Topic: Not charging well - Voltage Regulator? - 750 K8

[ZanVooden]

So did some work on my CB750K8 today after having some charging issue.

I ran through the test outline in the service manual, for the field coil, stator, rectifier and regulator. Everything check out until I got to test voltage across the regulator.

When the bike is running at 4000 RPM Im getting just a little under 11 volts through the black and white wires. The service manual says this should be about 14.5v. I tried adjusting the regulator (checking and adjusting the core and points gap and actual voltage setting) but didnt get anymore voltage no matter what RPM the engine ran at.

The battery is new, and is fully charged. When I hook the voltmeter to the battery I never read more than 12 volts +- .5v.

Like I said I had conitunity where the serivce manual said I needed it. Im just getting this low voltage coming from the alternator.

Anyone have any idea what is going on here? Do i need to replace something or adjust something?

[GammaFlat]

You might want to test the Rectifier.  TwoTired goes through the test procedure pretty well on this site. 

[GammaFlat]

Here it is: http://forums.sohc4.net/index.php?topic=2229.0

[ZanVooden]

Alright so I did the rectifier test and here are the result.
I've done for two rectifers, both off 750 K8's. The first rectifier (A) is off a running bike with a known charging issue, the second one (B) is off a bike that is currently be rebuilt and is unknown if it is charging correctly, as it is in pieces.

We are using a digital Multimeter for these test.

Test 1: Black lead of meter to green rectifier wire.
          A:                       B:
Yellow 1: infinity         |      9.8M
Yellow 2: infinity         |     13.5M
Yellow 3: infinity         |     13.5M

Test 2: Red lead of meter to green rectifier wire.
          A:                        B:
Yellow 1: 14.7M          |       2.5M
Yellow 2: 6.6M           |       3.0M
Yellow 3: 8.1M            |      2.7M

Test 3: Black lead of meter to red/white rectifier wire.
          A:                         B:
Yellow 1: 2.0M            |       2.8M
Yellow 2: 2.2M            |       3.8M
Yellow 3: 2.3M            |       2.5M

Test 4: Red lead of meter to red/white rectifier wire.
           A:                         B:
Yellow 1: 4.6M             |       14.0M
Yellow 2: 4.2M             |       7.2M
Yellow 3: 5.0M             |       5.3M


As well as this I've found no shorts in the harness to ground, also tested the stator and field coil and both showed within spec.

I believe the problem I am having is with the rectifier, can anyone confirm this to lead me in the correct direction of future steps.

Thanks.


 

[Spanner 1]

Here's the thing about DM's.... to test diodes you must use the diode setting on the meter instead of the regular Ohms scale. It should be the first 'click' up from off and has a diode symbol. When on this setting, the meter applies a higher power to the diode to 'turn it on' so to speak, Ohms scale does not. This setting also gives a continuity 'beep', tip the black  and red leads together to hear.   So, each diode should 'beep' in one direction and not beep with the test leads reversed.... no beep at all = open circuit,  beep both ways = shorted...... hope that makes sense, good luck.

[ZanVooden]

I had used the resistance setting because other threads and the procedures in FAQ had only referenced ohm readings for this test.
My meter does have a diode test mode.  When I switch it there the display reads 1.529v and when I touch the leads together it reads 0.00.  It doesn't beep.  It only beeps when I check continuity.  When I check the rectifier with this diode position I get the following results:

Test 1:  Black meter lead to green rectifier wire
Yellow 1:  1.52v
Yellow 2:  1.52v
Yellow 3:  1.52v

Test 2:  Red meter lead to green rectifier wire
Yellow 1:  .475v
Yellow 2:  .475v
Yellow 3:  .467v


Test 3:  black meter lead to red/wht rectifier wire
Yellow 1:  .470v
Yellow 2:  .472v
Yellow 3:  .467v


Test 4:  Black meter lead to red/wht rectifier wire
Yellow 1:  1.52v
Yellow 2:  1.52v
Yellow 3:  1.52v

What do these readings mean?

