Charging System

If it's broken or just needs tweaked

Moderators: Volker_P, tidd650

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Tunes81CB
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Joined: Thu May 17, 2007 5:12 pm
Location: Greensboro, North Carolina

Charging System

Postby Tunes81CB » Sat May 19, 2007 8:01 am

I am new to the forum. So far I am happy with it all. So many tech tips. I have a 1981 CB650. The battery died on me the other day going home from work. I drive 50 miles one way! Had to wait for trailor. I connected my multi meter to the battery after charging overnight. 12.4VDC. Started bike then checked at different RPM's. Seems to get up to 14.6VDC. At around 4500RPM's it drops to 12.2VDC. I noticed the headlight go dim at higher RPM's. My test results were good on the Reg./ Rectifier. Cleaned the rotor and checked brushes. Still no luck. Anyone have any ideas? Gas is almost $3.50gal..
Thanks. :)
Tunes81CB

Pinhead
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Postby Pinhead » Sat May 19, 2007 10:25 am

Sounds like your rotor windings are coming apart at high RPM. I can't think of anything else that would kill the alternator at high RPM.

Just a note for future reference: If you get stranded due to a "dead" battery, disconnect all of the fuses below the ignition key and you'll make it quite a bit further. I drove for a few days like that when my alternator wasn't working. You'll have to push start it but at least you won't have to trailer it home.

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holysmokes
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Postby holysmokes » Sat May 19, 2007 2:23 pm

left hand engine cover, under it is the charging rotor, use a multi meter, check for resistance across the slip rings

should be 4.4 ohms

http://cgi.ebay.ca/Honda-cb-650-750-900 ... dZViewItem



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Pinhead
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Postby Pinhead » Sat May 19, 2007 4:20 pm

That is true. HOWEVER, if the rotor works at idle and then "flys apart" at high RPM, it could very well test good when it's not spinning, but then quit working at speed.

Edit: If I were you, I'd get the one linked above. It's a good price for a rebuilt rotor and it should last for a LONG time.

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Tunes81CB
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Location: Greensboro, North Carolina

Postby Tunes81CB » Sat May 19, 2007 4:37 pm

I have reviewed your replies and thank each of you. I have a parts bike and will check both rotors. I just hope that if I have to remove them, they will come off easy. Wish me luck!
Tunes81CB

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holysmokes
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Postby holysmokes » Sat May 19, 2007 4:50 pm


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Volker_P
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Postby Volker_P » Mon May 21, 2007 3:20 am

Welcome here! :D
I agree that it looks like a rotor rpm problem. One could repeat the measurement at the regulator input side just to be sure.
Rebuilt rotors quality may be fine or poor dependent on who did the rebuild. In case you know nothing about the rebuilder, I would prefer an old original one.

holysmokes wrote:http://www.cb900c.net/forum/viewtopic.php?t=899

One needs a spare rear axle for the described procedure. :wink:

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holysmokes
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Postby holysmokes » Mon May 21, 2007 7:57 am

or love the one you got

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Tunes81CB
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Got it working

Postby Tunes81CB » Tue May 22, 2007 5:46 pm

It was the rotor! I am back on the road! Thanks to all!
Tunes81CB

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Volker_P
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Postby Volker_P » Fri May 25, 2007 3:07 am

That's good news!
Happy riding. :D


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