Hot main fuse/blowing...rectifier problem?

Hello, newbie here, first bike. I bought an 83 xs650 a week ago, 23k miles. Driving on freeway and bike dies. Found the main fuse to be blown, replace, spare blows. Now the next fuse wants to blow/starts getting very hot very fast that it starts melting fuse panel. Would a faulty regulator/rectifier cause this? or a simple short? where to start?

Any help would be appreciated. Dan

The tail light gets is power from the main fuse. The tail light power wire often rubs on the housing and shorts to ground. Under the seat unplug the blue wire to the tail light. If this stops the fuse blowing, you found it.
Leo

I unplugged the tail light and fuse still gets hot. I also unplugged everything except the one that was powering the cluster that tells me the bike is in neutral. I removed the regulator there was some corrosion in the connector and I started following the haynes manual for testing the regulator (which is aftermarket-Tour Max, if it matters). The book told me to use the ohm scale on my multimeter and connect one probe to the black lead in the connector and the other probe to the base of the regulator (that's just any part of the metal regulator with the fins right?). Well the book said I should have 0 resistance but my meter doesn't do anything. Is the regulator bad? Should it be replaced? Should I do other tests before replacing it? The main fuse still gets hot without the regulator plugged in.
Thank you for your help.

Shorted windings in the alternator rotor will also cause what you're describing; clean the slip rings and take a reading.

If you remove all the fuses except the main fuse and it still gets hot with just the key on, in neutral, pretty sure its the rotor, the windings are shorted. This is about the only component connected at this time that will carry enough current to super heat the main fuse without it melting. A 'Short" usually causes the main fuse to blow immediately.

Read the rotor's resistance. Needs to be around 5 ohms +/- 20%

Right, Ken, a dead short usually does that; but those old rotors can do some mighty unusual things. I just finished a total rewire job on a B-model; cleaned the slip rings and ohmed the rotor at the git-go and got a healthy-looking 5.2. At first fire, the motor fell on its face at 2K rpm--and revved right up as soon as I unplugged the alternator. Ohmed the rotor again--no resistance. Installed a good rotor--revved right up. The 20A main fuse never blew. Here's the punch line--the bad rotor read 5 ohms again as soon as torque was relieved on the nut. I've never had one lie to me that way before, but I'm told it's not that uncommon.

Theblack wire is ground. I don't think the case on the reg/rec's are connected to ground, just there for cooling.
Just dug a stock reg/rec out of the parts bin and there is no connection between the black wire and body of the reg/rec, so I doubt yours will either.
If you floow the rest of the reg/rec tests the numbers may not match the book but should be simular.
I have a rotor that test right a 5.5 ohms at room temp but after a 1/2 hour ride it climbs to around 8.5 ohms and the charging falls off according to the temp.
Leo

grizld1 said:

Here's the punch line--the bad rotor read 5 ohms again as soon as torque was relieved on the nut. I've never had one lie to me that way before, but I'm told it's not that uncommon.

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That is a weird one. Try a current test on the rotor you removed. Just connect 12 volts to the slip rings with an amp meter in series with one meter lead. For meter protection (if it's safety fuse is not intact,) you might want to fuse the circuit with a 5 amp fuse.

You could also do a constant load test by connecting a battery or charger to the rotor. Use alligator jumpers and clip on to the tabs the rotor windings terminate at. Set up the amp meter circuit again and let is set for 10-minutes or so, see what the current does. Might try slapping the crap out of it a few times and see if it screams. Just kidding.

First of all you guys are awesome. I disconnected the brushes and the heating stop. I was wondering if anyone could tell me a good way to clean the slip rings? And the brushes?

pdxxs650 said:

First of all you guys are awesome. I disconnected the brushes and the heating stop. I was wondering if anyone could tell me a good way to clean the slip rings? And the brushes?

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Hate to tell you but poor brush connections will not cause current heating. This is a high current loading effect causing the heating.
You really need to mconfirm the rotor's resistance (5 ohms), better yet read it's current (2.25 amps) +/- 20% on both. If you see < 4 ohms or > 3 amps you'll need to replace the rotor.

Ken, that rotor already lied to me once, and it can't be trusted; it's going to Alabama to learn better ways. I've loaned the owner a working one for the time being.

Alright my rotor is garbage now. I cleaned it up and still can't get 1 or 2 ohms, and it was kinda grooved. Disconnected one of the brushes just so I can ride it around my neighborhood a little and put it back on the trickler.

Thanks again fellas. But now I am wondering....

What should I know about changing a rotor? Can a use a gear puller or do I need that special tool? Should I also replace the brushes?
and I guess how far can I go without an alternator?

If you are still using the stock glass fuses, I would replace them with the blade type. Just replaced them on an 83 because the main fuse was getting so hot things were melting. The new fuse holders and fuses seemed to take care of the problem.

pdxxs650 said:

Alright my rotor is garbage now. I cleaned it up and still can't get 1 or 2 ohms, and it was kinda grooved. Disconnected one of the brushes just so I can ride it around my neighborhood a little and put it back on the trickler.

Thanks again fellas. But now I am wondering....

What should I know about changing a rotor? Can a use a gear puller or do I need that special tool? Should I also replace the brushes?
and I guess how far can I go without an alternator?

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Changing the rotor is not that hard. You remove the left engine cover, then loosen two Phillips screws and the stator comes off, then you remove the rotor retaining nut/washer and using a puller you remove it.

The rotor has a tapered center that mates to the crankshaft. Some say this allows them to beat the rotor off but I say you damage bearings doing this. Not sure if you could pull it with a jaw type puller. The puller is $11.00 from Mikes plus shipping. I'd add a set of brushes and think of any other items I might need like an oil filter, air filters, new fuse block (If needed) and such to make the shipping cost worth while.

As to ride time... Had a fellow 650 owner lose his rotor at the Townsend TN Rally in the Smokies. Battery went dead. I switched batteries with him and he got a little over 2 hours of riding out of my battery with the headlight fuse pulled. We then switched batteries again and it got him through the day's ride and back to the hotel. All was good. Same thing happened at the LBL Rally to another rider last year and we swapped batteries. He got about the same 2 hours of ride in on the battery. Yours could vary a bit depending on your battery type, age. NOTE: Always nice to have a fellow rider with you if you venture out very far with no alternator.

PS:
A groved rotor tends to mean worn brushes and or binding brushes in the carrier. Definitely check and clean the brush carrier. Make sure the brushes float freely in it.

If you use a regular puller you may pull the rotor of in pieces, this makes it hard for Gary at Custom Rewinds to do his job. Call 800-798-7282 and talk to him, he often has pullers to loan. He may have a rotor already to go, he sends you the new rotor and puller, you send back the old rotor and the puller.
Why risk a new rotor with old brushes, brushes don't cost much.
Leo