No charging in 503

[knuckle buster]

First serious ride on 503 this weekend. Left with fully charged battery. Had old rotted out rectifier in first few runs around the yard earlier this winter,and installed NOS one just before taking on ride this weekend .After a dozen starts and running around for a few hours not enough juice to crank it over,new battery and newly rebuilt starter. Started and ran fine with one pull. Could the old can of rust/rectifier have shorted something in charging coil? What voltage should I be seeing from the motor to and from the rectifier?

[Go Go Diablo]

There are a couple of ways to check your charging system.

One simple way to see if there is any voltage/current being generated is to remove the red wire from the rectifier and see if there is power there when the engine is running. The two yellow wires coming from the engine are putting out an AC current and these hook to the two side by side terminals on the rectifier. Within the rectifier, the AC current goes through two diodes and the current comes out the single terminal on the rectifier. If there is power at the single terminal, then at least one of the diodes is good. If not, then on to step two.

If there is no voltage on the single terminal, then you can try hooking an AC meter to the yellow wires coming out of the motor and seeing if you have voltage here. If no voltage, then the problem could very well be in the motor with the lighting coil. If there is voltage, then remove the rectifier from the Diablo and pull the cover off and check the internal fuse.

If there is voltage on the single terminal, then check voltage at the battery. Remove the drive belt. Hook a DC meter to the battery. With the engine idling, note the voltage. Then rev up the motor and the voltage should climb slightly.

The charging circuit puts out only milliamps of current. When I drive my 503 during the day, I leave the headlights off so all available charging power goes into the battery.

That's my 2 cents for starters. Let us know what you find.

[knuckle buster]

Did some checking and at a fast idle just before clutch engagement I got readings of 4.7 volts AC on one side of coils and 7.5 volts AC on the other with a output from the rectifier of 5.5 volts DC. The voltages are kind of hard to get a stable reading on from coils.don't know if that is an AC voltage issue from coil working ittermitantly or not.

[Go Go Diablo]

I guess the best test is to hook your meter up to the battery and rev the motor. That's a good test.

[knuckle buster]

Max voltage at WOT is 9.5,not a good sign. Maybe a dumb question,are the charging and ignition coils interchangeable, or do I need the specific charging coil?

[Go Go Diablo]

Under the flywheel is an ignition coil (black) and a lighting coil (copper wire). You cannot get them mixed up. The same lighting coil is used in the 54R motor (Diablo 500 and 502) as used in the 190R motor (Diablo 503). The only difference is the 500 and 502 hook up to only one pole on the lighting coil and the 503 hooks up to both.

DSC00486.JPG (162.85KiB)Viewed 7608 times

Something else to check is your Voltage Rectifier even though you have a new one. The Diodes in the rectifier are like check valves for current. They let current travel one way through them and stops it in the other direction.

Pull the three leads off. Set your Volt/Ohm meter to the Diode setting or the Ohm setting. Place one lead on the single terminal and the other on one of the side by side terminals. If you have no resistance, place the lead on the other side by side terminal and you should not have resistance there either. Then swap your meter leads and put the other lead on the single terminal. If you had no resistance before, now your meter should show something like 480 ohms or some sort of measurement that says there is continuity. If you have that, again, swap your lead to the other side by side terminal and it should have a reading too.

If no reading either way, pull your rectifier out and pull the top off and check the internal fuse.

What is a WOT?

[knuckle buster]

That would be...WIDE OPEN THROTTLE

[knuckle buster]

OK, Bruce here is what I found....With the ohm meter set at 20K scale had readings of 10.35 and 9.86 on terminals. Nothing when reversing leads, opened it up and fuse looks good and has continuity.

[Go Go Diablo]

That test would tell me the problem is not in the Voltage Rectifier.

The next thing I would try is to test the lighting coil. If I remember right, you should be able to take an ohm reading between each yellow wire from the motor to ground. Do this from the wires to the voltage rectifier. Again, pull them off the rectifier.

Hook one of your leads to the yellow wire and the other to the motor housing being careful to not be touching the leads or the ohm meter will read your body resistance. What you should see when you first hook it up is the Ohm meter go to zero. Then within a couple of seconds, it should begin to climb in resistance. Not much, maybe only a few ohms, but this is normal. If it stays at zero, there is a problem for sure.

[snocatpete]

just following this conversation, I am sure this is not a problem but something to look at anyway - the wires going into the junction block on the side of the engine beside the carburetor I have seen where these wires are extremely frayed and holding by one or two strands even though the screws appear to be tight they could be falling out or broken in there. If this is the case, this can create a pile of resistance in your charging circuit. Just another idea of something to check.