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Discussion Starter · #1 ·
In the service manual there is only a resistance test for the alternator. Basically measure the three yellow wires against each other and they should be near 0 ohms to show each winding is OK.

The service manual also states to check each yellow wire (winding) to earth and it shouldn't be a short (0 ohm). My readings to earth are about 0.5 ohm, very small but should it be a high resistance (i.e no continuity) or does the centre of the 3 windings connect to earth and what I am measuring is one coil to earth?

Is there a voltage (running ) check for the alternator? Most bikes run at about 30-60v AC.

All this has come about because I have some charge voltage but not much (12.5v) and it should be 14 ish volts. I wanted to start with the alternator test before I dive into the regulator.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Given that you want to find infinite resistance to ground, very low resistance would indicate a shorted winding. You'll need to replace the stator.
Stators in a Turbo lead a hard life, from what I've read. I think it was Pim who conducted some tests with a modern rec/reg, finding much lower operating temps in the stator. That upgrade might be worthwhile to extend the life of the replacement.
 

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Discussion Starter · #3 ·
I did some voltage tests with the alternator unloaded (regulator/rectifier not connected) and I get about 40vac at 3000 rpm which seems reasonable. With the regulator connected that drops to around 10vac. If I run an ammeter instead of the main fuse I am seeing negative current although the system is trying to charge as the current goes up and down with revs but never meets the magic +5amps or so for good charging.

A voltage check across the battery also show an attempt at charging but it never reaches 13v-14v which it should.

Could it be a bad regulator sinking the amps?

I will try the resistance test on the regulator next.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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You could always start with the regulator. Unless I'm mistaken, your turbo uses the same rec/reg as a regular CX or GL. Are there any members near you who might lend one for a test.
I do think, though, from the results of your resistance tests that your stator is at retirement age. I'd repeat those tests to verify.
 

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Discussion Starter · #5 ·
If the alternator was shorted to earth I wouldn't expect any output and I have a rising output with revs. I agree it could still be breaking down under load.

I know the turbos eat alternators but I would like to run more tests on the regulator first. it is outputting a voltage just not enough.....
 

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Do an AC stator test - with the engine running at idle i`d expect to see about ~30VAC and when engine speed is raised the voltage goes up sharply to about 60/70.
What voltages are you seeing on each of the three phases under those conditions and are they similar?
This test may be moot, however. If you`ve already seen continuity to ground from any of the phases the stator is toast.
 

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Discussion Starter · #7 ·
I just resistance tested the alternator again to make sure I wasn't going mad. Winding to winding is about 0.5 ohm but i DEFINITELY have a winding to earth low resistance as well so I guess its toast!

Time for the triple bypass!!

Anyone recommend a good alternator?
 

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Discussion Starter · #9 ·

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'84 CX650E that is evolving into a GL500
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Just to be sure, did you unplug the regulator from the stator before measuring the resistance to ground? If you did and you had any measurable connection to ground (the reading should be the same as when the meter leads are not connected to anything) you definitely need to replace the stator.
 

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Discussion Starter · #11 ·
Yep, completely unplugged the alternator and definitely grounding. Its weird it sill does something but that is the nature of these things.

I been scanning the forum for a definitive 500 turbo triple bypass thread (ideally with a parts list). Does anyone know of one. Is it basically the same as the standard CX?

Appreciate the help, big task ahead.....
 

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Does your 12.5v only appear at idle, but increase when revved?
 

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Discussion Starter · #13 ·
It does increase but never makes 13/14v. Looking at the amps (remove main fuse and put ammeter in line) it does generate some charge.

Its very strange, the alternator has a bad resistance check but i get some voltage and current, just not enough.

I've cleaned all the connectors up as well now. Will keep testing.

A good link to a good turbo triple bypass thread would be much appreciated. :p just in case.....
 

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'84 CX650E that is evolving into a GL500
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The stator's windings are connected in a "Y" like in the drawing below. If one winding has a short to ground but the others are OK the resistance between the yellow wire connected to one of the good windings and ground will be the resistance of that winding plus the resistance of the portion of the failed winding between the common connection for the windings and where it is shorted.
If there is only 0.5 ohm between the ends of 2 windings that will always be less than 0.5 ohm and could be as low as 0.25 ohm (which may be less than your meter can measure accurately).

Rectangle Slope Font Line Parallel


Because of the short, even if all 3 windings were producing the full AC voltage (which is still possible), as soon as you connect the rectifier the diodes in the rectifier will shunt some of it because of the short, but only half of the wave. That means that only the other half will be present at the rectifier's output and there won't be enough power to charge the battery.

FWIW, when mine failed I think I had something like 11.5V at the battery with the engine idling and 12.5 at 80+ Km/h so I carried a charger in the sidecar and plugged it in while I was working until I could swap in a better stator.
 

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Discussion Starter · #15 ·
Sounds like exactly the scenario I have. Thanks for the explanation.

Engine out it is then!

Just need to track down the best triple bypass thread now!

Thanks
 
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