Thanks

[Bodi]

With your meter reading with no connection, that looks like a good rectifier: good diodes test at around 0.5V. Digital multimeters usually can go above 1.529v on diode test - this is actually less than the forward voltage of many LEDs. If it only has one AA (or other 1.5v nominal) battery then that's all it can do. Mine has one AA cell and one 9V battery, the diode test works up to 6V at least and reads "inf" or "error" with no connection between leads.

[ZanVooden]

Thanks Bodi, mine has a 9v battery.  But if the rectifier is good, now I'm stuck. I'll recap what I've done so maybe some of you guys tell me where I've gone wrong.

This bike was just rebuilt (frame up).  It wasn't running when I got it but it had engine problems.  The battery was really old and had frozen several times so I put a new one in.  After the build I had to charge the battery a couple of times during carb adjusting, sync'ing etc.  Then I rode it about 100 miles over several trips while working out little "bugs".  During one of these trips it died and was completely dead.  No lights, nothing.  I took the battery out of another 750 and with voltmeter on the + and - posts of the battery I had 14.5 or so volts at 4-5,000 RPM.  So I got the battery replaced under warranty but left the "loaner" battery in while I filled and charged the new one.

I started riding it again and put almost another 100 miles in it and just I was getting home from one of these 20 mile or so rides, I noticed the turn signal flashing very slow or not at all.  I turned off the engine in the driveway and it didn't have enough to start. 

So I put the new battery in it yesterday to start testing.  So now I have a new battery reading about 14V.  I start the engine and run it to get it warmed up and the headlights are on.  I check the voltage again and I'm now at 11-12v.  I rev the engine to 4-5,000 and it doesn't pick up any. 

My service manual gave me basic tests for checking continuity and opens for the stator, field, etc and everything was good.  The last step (after adjusting the points and the core gap of the regulator) is to adjust the regulator.  I adjusted it to where there was no tension on that little spring and it still doesn't charge.  I switched it with the regulator from my other 750 and still no change. 

Then I started searching this site, reading threads, and chose the procedure in FAQ by cb750_chris.  These are the highlights:
1.  Checked resistance between (-) battery lead and black regulator wire.  Should be 0 but my meter read .7 (which from what I understand is the same as 0).

2. Tested fro resistance between regulator I and F poles.  He said if it is greater than 0 it is out of spec.  I had .2 (which I take as being close enough to 0).

3.  Check for resistance between the white wire and ground.  I had 7.4 and he said it should be between 4 and 8 ohms.

4. I tested resistance between the 3 yellow stator leads.  He said less than 1 ohm is good and I had .7.

5.  I checked the resistance between each of the 3 stator wires and ground and the result was infinite which is desired.

6.  I disconnected the rectifier and tested the resistance of the 3 stator wire and I had the desired 0 resistance.

7.  I checked each of the 3 wires to ground and each had infinite.

8. That's when I checked the ohms readings at the beginning of this thread on both this rectifier and the one from the other bike (identified as A and B).  That led me to the most recent suggestion of using the diode test which as reported shows the rectifier as good.

As I said, I am now stuck and don't know which route to take now.

PLEASE HELP!  and thanks

[Bodi]

There are a couple of tests you can do.
You can do a running test of the rectifier but you need to contact the three yellow wires while they're connected, with the engine running. The voltage to ground on each yellow wire should be around 12V AC in this condition. If a diode is "open" then the voltage will be higher on one or more wires, maybe 40V or so.  A "short" diode will give you a very low voltage.
The other test is to pull the black and white wire terminals off the regulator and push them together. They don't actually mate but you can slide one edge roll into the other. Or use a clip lead to connect them. With a charged battery (important!) the system or battery voltage should go above 14V at 2500 rpm or so and over. This connection bypasses the regulator and puts the alternator into "full on" ... no good for riding as a working alternator will boil the battery dry pretty quickly. If this test shows the expected 14+ volts then the alternator is OK and the problem is in the regulator. If it doesn't work right then there's a wiring or alternator problem.

