes, AC current skin depth is important at high frequencies, like RF.

But, at low frequencies it's much less important, e.g., at 60Hz skin depth is about 8.5mm.

In any case, we're talking about alternator-to-battery circuits here which are DC, not AC.

Bill
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Old 13-05-2013, 11:32   #39
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Re: 2/0 wire being burnt from Alternator

Less "air" in a fine strand cable of equal cross section than a thick strand. Thus more copper crossection for DC also. Anyway, it would be great application of a cable between a vibrating engine and fixed bulkhead.
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Old 28-05-2013, 21:02   #40
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Re: 2/0 wire being burnt from Alternator

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Point is, s/s is nowhere near as good a conductor as is copper or silver or gold, etc.

How about brass ? Can't find copper nuts, and as for silver and gold.....!!!

Thanks
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Old 28-05-2013, 21:42   #41
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Re: 2/0 wire being burnt from Alternator

Wouldn't worry too much about nuts and washers. S/s is fine, so long as they're on the outside, i.e, used to press the bare lug against the stud.

Bill
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Old 29-05-2013, 06:33   #42
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Re: 2/0 wire being burnt from Alternator

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Originally Posted by btrayfors View Post
Wouldn't worry too much about nuts and washers. S/s is fine, so long as they're on the outside, i.e, used to press the bare lug against the stud.

Bill
OK. Thanks.
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