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[Roy]

I have a strange charging problem on this Bike. It no longer has the Selenium rectifier which has been replaced with an electronic one. The Alternator voltage varies up to about 20 volts and the DC output from the rectifier about is about 7.5 volts which to my mind is adequate. As soon as I connect the DC wires from the rectifier into the wiring harness the voltage at the Battery decreases to about 5.5 volts and reflects no further charge. If I connect the same wires from the rectifier to a free standing battery I get a good positive charge of 7.5volts. The Bike is positive earth and I have double checked the entire wiring system but have been unable to establish where the problem is. I have even thought of changing the wiring to negative earth which to my mind is a lot less complicated and more understandable. I have also swopped the batteries around in case it was faulty but no difference. Any suggestions would really be appreciated

[Mark M]

Roy, it sounds as if there is a break somewhere in the wiring. Is there still an ignition switch in the loom or has this been replaced with something simpler? I'd look to see what the voltages either side of whatever isolating switch you have actually are and suspect either the wiring in this area or the switch itself, certainly as a first place to look!

REgards, Mark

[Roy]

Hi Mark. It still has the original ignition switch on the side cover where the battery is housed. The switch has the emergency start feature and all that works perfectly. The wiring is basically the same as my Crusader except the trials bike did not have a headlamp or a tail light. I also thought the ignition switch may be faulty and I think that I will start by spraying it with switch cleaner in case some of the contacts are dirty. The Bike was stored for most of its life but the motor still runs perfectly and starts so easily and it is only the charging system that is a problem. Thanks for your thoughts and I will keep you posted.

[Hopeless Rider]

Hi,
The problem lies within your alternator stator. The windings are breaking down due to age and shunting down the charge when you connect it to the battery on the motorcycle. This fault is confirmed by not happening when you connect an external battery to the charge wires. This is because this battery is not earthed through the motorcycle. If you have access to a old 500v Megger meter (most people don’t as they are seldom used these days) you can test the alternator output leads of the alternator to the stator frame. Readings should be in the Meg ohms not Kilo ohms. Some digital Meggers might do but in my experience are not that great, especially the modern ohm meters bought for 15 pounds at the local electrical store. Hope that this helps. Regards.

[Roy]

Thanks Hopeless Rider that has given me another idea to do a test. I will also do a continuity test from the AC wires to the frame. I am also going to disconnect the coil positive wire and the contact breaker wire from the existing harness and couple the coil up to the external battery, start the bike and see what it charges. If still good then I will run a wire from the external battery to the frame and see what the readings say then.Thanks for your advice.