Topic: CB 500 weird alternator readings

[Alex]

Hey folks,

So, I have huge issues with my charging system, but I'm on my way to fix it all.

When checking my alternator between the 3 yellow wires, it shows 1,2 ohms.
According to the manual it should be somewhere around 0,35-0,5 ohms.
What I can read, everyone talks about the alternator being bad when the values are under 0,35,
but can't find any info on when the values are more than double from what it should be.

I changed the alternator to a used one from a friend, where his bike worked fine.
But I get the same reading. 1,2ohms.

Is the alternator really toast?
And why would the one from my friend (which read 1,2 but worked fine) not work on my biek?

[strynboen]

test your multimeter on a restistervith a novhn value..it can be a veak batteri or korosion on the vires,,have you thek the cabel Shues..and vires for broken isolation

[Alex]

I use the multimeter every day at work and has not given me any weird readings before, but it does not hurt to check!

[Alex]

So, I checked the multimeter which works fine, have a brand new reg/rec and battery, but it still doesent charge correctly.

Is the alternator reading of 1.2ohm that big of a problem?
Could the rotor be a part of the problem?
I've seen some people change the rotor in the cb650 / cb750 and at the same time saying that the higher ohm reading from the alternator is not as important.
Could this be a similar problem?

I'm really loosing it here. Been searching for this charging problem for almost 3 months now..
Good thing I'm not quitting my day job..

[jaytee-nz]

Alex - you are better off posting this in the SOHC/4 Bikes section as that is for general "help" type questions. This section is for build projects.

[calj737]

So, I checked the multimeter which works fine, have a brand new reg/rec and battery, but it still doesent charge correctly.

What brand and model Reg/Rec did you buy? What battery did you install? Did you replace these items to solve your “charging problem” and encounter the same results? If so, that was probably money not well spent...

I refer people to this chart who use me solid state Reg/Rec:
https://cdn.shopify.com/s/files/1/1091/5694/files/fault-finding-diagram.pdf?235929069374954073

More than likely, your root cause is poor connections and corrosion within the harness. Follow the chart and attend to the actual faulty component or issue and you should be fine provided that your RR is the correct unit.

[TwoTired]

Common mistake is to absolutely trust the digital meter display without understanding the tool's capabilities.

Very low ohm readings are usually measured with a milliohmeter or Wheatstone bridge.
Did you look at the digital meter specs. for accuracy details?
Did you subtract out the meter lead resistance and internal resistance from the displayed value in your measurements?  Did you add the error factor built into your meter?

All wires will have an ohms/foot rating, as it is impossible to have no resistance in a conductor of electricity with today's technology.

What follows is a troubleshooting aid/process.
Cheers,

Charging system methodical verification checks, CB750, CB550, CB500, CB400, and CB350.

Begin with problem verification and characterization with recorded data.
A -- Fully charge a known good battery.  Let it rest for 2 hours, off the charger, and measure the battery voltage.  (Target is 12.6-12.8V.)
B -- Start the bike and measure the battery voltage at idle, 2000, 3000, 4000, and 5000 rpm.
C -- Repeat the measurements of B with lighting off.

The above tests identify charging system success, failure, or degree of "faulty".  The success voltages are listed in the Shop manual.

D -- Assuming the above indicates faulty, do check the RECTIFIER diodes with a diode tester or ohmmeter capable of testing diodes and uses more than .7 volts to make the test(s).
Of the twelve test made in D, six must read low ohms and six must read very high ohms.

E- assuming no faults were found in D,  Measure the white and green wires disconnected from the REGULATOR.  CB750s should 6.8 ohms - ish,  CB550s/350s/ and 400s should read 4.9 ohms- ish.

F- If there are no bullet holes or road rash/divots on the alternator case, the stator is probably good.  But, you can check for yellow to yellow continuity (.35 ohms) among all the wires, and that no yellow wire has continuity to the engine case.

G- Assuming no faults found in D, E, and F, measure the disconnected terminals of the REGULATOR.  The black and white terminals should measure zero ohms (subtract meter error if there is any).  Higher than Zero ohms, indicates internal contact contamination needing cleaning and attention per shop manual.

H - Assuming D, E, F, and G have not found faults. We can verify all the of the charging system minus the regulator is functioning correctly, by using a temporary jumper to connect the disconnected white wire (normally attached to the REGULATOR) and connecting the White directly to the the battery POS terminal.  Repeat the B and C tests.  However, if at any time the battery voltage rises above 15V, stop the test.  Such an indication would prove the charging system capable of maintaining a known good battery.  If this test never achieves 15V, then there is a wire/connector issue in either the ground path leading back to the battery NEG terminal, a wiring/ connector issue withe the rectifier RED path to the battery POS terminal, or you made a mistake in D through G.

