Topic: Nightmare CB750 Charging Issues

[hip]

I'll start by saying that I have read a lot of topics on CB750 charging issues, I understand how to properly test the charging system based on the HondaChopper steps and other tips people have offered in the forums, yet I still cannot get the thing to charge.

My bike is 1975 CB750K with a brand new SparckMoto custom wiring harness, reconditioned field coil & stator, and new reg/rect.

What I have concluded:
 - The field coil is not magnetising as I only get 0 to 0.08V output on the white wire from the reg when the ignition switch is turned on (bike not running) and also when the bike is running. I have confirmed a good ground to frame of the green wire.

 - The bike will charge if I bypass the regulator (plug the black wire into directly into the white going to the field coil). This should mean that everything else is working correctly, and it is the regulator that is letting me down. I have tested the field coil and stator following the HondaChopper test and they all test OK.

 - I have tried 3 different brand new reg/rect units and all have the same outcome - zero to 0.08V output on the white wire. All units have no continuity between the black and white wires, even when they are off the bike. Is it possible they are failing when I plug them into the bike? I did not test for continuity before they were plugged in. Should they have continuity between the black and white?

 - When I plug an old CB400F regulator into the harness I get output to the field coil (that then magnetises), however the bike doesn't charge properly. This regulator shows continuity between the black and white.

Please help! I've been trying to sort this issue out for 4 months now with no success.

[scottly]

The regulator should provide 12 volts to the white wire, with the ignition on and the bike not running, assuming that the black wire has the 12 volts to supply it. Are you using stock mechanical regulators? If so, then you should have continuity between the black and white terminals.

[hip]

Scottly, I have been using brand new combined reg/rect units.
I have confirmed that there is no voltage drop from the battery to the black wire, and it is supplying the full 12V from the battery to the regulator via the black wire.

[scottly]

By combined, you mean solid-state. The continuity test doesn't work the same as a mechanical unit. Which reg/rect units have you been using? (Please be more specific than "e-bay" or "Rick's", as that covers a bazillion different possibilities. )

[hip]

Sparck has supplied me all 3 units I have tried.
The first two have been the 3 Phase Reg/Rect, then the 3rd unit was from another supplier that Sparck sent me, which I'm pretty sure is an ElectroSport unit.

[Patrick]

Electrical problems are almost never the stator or field coils. It's more likely corroded connections or grounds or fuse sockets, or rust in a component. Put it back to stock and start running some tests. Find out what doesn't work before you start replacing things. You can never know if you caused a new problem by replacing a part that might work. Have you worked on bikes or electrics before?

Patrick

[scottly]

Knowing where you bought it doesn't help identify which regulators you've tried. If you are using a '79 or newer style regulator, the connections need to be modified. Some aftermarket reg/rects are proper for the SOHC, but the wires in the plug may not be in the proper location. The stock regulator has three connections: the black wire supplies the reference voltage, the green wire provides the ground that the reference voltage is compared against, and the white is the output to the field coil, which has the other end grounded through the harness. The '79 and later systems control the ground side of the field, with the other end of the coil connected to battery + with the ignition switch on. 

[hip]

These are the units:




I've worked on a bunch of bikes before. My previous builds can be seen here:http://www.saltyspeedco.com/bikes

This is the bike in question:


There are no issues with corroded terminals as everything is brand new.

[martin_uk]

I am on my 4th CB750 restoration and as an extra precaution, always use extra earth wires back to battery terminal, inc one to rectifier and coil lead earth point  to make sure there is not an issue.

As already mentioned, replace any suspect connectors and examine carefully and test the loom and connectors that connect to alternator leads and also fuse block.

[Bodi]

Since your alternator charges with the regulator bypassed and you've tried several units, the problem would appear to be with the wiring - not the regulator/rectifier or alternator coils. How have you connected it? I believe this is a drop-in replacement to plug into the stock rectifier cable, with the two loose wires meant to connect to the stock harness wires for the original regulator. The green regulator wire is not used with it.
The wires on the plug are 3x yellow for the 3 stator coil wires plus green to frame and red to battery +.
The loose black is for switched power and white is for the field coil. The most likely problem from your description is that you don't have switched +12 on the black wire.
Depending on which type of regulator it is, the other field coil wire goes either to ground or switched power. You have it grounded (you say it charges when white is held to +12).
Stock SOHC 750 regulators ground the field coil, DOHC and many aftermarket ones connect it to power.
If you confirm the black wire has switched +12, possibly your regulators have all been the "other" kind.
Since this looks like one designed for SOHC engines it should work with your bike normally, but check with a tail light bulb if it will light from white to battery +. This should not damage either type of regulator: the "right" kind will light the bulb from white to ground (with key on) and the DOHC type should light it from white to +12.
If it is the rectifier polarity, just connect the field coil return wire (also white at the coil but it goes to ground somewhere in the harness) to a switched +12 wire (standard color is black). Field coil connections are non polarized, + and - can be either way.