15 replies to this topic

[Woody2332]

Need to know the amp of the brown wire that goes from starter solenoid to the alternator, the thickest one of the two brown wires, goes to the middle section of the plug that goes into the alternator? And where can I get the wire from as my is fried, that's another thing how would of that happened?

[Captain Mainwaring]

Depending on the year...these can be fusible links. 

The frying is the link doing it's job for some reason and protecting the alternator.

 

Many reasons as to why, could be the alternator ran away and decided to overcharge, diodes packed up and dumped to earth.

I'd personally look at the alternator myself to start with - take it off the car and get a reconditioner to stick it on a test rig rather than risk blowing the link again.

All of this assumes you have a fusible link - if you don't, you'll have had a fair old puff of smoke when that cable let rip, together with substantial damage in that area. 

Don't replace any cables before you find the cause of the failure, from google the hypalon links aren't available but many people replace with either inline fuse or solid cable.

[tiger99]

The wire needs to be rated for the maximum current that your alternator outputs, and that depends on which alternator you have, but will usually be between 45 and 80 amps. There actually should be two thick brown wires on most alternators, each rated to carry half the current, and they need to be the same length so they do share the current properly. If it is a Lucas with the two large and one small terminals, both teh large ones should be used, but sometimes there is a large screw terminal which is even better.

 

It fried because either it was too thin, or the alternator has shorted internally and power from the battery fried it.

 

Do not crimp that wire, or any other wire on the car, with a cheap crimp tool, or it will almost certainly fail again very soon.

[zony]

Mine fried when a friend (he was sort of) tried to help jump my car off his and he had his -ve and +ve crossed.

 

As my battery was almost flat it took a while. But after a couple of seconds I could smell the sweet aroma of cordite and plastic. Expensive night.

[Captain Mainwaring]

The wire needs to be rated for the maximum current that your alternator outputs, and that depends on which alternator you have, but will usually be between 45 and 80 amps. There actually should be two thick brown wires on most alternators, each rated to carry half the current, and they need to be the same length so they do share the current properly. If it is a Lucas with the two large and one small terminals, both teh large ones should be used, but sometimes there is a large screw terminal which is even better.

 

It fried because either it was too thin, or the alternator has shorted internally and power from the battery fried it.

 

Do not crimp that wire, or any other wire on the car, with a cheap crimp tool, or it will almost certainly fail again very soon.

 

 

If it was the OEM wire then it wasn't too thin unless the OP put a monster sized alternator on it, even then remember that 1mm2 of bare Cu will melt at 80 odd Amps in 10 seconds - to melt something as large as the OEM cables would take a fairly substantial short circuit.

 

If the car is fitted with a fusible link, could be this - if OEM copper, then most likely that a termination has failed.

 

Cables, especially for low voltage need to be rated much above their normal carrying current because of voltage drop.

 

For what it's worth, 10mm2 cable is rated at 70-80A running, but short circuit melt current will be substantially higher than that - 6 gauge will melt at 660A.

OP needs to find "why" first,

[zony]

The fusible links are hard to find. Almost impossible. I was lucky as I found a couple of scrapped cars to rob from.

[tiger99]

Captain Mainwairing, you are substantially correct, as far as rapid melting is concerned. I was thinking more along the lines of one of the two wires being missing, and a thumping great alternator fitted, which would result in the wire getting hot enough to greatly soften the insulation after a while. Not immediately, of course, as you point out. I was assuming that the insulation had melted. I am not sure that the copper actually melted, if so it would be in line with your figures.

 

If that happened quickly, it would suggest a good battery and a shorted alternator. Depending on the type of battery, 400 to 1000 amps would not be unreasonable into a dead short. But I have never seen an alternnator which was a dead short internally. Anything inside would melt at that sort of current, and the fault would probably have to be right at the terminal.

 

You will know this, but others may be interested in knowing that the alternator itself has no real way of outputting a current much in excess of its rating. A gross overvoltage is possible if the regulator fails, and that can fry the battery and other electrical items, including the rectifier diodes in the alternator itself, but the current will remain only slightly above the rating at all times. It is limited by leakage inductance in the windings, which keeps the current approximately constant even in severe overspeed conditions and with full field excitation due to a shorted regulator. Not that the regulators fail that way normally, you usually get no output, because the transistor usually fails open circuit..

[KernowCooper]

A 10" run of 6gauge will carry upto 80amps, see below wire to amps information

Attached Files

•  Wire Gauge and Amps.png   9.01K   11 downloads

[Woody2332]

There is a thin and thick brown wire, the thicker one of the two has fried, (the insulation of the wire) and what your saying is my alternator needs replacing, and I have to go scrap yard to find a replace ment wire? And can't I just use the original crimp and resolder it back on?

[Woody2332]

And if it is 10" of 6 amp, when can I get it from?

[KernowCooper]

Its 6 gauge not 6 amp and that rating is on a 10ft length , maybe Halfrords has some ? or a electrical factors near if you have one

Edited by KernowCooper, 30 June 2013 - 10:02 AM.

[Captain Mainwaring]

There is a thin and thick brown wire, the thicker one of the two has fried, (the insulation of the wire) and what your saying is my alternator needs replacing, and I have to go scrap yard to find a replace ment wire? And can't I just use the original crimp and resolder it back on?

 

 

You need to find out why - there is a fusible link in there for a reason. If you go replacing it with solid, then you may well do more substantial damage. If that wasn't a fusible link and you melted it, then something has definitely gone pair shaped.

[Woody2332]

It was the previous person trying to jump start off the front of the car and doing it wrong

[tiger99]

So he connected it the wrong way round? If so, your alternator is fried, which explains why the wire fried, because the alternator diodes overheated and shorted. The winding insulation will also be well fried.

 

Or did he try to jump it from the alternator terminal, the right way round, in which case only the wire fried?

 

To get a quick, correct answer, especially to electrical problems, you should be sure to tell us exactly what happened.

 

There is nothing at all wrong with jump starting from the front, but you must always connect positive to positive and negative to negative, and take care that the positive connection, to the incoming battery terminal at the solenoid, does not short against anything. The negative is easy, a cylinder head bolt will do.

[Woody2332]

Money isn't a issue, I will just buy both