Topic: DOHC regulator/rectifier on SOHC

[Honda d Urto]

Hi there!  I have a 1972 CB750 Four and I know that the DOHC one piece regulator/rectifier,  can be used on the CB750 SOHC to replace the stock parts.  Can anyone provide me with a pic and/or a part # for this specific part so that i can check with the local salvage yard? Thank you

[StephenB]

I think that topic deserves an answer, not only because I want to know if anybody had used a 19777/78 or later recifier/regulator combination on a pre-1976 CB750.
Or to turn the question around: are the alternators the same on later engines (which concerns the rectifier only)? 3-phase 120deg apart, I would think? No problems with the regulator spec obvioulsy, it is a 12V electrical system with a 12V battery after all!!

Anybody?

Stephen

[StephenB]

Urb posted that earlier on greenspun:

BEGIN Quote:
The SOHC uses an electromagnet (field coil) that spins inside the electrical field of the stationary stator to generate a current. When the regulator senses voltage greater than 14.4 or so volts it shuts down the power electromagnet and the voltage drops until it reaches 14.4 volts at which time the regulator switches the electromagnet back on. Constant voltage is maintained this way. On the DOHC bikes a permanent magnet in the rotor is used to create current as it is spun inside the electrical field of the stator. The regulator senses when the voltage goes over 14.4 volts or so and puts some of the generated current to ground to keep the voltage from going over this set amount. This grounding of the current generates heat and is probably one of the reasons why the charging systems on the DOHC bikes are prone to problems. Basically the regulator on the SOHC bike is an voltage dependent on off switch for the field coil while on the DOHC bike (and 650) it is voltage dependent variable connection to ground
END Quote

I thought it was the other way round. Anyways, if it is true in general that one uses a permament magnet and grounding overvoltage and the other one an electromagnet reducing its voltage if sensing overvoltage, that would be the regulator part of the combination which is entirely different in its design.

So, it obviously won't work to use a DOHC combination of rectifier/regulator on a SOHC. That's for sure. Right?

Questions remains: 1969-1976 SOHC vs 1977-1978 SOHC? Same voltage generation principle? Which one? Or was the 1977 CB750K already a DOHC? I am not at all familiar with those.

Stephen

[bryanj]

They DOHC will work as both have excited rotors albeit the dohc having brushes, Somwhere i have a diagram which if i can find i will get back to you with

[cb750_chris]

Has any one used the Electrex R/R on a SOHC?  Den. Kirk has it listed as part # 21-0553 for $111.99 in the 2003 metric catalog. 

I have gotten away with used R/R's in the past but it would be nice to go with a new modern one on our SOHC bikes.  I wouldn't trust a selenium rectifier unless it was brand new.  Even an NOS one will not have good resistance as the selenium will deteriate over time.   

For my restoration I'll probably put an NOS one on just to keep it original.  If I had a rider I'd want to get away from the Selenium. 

[RxmanGriff]

I have the Electrex on my 75 750F. I don't think it has cured all my problems but it is a great replacement. And the connector matchs perfectly. At least now I do not have to worry about 2 components that I was not sure about. Only problem is the mounting didn't match perfectly so I had to fabricate a "plate" for it. No big deal. I think I am still losing voltage somewhere within my wiring harness and it seems the battery goes down. The folks at Electrex were great to work with !!! top notch help !! They even suggested that I bypass my wiring harness to avoid the drain by adding additional wiring directly from the new unit to my battery as a tempoarary fix until/if I can locate the short. 

[BrianAdair]

I'm dragging this thread back up....

I am wiring a DOHC reg/rec to my K7, I thought it looked pretty straight forward i found these pics.



The question I have is, on the SOHC rectifier there is a RED/WHITE wire that goes to the solenoid, and then goes back through to the main fuse. I am assuming this is how the sohc sent the charging voltage to the battery, and then to power went through the main fuse and harness...?
If I wire the DOHC solid state reg/rec up like the pictures above, does this eliminate the RED/WHITE jumper wires, since the WHITE/RED on the DOHC regulater goes to the battery?
I would still have the RED wire going from the battery through the main fuse to the harness,.

Also why do you switch the wires opposite, the WHITE and GREEN?

[BrianAdair]

I think I figured it out.
I'll post pics when I get it made up.
Also think I figured the color change between the GREEN and White wires out.

The SOHC Green all goes to ground,White is to the Voltage Regulator, from the alternator, then sends power out through the black.

On the DOHC I'm guessing the White is the ground, as the black is the power wires.

[HondaMan]

I think I figured it out.
I'll post pics when I get it made up.
Also think I figured the color change between the GREEN and White wires out.

The SOHC Green all goes to ground,White is to the Voltage Regulator, from the alternator, then sends power out through the black.

On the DOHC I'm guessing the White is the ground, as the black is the power wires.

