Charging problem

NorthernEngine · Feb 12, 2015

Hope someone can help as this is doing my head in... and costing me a fortune!

I have a 1995 300tdi. When I start it up, the battery / charging light stays on, and the rev counter doesnt work. Volt reading across the battery drops slightly when running.

If I rev it up to around 2500 / 3000 rpm though, the light goes out and the rev counter jumps into life. the light stays out and the rev counter continues to work when allowed to drop back to tickover. Volts reading goes up to 14.something and remains, so it would appear all is well after the initial revving.

I have tried 3 second hand alternators, and have just fitted a brand new one out of the box - same issue.

Any ideas chaps?
Thanks in advance!

The V8 man · Feb 12, 2015

So why dont you just rev it up after initial start up if everything is ok after that ?

The Mad Hat Man · Feb 12, 2015

loose connector at back of Alternator or broken/intermittent wire.

NorthernEngine · Feb 12, 2015

I could, but Id rather fix the fault incase it gets worse.... or fails completely. Most likely on a dark, wet night, miles from anywhere, when Im already running late....

mr glee · Feb 12, 2015

check the alternator drive belt,check the belt tensioner is not sticking.if all ok disconect the battery and check your earth straps and the connections to the engine bay fuse box and alternator clean them up and this might cure it.

NorthernEngine · Feb 13, 2015

Hopefully just the belt! I'll get to check later this morning.
Is there a way to correctly tension the belt, or is it ok doing it by feel?

jonathanp · Feb 14, 2015

Hi

There is a single wire to the alternator , I think it is to the W terminal, this connection needs to be remade with a new female connector..

The belt is self adjusting with a tensioner that is just in front of the thermostat housing. You should be able to move left to right using a 15 mm ? socket on the nut on the front of it. It will return to central position under spring tension. Do not move it too much.

It is possible your idle speed is a little slow, but more likely the alternator connections are dirty.

Remake the earth connections as well . Engine to chassis, to body etc

The alternator is working OK, but after 20 years of life the connections get dirty and corrode, both the wire to connector and the connector itself

Regards

Jonathan

NorthernEngine · Feb 17, 2015

Thanks fellas - all working again, plus a second alternator now mounted which will get wired tomorrow for the 2 winches.

oldskool · Feb 18, 2015

NorthernEngine said:
Thanks fellas - all working again, plus a second alternator now mounted which will get wired tomorrow for the 2 winches.

So what fixed it then??

NorthernEngine · Feb 18, 2015

Seems I had a gremlin! Weirdest thing, and no wonder it had me stumped...
Seems the Disco didnt like having a diode added, even though the diode tested out fine and worked as it should (I tried 3 of them!). But whats REALLY weird is that if I put the meter across the alt output when running, I got charge at 14.4V... but if I added the diode but didnt connect up the other end, and put the meter across the end of the wire again (NOT across the diode, just from the end of the wire, BEFORE the diode, same as before), it stopped charging! Spoken to many electrickery genius type folk, who reckon this is impossible, but my Disco managed it somehow!
Was worth checking all connections, belt etc anyway for peace of mind!
Now just got to wire in this 2nd alt....

Charging problem

NorthernEngine

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The V8 man

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The Mad Hat Man

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NorthernEngine

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mr glee

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jonathanp

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oldskool

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