[ZanVooden]

Thanks Bodi,  I just checked and battery is only at 12.75 volts right now.  Which I believe needs to be up around 13.5 to be be fully charged, right?

I did try just the first test you describe (12V AC with engine running) and I had very little voltage on all three.  So I guess I will have to let the battery charger charge it up overnight.

[Spanner 1]

I think your regulator is 'stuck'...it has points kinda like your ignition... might need to be shone-up to make connection... 'points' can be touching but not passing voltage...... worth a look IMO.

[ZanVooden]

Thanks Spanner but I've had the cover off the regulator.  The points looked good and I ran a piece of really fine sandpaper over them and then adjusted the core gap and point gap both to the low end of the range allowed provided in the manual. 

I'm open to more suggestions - keep 'em comin'!

[scottly]

The other test is to pull the black and white wire terminals off the regulator and push them together. They don't actually mate but you can slide one edge roll into the other. Or use a clip lead to connect them. With a charged battery (important!) the system or battery voltage should go above 14V at 2500 rpm or so and over. This connection bypasses the regulator and puts the alternator into "full on" ... no good for riding as a working alternator will boil the battery dry pretty quickly. If this test shows the expected 14+ volts then the alternator is OK and the problem is in the regulator. If it doesn't work right then there's a wiring or alternator problem.

[Spanner 1]

O.K...... if your stator reads under 1 ohm and your field reads 4-8 ohms and there is 'some' voltage on the white wire from the reg.,... then your rectifier is kaput if no AC voltage detectable on any of the 3 yellow wires.....imho.

[1080]

You should have 12 volts dc coming off of the white lead of the regulator & ground. This feeds the supply voltage for the alternator.

Check if you have voltage coming off the red/white wire & ground of the rectifier. Check the red/white wire to the battery.

Good luck.

[Bodi]

A fully charged battery should stabilize at about 12.5 volts after siting off the charger for a half hour or so. The only way to see if it is really fully charged is by testing the specific gravity of the electrolyte acid. To charge the battery the voltage has to be higher, and at full charge the battery should float at around 14.5V, with very little (100mA maybe) current flowing into the battery.
I am puzzled by the low voltage on your yellow wires when running. The three phase alternator produces an AC voltage on all three wires, each wire's voltage waveform 120 degrees out of phase to the other two.
The rectifier sorts out this assortment of instantaneous voltages. On each input terminal there's a diode pointing from ground towards the terminal and another pointing from the terminal to the "+" output terminal. Whenever one wire has a low or negative voltage referenced to one of the other wires, current flow through the diode to ground on that wire and back on another wire with positive voltage through its diode to "+".
At any instant there should be current flowing through two of the three wires to the load. Because if these diodes the voltage on any wire can not go "negative" to ground more than the voltage drop of the diodes. When the voltage on a wire is positive, the current goes out to the "+" terminal connected to the battery. The battery itself limits the positive voltage, anything above battery voltage will be absorbed by the battery.
I haven't measured this with a meter but I have checked it with an oscilloscope. The voltage waveform on each wire with a good rectifier was a flattened half sine wave, the half going below zero volts missing and the positive half flattening out at about 15V. With a bad (open) diode I saw a confused waveform with the voltage going below ground voltage. I didn't have a "short" diode, for these diodes that is somewhat rarer than failing "open".
It seems as if you have no output from the alternator if there is no AC voltage to ground on the yellow wires when connected and running. All your measurements look good though.
Did you try the full-on test with the black and white regulator wires connected together?
Can you measure the field coil current? You need a meter that will measure amps, the coil should be around 2 amps: just disconnect the white wire and put one test lead on that wire and the other on the black terminal, then turn ignition on. Even just removing the white wire and touching it to the black wire terminal (ignition on) is useful - a good coil and wiring will show a nice spark when you touch and remove the white wire.

