Author Topic: Charging Problems (Read 3736 times)

mstang460 · « **on:** March 19, 2006, 01:55:10 PM »

I have a 1978 CB 750K. I have searched the previous post's on charging issues and have still not been able to diagnose my problem. I have no charge with a reading taken at the battery terminals, it just drains the battery when its running even at high r.p.m's the reading is about 11.90 with the bike running and 12.5 off. I have bypassed the regulator and still the same results. However if I check the voltage at the rectifier harness with ground being the green wire and positive being the red with white striped wire I get a reading of about 12.9 volts with the headlight fuse removed and the bike running at 3,000 r.p.m. If I keep the ground lead of the voltmeter on the green wire and take the positive lead back on the battery terminal and get a reading of 12.9 instead of the reading of 11.90 that I get if I use the negative terminal as the ground. I have checked the resistance at all the yellow wires coming from the alternator the give a reading of about 0.7 volts. I'm pretty lost and would appreciate any help with diagnosing the problem.

Thank You

oldfart · « **Reply #1 on:** March 19, 2006, 03:17:42 PM »

Give this link a try.

http://home.earthlink.net/~trinomial/SOHCcharging.html

clarkjh · « **Reply #2 on:** March 19, 2006, 04:27:48 PM »

I found this awhile ago and put on my site. Just a flow chart but might help.

http://www.cryscom.nb.ca/PDF_Docs/fault_finding.pdf

Hope it helps with tracking down your problem.

James

Bob Wessner · « **Reply #3 on:** March 19, 2006, 05:09:18 PM »

How's the overall condition of the connections and grounds? Have they ever been cleaned? If not, might want to start there and then move on to the more tedious testing. Bad, or faulty contacts can have you chasing yourself.

Bodi · « **Reply #4 on:** March 19, 2006, 07:44:53 PM »

Something's fishy if you're losing a volt between the rectifier and the battery, the wiring shouldn't be losing that much.
First, where does the rectifier connect to the frame ground? I think the stock ones ground directly through the mounting bolt; the green wire carries ground to the various lights and such that don't use the frame for ground. So I would unbolt the recticfier and sand clean the mounting points both on the rectifier and on the frame.
Second, I doubt if the battery ground cable is funky or else that starter motor would have major issues... the starter current is so much higher than the charge current. So check the red/white wire and the rectifier connector terminals.
As a general suggestion, take the time to clean all the bullet connectors throughout the wiring harness. As they get corroded and drop voltage the charging system is affected - the regulator reference voltage feeds from the ignition switch and through a lot of wire and many bullets. I hlike to install a little relay that connects the regulator directly to the battery when the ignition is on; once I'm sure the reference is reliable the regulator can be adjusted to supply the correct battery voltage to keep it properly charged (about 14V). This helps prevent overcharging and battery boiling - that's what you get when the regulator reference is a few volts lower than the battery voltage - but it's still a pretty good idea evenb though you seem to be having undercharge.
It's not good that you don't get charge current with the regulator bypassed. There may be corroded connectors in the field circuit (or the stator output wires), check the engine connector and look for bullets under the engine cases. I am not sure about the 750 but other models have bullets between the engine plug and the actual alternator and these are famously troublesome. They run at high temperature and carry a lot of power all the time. I like to solder them, eliminating the bullets.

mstang460 · « **Reply #5 on:** March 21, 2006, 02:44:20 PM »

Thank you all for your input all of it has helped, however I hit a small bump by being ignorant. I was performing the steps that one of you gentle men referred me to. I checked what I think is resistance of the field coil. Where the wiring harness comes out from the engine I measured the resistance between the green(ground I assume) and white (power wire I hope) wires. I got a reading of 7.1 which from the steps says is bad and indicates a open field coil? I am not sure what that means and how I would go about repairing or or replacing the field coil. Thank You all again for your help.

clarkjh · « **Reply #6 on:** March 21, 2006, 03:01:48 PM »

If the voltage was from my flow chart, Please remember it is for a Susuki and not a Honda, check your manual for correct voltages. Or one of the other gents can give you the voltages. The chart will just help in running the problem down. Sorry if this confused you.

James

TwoTired · « **Reply #7 on:** March 21, 2006, 03:36:51 PM »

The resistance of a CB750 field coil is supposed to be 7.2 ohms. 7.1 ohms is well within unit variance and measurement errors for the test.

If you are still having problems, keep looking.

Cheers,

clarkjh · « **Reply #8 on:** March 21, 2006, 03:43:02 PM »

TT
could you take a look at the chart and let me know if any of the specs should be changed to show what our SOHC/4 should be reading.
Thanks

James

mstang460 · « **Reply #9 on:** March 21, 2006, 06:12:08 PM »

Thank you again for your responses. It was not the chart that I got that spec from it was the diagnosing steps link that the other gentleman gave me. I will discard that step I suppose.

