3rd New generator won't charge

Nevis · Post by **Nevis** » Sun Sep 27, 2009 9:31 am

I have recently bought a new generator after my original one broke up.
I have so far taken 2 back because they would not charge but the 3rd is exibiting the same problem so I wonder if its something I'm doing / not doing that's causing the problem.
What I have done so far -
My Dexta is positive earth so I mounted the generator and polarized it by briefly connecting a jump lead between the negative battery terminal and the small connector on the generator which produced a nice spark.
When connected up the charge light would not go off. I then checked the generator output by connecting the 2 terminals together and checked the voltage to ground at about 1000rpm - this produced 0.7v (shoud be 15 - 20v).
I then performed the motor test by connecting the wire joining the 2 terminals to the battery via an ammeter. The generator turned in the same direction as engine rotation and drew 5.7A which seems ok.
This last test would seem to indicate that the generator is ok but still I get no charge.
Am I just unlucky and have had 3 bad generators or is there something else I should be doing?

Thanks
Andy

GERRY · Post by **GERRY** » Sun Sep 27, 2009 10:04 am

Hi Andy dont know if this wil be of any help to you but did you rev the engine up when you had every thing connected up ,you will have to do this to start the alt working , i returned anew alt thinking it was faulty and found when i enstalled the next one that ishould have reved the engine to excite the the alt . hopes helps Gerry

Post by **Brian** » Sun Sep 27, 2009 10:53 am

Andy,
Have you fitted a new regulator? 90% of all dynamo faults are due to the regulator.

Fords instructions to all service staff in the 1960's was fit both.

Nevis · Post by **Nevis** » Sun Sep 27, 2009 7:29 pm

I didn't change the regulator - could that have damaged the dynamo and caused the problem I am seeing?
The previous dynamo worked perfectly but just fell to pieces when the bearings went so up until now I had not suspected the regulator.
On a run today to pick up a plough for a friend the charge light just went out at 2200 rpm.

Andy

Post by **Brian** » Sun Sep 27, 2009 7:39 pm

Yes, a faulty regulator will wreck a dynamo quite quickly. From what you say, that sounds like your problem.

Nevis · Post by **Nevis** » Thu Oct 15, 2009 8:48 am

Update - I got a new dynamo + regulator and installed both.
The charge light still did not go out so I checked the output from the generator by connecting the 2 terminals together and checking the voltage to ground - 1.5v at 1000rpm this is now getting very strange.
I noticed that the new pulley is slightly larger diameter than the original so I swapped the pulleys over. The charge light then went out at 1400 rpm and the voltage reading is 2.0v at 1000rpm. So the smaller pulley has made some difference by increasing the dynamo rpm.
The original dynamo before it completely fell to pieces produced 15v at 1000rpm using the same voltage test and charged perfectly.
Its almost as if the new dynamo spec is completely different from the original.
Any thoughts on this?

Andy