2/0 wire being burnt from Alternator

[Kettlewell]

Hopefully your shunt isn't heating up too. I have had a shunt go bad on me, and it wasn't immediately apparent but its resistance got to be too much. Another thing that can happen is that someone installs a larger alternator at a later date and doesn't upgrade the shunt to match the amperage of the alternator.

[macbeth]

Originally Posted by Kettlewell

Hopefully your shunt isn't heating up too. I have had a shunt go bad on me, and it wasn't immediately apparent but its resistance got to be too much. Another thing that can happen is that someone installs a larger alternator at a later date and doesn't upgrade the shunt to match the amperage of the alternator.

Good point about the shunt ! I'll check that too. I had the alternator for a year, then purchased the shunt to match it, so OK on that point.

I'm thinking about going down a gauge, i.e. from 2/0 to 1/0. It will be easier to make the loop, and 1/0 is good to 150amps, which I'll never reach. The 2/0 is much more stiff and I'm beginning to believe that vibration was a major cause.

[hellosailor]

Copper terminals: Better to use tinned copper on a boat. Crimped, not staked. Cheap enough to order up a replacement for that burned piece from genuinedealz.com or someplace else, and have it made up professionally.

It is possible that whoever made up the last wiring did not use wire rated for engine spaces, and it is the normal heat of the engine bay that is burning it up. If you stick a hand in there, is it the wire that is hot? Or the space? (For about $25 these days you can buy a non-contact IR thermometer to see numbers.)

If the problem is ambient heating, from something like an exhaust manifold or pipe that was just run too close to the wiring, there's thermal insulation that can also help. For the cable, and for the parts.

[Kettlewell]

If you stick a hand in there, is it the wire that is hot?

I wouldn't grab that wire if it is melting the insulation!

[macbeth]

Originally Posted by hellosailor

It is possible that whoever made up the last wiring did not use wire rated for engine spaces, and it is the normal heat of the engine bay that is burning it up. NO IT IS NOT ! THE ENGINE ROOM IS NORMAL TEMPERATURE. If you stick a hand in there, is it the wire that is hot? I DON'T FANCY TOUCHING WIRES THAT HAVE 80 AMPS FLOWING THROUGH THEM, BUT I ASSURE YOU, ITS THE WIRE THAT'S GETTING HOT ITSELF. Or the space? NO. (For about $25 these days you can buy a non-contact IR thermometer to see numbers.)GOT ONE THANK YOU, BUT ONLY THIS WINTER. GOOD IDEA, I'LL TAKE IT CRUISING NEXT TIME.

If the problem is ambient heating, from something like an exhaust manifold or pipe that was just run too close to the wiring, there's thermal insulation that can also help. For the cable, and for the parts.

NOT APPLICABLE. THE EXHAUST IS ON THE OTHER SIDE OF THE COMPARTMENT, AND THERE ARE NO NEARBY HOT ENOUGH PIPES TO DO THE DAMAGE.

[dannobee]

OK, we're getting somewhere. Is the shunt hard mounted to something other than the engine? A 6" 2/0 cable won't give much, and if it's mounted to something other than the engine, the natural vibrations of a running engine will work harden the copper wire.
Like I said previously, if the failure was due to excessive current, there would be fretting on one of the terminals before that cable gave up the ghost. And I seriously doubt that your 120 amp alternator will ever generate enough amperage to cook a 2/0 cable.

[Ziggy]

Originally Posted by Kettlewell

I wouldn't grab that wire if it is melting the insulation!

A great use for an IR pyrometer, if you have one. And if you don't, they're pretty inexpensive.

[Cheechako]

00 should be more than enough for a 100 amp alternator... do you have regulator issues? How long does it put out 90 amps? Most my 100 amp alternators with a good regulator might put out about 85 amps for 15 mins max... then taper off...