[ZanVooden]

Bodi,
I confirmed a fully charged battery.  The rechecked the runnuing test of the rectifier.  With all wires and connectors in place, the engine running, and meter set to AC Volts I probed the connector for the rectifier with one lead and touched ground with the other.  All three yellow wires to ground read .2V.

Then I jumped the black and the white wires together after pulling them from the regulator, started it up and checked DC voltage at the battery terminals and had the following:
13.5V at idle
14.5V at 2,500 RPM
15.7V at 5,000 RPM

1080 suggested checking voltage at the red/wht wire to ground.  I had 13.7v

Back to Bodi,  I measured field coil current (at least I tink I did it right).  I pulled the white wire off the regulator and inserted a test lead with meter set to 10A position.  The other lead I touched to the still connected black wire.  When I turned the ignition on I saw a brief reading of .2amp while the switch was turning.  When it stopped at the "on" position it went to 0.  I believe when I turned the switch back to off I saw a brief indication of .2amps.  As I was doing this I could feel the contacts move in the regulator as I was holding it.

[scottly]

Then I jumped the black and the white wires together after pulling them from the regulator, started it up and checked DC voltage at the battery terminals and had the following:
13.5V at idle
14.5V at 2,500 RPM
15.7V at 5,000 RPM

The above test points to a bad regulator.

[ZanVooden]

Thanks, Scottly
I have just been reading your work with campionic (earlier this year).  What a project!  I commend you for your persistance with that situation!

I have ordered a voltage regulator off ebay.  I have another 750K8 that I borrowed the regulator from at the very beginning of this thread.  I didn't help so it must be bad also.  I didn't run it before I tore it down for a complete rebuild so it very well could have a charging problem also.

Bodi, you've been working with me.  Do you agree with Scottly?

Thanks guys

[Bodi]

Yes. Scotty is right, since you have good voltage with the regulator bypassed, then the fault is in the regulator. Your field current measurement is faulty - you would have to measure from the disconnected white wire to the black wire, or (since your regulator seems fooked) between the black and white terminals with the wires connected. I read your report as saying you measured from the disconnected white wire to its terminal... since the regulator isn't making the internal connection to the black wire you won't get any current there.
A good original regulator would be good, or you can get the Oregon Electric solid state replacement, or use a car alternator regulator module as described in several posts here.

[1080]

I would check your regulator contacts points. They must not be making contact.
They can be restored, unless the contacts are toast.

[1080]

Cleaning point contacts. Mark the original screw position before disassembling.
I use a fibreglass pen made for cleaning contacts & printed circuit board paths.
You can use a point file as well.

[ZanVooden]

Bodi, I ended up buying 2 regulators on ebay last night so I will try one as soon as it arrives.

1080, A couple of questions re: cleaning teh contacts.
1.  In my search to fix this I did run a piece of fine sandpaper across both point contacts.  Would this have been sufficient?
2.  I've elsewhere on this site that filing points is not good as they pit again right away.  Your thoughts on this?

After the sandpaper treatment on the points I adjusted the core gap and point gap per the manual.  I then reinstalled the regulator and when I didn't have any charging, I tried to adjust it with very little or no response.  If it was shot then I can understand it but that is what led to posting this thread.

[bryanj]

Sandpaper is BAD news as its really bits of glass and they get impregnated into the contact material stopping good contact.

Snap on used to sell flexible contact files which were good or i used a small diamond file that a patternmaker friend gave me

It would be unusual for two regulators to be bad, check out the ground contacts on the regulator cables and that you are getting full battery voltage between the black(battery switched power) and ground as ignition switch plus bullet connectors can go high resistance and give a volt drop

[ZanVooden]

Thanks bryanj,
I will get a points file for future use and check the grounds and confirm the voltage at the black wire tonight when I get home.