TwoTired · « **Reply #10 on:** March 21, 2006, 06:34:50 PM »

clarkjh, I decline the work asignment at this time. It's a big flow chart. Maybe later when I have an hour or two to circumvent boredom. I got as far as noticing the filed coil measurement they want doesn't coincide with Honda specs. But, then I got hungry and...

mstang460,

Did you say you jumpered the white and black wires at the regulator, and with the engine going 3k, still had only 12.9 V at the rectifier output green and Red/wht?

If so, better check the rectifier diodes individually, there are six, to see if some are open. Check both meter polarities (diode test function on DMM) across each yellow to green and the yellow to red/wht. 12 tests. Each diode should show conductivity in only one polarity direction.

Also, the yellow wires from the alternator are AC power. Switch yor meter to read AC not DC when looking for an output on those wires. Even then, don't expect much output unless the field coil has 12V on it.

Also, given what you said about voltage shift rect. to battery, better check the green wire integrity from rectifier to battery minus terminal.

Cheers,

clarkjh · « **Reply #11 on:** March 22, 2006, 03:18:42 AM »

No prob TT. I can't seem to get past the first page, I haven't done any electrics since high school. I start reading and then my brain says "I need another beer", then so much for reading.

James

mstang460 · « **Reply #12 on:** March 26, 2006, 02:41:14 PM »

Two Tired or anyone else who knows. Iam still a little confused on how to check the regulator's diodes and I am not sure I have the DMM function on my meter is there something else I can do to see if the regulator is working. Thank You again

TwoTired · « **Reply #13 on:** March 26, 2006, 03:48:41 PM »

There is a significant difference between the regulator and the rectifier. Which are you trying to check? I thought it was the rectifier you suspected. That is the one with diodes.

It the bike stock? Or, does it have an integrated regulator/rectifier?

Which meter are you using brand/model? Internet reference picture?

Cheers,

mstang460 · « **Reply #14 on:** March 27, 2006, 02:00:20 PM »

Two Tired or to whom it may concern Iam sorry I have no idea why I wrote regulator, I did mean rectifier. Yes the bike is stock. It has the stock regulator and rectifier they are seprate pieces. I have a craftsman digital multimeter here is a link to picture of it http://www.sears.com/sr/javasr/catalog/product/imgProduct.jsp?img=/is/image/Sears/03482146000

Also I switched my meter to AC to check the voltage output on the 3 yellow stator wires. While connected and with the bike running and headlight on the voltage between any of the two wires at a time was not over 11 volts AC even with bike running at 3,500 rpm. I read somewhere that it should be 25 volts. I dont know if this is correct or if this test has any worth. Also the bike was reading 12.1 volts during this test. Still not charging.
Thank You again

TwoTired · « **Reply #15 on:** March 27, 2006, 02:43:17 PM »

11VAC, even 25 VAC is pretty dismal if the alternator is in full charge mode. However, an important part of the test configuration is knowing there is 12V on the field winding while spining the rotor at 3500 RPM. Jumpering the black and white wires at the regulator assures the alternator will be all it can be. In fact, you should get something like 50VAC with those conditions. Since you have a voltmeter, measure the DC voltage going to the Field coil, across White and Green wires

Your meter has a diode symbol on the very lowest resistance range setting. Use that setting to check rectifier diodes. 12 tests.
Black test lead on the Green, Red test lead on Yellow (A) Result= ______
Black test lead on the Green, Red test lead on Yellow (B) Result= ______
Black test lead on the Green, Red test lead on Yellow (C) Result= ______
Black test lead on the Red/Wht, Red test lead on Yellow (A) Result= ______
Black test lead on the Red/Wht, Red test lead on Yellow (B) Result= ______
Black test lead on the Red/Wht, Red test lead on Yellow (C) Result= ______
Red test lead on the Green, Black test lead on Yellow (A) Result= ______
Red test lead on the Green, Black test lead on Yellow (B) Result= ______
Red test lead on the Green, Black test lead on Yellow (C) Result= ______
Red test lead on the Red/Wht, Black test lead on Yellow (A) Result= ______
Red test lead on the Red/Wht, Black test lead on Yellow (B) Result= ______
Red test lead on the Red/Wht, Black test lead on Yellow (C) Result= ______

Report what you find.
Cheers,

mstang460 · « **Reply #16 on:** March 28, 2006, 04:08:44 PM »

Are the diode checks to be done with the bike off or running at a specific R.P.M
Thank You

crazypj · « **Reply #17 on:** March 28, 2006, 04:11:19 PM »

On or off bike, not running (your disconnecting reg/rect.)
PJ

TwoTired · « **Reply #18 on:** March 28, 2006, 05:06:33 PM »

The rectifier has a plug going into the harness. Disconnect that and you can make all the tests on the terminals of that plug from the rectifier.