I - (not used, can be confused with L)

J -  The only parts that remain to prove or expose are the REGULATOR (in active mode) and the electrical path between the battery POS terminal and the black wire that connects to the REGULATOR.

K - Lying to and starving the regulator
The regulator can only do its job correctly if it gets a proper voltage report of true battery voltage status.  The Vreg monitors the Black wire for this status.  Measuring the voltage lost between the Battery terminals and the Vreg connections identifies problems that are not really the charging system's fault.
Two connection paths must be checked, the Battery POS terminal to the Black wire connection at the VReg, and the Battery NEG terminal to the Green wire connection to the Vreg.  A volt meter can measure these losses directly by placing a probe between the two identified points, Black path and then the green path.  The numbers are summed and the error seen by the Vreg quantified.  Anything over .5V loss is cause for concern and anything over 1V is a certain issue to be corrected.  Each connector, terminal, fuse clip, or switch in the pathway can cause voltage reporting loss.

The regulator also passes the received voltage on to to the Alternator field coil to create a magnetic field within the alternator,  The voltage level determines the strength of the magnetic field and the maximum output capability of the alternator.  Therefore, starving  the Vreg of true battery voltage leads to reduced max output capability of the alternator.

L - regulator operation/verification.
  The Vreg sends voltage to the alternator field in response to measured voltage which is battery state of charge.  Any voltage at the battery of less than 13.5V sends full black wire voltage to the alternator's white wire.  The alternator output will vary with RPM, even if "told" to produce max power by the Vreg.  If the alternator has enough RPM to overcome system load, any excess power is routed to the battery which will raise the battery voltage (slowly if depleted and rapidly if nearly full).   When the battery reaches 14.5V, the regulator reduces the voltage to the alternator, reducing output strength and preventing battery overcharge.  If the battery exceeds 14.7V, the regulator clamps the alternator field coil power to zero (0V), effective shutting off the alternator.

Because, there is electrical load from the system, an alternator that is not producing power allows the battery to deplete and the voltage falls.  The Vreg responds by turning the alternator back on in accordance with battery state/ charge level.

The Vreg state changes can be monitored/verified by observing the battery voltage state, and the White wire to the alternator field.  (Two meters are handy for this.)  The "trip" voltages can be adjusted with the adjust screw, while changing engine RPM and electrical load that the bike presents to the battery/charging system to "make" the battery reach the voltage levels need for the set trip points.  IE. with load reduced (lighting off) and the engine above 2500 RPM, a charged battery will attain 14.5 V.  Anything above that and the adjust screw needs to be backed out to keep the battery safe from harm.
The shop manual outlines bench set up mechanical adjustments that should be performed on unknown or tampered units.  These should be resolved before final trip point adjust tuning.

Note that while the system is working, the Vreg can change states rapidly before your very eyes., changing 5 times or more while you blink.  Therefore, you may have to mentally average values measured on the White wire if your selected meter doesn't do that for you.

[Bodi]

The stator coils are almost immune to failure unless physically damaged if the bike is crashed. Since you read the same resistance on your suspect assembly and with a "known good" one... it is pretty much not a problem. Most likely this is a problem in the wiring harness causing a reduced field coil current.

[Deltarider]

Alex, have you checked where the alternators wires exit the top of the left crankcase cover (aka sprocket cover)? On a CB500 that's the spot where the harness and wiring is easily chafed...

[scottly]

Most likely this is a problem in the wiring harness causing a reduced field coil current.

I agree. Alex, disconnect the white wire from the regulator, and measure the resistance from the white wire to the battery negative terminal; this should be about 5 ohms.

[Alex]

Alex - you are better off posting this in the SOHC/4 Bikes section as that is for general "help" type questions. This section is for build projects.

Ok!
Could you tell me how to move it?
Have not done it before and can't seem to find how.

[Alex]

So, I checked the multimeter which works fine, have a brand new reg/rec and battery, but it still doesent charge correctly.

What brand and model Reg/Rec did you buy? What battery did you install? Did you replace these items to solve your “charging problem” and encounter the same results? If so, that was probably money not well spent...

I refer people to this chart who use me solid state Reg/Rec:
https://cdn.shopify.com/s/files/1/1091/5694/files/fault-finding-diagram.pdf?235929069374954073

More than likely, your root cause is poor connections and corrosion within the harness. Follow the chart and attend to the actual faulty component or issue and you should be fine provided that your RR is the correct unit.

Hey!
I'm using an ESR240 reg/rec with a JMT HJT9B-FP battery (12V, 190CCA).
Are any of them a bad choice?

