Topic: Running a 750 without the alternator/rectifier/regulator?

[wohali]

If I understand correctly, in a stock configuration, the CB750s use an electromagnet design for the alternator. I think this means that if I don't power up the electromagnet, the three coils in the alternator won't produce any current, and I can run the bike solely off of the battery for a short time with the alternator coils unplugged. Is this correct?

The key to this setup would be simply removing the regulator (and, for safety, the rectifier) from the wiring harness. Based on the factory diagram for the F3 (what I own), this should let me perform my short test.  Naturally the battery would go right back on the tender after the test =)

Will this work, or have I missed something? I don't want stray current coming out of those 3 yellow leads and arcing to the frame.

[GammaFlat]

I believe you're correct in that it would be safe.  The VR drives the alternator by increasing the voltage to it in order to get more out of it.  The generation should be nil while that stuff is disconnected.  Heck, I think all you gotta do is disconnect the "8 place shell connector" that goes to the engine to be sure you're not "hooked up". 

Whilst on the topic... it makes sense to consider your options carefully when you consider using an aftermarket voltage regulator.   I think at least some of the aftermarket units are in a "shunt" arrangement and run the alternator flat out all the time and dump unneeded charging capacity back to an "out of phase" coil of the alternator (so you don't overcharge your battery).  Those two things make the alternator heat up a lot more and can cause pre-mature failure... lots of people are having good success with them however. 

I'm curious to hear from others though.  One of our sage experts will hopefully jump in.

[wohali]

I'm planning on running a stock regulator, but have had to replace the rectifier as all of the diodes were blown out. A $6 Digi-Key part fixed that up just fine; not quite the "resto" I was hoping for, but a hell of a lot more reliable than germanium diodes!

From what I've pondered about the shunt regulators, the big problem would be overheating. The gauge of the wire in the alternator coils is pretty small, and the air/oil circulation may not be sufficient to cool them enough, esp. at idle speeds. Perhaps if you had an oil cooler, or rewound your alternator (!!!) with thicker wire it might work...

[GammaFlat]

The gauge of the wire in the alternator coils is pretty small, and the air/oil circulation may not be sufficient to cool them enough, esp. at idle speeds. Perhaps if you had an oil cooler, or rewound your alternator (!!!) with thicker wire it might work...

From what I understand, the insulation gives up and it starts to short.  If somebody wanted to make a lot of us happy, they'd come up with an inexpensive, higher capacity alternative to the factory alternator.  There are lots of folks that want to run more than the factory accoutrements. 

[TwoTired]

1.  Yes you can run the engine with a total loss electrical system.  It will run as long at the battery has enough power to charge the coils.

2.  The stator windings use very large wire sizes, and are quite robust, barring attacks from asphalt or big bubba with an axe.

3. Field coils have smaller wire sizes, but are also quite robust with the normal voltage fed to it.  They are also susceptible to asphalt and bubba attacks.

Most SOHC4s have stationary Field coils.  The CB650s are different, and the excited field coil is part of the rotor.  The heat, and centrifugal forces do corrupt the wire insulation on occasion.

As far as making people happy with a new design, you are only allowed 2 of the following:
Cheap
Good
Fast

[wohali]

Thanks for the advice! I just didn't want to reassemble everything, and I'm still redoing the harness. Without the regulator and rectifier installed, it ran just fine.

[the architect]

If you're interested in running modern, inexpensive solid state components with much smaller form factors . . . .

Here's your regulator - $15 from Autozone: http://www.autozone.com/autozone/parts/_/N-5yc1s;jsessionid=297C51EC0800179DA9A905DE395B84E9.diyprod2-b2c4?itemIdentifier=130187

And here's your rectifier - $16 from DigiKey: http://parts.digikey.com/1/parts/432147-rect-bridge-3-pha-800v-35a-d-63-36mt80.html

You can check my build thread (in my signature) for my own approach to implementing these.  A year latter and a decent amount of miles, and it's all working nicely still.

Cheers!

[Spades]

You are correct about running off just the battery. I have done this recently while trying to get the bike back home after my fusebox and rectifier bit the dust at pretty much the same time.

It does work and didn't cause any damage .. that I know of. You will know when your battery is dying because your power does also.