Since it is now no longer electrically attached to the bike, there is no need for the engine to be running. In fact, this is a resistance check. Such tests must be done without any external power applied to the devices under test. The meter itself must supply all the power needed for the test results to be meaningful.

Cheers,

mstang460 · « **Reply #19 on:** March 30, 2006, 01:28:29 PM »

Two tired here are my findings:
Black test lead on the Green, Red test lead on Yellow (A) Result= nothing______
Black test lead on the Green, Red test lead on Yellow (B) Result= nothing______
Black test lead on the Green, Red test lead on Yellow (C) Result= nothing______
Black test lead on the Red/Wht, Red test lead on Yellow (A) Result= _559_____
Black test lead on the Red/Wht, Red test lead on Yellow (B) Result= _573_____
Black test lead on the Red/Wht, Red test lead on Yellow (C) Result= _570_____
Red test lead on the Green, Black test lead on Yellow (A) Result= _560_____
Red test lead on the Green, Black test lead on Yellow (B) Result= _550_____
Red test lead on the Green, Black test lead on Yellow (C) Result= _547_____
Red test lead on the Red/Wht, Black test lead on Yellow (A) Result= nothing______
Red test lead on the Red/Wht, Black test lead on Yellow (B) Result= _nothing_____
Red test lead on the Red/Wht, Black test lead on Yellow (C) Result= _nothing_____

In the places where I put nothing the meter did exatley that when I tried to test those two wires.
Thank you again for all your help.

TwoTired · « **Reply #20 on:** March 30, 2006, 02:23:28 PM »

Looks like a good rectifier to me.

Did you try jumpering the regulator, yet?

mstang460 · « **Reply #21 on:** April 08, 2006, 08:33:53 PM »

Sorry I haven't been able to reply, Yes Two Tired I have jumped the regulator it gives me a reading at the Battery of 12.01 at idle then, 12.02 and so on as I increase the rpm but when I get up to 4,000 rpm the reading is only at 12.53 roughly sometimes a little higher sometimes lower. Also to be noted that at the rectifier as reading of 13.5 is reached at 4,000 rpm. Using the red and green wires. Also the harness at the rectifier becomes very warm when the rpm's are this high. Is that usual? Iam lost and any help would be greatly appreciated.

Thank you

mstang460 · « **Reply #22 on:** April 08, 2006, 08:38:29 PM »

I forgot also with regulator jumped the VAC between the yellow wires is still only about 11

TwoTired · « **Reply #23 on:** April 09, 2006, 11:45:38 AM »

It would seem you have multiple issues. Also, a reminder that the bike MUST have a known good battery that is fully charged, in order to have sensible readings in the charging system. A low or bad battery will give test readings that will mislead proper diagnosis.

one concern is the low AC voltage from the alternator. Details are very important here. A misplaced test probe or test condition can give meaningless, undiagnosable data.

1. Place your DC voltmeter probes on the green and white wires at the regulator terminals. With the ignition on and the white and black wires jumpered you should read very near the battery voltage potential.
What reading do you get? ______
1.5 What is the reading directly across the battery terminals?_____

2. Discribe where, exactly, are your meter probes when when you measure the rectifier at 13.5v? _______
The rectifier output is directly connected to the battery terminals.
3. How could the voltage at the battery be any different? (Retorical) Describe where are your test lead probes?_____

**** Disconnect your battery POSITIVE terminal from the bike. Leave it dangling, unconnected to anything. ****
4. Use an ohmmeter to measure continuty between the battery minus terminal and the regulator green wire. What resistance do you measure?_____
5. Use an ohmmeter to measure continuty between the battery minus terminal and the rectifier green wire. What resistance do you measure?_____

6. Use an ohmmeter to measure continuty between the battery POSITIVE cable (not the battery) and the rectifier Red wire. What resistance do you measure?_____

7. Use an ohmmeter to measure continuty between the battery POSITIVE cable (not the battery) and the regulator black wire with the ignition switch turned ON. What resistance do you measure?_____

Quote from: mstang460 on April 08, 2006, 08:33:53 PM

Also the harness at the rectifier becomes very warm when the rpm's are this high. Is that usual?

No. Are your connector contacts corroded? Do you see any signs of wire insulation melted? How about the harness black wrapping tape?

techy5025 · « **Reply #24 on:** April 09, 2006, 06:41:40 PM »

The stator bullet connectors that are behind the transmission cover and chain cover are
notorious for overheating as they tend to attract oil and grime, develop Resistance and
overheat.

None of the tests conducted so far indicate a bad part. You might try connecting the
battery to a low amperage (one to two amp) charger, let it charge and then measure
the voltage with the charger connected.....should be 13 volts or so. Eleven or so
would indicate a shorted cell.

Also, with a battery connected, I doubt if the stator to stator ac output is 50 volts even
with 12 volts on the field....assuming good connections of course.

Jim

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Author Topic: Charging Problems (Read 3736 times)

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