No, these were installed because the bike is a total rebuild.
The wire harness is totally remade, following the Gordo550f schematics I once got from you.
Connections have been checked x10.

[Alex]

Alex, have you checked where the alternators wires exit the top of the left crankcase cover (aka sprocket cover)? On a CB500 that's the spot where the harness and wiring is easily chafed...

Good tip!
But yeah, I checked that too.
Good thing I got another used alternator though,
because when I took the old one off the crankcase I accidentally ripped one of the leads of at that very spot. :S

[Alex]

Most likely this is a problem in the wiring harness causing a reduced field coil current.

I agree. Alex, disconnect the white wire from the regulator, and measure the resistance from the white wire to the battery negative terminal; this should be about 5 ohms.

Ok!
Tried it yesterday and it showed 4,7ohms

[Alex]

Common mistake is to absolutely trust the digital meter display without understanding the tool's capabilities.

Very low ohm readings are usually measured with a milliohmeter or Wheatstone bridge.
Did you look at the digital meter specs. for accuracy details?
Did you subtract out the meter lead resistance and internal resistance from the displayed value in your measurements?  Did you add the error factor built into your meter?

All wires will have an ohms/foot rating, as it is impossible to have no resistance in a conductor of electricity with today's technology.

Wow! Thanks for the step-by-step manual!

Well, that got me thinking now.
When using my multimeter on any known resistor, it shows the right value.
But when checking the meter lead resistance it says 0. Not OL, but 0. Seems weird to me, but maybe thats a reason to buy a new one?

How do you mean "digital meter specs"?


Thank you to everyone that has answered so far!
Your help is greatly appreciated!

[calj737]

Since you followed Scottly’s advice and got 4,7 ohms at the alternator, what is the actual problem you’re chasing down?

You’re spoon feeding us in drips about the bike. You replaced the stock Reg/Rec with an ESR unit, did you also install an M-Unit? Is your bike not charging now? If this is your actual problem, please list exactly what changes have been made, what components you are now using (stock or aftermarket switches and controls) and give us picture or diagram of how you have things wired. It will really help us to help you without playing 20 ideas to unknown questions. 

[Bodi]

If you touch the leads together the resistance between them is zero, so reading zero is pretty good.
Agreed that more info is needed. I don't know "Gordo"'s drawing. A homebrew harness can hold many surprises. This makes helping you difficult...

What's needed for the alternator is simple: regulator grounded and powered by battery "+" voltage or as close as possible - switched by main power switch (key or whatever). Field coil wired directly to regulator output and ground. Three stator coil wires connected directly to rectifier input. Rectifier output (red wire) connected directly to battery "+" as well as the rectifier case grounded by mounting bolts or its ground wire connected to frame ground or battery "-".
With this, spinning the rotor can produce power.

[TwoTired]

When using my multimeter on any known resistor, it shows the right value.

Do you have a one ohm resistor to measure?

But when checking the meter lead resistance it says 0. Not OL, but 0. Seems weird to me, but maybe thats a reason to buy a new one?

No. Zero resistance is perfect continuity.   In reality, a physical impossibility.  We can get pretty close, though.  Some meters have a feature to zero out internal and meter lead errors.  Like motorcycles, all meters are not the same.

How do you mean "digital meter specs"?

The manual that comes with your meter states its accuracy capabilities.  Something like - a percentage of reading scale plus or minus X digits on the display.

Cheers,

[Alex]

If you touch the leads together the resistance between them is zero, so reading zero is pretty good.
Agreed that more info is needed. I don't know "Gordo"'s drawing. A homebrew harness can hold many surprises. This makes helping you difficult...

What's needed for the alternator is simple: regulator grounded and powered by battery "+" voltage or as close as possible - switched by main power switch (key or whatever). Field coil wired directly to regulator output and ground. Three stator coil wires connected directly to rectifier input. Rectifier output (red wire) connected directly to battery "+" as well as the rectifier case grounded by mounting bolts or its ground wire connected to frame ground or battery "-".
With this, spinning the rotor can produce power.

Ok!
You're right, I should have given you more detailed info at first.
I'll try to make it as easy to understand as possible.

1. Wiring
This being a complete rebuild, I wanted to rewire everything.
Stock wire harness in the trash and these are the things used instead:

1. M-unit v2
2. ESR240 reg/rec
3. Starter solenoid (with internal main fuse)
4. JMT HJT9B-FP battery (Lithium) (12V, 190CCA)

Everything is wired the same way as in a pdf I got a while back, attached to this post.
Only change from the pdf, is that the power to the M-unit and key switch are coming from designated outputs from the starter solenoid.

2. The problem.

I get everything hooked up.
Starts like a dream.
Carburetors are rejetted from 4/4 to 4/1 and beefier size due to pods.
Meticulously cleaned and synced.

