john1c
XS650 Enthusiast
My 78' will start without the regulator plugged but as soon as I plug it in, the main fuse pops. I was told that a bad regulator alone should not be blowing my main fuse. True? Should I be looking at the rotor now?
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regulator or rotor?
- Thread starter john1c
- Start date
pamcopete
Ride.Enjoy.Life is Simple
john1c,
The regulator supplies battery voltage to the rotor on the alternator. Generally what happens is the rotor shorts and blows the fuse, but if you unplug the regulator, there is no path for the current to go to the rotor.
The other possibility is that the crude contacts on the equally crude mechanical (relay) regulator short out. One of the contacts is battery and the other is ground the third contact goes to the green wire to the brush on the rotor, so when they short out, that blows the fuse.
To figure out which one is causing the problem, remove the brushes from the alternator and measure the resistance between the copper slip rings. Should be 5 Ohms. With the brushes removed, turn on the key and see if the fuse still blows. If it does, then it's the regulator, if it doesn't, then it's the rotor.
The regulator supplies battery voltage to the rotor on the alternator. Generally what happens is the rotor shorts and blows the fuse, but if you unplug the regulator, there is no path for the current to go to the rotor.
The other possibility is that the crude contacts on the equally crude mechanical (relay) regulator short out. One of the contacts is battery and the other is ground the third contact goes to the green wire to the brush on the rotor, so when they short out, that blows the fuse.
To figure out which one is causing the problem, remove the brushes from the alternator and measure the resistance between the copper slip rings. Should be 5 Ohms. With the brushes removed, turn on the key and see if the fuse still blows. If it does, then it's the regulator, if it doesn't, then it's the rotor.
john1c
XS650 Enthusiast
It's not 5 ohms. Should I still remove the brushes to do the test? Or can we say the rotor is definitely the culprit?
pamcopete
Ride.Enjoy.Life is Simple
john1c,
Yes, because the regulator can influence the reading, or you may have a short in the brush holders themselves.
Yes, because the regulator can influence the reading, or you may have a short in the brush holders themselves.
john1c
XS650 Enthusiast
Green wire from harness to ground - meter moves to 0.
With the alternator cover removed and brushes off, the two leads from meter placed on the inner and outer rings of the rotor - the meter moves to 0. Then with the regulator plugged in and key turned to on... the fuse didn't blow.
With the alternator cover removed and brushes off, the two leads from meter placed on the inner and outer rings of the rotor - the meter moves to 0. Then with the regulator plugged in and key turned to on... the fuse didn't blow.
pamcopete
Ride.Enjoy.Life is Simple
john1c,
Looks like a shorted rotor, probably the most common failure in the XS650 electrical system.
My recommendation is to get a replacement rewound rotor from Custom Rewind in Birmingham, AL 800-798-7282. Talk to Gary. The rewound rotor is $125 plus your core, so it is important that you use the proper rotor puller tool so you do not damage the rotor. That tool is available from www.mikesxs.com for $11. Sometimes Gary at Custom Rewind has a puller that he can loan to you. Talk to Gary.
Meanwhile, lets be sure that your rotor is in fact shorted.
1. Did you use the lowest range on your Ohmmeter? Typically 200 Ohms.
2. Go to Radio Shack and buy 2 10 Ohm resistors.
3. Connect the resistors in parallel.
4. Measure the resistance of the two resistors in parallel.
5. Should be 5 Ohms.
This little test will verify that your meter is working properly and that you did the measurement correctly before you blow $125 + shipping.
Additional notes.
1. I would suggest that you do not buy a used rotor on EBay. That's a real crap shoot. Likewise, do not buy a new rotor. In other words, you might find cheaper, and you can definitely find more expensive rotors, but you can't find a better rotor than Custom Rewind.
2. Be sure to remove the nut on the crankshaft before using the puller to remove the rotor.
Looks like a shorted rotor, probably the most common failure in the XS650 electrical system.
My recommendation is to get a replacement rewound rotor from Custom Rewind in Birmingham, AL 800-798-7282. Talk to Gary. The rewound rotor is $125 plus your core, so it is important that you use the proper rotor puller tool so you do not damage the rotor. That tool is available from www.mikesxs.com for $11. Sometimes Gary at Custom Rewind has a puller that he can loan to you. Talk to Gary.
Meanwhile, lets be sure that your rotor is in fact shorted.
1. Did you use the lowest range on your Ohmmeter? Typically 200 Ohms.
2. Go to Radio Shack and buy 2 10 Ohm resistors.
3. Connect the resistors in parallel.
4. Measure the resistance of the two resistors in parallel.
5. Should be 5 Ohms.
This little test will verify that your meter is working properly and that you did the measurement correctly before you blow $125 + shipping.
Additional notes.
1. I would suggest that you do not buy a used rotor on EBay. That's a real crap shoot. Likewise, do not buy a new rotor. In other words, you might find cheaper, and you can definitely find more expensive rotors, but you can't find a better rotor than Custom Rewind.
2. Be sure to remove the nut on the crankshaft before using the puller to remove the rotor.
john1c
XS650 Enthusiast
Hope I didn't do something really stupid. My only Ohm setting seems to be "Ohm X1K" which is what I have been using. Can you take a look at my meter and tell me if I have been using the right setting?
In addition, I have never checked my stator. Should I automatically assume that since I need to replace the rotor, I need to also get a new stator as well?
Or should I do the banshee swap thing?
In addition, I have never checked my stator. Should I automatically assume that since I need to replace the rotor, I need to also get a new stator as well?
Or should I do the banshee swap thing?
Last edited:
pamcopete
Ride.Enjoy.Life is Simple
john1c,
The Ohm X1K is not a low enough scale to measure 5 Ohms accurately. Harbor freight has a decent Digital meter for about $10 that will do the job, or borrow a meter, or just take a chance and blow the $125.
Having a shorted rotor does not affect the stator. Two different things that just happen to work together, so it's not likely that the stator is also shot, but, then, we are not even sure if the rotor is shot.
If you are going to do anything like a Banshee swap, then get a decent meter first because you will need it for that project, then you can test your rotor to see what you should be doing.
The Ohm X1K is not a low enough scale to measure 5 Ohms accurately. Harbor freight has a decent Digital meter for about $10 that will do the job, or borrow a meter, or just take a chance and blow the $125.
Having a shorted rotor does not affect the stator. Two different things that just happen to work together, so it's not likely that the stator is also shot, but, then, we are not even sure if the rotor is shot.
If you are going to do anything like a Banshee swap, then get a decent meter first because you will need it for that project, then you can test your rotor to see what you should be doing.
john1c
XS650 Enthusiast
Harbor Freight often has the # 90899 on sale for around $6 if you find the add in many magazines you can get another 20% off with the coupon. A very good meter for the price.
Harbor Freight is your freind.
Harbor Freight is your freind.
