I set up my 79xs650 alternator in my lathe today as I was not getting voltage at the brushes, so I put the rotor on a mandrell and set up a jig on the tool post for the stator housing wired up to a battery then started the lathe which was running at about 900 rpm, I then tested the ac voltage coming out which was hovering at about 9volts, bearing in mind it is spinning at about 900 rpm instead of 1200 idle speed, does this sound like it's doing what it's supposed to be.
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Alternator testing
- Thread starter kevski
- Start date
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- Tags
- electrical
i had an issue similar, try the slap test (look it up on youtube, here, etc.) I ended up replacing the rotor http://www.amazon.com/gp/product/B0068G2M10?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00 and then the brushes with http://www.amazon.com/gp/product/B006GFNRTY?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00
there is a ton of information in the forums and you can look at pg 5 of my build to see the issue i had and the results. http://www.xs650.com/forum/showthread.php?t=38568&highlight=omaha&page=5
Good Luck!
there is a ton of information in the forums and you can look at pg 5 of my build to see the issue i had and the results. http://www.xs650.com/forum/showthread.php?t=38568&highlight=omaha&page=5
Good Luck!
9 volts AC sounds low even at 900 RPM
Testing 101 what do the rotor and stator ohm out at?
Testing 101 what do the rotor and stator ohm out at?
First thing I done on the bench was the slap test I passed 11 volts from an old battery through the rotor and it picked up a screwdriver from over 1/2 inch away got 5.3 ohms on both slip rings, the stator is giving out less than 0.5 ohms on each wire, the wires to the tips of brushes 0.4 ohms, what I noticed with fully charged battery on the bike is less than 1/2 a volt getting to the brushes through the green wire which is a switched live from reg/rec also tested.
The main harness has always been a mess and I have rectified some of this I have bought a new one from mikes xs to be put on over the winter, what I was really wondering was if at the rotation speed of 900 rpm the 9volts would be acceptable with the hope that when all back on the bike and 12 volts getting too the rotor and correct idle speed it would give out what it's supposed too, I guess I will have to wait and see, I do have a PMA which I have had to send back already as two of the stator connections had come apart, I may as well ask now, instead of using the rectifier that come with the PMA is it feasible to put the PMA through the new harness where the original alternator would have been plugged in to save having to cut into the new harness or extending the rectifier leads so I can place it in a cooler spot as the new one is much larger.
The main harness has always been a mess and I have rectified some of this I have bought a new one from mikes xs to be put on over the winter, what I was really wondering was if at the rotation speed of 900 rpm the 9volts would be acceptable with the hope that when all back on the bike and 12 volts getting too the rotor and correct idle speed it would give out what it's supposed too, I guess I will have to wait and see, I do have a PMA which I have had to send back already as two of the stator connections had come apart, I may as well ask now, instead of using the rectifier that come with the PMA is it feasible to put the PMA through the new harness where the original alternator would have been plugged in to save having to cut into the new harness or extending the rectifier leads so I can place it in a cooler spot as the new one is much larger.
Would be good to see a pic of the stator/brush area. I'm guessing you may have a mix of old and new charging components. Like you say a 79 rotor should have one brush grounded right to the stator. The other gets power from the old style separate mechanical regulator. Then there are "new style" regulators that provide the ground for one brush the other is hot from the ignition switch. So test your rotor stator by supplying 12 volts to one brush, ground to the other see what the stator puts out then.
With only 11 volts applied to the rotor the magnetic field will be low. This might be the reason for low AC volts.
Fully charge the battery you test with then repeat the test.
11 volts is around 25-30% low, this might lead to the AC volts being 25-30% low.
9+25%=11.25 This is about what I get bypassing the reg at idle.
Leo
Fully charge the battery you test with then repeat the test.
11 volts is around 25-30% low, this might lead to the AC volts being 25-30% low.
9+25%=11.25 This is about what I get bypassing the reg at idle.
Leo
Thankyou for that Leo, when back from holiday I shall put it back on the bike and make sure I get a good feed to it, hopefully it will work, at the moment with a fully charged battery I have less than 1 volt coming. from the harness
AFAIK there is no "grounded from the brush wire into the harness". And yes it makes a difference. If you have one brush that is +12 hot, with the regulator unplugged ground the other brush and see what the stator puts out.
As far as a PMA yes white wires are white wires either stock or PMA but the regulator is completely different for a PMA
As far as a PMA yes white wires are white wires either stock or PMA but the regulator is completely different for a PMA
Being a 79 it should have the separate reg and rec. This set up has the power go from the reg on the green wire to one brush, through the rotor, out on the other brush, where it gets grounded to the stator as well as on the black wire to the harness ground.
Leo
Leo