That's backward:
on the SOHC the WHITE is the power TO the field coil, from the voltage regulator. The other side of the field coil is grounded. The BLACK is the IGNITION, which senses the bike's voltage (more accurately stated, "current") as the battery waxes and wanes.

The SOHC system is a current-limiter design. It uses the current that passes through a fixed-impedance coil (the voltage regulator's relay coil, to be precise) to pull a contact away from the HI charge contact inside the regulator. When this contact is open, the current to the field coil is limited by the big resistor on the back of the voltage regulator: this drops (or "slows down") the amount of power the alternator makes, so it won't boil out the battery with too much power.

If your 750 has low voltage, the first thing to do is clean the ground cable where it contacts the engine. By "clean", I mean remove it from the frame, wire brush it and the end of the engine's aluminum where they touch, then oil or grease it a little and reassemble. Next thing is to check the physical condition of all of the 12 connectors blades found in the system: they are now almost 40 years old, and corroded. They were intended to have a 5 year life in the 1970s.

Finally, check the rectifier you have, see if it has been electrically damaged. This happens when someone hooks up a battery charger of more than about 6 amp capacity (with it already plugged in and turned on). The open-circuit voltage on today's made-in-China 6 amp chargers can approach 50 volts if the unit is powered up and THEN cnnected to the battery: the OEM rectifiers on these bikes were rated as low as 15 volts on the K0-K2 bikes (check the Honda manuals, it clearly shows this spec), and only 40 volts until the K6. This peak voltage can punch tiny holes in the diode's junctions: after a time, these holes grow with current pasing through (via electron erosion, just like water erosion), and the rectifier slowly develops an electrical leak, much like a valve with a pitted face.

Also, severely cruddy connectors, and those with blackened nylon housings, should be replaced, as the black stuff is conductive (i.e., "electrically leaky") between the 3 phases of the alternator when the connector is warm. 

[Pinhead]

Check out the link in my signature.

[BrianAdair]

I think I figured it out.
I'll post pics when I get it made up.
Also think I figured the color change between the GREEN and White wires out.

The SOHC Green all goes to ground,White is to the Voltage Regulator, from the alternator, then sends power out through the black.

On the DOHC I'm guessing the White is the ground, as the black is the power wires.

That's backward:
on the SOHC the WHITE is the power TO the field coil, from the voltage regulator. The other side of the field coil is grounded. The BLACK is the IGNITION, which senses the bike's voltage (more accurately stated, "current") as the battery waxes and wanes.

The SOHC system is a current-limiter design. It uses the current that passes through a fixed-impedance coil (the voltage regulator's relay coil, to be precise) to pull a contact away from the HI charge contact inside the regulator. When this contact is open, the current to the field coil is limited by the big resistor on the back of the voltage regulator: this drops (or "slows down") the amount of power the alternator makes, so it won't boil out the battery with too much power.

If your 750 has low voltage, the first thing to do is clean the ground cable where it contacts the engine. By "clean", I mean remove it from the frame, wire brush it and the end of the engine's aluminum where they touch, then oil or grease it a little and reassemble. Next thing is to check the physical condition of all of the 12 connectors blades found in the system: they are now almost 40 years old, and corroded. They were intended to have a 5 year life in the 1970s.

Finally, check the rectifier you have, see if it has been electrically damaged. This happens when someone hooks up a battery charger of more than about 6 amp capacity (with it already plugged in and turned on). The open-circuit voltage on today's made-in-China 6 amp chargers can approach 50 volts if the unit is powered up and THEN cnnected to the battery: the OEM rectifiers on these bikes were rated as low as 15 volts on the K0-K2 bikes (check the Honda manuals, it clearly shows this spec), and only 40 volts until the K6. This peak voltage can punch tiny holes in the diode's junctions: after a time, these holes grow with current pasing through (via electron erosion, just like water erosion), and the rectifier slowly develops an electrical leak, much like a valve with a pitted face.

Also, severely cruddy connectors, and those with blackened nylon housings, should be replaced, as the black stuff is conductive (i.e., "electrically leaky") between the 3 phases of the alternator when the connector is warm. 

Thank you for the detailed explanation, HM!

I'm not sure what kind of shape my regulator or rectifier are in.
The bike wasn't running when I bought it, and all the wiring and electrical components were a rats nest, with some (home made extra auxiliary light harness tied into it)  in a box with the rest of the parts, that the PO had removed for a restoration that he never started, or finished.
I am rebuilding from ground up, and trying to clean the wiring up and eliminate some things that, I don't need/want.
I wanted a solid state all in one unit for the cleaner look. I was looking at buying an aftermarket SOHC reg/rec but they are aroud $110 to $130 and I got this DOHC one for $30 it's a NOS from a local guy, so saved some $

I think I have it right, I just had it backwards in the way the current flow is in my explanation.

I'll try and get some pictures tomorrow and post in a new thread of my harness with what I have, and have rerouted, removed, to make sure I'm not messing up....