Topic: No voltage from stator

[acolman]

Hello from Colorado.  New member here, and I have my first questions and looking for some advice.  I am a lifelong machine designer and service technician, so I know my way around mechanical and electrical devices, and certainly multimeters.  I do most of my own service work, rebuild an occasional engine (both auto and motorcycle) and have success doing it.  I just finished rebuilding the engine on my CL360 and it runs really strong. 

I purchased this 750 late this summer and have ridden it locally from time to time since purchase.  I have had to charge the battery from time to time, and knew I would have to dig into it sooner or later.  Well, it is now sooner!  The bike has an aftermarket combination regulator/rectifier (unknown brand) and battery voltage is good and starter drains it to about 10.3 volts during cranking, so that appears to be good.  The battery voltage stays fairly constant at about 12.5 volts while running, no matter the RPM.  But the coil is only putting out a small amount of voltage - maybe 1 or 2 volts, and goes up only very slightly with increased RPM.  I have made the checks as recommended in the service manual (yes I have a genuine Honda service manual) and can't find anything wrong except the stator resistance is high at 8-9 ohms from wire to wire, measured at the plug coming from the Stator.  It is consistent between all three.  The manual specifies .2 ohms resistance, so it is high, but it is not open.  The field coil measures a little over 7 ohms, and the standard is 7.2.  Nothing is shorted to ground.  I have not removed the stator side cover yet. 

Now to my questions:

Is the stator resistance too high and thus causing no voltage to be generated?
Are there better alternatives to the 'stock' stator and charging system out there?

Any suggestions you have are certainly welcome and appreciated.  If more details are needed, please let me know and I will be happy to provide them.

[scottly]

the stator resistance is high at 8-9 ohms from wire to wire, measured at the plug coming from the Stator.  It is consistent between all three.  The manual specifies .2 ohms resistance, so it is high, but it is not open.

Your measurements are probably incorrect. Is it really .8-9 ohms? Most meters are not capable of reading .2 ohms, and the fact that your readings are consistent means the stator is probably not your problem.
With the key on, is the field coil magnetized? If not, there will be no output from the stator.

[TwoTired]

It is very very unusual for a stator on these bikes to fail unless you can see axe marks or bullet holes in it.   The yellow wires should be pretty low resistance.  And usually only very high end or specialty resistance meters can accurately measure 0.2 ohms.  Note that the meter leads can easily have 0.1 ohms each.  Put the probes together.  Whatever you read must be subtracted from any circuit low ohm reading you take.

There are connectors under the cover that can corrode and add resistance, if you are measuring from the rectifier connections.  Where you measure matters.

The stator can make no power unless the field coil is energized to make an electromagnetic field.  You’ve checked resistance.  Now see if it is getting voltage to the field wires.  If you can verify 12v to field wires, ferrous metals should be attracted to the alternator case.  Then spinning the rotor should generate voltage in the stator wires.

Cheers,

[newday777]

Hello from Colorado.  New member here, and I have my first questions and looking for some advice.  I am a lifelong machine designer and service technician, so I know my way around mechanical and electrical devices, and certainly multimeters.  I do most of my own service work, rebuild an occasional engine (both auto and motorcycle) and have success doing it.  I just finished rebuilding the engine on my CL360 and it runs really strong. 

I purchased this 750 late this summer and have ridden it locally from time to time since purchase.  I have had to charge the battery from time to time, and knew I would have to dig into it sooner or later.  Well, it is now sooner!  The bike has an aftermarket combination regulator/rectifier (unknown brand) and battery voltage is good and starter drains it to about 10.3 volts during cranking, so that appears to be good.  The battery voltage stays fairly constant at about 12.5 volts while running, no matter the RPM.  But the coil is only putting out a small amount of voltage - maybe 1 or 2 volts, and goes up only very slightly with increased RPM.  I have made the checks as recommended in the service manual (yes I have a genuine Honda service manual) and can't find anything wrong except the stator resistance is high at 8-9 ohms from wire to wire, measured at the plug coming from the Stator.  It is consistent between all three.  The manual specifies .2 ohms resistance, so it is high, but it is not open.  The field coil measures a little over 7 ohms, and the standard is 7.2.  Nothing is shorted to ground.  I have not removed the stator side cover yet. 

Now to my questions:

Is the stator resistance too high and thus causing no voltage to be generated?

Are there better alternatives to the 'stock' stator and charging system out there?

Any suggestions you have are certainly welcome and appreciated.  If more details are needed, please let me know and I will be happy to provide them.

Welcome aboard acolman from NH! I lived up in Breckenridge in the late 70s into 1980. I still spend 4-5 days riding in Colorado on my cross country trips, lots of friends there to visit too.

"Are there better alternatives to the 'stock' stator and charging system out there?"
For the CB750 Yes there is! Another member, Anders, is modifying an R1 system that replaces the stator and reg/rectifier. I stopped by his shop last weekend and had a great talk with him on the conversion. The cost is up from the original production run in 2009, now at $800. Contact Anders in the link. With this conversion you can run heated gear to extend your riding in cooler weather. I'll be getting at least 1 myself shortly.


http://forums.sohc4.net/index.php/topic,117735.0.html

[acolman]

Hello again everyone, I am sorry that I have not replied earlier, I have been out of town all week on business and just not was able to get back to the forum.  Thanks all for your great information.  I was using a Fluke meter to check the resistance, and I double-checked it with another meter I had and it was about the same.  However, I posted incorrectly - it was actually 0.8-0.9 ohms and not 8-9.  I will try the field coil magnetism and voltage test when I get home this weekend.  I will also pull the cover and check for any corrosion and clean the connections.  Thanks again!

[scottly]

I will try the field coil magnetism and voltage test when I get home this weekend.  I will also pull the cover and check for any corrosion and clean the connections. 

Do the magnetism test and post your results. Do not pull the cover yet.

[acolman]

Hi again, and thanks for your suggestions.  I was not getting 12V to the field coil on the white wire.  I double-checked all the wiring connections and they were good.  There was voltage on the black wire going to the regulator, but not on the white wire coming out of the regulator.  I took the test one step further and put 12v on the white wire going to the field coil, and voila - magnetism on the stator cover.  Unless I am thinking wrong, the regulator is shot and needs to be replaced.  As mentioned before, this has a regulator/rectifier combination of unknown origin.  If you agree, then I will start hunting for one.  I know there are probably plenty of cheapies on Ebay, but do any of you have good experience with any particular one?

[bryanj]

Yes your test suggests the reg is shot

[acolman]

Well, I changed the regulator/rectifier and it is now working properly.  Thanks to everyone that contributed!

[newday777]

Well, I changed the regulator/rectifier and it is now working properly.  Thanks to everyone that contributed!

Good to hear it's working again.