Odd alternator issue.

[Chris Green90]

Hi guys having an odd little issue with my alternator.

on tick over c.750rpm it is charging fine at around 14.8v however if I run lights and such like (Not loads of stuff just the usual for driving in the dark and cold) it drops under 12v unless you bring the revs up to 800. Not a major problem if doing a run but sat in traffic its not charging the battery.

It is an after market alternator rated at 205 amps. Now when it arrived the pulley it came with was damaged so I swapped it out for the one from the old OE one.

It seems as though the alt is not spinning up to full speed at tick over and I wondered if it could be due to the fact maybe that the OE pulley is slightly larger than the one supplied. Admittedly I do have a couple of earthing issues on the truck which I am going to have a look at tomorrow but personally I don't think that would cause the above symptoms???

Any ideas anyone

Cheers
Chris

 

[fridayman]

Those voltages do seem odd. Even the high voltage seems higher than I would expect, but someone more qualified than me will probably chip in. If both high and low voltages are odd, I wonder if the regulator is working properly?

 

[Andrew T]

It's goofed, it can only produce the voltage without any load or you have a loose connection or an earth problem.

also check the battery terminals are tight too

 

[Gary Stockton]

Pulleys the same size? Will internal speed alter output, or is rectifier goosed?

 

[Chris Green90]

'S'all good peeps. Thanks for the responses. I knew I have a bit of an earth issue but didn't think that would affect it in that way.

Anyway been round the truck today and cleaned up all the earths and added a couple more in some strategic places. (future plans). Also when I put the alternator in I upgraded the pos wiring. the length I has was a little long and has been rubbing against the belt and has frayed so replace that as well. Cranked her up and all's well.

Cheers guys
Chris.

 

[Chris Green90]

I have taken the winch off recently so thats quite a sizable earth that has gone walkies. I am thinking that this is why it has shown itself.