Unusual electrikery one

1997 LR90, 200TDI Disco engine
Last spring alt was squeeling like a stuck pig. Took it to me mates garage and alternator was shot. Replaced with a new one (100Amp).
Fast forward to January.
Started squealing again, took it back and the alt was burnt out......Warranty replaced.....still squeals!! and gets hot as it seems like load is too high, you can see the belt jump when cable put on alt....Disconnected battery but left everything connected (all running from alt, not across batt) all ok. Replacement battery purchased.....
2 days later, went through some water (not loads) and starts squealing again! Alt disconnected and drove home.
No fuses have blown so i'm thinking it must be between alt and battery that the issue is. If it was anything else drawing that kind of current fuses would have blown.
I'm disconnecting everything except whats needed to run the vehicle (all my aux wiring).
I've not had chance to do anything yet but am I correct in thinking the brown cable goes from the alt, to the starter and teed to the battery? If so then somewhere along this route it must be earthing or something to draw that much amperage (100A alt) i've not actually measured the current yet.

squealing could also be the belt. You got a new belt for it? Also over tightening the belt can put to much force on the bearing, causing premature failure

New belt fitted and if anything slightly slacker than over tight

You shouldn't run with the alternator disconnected as you can damage the regulator/rectifier

Kwakerman said:

You shouldn't run with the alternator disconnected as you can damage the regulator/rectifier

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I did wonder that to be honest...oh well, better damage that than burn another alternator out.....I guess!

Ive never measured high currents before, if i remove the alt lead and stick my meter in between, switch to Amps will it measure the amps being drawn or jut melt the meter wires and fry the multi meter?

Unless you have a very high current meter (50Amps+?) you will probably damage your meter or blow its fuse. When you start your engine the alternator will try and put back the power into the battery that the starter has just used. That will result in a short duration high current flow. I don't think the brown cable is shorting as that would also result in a flat battery as there is always battery voltage on those cables. Are you using cheap alternators or quality items?

I'm not sure, I would imagine decent ones, knowing the chap who is doing the work for me. Not having any problems with the battery going flat, or what was the old one.
Could be an interesting fault finding job then

If you can borrow a clamp meter you don't have to break into the wiring and see what currents are being drawn. Something like this will do (make sure it has DC current measurement)

I was looking at those earlier but they were AC Current, for that price i've decided to treat myself, can never have too many toys
Should make life a lot easier

Do a bit of research, that was just the first one I spotted, may be cheaper ones available.

Have you got the correct belt profile fitted? Is your wiring up for a 100 amp alternator? Start with the basics. The problem started when you started using more lectrics, heater , wipers, lights.

nobber said:

Have you got the correct belt profile fitted? Is your wiring up for a 100 amp alternator? Start with the basics. The problem started when you started using more lectrics, heater , wipers, lights.

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The chap who replaced the alternator and belt is a reputable guy so i'm sure he will have used the correct parts. Not sure about wiring, assume you mean is it man enough? It is the original wiring but surely the alt will only put out the amps reqd, not 100A all the time?
Nothing extra being used, winch fitted but thats via an isolating switch and roof lights that also have an isolation switch, which is turned off.

If the wire is too small it can back up the current thus overheating the alternator. The alternator will dump as much current as the battery needs. A poor earth will also cause the alternator to work harder, poor ground = alternator working harder & inadequate wiring = hard working alternator to back up and burn out.

You can piggyback a new wire from alt to battery, no need to rip the existing wire out.

Thanks Nobber, the list of things I need to check is getting longer....Still. there's only one way to learn about my vehicle...I could just take it to my mate to look at but think its time I started finding out how it all fits together myself

Interesting.
Bought a clamp meter
No load, everything connected 13.7A
Everything on including roof lights 36.3A Took it for a run to about 3 miles from home, all ok.
Sprayed alternator belt with some water.....started squealing for about a minute, checked current and about 13A. Stopped squealing after about a minute.
Drove home all ok.
Turned engine off then back on and it squealed for a short time.
Touched alt and it was fairly hot, could touch it but was getting uncomfortable!
I'm now questioning the quality of the replacement alternator!!

Don't forget that the alternator will be replacing the power used by the starter for about the first 10 - 15 minutes of running (which will probably be the 13A readings) Try going for a longish run and then retry measuring the current before you stop the engine, will probably be down to a couple of amps by then.

Thanks, will try that.
Should the alt get hot after driving about 6 miles?
Any idea why it squeals when wet? (well, damp, it wasn't soaking wet)

An alternator delivering 13 amps at 14 volts will be consuming something like 200 watts of power which has to be delivered by the pulley. 36 Amps is 500 watts+ and the full 100 Amps is nearly 1.5 Kw. It doesn't take much water on the belt to reduce the friction and cause the belt to slip.

I hadn't thought of it like that.Perhaps i need to ensure its a decent belt on it, is the ones with notches taken out better than the smooth ones?

Notched belts are generally used for small diameter pulleys. One thing to be aware of is that if a belt is worn, or too narrow, it sits lower in the pulley, if it gets to the point where the narrow tip of the belt is actually running on the bottom of the pulley groove it will actually reduce the amount of power it can transmit eventhough the belt is tight. A belt uses the flank sides to transmit the power, does the bottom of the pulley groove look polished?