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RedRooster

Alternator Excitor voltage

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Hi,

how much voltage should i drop over the ign Red 2.2W bulb? currently getting 4volts so exictor only getting 8v to the alternator & not charging the battery.

Thought i found it when one of the ignition white wires from the ignition switch was low to earth, so changed that & now the fuel pump doesn't work so guessing i was seeing the pump coil & not a true earth reading, just need to remember how i wired the pump up so i can disconnect it to test the insulation.

 

 

 

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Should add when i by pass the Ign red light circuit with a feed direct from the battery to the alternator excitor i get 13.5v output from the lternator which seems a bit low but is still higher than the battery 12.8V, so the battery would charge.

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Well not sure what i've done today but if i connect exciter from the alternator to the 12v switched ignition switched white to the fuse box to give 12v (battery voltage) then it now doesn't charge?

 

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Is this a Lucas ACR alternator? If its the three-pin connection type the third pin is only an 'exciter' input until the engine fires up. Once the alternator is spinning the field excitation comes from an internal connection to the 'triple' rectifiers and the lamp goes out because the voltage is about the same on each side of it. If yours is still lit with the alternator running there is a fault in the alternator. Connecting the indicator pin to 12v will not help.

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If you have 12v on the exciter wire and no charge, sounds rather like a dead alternator.  The 13.5 you were getting before was an unpromising sign as should be more like 14v.

Check brushes and internal connections if you wish - beyond that likely to be regulator or diode pack given up.

if old ACR series consider replacing with A127 series which are slightly less ancient tech.

Nick

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It was a brand new alternator which even came with a test certificate saying 14.5V output, so either its dead out of the box or the car wiring is dodgy which i can't find.

Have another one to try so will do that later today then let you know.

Brad

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Inreplaced the tired 17acr on my ‘6 with a new 45A 18acr from ebay last spring, the difference is notable.

voltage after startup is higher, and the alternator co-es significantly better with wipers, lights etc during ‘summer’ !

mine worked out of the box without any prep.

hope you get your’s sorted, sounds faulty to me.

 

steve

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It was a brand new alternator which even came with a test certificate saying 14.5V output, so either its dead out of the box or the car wiring is dodgy which i can't find.

Have another one to try so will do that later today then let you know.

Brad

 

Seems the new alternator was u/s out of the box, had to make a new adjuster bracket as the old belt was a bit worn & i had modified that for the next engine upgrade, anyway all good now & i saw 14.5V so happy again.

IMAG2655[1].jpg

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