When testing the bike, everything seems to work fine while riding around the block.

Checking charging, but the battery is pretty static at around 13,2V.
Does maybe increase 0,2-0,3V (at the most) when reving up to around 5000rpm.

When the bike gets warm (normal riding temp), the bike starts to lose power.

Checking charging again, but now the battery voltage has started to drop with 0,1-0,2V per second.
When reving up to around 5000rpm, the voltage doesn't increase, but stays at whatever value is presented at the moment for about 1-2 seconds.
Voltage continues to drop until around 8V where it stops dropping.

The M-unit , solenoid, reg/rec and battery are all brand new.
Reg/rec is tested and works perfect according to measurements.

3. My thoughts

Starting off with a disclaimer:
I may have used the word alternator for the wrong part, I don't know.
Being Swedish, I thought the combination of stator and field coil was the alternator.
Is that right?

Any way,
the field coil shows 4,7 ohms which should be correct according to the Clymer manual I got.
None of the 3 yellow wires from the stator are connected to the stator ground.

BUT! The stator should read 0,35-0,5 ohms, but show 1,2 ohms.

By glancing at Ohm's Law (not sure it's applicable here),
an increase of resistance should increase the voltage.

Since my old reg/rec just stopped working, I'm thinking that the stator puts out too much power,
burns the reg/rec and the charging problem is a fact.

Though Ive seen that people that have cb750's change the rotor when encountering similar problems to mine,
but as far as I know the 750 rotor is different from the cb500 and is in the case of the cb500 mostly just a lump of metal without any electronics?


I hope I described my problem as good as possible.
Tell me if you guys need more info!

And once again, thanks for all your help!

[calj737]

On your new R/R, there were 3 loose wires. How and where did you connect them? In the attached diagram, it shows connecting the loose GREEN to a bare metal ground. Have you done that?

If your battery is not charging, or is "discharging", and all components are new and in working order, it fails to a wiring fault on your part (more than likely). So how about some clear photos of how you connected the R/R and where the 3 loose wires go.

[Alex]

On your new R/R, there were 3 loose wires. How and where did you connect them? In the attached diagram, it shows connecting the loose GREEN to a bare metal ground. Have you done that?

If your battery is not charging, or is "discharging", and all components are new and in working order, it fails to a wiring fault on your part (more than likely). So how about some clear photos of how you connected the R/R and where the 3 loose wires go.

Wow, quick answer!

What color does the 3 loose wires have that you're referring to?

The ESR240 I have got has these wires;

Yellow - Stator lead 1
Yellow - Stator lead 2
Yellow - Stator lead 3
Green - Connected to field coil green cable + chassis ground.
White - Connected to field coil white cable.
Red - Connected directly to battery +
Black - Connected to M-unit AUX

"If your battery is not charging, or is "discharging", and all components are new and in working order, it fails to a wiring fault on your part (more than likely)"
I mean, I guess you're right, because I can't see why it wouldn't work.
But you don't think the stator putting out 1,2ohms is an issue?

[calj737]

What color does the 3 loose wires have that you're referring to?

The ESR240 I have got has these wires;

Yellow - Stator lead 1
Yellow - Stator lead 2
Yellow - Stator lead 3
Green - Connected to field coil green cable + chassis ground let's see a photo of this please.
White - Connected to field coil white cable.
Red - Connected directly to battery +
Black - Connected to M-unit AUX

But you don't think the stator putting out 1,2ohms is an issue? I do not.

[Alex]

Green - Connected to field coil green cable + chassis ground let's see a photo of this please.

So you think this might be the culprit?

Is it NOT supposed to go to chassis ground, or do you think the connection is bad?
I'm out of town and can't get pictures for some time, but I have basically made a Y-connection from the green wire coming from the R/R.
One to the field coil green and one to chassis ground.

[Bodi]

No, that's exactly right. Not sure what a picture would prove.
The battery "-" has to be securely connected to the frame and engine cases for things to work, of course. Usually that's via a heavy cable to one of the engine hanger bolts, with the frame paint scraped off where the bolt and cable terminal touch it. You can use an external tooth lockwasher - these pierce the paint or powdercoat for a good electrical connection - but those are not easy to find in the large size needed.

[calj737]

Alex - take the following voltage readings when you get back to your bike:

From R/R BLACK to battery POS (this measures voltage drop through the harness). This should be well under 1.0v, much closer to 0.5v.
Voltage reading at LOCK with engine running at idle and 5,000 RPMs.
Voltage directly at battery for same conditions as taken for LOCK.

Somewhere in your installation, the R/R is not generating a charge because its losing reference to the battery's condition. That's my opinion and position on your situation.