CB900C charging problem - Motorcycle Forum
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post #1 of 14 (permalink) Old 08-14-2010, 10:03 PM Thread Starter
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CB900C charging problem

I have an 1980 CB900C that is not charging the battery. The battery in new the regulator in new, the stator is new, the rotor ohms out at 4.6 and I checked all the wires. What am I missing?

What is this? is it part on the charging system? I can't find it in any diagrams.
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post #2 of 14 (permalink) Old 08-14-2010, 10:54 PM
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Hi, That may be the "bridge diode" It is needed if your stater is making ac. The bridge converts the ac output to dc for the battery! It is usually close to the stater! I really can't see much in your pic as it is out of focus ! ! LaTeR

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post #3 of 14 (permalink) Old 08-14-2010, 11:05 PM Thread Starter
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I disconnected it and did a diode test on it and it test OK. I also for I have 13.8 volts going to the battery when running. The battery will hold a charge just sitting for a few days. The problem I had was after riding for about 4 hours today the battery went dead and I had to catch the bike in gear to to get it started. Maybe a bad battery or loose connection. It wasn't charging before and I went through all the connections with WD40 and it started charging again. I am lost as to why my battery is going dead.

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post #4 of 14 (permalink) Old 08-14-2010, 11:43 PM
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Quote:
Originally Posted by vanman250 View Post
Maybe a bad battery or loose connection. It wasn't charging before and I went through all the connections with WD40 and it started charging again. I am lost as to why my battery is going dead.
You just answered your own question. Just stick with it.....and check the voltage more often (which you should have done before replacing ALL those expensive parts !!).

If you never catch the charging voltage down below 12.6 (assuming your meter is right), then you are back to bad connections or a bad battery......which can have bad connections inside.

You probably should carry that meter with you until you get things ironed out.

Maybe you should now go thorough those same connections again......only blowing the WD40 OUT this time !!

P.S. Don't count on the bike to recharge the battery. If it is so weak that the bike dies.....or the starter won't turn....then it needs an complete external charge.
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post #5 of 14 (permalink) Old 08-15-2010, 10:41 AM Thread Starter
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Luckily I didn't put all those new parts on the bike. The previous owner did. I bought it with a carb and electrical problem. I am going to go back through all the wires again. Every time I out the volt meter on it shows it's charging.

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post #6 of 14 (permalink) Old 08-15-2010, 12:01 PM Thread Starter
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Well I ran through all the wires again. at 2500 rpm I was at 13.6 Volts at 5000 I was at 13.9 volts. I couldn't get it to go below those numbers no matter how much I jiggled the wires or the bike. I made sure the battery had a full charge and if it goes dead again I am going to have the battery tested.

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post #7 of 14 (permalink) Old 08-15-2010, 12:27 PM
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Quote:
Originally Posted by vanman250 View Post
I made sure the battery had a full charge and if it goes dead again I am going to have the battery tested.
Good plan.

One more thing: If you haven't already, you should disconnect and inspect and clean (scrape) the connections at both ends of the main battery cables. Corrosion sometimes hides inside the connections where you can't see it. Disconnect the negative cable at the battery first and reconnect it last.
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post #8 of 14 (permalink) Old 08-15-2010, 01:13 PM Thread Starter
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I have had the battery out and everything looked very clean but I didn't actually clean them. I have cleaned every other connection so why I didn't do the battery connections is beyond me. I going to do that right now.

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post #9 of 14 (permalink) Old 08-15-2010, 03:09 PM
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I going to do that right now.
If it's not too late, that would be an excellent time to loosen and re-tighten the connections at the OTHER end of those cables too.
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post #10 of 14 (permalink) Old 08-15-2010, 03:46 PM Thread Starter
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Done. I went for an hour and half ride and so far it still has a charge. i guess we will see ho long that last.

Thanks
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post #11 of 14 (permalink) Old 08-15-2010, 03:54 PM
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i think with it being an '80 model the charging system might be a bit before my time so to speak. but if you have a manual, have you a picture/diagram of the rectifier/regulator. the manual should maybe have a test for this part. you obviously have a voltmeter to test for continuity, i.e broken connections
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post #12 of 14 (permalink) Old 08-15-2010, 09:46 PM
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The Honda DOHC bikes need to run above 3,000rpm to charge good, if you are riding in town or stop & go traffic at low rpm's you will have charging issues.
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post #13 of 14 (permalink) Old 08-15-2010, 11:18 PM
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Quote:
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The Honda DOHC bikes
Does that automatically mean something like "1985 and earlier" ??

If not, you need to qualify that statement because I think Honda still makes DOHC bikes and it doesn't really apply to ones with modern electronics.
The new ones start charging "good" just slightly off idle.
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post #14 of 14 (permalink) Old 08-16-2010, 06:58 AM
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I should have said "early" DOHC Hondas 79-83 had weak charging systems. You can find lots of info on this site: cb750c.com
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