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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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1979, charging, generator, voltage, xls

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  #21  
Old 9th February 2012
ryder rick's Avatar
ryder rick ryder rick is offline
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The generator light illuminates when there is a difference in potential between the orange wire and the A terminal on the Gen. If there is a diode in the light circuit the light can only illuminate when the orange wire is at a higher voltage than the A term. If there is no diode the light can illuminate if the A terminal is at a higher potential than the orange wire also. (more on that later)

If the gen light is coming on at less than full intensity the first order of business is to check the battery voltage @2500 rpm and also check the voltage at the A terminal. Those voltages should be the same or very close.

If the voltage at the A terminal is lower the generator output is low (for whatever reason)(bad reg, bad wiring, bad gen). If the voltage at the A term is the same as the battery (13.5-15v) or slightly higher (0.25v) the generator is working, and not the cause of the gen light.

There are many potential places for failure on an XL, for a working generator and a dim glow on the light the problem is usually on the ignition side of the light. Shorted or missing diode, bad wiring (molex connectors). Trace it back until you find the voltage drop.

A bad regulator can also cause this but usually not without causing low gen output. The A terminal wire needs to be large enough to handle 15-20 amps even though it only has to carry 10A steady. The same goes for the battery to the regulator wire. Too small a wire or a bad connection here can marginally limit generator output.

A working gen light polarizes the generator every time you start the bike. This helps get the generator started with an old style regulator.

The HD gen is a self exciting type, this means it starts itself or supplies it's own power to run (excite) the field. This is why the gen goes to full output if you ground the F terminal, this applies the full output voltage to the field coils. This also creates a snowball effect since the generated power excites the field coils and the field coils cause the power to be generated, the more power generated the more the field coils excite which in turn generates more power. This is how you can see 30v on the A term, this is also how you can blacken an armature!

Now for the diode. That little sucker has a twofold purpose, first it keeps the light from lighting (dull glow) if the gen A term has a higher voltage than the orange wire. This keeps the rider happy by not showing him how crappy his wiring is. That diode also does the rider a favor if he leaves his key on (which is harder to do if you have a working gen & oil light) and flattens the battery. You remember I said earlier that the gen light polarizes the gen & helps it get started? And I also said that the HD gen is self exciting?
With the diode in place all of the power created by the residual magnetism in the field poles can go to exciting the field coils the diode blocks any power from being wasted lighting the gen light. This assists the gen in getting itself started which in turn will supply power to your ignition and get the bike running if you push start it, with a dead battery.

This push start business may not work with a bad battery, but will work with a good but dead battery. Do not rely on the charging system to fill up a flat battery. Always start with a fully charged battery, charge overnight with an automatic charger like a Battery Tender for a full battery.

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  #22  
Old 14th March 2012
bykrdan bykrdan is offline
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Well, well, well... I just keep proving to myself I am no good with electrical work.

Slowly but surely, my charging problem crept back. In fact, as I was battling some burnt stator wires on my Shadow at the same time, I cannot now recall if in fact I did ever fully check the charging on the XLS. I do remember getting 13.5v at the battery from at least the Honda...

Anyway, I am back to the original problem; gen light goes mostly out, but for just the dimmest glow, at high RPM.

I "attempted" to do both the volts and amps output test on the generator last evening (even that turned into a circus...)

In my first couple attempts, I grounded the "A" terminal instead of the "F", and connected the "F" to battery positive, via volt or ammeter. The bike didn't like that setup at all, and the motor even bogged down slightly.

I figured out what I was doing wrong, and switched the connections. Now, the manual warns "don't run with the field grounded longer than necessary." I've been mostly careful to heed that, but I thought that until the armature was connected, no voltage was moving anyway, so no harm. But I got a spark from the generator when disconnecting the field, with the armature bare and the bike running - residual magnetism?

I got further confusion when testing with my multimeter - plenty of voltage coming out (up to 24v or 25v, with throttle) but NO amps; using the dash-style ammeter I got much closer to the expected 10A (60A scale, so a little hard to read actual results.) Maybe the fuse in the multimeter is already burned? Wouldn't surprise me at all...

Anyway, I was a little discouraged after hooking all back up because I thought the gen light was now glowing even brighter than before, but after a quick ride around the block, I think it's about where it was, and I'm thinking the generator is still good.

Did I blow a regulator that fast? I'm not positive it is properly grounded; I will check that first, but then I think I'll be in the market for a "known good unit."
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  #23  
Old 15th March 2012
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In my limited experience a flickering or dim gen light at riding RPM has been the result of sticking brush[es]. What i would do is clean the inside of the gen with electrical contacts cleaner, ensure that the brushes move easily in the brushes holder, and clean the grooves in the commutator. If you use a hacksaw blade you will first have to flatten the teeth else it will be too wide [unless you find one that does not have the offset teeth]. I prefer the edge of a small thin file [like a fingernail file].

Look for this condition ...



Note how the insulator is curved up under the brush spring. This is a very common problem. I have had no joy trying to fix it. The best is to use some sandpaper and file down the top or bottom edge of the brush until it moves easily..

Yes, we who are electrically disadvantaged must wield with care jumper wires, multimeter connectors, etc lest we do damage. First do the above cleaning. Then starting over, very carefully set up the gen amps test using the in-dash type ammeter that you have. Double check the connections! If you get 10 amps the gen is good. BTW, TSC has the 0-30 ammeters.
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  #24  
Old 15th March 2012
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on your stripped threads, try a thread restorer. they are a square file with threads cut into them and cost about $13 at a good local hardware. I have rescued many damaged threads with one of those, one of the handiest tools in my shop!

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