[macbeth]

Originally Posted by dannobee

OK, we're getting somewhere. Is the shunt hard mounted to something other than the engine? YES, IT'S MOUNTED TO SIDEWALL, AS NOTED IN A PREVIOUS POSTING. 6" 2/0 cable won't give much, and if it's mounted to something other than the engine, the natural vibrations of a running engine will work harden the copper wire. I LEARN SOMETHING NEW EVERY DAY !!
Like I said previously, if the failure was due to excessive current, there would be fretting on one of the terminals before that cable gave up the ghost. And I seriously doubt that your 120 amp alternator will ever generate enough amperage to cook a 2/0 cable.

Thanks for your response. So I've decided to go down to 1/0 wire which is more flexible, and making a loop out of the wire instead of going straight from Alternator to Shunt. This will make the cable length about 11". Difficult to make it any more due to positioning of Alternator and other "stuff" !

I'm also moving two other cables that were attached to the Alternator post over to the shunt end of the cable. Also replacing the ordinary metal nuts on the alternator output terminal (which were somewhat corroded) by SS nuts. I'm also sanding all terminals and connectors associated with the cable.

I'll report back when it's all done and I've done some engine time.

Thanks again.

[hellosailor]

macbeth-
Go to a hardware store and take a look at how they sell pre-packed copper tubing for refrigerator watermakers and icemakers. It is always coiled up, and you are supposed to leave any excess, as the coils also absorb any vibration from the fridge to slow down the work hardening in that line.

You might want to go to a longer cable, enough so you can make a full loop without "pinching" it in hard. I'm guessing more like 18" for a cable that heavy, so you've got a straight bit at each end going into the lugs. And again, worth ordering it in, or using a proper crimping tool (at West, etc.) to make sure those lugs are on TIGHT.

You might also want to check the engine mounts. We all ignore them but sometimes they break, sometimes they simply harden up and stop absorbing vibration. The folks who make them actually expect them to be changed every 5 years. They're probably OK but while you're in there...

[btrayfors]

One other thing. I alluded to this earlier ("mixed metals"), but should have been more specific:

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

[colemj]

Originally Posted by btrayfors

One other thing. I alluded to this earlier ("mixed metals"), but should have been more specific:

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.

Bill, do you mean this in general, or only in this specific alternator application? We have lots of high current gear on board that have stainless steel posts and hardware with copper lugs on the wires (Battery switches, relays, inverters, chargers, etc). Even our batteries are this way.

Mark

[btrayfors]

Originally Posted by colemj

Bill, do you mean this in general, or only in this specific alternator application? We have lots of high current gear on board that have stainless steel posts and hardware with copper lugs on the wires (Battery switches, relays, inverters, chargers, etc). Even our batteries are this way.

Mark

Mark,

Yes, I mean it in general.

I think if you check closely you'll find that most, if not all, of those "stainless steel posts" are really tin-coated copper. All of the Blue Sea Systems bus bars, switches, etc. are tin-plated copper. You can also find a number of bronze posts aboard.

Point is, s/s is nowhere near as good a conductor as is copper or silver or gold, etc. If you introduce a s/s piece of hardware -- such as a washer -- between a tin-plated copper lug and a tin-plated copper stud on a switch, for example, you've just introduced a significant point of resistance right where you don't want it to be.

Battery lugs are mostly lead, not s/s. The wing nuts which come with some batteries may be s/s, but they are intended to compress the lug(s) onto the lead battery posts. And....wing nuts don't belong on a boat anyway :-)

Bill

[daddle]

Originally Posted by Cheechako

00 should be more than enough for a 100 amp alternator... do you have regulator issues? How long does it put out 90 amps? Most my 100 amp alternators with a good regulator might put out about 85 amps for 15 mins max... then taper off...

Heh. 4 gauge is enough. 2 is conservative. 00 is still overkill. But 6 inches is not long enough between the engine and a fixed point ... One would think 18" or more would be prudent.

[Kettlewell]

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?