Duff alt.?? Major discharge and overcharging...

Jimbo4x4

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Mar 2, 2010
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Hey all, I gave my engine bay a hose down on Friday as there was baked on mud everywhere. I then gave it a half hour in the sun to dry off before moving it, and all worked as it should. Then, that evening I went to start it and there was barely enough juice between the two batteries to turn the engine over once. After a half hours fast rate charge they were just powerful enough to get old Rex running, and I drove out to Anglesey with no problems. Another run that evening went without a hitch.

However, Saturday morning we jumped in the truck to find, yet again, 2 flat batteries. A power pack did nothing. Niether did the builders van next door connceted to one or both batteries on jump leads. I left a spare battery connected to each disconnected battery for half an hour each to equalise the charge then when I reconnected it all there was once again enough juice to get the engine going.

Then half a mile down the road all the warning lights and buzzers come on. I backed my foot of the accelerator and they stopped. I put my foot back down again and they came back on, then I noticed the charge indicator was trying to push past its maximum reading of 16V! I switched the headlights on and everything went back to normal, until another 5 miles down the road when I had to put my blowers on full too. After this everything stayed in the green.

Obviously I don't want to have to drive round with my lights and blowers on all the time and disconnect a battery every time I stop for more than 30mins. What could be the problem? My initial thought was a dead battery but both seem to be holding charge okay, could it be the alternater? If so, is there any way of fixing it or do I need to replace it?

Any suggestions will be greatfully recieved
Jim.
 

Chris

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I had exactly the same symptoms and mine is a 90 of course. it turned out to be a faulty diode pack on the alternator. This allowed the batteries to drain straight to earth. I hit 18v at one point and boiled a battery.

Cost me quite a bit to fix and replace as I was up in the wilds at the time.

Chris
 

Crispin

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It could be the regulator which has gone bad, that may explain the over-voltage and could be discharging the batteries though it which is why they are flat after a while.

Having a built in voltmeter is a good thing :)
 

Jimbo4x4

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Mar 2, 2010
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Sounds like Chris has the word on this, thanks mate. A couple of other valued opinions have said a faulty diode aswell. Can I ask, how much exactly is "quite a bit"? (or ballpark figure?). I don't really have the time to do this myself at the mo, although I do know of a place that px's duff alts for refurbished ones. Muchos gracias..

Crispin said:
Having a built in voltmeter is a good thing :)
You're telling me mate, there's no way I would have known how to drive home without it!
 
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Chas

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My OEM alternator didn't like fording either, I got a s/hand one from Steff and the other is being repaired (as a spare) it was the rectifier gone kaput, but I don't know yet what the repair cost is :shock: , certainly less than a whole alternator.
Chas
 

Chris

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Well it was indirect spend Jimbo. The bearings went after Corwen so I got a Milner replacement. The pack failed the next day and that boiled the battery. I had to get a replacement and a charger and two trips to town blah blah. I then swapped the duff one with Carl and the new one went fine. Then I got new bearings from a certain Mr Magic Rubie and refurbished the OEM. That is running sweetly again. Sot total cost was more to to the bugg**y factor. But changing the diode pack is a couple of screws really.

C
 

Jimbo4x4

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I am in great_britain
Mar 2, 2010
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Wirral, GB
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Well then, went out to the motor this evening having not touched it since last night, and the one battery i left connected (to keep the radio memory etc) still has full charge! :o I also noticed while driving last night that even without my lights and blowers on the voltmeter was reading normal... so has it fixed itself? I suppose time will tell and it may well become an intermittent fault, but anything that means I don't have to take the alt off must be a good thing :)
 

BlackWidow

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Hi Jimbo 4x4,

Did you re-connect the other battery? If not then it is possible that the second battery is the fault. If it is really duff it will draw the good one down and also, for want for a better word, demand allot more from the alternator thus throwing the voltage regulator out of kilt'.

Just a thought any way.

Steve
 

Jimbo4x4

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I am in great_britain
Mar 2, 2010
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38
Wirral, GB
Garage
Thanks Steve, I did reconnect it. All has been well for the last week and a bit so I'm guessing the diode just had a bit of water ingress that shorted it out but that it's now dried out and working properly again :)

I've been disconnecting one battery if I'm leaving it for more than an half an hour away from home, just incase any gremlins return but tbh I think I'm home free now. Thanks for all the input anyway guys ;)
 
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