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Low charge voltage

Cbjoe82

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Im only getting 1.5 volts feed into my stator input feed wire...obviously low alt output...yes the battery is good....any ideas
 
Bear in mind that early DOHC can fail the rotor and it still pass the test specs, and the most common fail on them. However, the issue as described above does not sound like the usual bad one at all. The description in some error though as there are THREE stator 'feed' wires.........
 
In the 20+ years I was a bike mechanic, I never saw a bad rotor I couldn't diagnose with an ohm meter. I suppose it's possible but I've never seen it... Sometimes you get the symptoms of a bad rotor and it's a problem with the brushes or the slip rings on the rotor are corroded. That's one reason I always pull the alternator cover and test the rotor at the slip rings rather than at the end of the wires to the brushes... It only takes a minute to polish up the slip rings with a sanding sponge or a Sctochbright pad...

Tony
 
Positively the rotor, been there several times myself. Some test fine but open up or short at speed from centrifugal force, not all of the wire core is solidly glued on some of them. That means the wires can move around to abrade. I personally got stranded 200 miles from home one evening by one that ran slowly down until I was pushstarting it, then I slowed down from 70 mph to 45 and by the time I was home the battery had come back up enough to start bike again. Go back up faster riding local and the battery then runs down again. After checking all and no issues found I changed rotor alone and problem gone. As well on the DOHC sites others have reported it. I think it's worse on rotor rewinds as many of them are epoxy coated at the center and on the outside only and again the inner wire loops move around if not wound tight enough.

Here in Texas pretty much lower corrosion issues, I've not had any other DOHC alt trouble other than needing to change brushes from wear. The only issue I've had is with the rotors and why I go to them first every time. I changed maybe 5 of them over the years. I always check at the slip rings only and clean too. I had some stators cook pretty good to lose some epoxy but I simply patched them up with new glue and ran them some more, I rebuild all my own car alts as well. A bit of trivia here, the Ford PWM controlled alts are well-known for testing and retesting fine all day long and then still being bad. I tested plenty of them when I was in parts there for a bit. On those a similar issue to these Honda but a different cause, the diode leads stick way up to be soldered into a tinfoil thin gathering connector for the A/C, the tall leads and no support lets the heat combine with vibration to crack the lead to then touch/not touch in use and it drives people crazy when the regulators melt from pushing the field too high trying to get back lost charge. Ford only cares about selling more parts and their thing now and the rebuilders were forced to re-engineer that diode plate to hold the leads in a much more substantial way and problem pretty much gone then. I've rigged a couple of my own instead of buying the $200 alt by simply resoldering the cracked leads (often more than one is broke) to get them back on line for nothing. Years more of free use.

Every design of everything pretty much has a primary failure mode.

I did somewhat mis-speak above, I meant that the rotor was the most common fail, not that the rotor checking within tolerance was........
 
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Geezerbiker, Im new to the 79 CB 750K I am working on. So I "thought" either the regulator / rectifier were shot or the stator was shot because i wasnt seeing any rise in charging voltage when holding the leads to the battery posts and running up the RPMs. They werent all that expensive so I replaced both of them. Brushes look nice and plenty of length left before getting to the scribed wear lines.

So I am still getting the same reaction with the meter on the battery even with new R/R and stator installed. Like i said im a newbie to the Honda stuff and found this thread. I am also not up to snuff on terminology. So my question is what are the "slip rings"?? Those the lines the brushes slide against on the rotor?? I read the info from the link above taking me to the Oregonmotorcycles site.

So i am checking the OHMS between the two surfaces ( lines on the rotor the brushes slide on ) ...is that correct? Now i am thinking it may have been a bad rotor all along? No worries though in that i got new stator and R/R installed...least I know they are new and when they were installed so Im good with all that. Its only money....LOL
 
And another question. Will taking some fine sand paper to the rotor face and shine the area up be of any use?? This bike has sat in a barn for 14 years by the way so maybe there could be some oxidation hampering things????

EDIT...Reread Tonys post and it answered the question as far as polishing the rotor. Will for sure do this and see what happens.
 
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AMC49.....do you rewind these rotors and if so what the cost? And have you had any experience with used Ebay ones or is there a source for reliable aftermarket units???
 
I do not rewind. Many of the ebay rotors that are used are faulty and why they are for sale. Rick's sells new ones. Yes, the slip rings are the copper tracks that are embedded in the rotor outer surface, check there for resistance. Fine sanding is great.

'...i wasnt seeing any rise in charging voltage when holding the leads to the battery posts and running up the RPMs.'

Don't know what that means but leads better not be stator ones as that is a/c and a good way to tear up electrical on the rest of bike. Unregulated you can get as much as 75 volts there.

Run a bad rotor long enough and it takes out the regulator when it keeps ramping up field to make up for lost charge, the reg then overheats to burn up.
 
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I'm looking for a local shop to rewind them. In the meantime I send people to Custom Rewind in Birmingham, Alabama 800-798-7282. They rewind rotors and stators for most bikes.

Tony
 
AMC....leads from the multimeter is what i meant. Holding them to the battery shows no change in charging strength when running the bike at any RPM.
 
Ok... I set the multimeter on OHMs ( 20K setting ) and it went straight to all zeros. So guess the rotor is shorted internally...correct? Probably be calling that place in Alabama to see what a rewind will cost. Sanded the rotor face nice and shiney before testing.

EDIT.. I did find a place called Vintage CB 750 that has new rotors for $180.00 so I am hoping the rewind will be less. If its "close" to what CB750 wants then I will just get the new one.

Honda CB Charging Rotor
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Honda CB Charging Rotor
Honda CB Charging Rotor, Replaces OEM#31110-426-832.

This rotor is a high quality OEM style replacement for Honda field coil rotors. The field coil is wound to stock specifications. This rotor is an easy installation and provides years of trouble free reliability from your Honda engine. Easy bolt-in installation just like the stock rotor.

Fits: Honda CB750K (1979-82),
CB750F (1979-82) Supersport,
CB750C (1980-82) Custom,
CB750L (1979) Limited Edition
Part #: 24-2200


http://www.vintagecb750.com/parts/480/24-2200.jpg
 
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Use the lowest setting your ohms will go to, no K at all. Use like 10 or 20 or 50, the lowest you can get on your meter. K is way too high (X1000, 20K is 20,000) and you bury the 4.4 number or whatever in that rounding to appear possibly as a zero.

All the new alts will brag to be the best but are cheap Chinese parts using low grade magnet wire that can fault quick unless an American company clearly stating that they use better wire and glue. I'd go with the Alabama address before getting any cheap Chinese crap, the rewind is what makes the job quality and there is no good reason to buy new as there is really no advantage like with most parts. Price rules if you have to go Chinese, most will be coming from the exact same factory. $180 is too high unless made here. I've seen $125 before.
 
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I will retest with the meter set at as low an OHM setting it has...thanks. Im not an electrical troubleshooter by any means. Mechanical stuff i can figure out blindfolded though.
 
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