Alternator not working (Perkins A127)

Markus Antonius · 05-01-2022 5:24pm #1

This is for a tractor so not sure if allowed here (fairly sure this model is also used in cars...)

The alternator simply is not charging the battery. I initially thought there was a small trickle of charge but this was simply the battery recovering after starting.

I got a repair kit and replaced the slip ring (which was worn through to the plastic). I also replaced the rectifier and regulator/brush assembly but it's still not working!

Is this alternator for the scrap heap or is there anything else I could check?

littlevillage · 05-01-2022 5:34pm

Take out the Alternator and bring it to a professional who specializes in Alternator repair. Might be money well spent.

listermint · 05-01-2022 5:36pm

You'll get a replacement new alternator for that for anything from 100 to 150 euro. Personally I'd just replace it. Dick around with the old one as a spare if you get it working.

05-01-2022 7:47pm

Please share the pictures, may be somebody can notice something wrong. It could be nice to have a more background story about alternator. Feel free, because everyone can make a mistakes.

05-01-2022 7:51pm

Is there power in the signal wire to the altenator??

Markus Antonius · 06-01-2022 10:43am

https://www.boards.ie/discussion/comment/118423188#Comment_118423188

Yes, I'll post a few pictures after work!

Markus Antonius · 06-01-2022 11:01am

https://www.boards.ie/discussion/comment/118423200#Comment_118423200

Yes, there is nothing wrong with the connections to the battery. It is reading 12V at the alternator. Unusually the speedometer on the dash is working fine too despite it getting this reading from the alternator...

I don't seem to be able to generate any voltage by just spinning it on the bench so there is something funny going on somewhere.

Here's a picture of the same one I found online:

I noticed there is a plastic insulating washer missing from the terminal post (bottom left in pic above) and wonder if it's shorting at this point but can't see it touching anything. Also not sure what the "suppression capacitor" does but it looks like it might be worth replacing it if I could find one.

Markus Antonius · 06-01-2022 11:15am

Just checked online and the suppression capacitor simply absorbs any electromagnetic interference that might effect radio signals so there should be no problem here

06-01-2022 10:06pm

https://www.boards.ie/discussion/comment/118425828#Comment_118425828

have you signal power when tractor is stopped,but key on??

Ie: you have a charging lamp in dash

You wont be able to get it to generate voltage via spinning,unless your using proper test bench....

you need the signal wire via charge lamp,to 'excite' the altenator to give output....which then puts out the charging lamp

Markus Antonius · 06-01-2022 11:48pm

https://www.boards.ie/discussion/comment/118430297#Comment_118430297

Ah, I did wonder if the alternator needed to be 'live' in order to generate power. That makes sense then if it does. It still doesn't output 14 volts when running however.

Not sure what the signal light is. There is a battery light on on the dash when I turn the key to the first notch. I think this suggests a faulty alternator though.

06-01-2022 11:57pm

https://www.boards.ie/discussion/comment/118430898#Comment_118430898

The signal to 'excite' the altenator to begin charging,comes through the battery light in the dash.....(when altemtor charging,no longer provides earth for the battery light,hence light going out)

You need to check,if you have power from the key/battery light position on the signal wire (looks to be smaller of the 3 wires going into the block connector, on the pic you put up)

If all ok there,its most likely internally your issue,there is a rake of tests you can do via multimeter on windings etc...but realistically,its cheaper to replace

Markus Antonius · 07-01-2022 12:00am

Here are some pics if it helps:

Pic 1 - Alternator showing connections before I ever removed it

Pic 2 - Internals showing old slip ring

2022-01-06 23_54_43-IMG_20210801_192309326.jpg - Photo Gallery.png

Pic 3 - Showing old rectifier (just noticed the old rectifier has both insulating washers on it. It must have fallen off while I was repairing it or it's still on the old one)

Pic 4 - Showing Slip rings and new rectifier after repair (bad solder job but the connections are secure) You can see the terminal post at the top where I am missing the plastic insulating washer)

Markus Antonius · 07-01-2022 12:07am

https://www.boards.ie/discussion/comment/118430938#Comment_118430938

Yes I have a hunch it may be an issue with the windings on the inner stator that spins. All the connections looked good but there were points where some of the wires are in contact with the metal claws that surround the windings. I'm a bit disappointed it wasn't simply the worn out slipring you can see in pic 2 above.

That is useful info about the signal wire though, I didn't think about this. I might look a bit more into this before I splash out on a new alternator. I fully realise I will need to get a new one but curiosity and the learnings you get from trouble shooting are priceless.

Alternator not working (Perkins A127)

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