79 XS750 Stator

Garc

New Member
Own a ‘79 SE Special that I’m getting ready to sell. It’s never charged properly from my initial resto, just trickle charged and never went on long trips.

I presumed it was the R/R which was actually confirmed bad through continuity. However, continuity through 4 whites coming off the stator tested in spec but do not supply A/C voltage(<1 VAC to 9k RPM) when running direct to ground. No continuity through case which means not a shorting problem, NO magnetism on inner flywheel ring but not sure if it should have any static.

Manual says contact a technical expert to test stator so here I am guys. Brand new battery, is there a more modern charging method(cheaper) than finding a used $100 flywheel/stator and hoping it is good?

Thanks in advance,
Tim
 

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Garc

New Member
Doing a little more research says to test the field coil wiring as it may power the magnetic field. The previous bike owner(s) had been in the R/R harness wiring and removed a receptacle to the regulator side and my eBay replacement R/R may not have the same color coding. Guess and check tomorrow with it running unless someone has another idea that doesn’t need to go through my MAC 3-1 open pipe at night.
 

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Sonreir

Oregon
The green and the brown wires going to the stator are for the electromagnet. Without power running through them, there won't be any power on the white wires coming from the stator. The alternator should definitely be magnetized when the ignition switch is on (especially before the engine is actually running).
 

Garc

New Member
There is a black wire to the stator as well, does that need a chassis ground or is the R/R case sufficient? Since I’ll be doing some trial and error I wonder if a 9V would have enough juice.
 

Sonreir

Oregon
Depending on the model and year, sometimes Yamaha would use a black wire on the alternator side (instead of the green, I think?). To start with, I would disconnect the alternator from the harness, turn the bike on, then check voltage on the green wire and the brown wire to see where you're at. Pretty sure you should be seeing battery voltage on the brown wire going into the alternator.

9V might be enough, but the current matters, too, so you might not get enough power from a 9V battery.
 

Garc

New Member
See I don’t know if I have the eBay rectifier side wired correctly either.

If I power the red wire(on white/yellow side) direct to battery, green(currently disconnected in photo) goes 12VDC but not the other way.

Also do not know if polarity matters on regulator side green/red male unprotected spades plugged in to alternator.

I apologize for any confusion, tonight I’ll dive back in.
 

Garc

New Member
(3) A/C whites are going to (3) yellow in the eBay rectifier with (1) extra yellow to headlight relay, red from rectifier direct to battery, green from rectifier to key switch 12v

Magnetized(hopefully) field coil BLACK to red through eBAy regulator, green from field coil to green through regulator, OEM plug appeared as designed and brown was left open through original R/R
 

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Sonreir

Oregon
Looks like you've got the wrong R/R for your bike.

That one is for a high current three phase permanent magnet alternator. You need one for an electromagnetic alternator.

We have the one you need here: http://www.sparckmoto.com/Products/Detail/74

It's designed and color coded for the SOHC Honda fours, but it will work on your XS as well.
 

Garc

New Member
Interesting information, just curious how you know the replacement R/R(stated for 78-79 xs750) is not correct? The permanent mag uses all 3 wires?

Here is my alternator assembly. Are there no other ways to power the eMag, I might wire up the old r/r to see if I can get magnetism if the rectifier is bad, maybe combo until I receive the proper replacement.
 

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Sonreir

Oregon
The color of the wires on the regulator/rectifier is what I would look for.

In all cases I can think of, the color of the wire dictates its purpose.

For Honda, yellow is AC power from the stator, green is ground, and red is output to the battery. I suspect the R/R you're using is for an early Goldwing because most Honda R/Rs only use a single green wire and a single red wire. Picture attached of an R/R used on a Goldwing. To complicate matters, sometimes they will also have a black wire. The black wire is to "sense" system voltage so that the regulator knows when to kick in. In the pictured example, this is handled internally and so it's skipped.

Anyway... regulator/rectifiers designed for electromagnetic alternators will have two additional colors besides those used for battery, ground, and AC power. Sticking with the Honda theme, EM R/Rs will always have the black voltage sensing wire (brown on Yamaha and Kawasaki and Orange on Suzuki) because the R/R has to know when the bike is on or off, and not just if the voltage is at an acceptable level for charging. It will also have one more wire that provides power to the alternator field coil and/or, depending on the model and year, a return wire from the alternator to the R/R. Again, one of these wires (and possibly both) will be of a different color than the others we covered in the second paragraph.

For your case specifically, we have five wires from the alternator and the colors are 3x white, black, and green. The other wires on the R/R are black, red, and brown. So five wires (with three different colors) from the alternator means we're definitely dealing with an electromagnetic alternator. This means we need at least five different color wires on a matching R/R (white, black, red, green, and brown for Yamaha). In the R/R in your original post, only three different colors are represented, so we know we have the wrong type.
 

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Garc

New Member
R/R came yesterday, thanks again.

When I wire up tonight, the Red and green from the Rectifier both go where? Switched 12V or can I go direct to the battery?

Also, the regulator 3 wires are white/black/?green to my field coil black bottom and green/brown top of the plug/receptacle.

I'll read through your testing procedure thread again as I initially skimmed through.
 

Sonreir

Oregon
*Red to battery positive (or hot side of the solenoid, if that's easier)
*Green (that's bundled with the red wire) to ground or battery negative terminal
*Other green to the green (or sometimes black) wire coming from the alternator
*White to the brown wire coming from the alternator
*Yellows to the whites coming from the alternator (order doesn't matter so long as each wire gets connected)
*Black to a brown wire in the harness

Please let me know if you need more detail, trial and error is not advised.
 

Garc

New Member
Good, because I did check continuity and the case was not grounded anywhere. I am confident your advise will have me charging granted something is not haywire in the windings.
 

Garc

New Member
Fire and verify tomorrow.

Oh, how much amperage will that rectifier pull? I can’t trace the power back as it’s blind in wrap so I added a blade fuse to be certain. Probably goes to the starter, but if there is any residual draw just pull the power.
 

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crazypj

Split personality, I fake being smart
R/R should be able to handle at least 20 amps for a short period, It's very common for people to get wrong R/R when they have EM system, they get Permanent Magnet (PM) R/R and no output. It would have worked with 9v battery to field coil, just not for very long though. The R/R will switch field coil on and off, if you 'feed 12 v to iat idle you'll get about 17v, out don't rev it if you try that test, full field voltage can easily spike to 60+DC which tends to let the magic smoke out. You should have at least 7 wires on new R/R, maybe 8? (3 output, 2 for field coil - electromagnet,, ground, battery) If you have 8th wire, will either be a ground or sensing wire you should be able to compare with other connection colours
 

Garc

New Member
Still no white wire AC or battery DC increase voltage, tried swapping the 3 wires to the field coil around no change.

Coil must be trash.
 

Garc

New Member
My green wire with a male spade not in the plug has continuity direct to chassis. I believe my rectifier green ground may be separate, will run it direct to battery.


Do you have this R/R wiring diagram?
 

Sonreir

Oregon
I'll grab a diagram and post it up early next week.

For the field coil, we can test that, too.

Field coil wires should be either brown and green or black and green, coming from the alternator. In either case, use your multimeter to read resistance between the two wires. Then read resistance between each of the wires and ground.
Post up your readings and we'll take it from there.
 

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