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Knackered alternator diodes?

Post by MattA24 » Subscribing Member » Thu Oct 22, 2015 5:55 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 248
What ho,

An interesting electrical anomaly in my coachbuilt electrics (thank you, previous owner) has resulted today to a lot of hot wiring, and a nice new fault!

My dash alternator/battery light is now lit when the ignition is off, and goes out when the ignition is switched on.

If I disconnect the signal wire from the alternator, the lamp remains unlit at all times.

I assume that the alternator diodes have failed, and I need to either replace them or the alternator. Is this about the measure of it?

About 12 and a half miles from here there is a spare alternator sitting on the Deadford (as we call it), although I seem to recall that one has a moulded plug on the back, rather than the three spade connectors on mine. Will that be any trouble?

If I do drive 12 and a half miles with an alternator in this condition, would I be better to do so with the alternator hooked up as per usual, or with it's wires disconnected.

What larks!

Re: Knackered alternator diodes?

Post by MattA24 » Subscribing Member » Thu Oct 22, 2015 6:32 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 248
Ah, and having popped off for an hour without isolating the battery, my alternator is now also red hot, so that won't have improved matters.

:wall:

Re: Knackered alternator diodes?

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Post by Phil Bradshaw » Club admin » Thu Oct 22, 2015 6:57 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
Remove connector/s from alternator IND and BAT terminals.
Bridge IND wire to ground.

If warning lamp lights with ignition switched on then check voltage between wire and ground.
If reading obtained is battery volts then the alternator needs replacing or repairing.

Tests to locate what may be wrong with the alternator depends on alternator type (Lucas ACR, Delco-Remy)
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

Re: Knackered alternator diodes?

Post by MattA24 » Subscribing Member » Sat Oct 24, 2015 3:43 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 248
Hi Phil,

I saw you post after I had already swapped alternators. Whoops. I keep forgetting to subscribe to my own threads.

Is there are way to test the suspect alternator now it is out of the van? It's the all-metal cased type.

The replacement is the plastic-ended type, and is operating fine in the van.

Wider wiring issues solved by removing the various messy part-incarnations of camper electrics and putting in a new set :)

Cheers,
Matt

Re: Knackered alternator diodes?

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Post by Phil Bradshaw » Club admin » Sun Oct 25, 2015 11:05 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
Delco all-metal case alternator with a fault usually is best dismantled so that each component can be tested individually so that the unit ends up being fully rebuilt rather than just repaired and for pretty much the same effort.

Unfortunately as yet there isn't a Howto for the Delco unit; best there is at present is in A cooked engine (first page), just a build sequence without any of the test procedures.
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

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