AJS & Matchless Owners Club

I have owned this bike since 1983. It has been converted to 12v. I have a problem with the rectifier which when I switch on the ignition causes a voltage drop to 4v. The alternator has 2 wires joined and therefor the input to the alternator has 2 wires. All wiring diagrams show 3 input wires to the rectifier. I have opened the rectifier but am faced with a solid gel so I cannot see the connections. HELP.
Ken Pee

I think you're rectifier would be 2x positives and a negative. No electrical genius, but I was told a positive for your charging, a positive for the 'lighting' circuit and obviously your earth. This is what you see on modern machines with three phase alternators. Except there are lighting circuit phases.

Something is wrong here.

The alternator is a two-phase unit and definitely should not have any wires "joined". This would result in the alternator feeding a short circuit and will cause it to burn out.

It sounds like you've got a single-phase (i.e. two input wire) electronic regulator/rectifier fitted. This has probably failed or burned out. This can be caused by the alternator stator becoming shorted to earth when the insulation fails.

First thing: disconnect all the alternator wires and check that the alternator windings are free of any connection to earth (i.e. high resistance >10k ohms). Once you've checked that is OK, you can then look at the regulator/rectifier. It's highly likely you need a new one.

Single phase 6 volt alternators were 3 wire, one set of coils for daylight riding (less power required) and another set for using lights while riding. When converted to 12 volt, both sets of coils are connected all the time and an electronic regulator/rectifier is used; this only has 2 wires for ac in and 2 wires for dc out. I have checked my reg/rec using a 12 volt ac output transformer (from some unknown appliance - probably a printer) and checked that there was dc output, which is much lower voltage due to inefficiency of the conversion.

Rob C

ps: I can't remember which wires are connected to create a 2 wire output of the stator, but a search will provide the answer, because it is a common conversion on Brit bikes. I eventually replaced my original stator with a 2 wire potted item when the original vibrated itself to pieces.

Hi Ken,
Long time no see.
I had this problem a few years back. Mine was the stator had developed an internal fault to earth, which blew the rectifier. A new stator and rectifier solved the problem. I think I got them both from Paul Goff.
Hope this helps,
Les

les ward wrote:Hi Ken,
Long time no see.
I had this problem a few years back. Mine was the stator had developed an internal fault to earth, which blew the rectifier. A new stator and rectifier solved the problem. I think I got them both from Paul Goff.
Hope this helps,
Les

Les, maybe we'll get an offer of an all expenses paid holiday to go out and fix it for him! Then catch up on all the things he's missed since leaving ( that'll take all of 5 mins!).

Thanks for the clarification, Rob!
I was wrong - I thought these were 2-phase alternators, not 2x 1-phase. In which case, it's OK to join the wires...

Still suspect a short to earth on the stator. This will pop the diodes in the electronic regulator fairly quickly...

Thanks All,
I can't believe your swift responses. It certainly looks like the stator has caused the problem. i am certainly isolated in Cyprus (please spare your handkerchiefs and the tears). No free holidays but any one out is free to call me. You would get free drinks. Les great to here from you hope you are well
Regards
Ken

ken pee wrote:Thanks All,
I can't believe your swift responses. It certainly looks like the stator has caused the problem. i am certainly isolated in Cyprus (please spare your handkerchiefs and the tears). No free holidays but any one out is free to call me. You would get free drinks. Les great to here from you hope you are well
Regards
Ken

Like the hidden pun there Mr Pee. Are you keeping well? Been a few years now since we last saw you. Still pass your old place by the Horse and Jockey quite often.

Hi Les
Further to our recent " conversation" who is Paul Goff please. Also ajscomboman knows me am I allowed to know his identity
ken