Alternator 55amp no load damage

[RC68Westy]

Advice please guys

I swapped engines and didn't modify the Generator/Alternator wiring at the time ... Ran the engine to check it was ok, but the Alternator wasn't wired to the battery. Now I've done the wiring the Alternator is not putting anything out, on the voltage test

I suspect that the lack of load has caused the Alternator to kill itself ... So my question, is the Alternator repairable? with regulator, diodes, or ... Or do I have to buy a whole new unit?



Cheers Rob

[TomWesty]

Are you absolutely certain the Alternator is wired in correctly?
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[Tcash]

Alt wiring

[busdaddy]

Running an alternator disconnected can't harm it in any way, you've got other issues.
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[TomWesty]

Does the alt/ gen light come on when you turn the key to "on"? If not it may be burned out and the system will not charge without it. It should come on when the key is turned and then go off when the engine starts and idles.
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[telford dorr]

If the alternator was run with no idiot light connected, then the alternator did not excite, and no damage was done. If a light was connected, then keep reading.

Actually, running an alternator open circuit can damage it, if the regulator is messed up. An alternator can put out lots of voltage (remember the old "run your 120 volt power tools on your truck alternator" boxes they used to sell - until they got tired of the flack they got from people cooking their alternators?) It can put out enough voltage to pop the diodes. A load of some kind (like a battery) will prevent this from happening.

With a couple hundred thousand microfarads of load capacitance (like one of those big stereo power filter caps) and a good regulator, an alternator will work fine without a battery. Test run engines all the time this way.

Easy test (for alternators with external regulators):

- disconnect the alternator wiring both (regulator and battery connection).

- apply 6 volts (or less) to the rotor connections (green [+] and brown [-] wires). A 6 volt battery charger works well for this.

- slowly spin the alternator while measuring the voltage on the red wire and alternator output stud (both should show the same voltage). As you increase the alternator speed, the voltage should increase. Limit the speed so that the voltage stays below 15 volts. If the voltage on the red wire and the stud terminal track each other, the alternator is probably OK.

You can do this test on internally regulated alternators, but it requires dissection to disconnect the regulator, and thus the alternator needs to be out of the vehicle.
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[RC68Westy]

Guys, thanks for the replies. To answer your points

The wiring to the light is as per the CIP schematic ...

However the wire off B+ goes direct to the battery and not to the starter, on the live battery terminal clamp there are 2 wires, one very thick to the starter and another smaller one that previously was connected to the regulator (that was attached to the Generator, on the other engine)

I could try wiring the B+ direct to the starter as per the diagram ... Seems an obvious thing to do

The light does work, in that, it is on with key in and engine not started, and it goes off when the engine is running. All looks ok, but when I put a meter on the battery with the engine running it is at 12.6v and not 14v+

The Alternator itself is a 55amp Generator replacement sort with an internal regulator and a spade connector for D+

I would be chuffed to bits if I haven't nadgered the Alternator, I don't understand this at the moment though

[RC68Westy]

So I put a meter between the +ve terminal on the battery and the stud on the solenoid and there was intermittent resistance. So took off terminals wire brushed them and then brought the wire from B+ to the same stud.

Started her up and voila 14v at idle speed at the battery

So thanks for dispelling my false conclusions and helping point me towards finding the issue

One last question as the terminals at the starter motor were crusty would dielectric grease have prevented this? - I was going to buy some and put it on the bulb holders but I saw something that says it's non conductive so that doesn't make a whole lot of sense to me

[busdaddy]

Good to hear it was a minor fix.

Dilectric grease works OK, Vaseline or even wheel bearing grease works fine too, anyhing oily to prevent the corrosion and repel moisture will do.
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[telford dorr]

[RC68Westy]

Thanks for the help

I'll give the grease a go

Cheers

[Tcash]

The only problem I have found with dielectric grease, is that it attacks some plastics in the light fixtures.
Some manufacturers use a white paste, I do not know but I think it is Lithium grease.

DeoxIT® DN5


I started seeing a liquid sealer being applied to grounds and starter connections from the Manufacturers. It dried to like a hard plastic. I have not been able to source it. This is the closest I could find to it.
liquid tape

Good Day
Tcash