2/0 wire being burnt from Alternator

[macbeth]

I have an Alternator that on it's associated gauge can say it is putting out 90 amps. The alternator output, via a thick wire, is connected to a shunt which provides, via thin wires, the input to the gauge and also, via thick wires, passes back the current to the battery.

The short piece of wire, about 6" long, from the Alternator to the front of the shunt is 2/0 (or 00) gauge. Over two years it has gone solid, black, corroded and burnt off the cover !

The wire from the other side of the shunt, also 2/0 gauge, going to the battery, is perfectly OK. So are the thin wires going to the ammeter.

I have not yet determined whether 3/0 (or 000) gauge wire and associated connectors are available, or whether this is the right approach to replace the 6" long piece of 2/0 wire.

I thought I would like to get some comments from the experts on this forum first !!

Thank you.

[daddle]

High resistance connections. Corroded terminals or bad crimps or whatever. 90A cannot heat the conductor of a 2/0 wire, which is overkill already.

[macbeth]

Originally Posted by daddle

High resistance connections. Corroded terminals or bad crimps or whatever. 90A cannot heat the conductor of a 2/0 wire, which is overkill already.

High resistance connectors: These are heavy metal connectors, similar to

5 Big Bare Copper Ring Lug Terminal Connectors 2 0 Wire AWG 1 2" Stud Molex | eBay
made of grey metal.

Corroded terminals: Certainly not !

Bad crimps: Whacked with a hammer in a special crimping device which indents some of the metal into the wire.

I'm sorry, I don't think it's that straight forward !

[awpptdt]

Daddle is correct, there is a bad connection on one or both ends of your 6 inch 2/0 wire. A bad connection will get hot which will increase the resistance making it hotter and so on. 2/0 copper would be good for around 150 amps. J.T.

[colemj]

6" of 2/0 will be good for well over 150A. I agree, there is a connector issue. If the current wire is now without cover, etc., why not make a new 6" piece and see if it also gets hot? You shouldn't be using it now anyway.

The only other thing I can think of is that somehow the shunt is grounded and you effectively have a short on that side of it.

Mark

[daddle]

Originally Posted by macbeth

Bad crimps:[/COLOR] Whacked with a hammer in a special crimping device which indents some of the metal into the wire.

There's the prime suspect.

Trival diagnostic: Using an accurate voltmeter, with the alternator working hard, measure the voltage across the various interfaces.

Burning a big wire implies significant watts being dissipated. 20, 50, 200? So the voltage drop in one of the parts is going to be obvious:

50W / 90A = 0.6V

Measure each of the four interfaces: stud to crimp terminal, terminal to wire, etc.

[nitpik]

Are you telling us that your shunt is in the Positive alternator feed to the battery? (unusual?)
Daddle suggested the possibility of corroded connections, not connector. The connectors you referenced from eBay should suffice, 'though if in salt water it would be better if they were tinned, and they don't appear to be over-spec'd in terms of wall thickness.
Without laying eyes on the situation, I would tend to agree with Daddle - suspect the connections first.
I hope you are not holding up a hammer-crimped connection as the epitome of fine electrical workmanship? If no Deox or adhesive-lined heat shrink was used, corrosion could most certainly have got in there, and it was not likely a 100% connection in the first place.

[David M]

150 amps is close for 2/0 if you don't account for the run or temperature. You can put a shunt on the hot side if the meter is analog or if digital you add a special type of converter which 'fools" the meter into thinking it is on the negative side. All a current meter does is measure the voltage across the shunt which converts directly into current. I did this with my two alternators so I would know if they are close to being overloaded and to give me an idea of what the load is on my DC system.

You have to make sure you shunt is rated for or greater than the amount of current that is going to be run through it.

There is one way the insulation of your 2/0 wire could have melted and that is if the hot side of your alternator shorts out.

You only need 2/0 wire for your alternator if it capable of producing near 150 amps, and this is dependent on the run where the greater the run the more below a 150 amp alternatior you can justify using 2/0 cable.

[Kettlewell]

He said the alternator is putting out 90 amps.

[David M]

He didn't say if 90 amps is it rating. I am underway right now with two alternators rated at 110 amps where one is producing 28 amps and the other 24 amps.

[btrayfors]

AWG 2/0 is plenty big enough.

There's definitely a connector problem....loose, bad crimp, or surface corrosion most likely. Could also be dissimilar metals, defective shunt, etc.

The return wire (negative) should be same size as the positive wire, and should go directly to the alternator ground, not the engine.

FWIW,

Bill

[s/v Jedi]

Originally Posted by btrayfors

AWG 2/0 is plenty big enough.

There's definitely a connector problem....loose, bad crimp, or surface corrosion most likely. Could also be dissimilar metals, defective shunt, etc.

The return wire (negative) should be same size as the positive wire, and should go directly to the alternator ground, not the engine.

FWIW,

Bill

+1 high resistance connection between altermator and shunt or a short from shunt to negative. Measure voltage drop, i.e. positive meter-lead to alternator and negative lead to shunt. Voltage should be at or very near 0V.

[dannobee]

Which shunt? Do you have a picture of the installation?

If high resistance was the problem, you'd likely see fretting on one of the terminals. 2/0 wire is PLENTY big. You have another problem.

[noelex 77]

Originally Posted by macbeth

The short piece of wire, about 6" long, from the Alternator to the front of the shunt is 2/0 (or 00) gauge. Over two years it has gone solid, black, corroded and burnt off the cover !
.

If the wire has developed black wire corrosion this may be the problem rather than the connections, but the wire obviously needs replacing so its a bit academic.

A wire connected to the engine with a shunt mounted on a rigid part of the boat needs some thought about vibration protection.
Six inches sounds a bit short to allow for sufficient movement to prevent strain on the joints.
You may consider making it a little longer.

[macbeth]

Originally Posted by noelex 77

If the wire has developed black wire corrosion this may be the problem rather than the connections, but the wire obviously needs replacing so its a bit academic.

A wire connected to the engine with a shunt mounted on a rigid part of the boat needs some thought about vibration protection.
Six inches sounds a bit short to allow for sufficient movement to prevent strain on the joints.
You may consider making it a little longer.

A. Obviously I'm going to replace it - today ! BTW, it was initially sealed with shrink tube. I'm going to do better this time. And it addition to crimping, I'll solder it, and use copper terminals.

B. The only bad connection I can think of is that there are three wires attached to the Alternator output terminal. I'll move the other two to the other end of the wire, i.e. shunt connection. Also the nut on the Alternator output terminal was a little corroded - it was ordinary metal - I'll change that to SS.

C. Referring to the quote above, yes, the Alternator is on the engine (obviously !!), but the shunt is on the nearby sidewall. I guess vibration could be an issue ?? I'll make a loop this time, making it 9" to 12" long.

D. The alternator is rated at 120amps, but I'never seen the output that high.

E. When I've made the new loop, I'll take the measurements suggested above.

F. The shunt and associated gauge were made for high amps - the gauge's dial goes up to 200 amps !

G. Thanks for opinions ! Any more ?