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Old 10-24-2012, 04:27 PM   #16
YOUNZ OP
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The flywheel on the end of the crank is a heavy cylinder that rotates around the center coil and is surrounded by the stator coil, both coils are stationary. The steel cylinder isn't magnetic. It seems the coils are OK. Now, it's back to checking the regulator/diode side. I'm sure I could somehow bypass the regulator/diode system and check the alt. output, but I don't want to harm the coils in the process. On a car, I would just energise the field terminal to get output, if the coils were OK.
I hope I don't have to check every wire for continuity from the alt. to the reg system because other systems use the same color wires. Oh, the joys of an unknown old motorcycle!
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Old 10-24-2012, 04:37 PM   #17
Grinnin
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Originally Posted by YOUNZ View Post
Isee you are reading from the red wire to the white. I just checked mine in the same manor and got the same reading. Prior, I was testing from white to ground and got zero.
I measured from green to white, not from red to white. Do you have a red wire on the field coil or is that a typo? There ARE red wires on the rectifier.

If you get 7 or so ohms measuring wire-to-wire, but get 0 ohms measuring white-to-ground when the parts are in place, it could be that the white wire shorts when it's assembled.

But then again it sounds like you know what you're doing but just need help with this odd alternator.
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Old 10-24-2012, 05:04 PM   #18
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Originally Posted by Beezer View Post
something in the generator system has to move in order to generate... there a permanent magnet on the crank, rotating in the middle of the field coil yes?
No.



I stole this diagram and photo from Practical Machinist. Part 7 is the field coil which is bolted to the engine case. Part 6 is the set of generating coils which is bolted to the engine case. Part 3 is the rotor. It is steel, but it is not permanently magnetic; it is magnetized only when the field coil is energized. It does NOT have wires going to it; this diagram must be cut from a more comprehensive one.

The left photo is the rotor alone. The field coil is magnetized so that left is North and right is South and that the wave pattern in the rotor causes the magnetic field to switch from N to S to N to S . . . . But the rotor is not permanently magnetized, but only pulls the magnetic field from the field coil.

The right photo has the rotor beside the nested field coil and generating coils. The rotor spins in the space between the field coil and the generating coils.

So many motorcycles use permanent magnet alternators and generate the maximum amount of electricity all the time then dump some with the regulator. In 1969 Honda tried generating only what was needed by changing the strength of the field coil to generate only the electricity that was needed.

EDIT: To correct polarities.
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Grinnin screwed with this post 10-24-2012 at 06:44 PM
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Old 10-24-2012, 05:18 PM   #19
YOUNZ OP
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That is the type of system I have. The red to white wire was a typo, it's the green to white wire.
If I manually close the points in the regulator, I should get output from the alt., correct?
But that doesn't necessarily mean the reg. is defective, does it?
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Old 10-24-2012, 05:21 PM   #20
Grinnin
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More resources for YOUNZ

I have a Honda-published manual downloaded from this page:
http://forums.sohc4.net/index.php?topic=17788.0

I BELIEVE that I have the third one after SOHC4 Motorcycles, but I'm not going to download again to check because it's 1,200 PDF pages. It has the CB750 plus a general Honda manual plus many magazine articles and reviews.

Even though it doesn't list 750A, it gives many specs to help interpret electrical measurements.
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Old 10-24-2012, 05:35 PM   #21
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Originally Posted by YOUNZ View Post
That is the type of system I have. The red to white wire was a typo, it's the green to white wire.
If I manually close the points in the regulator, I should get output from the alt., correct?
But that doesn't necessarily mean the reg. is defective, does it?
The regulator has a spring pushing the arm up. When the arm is up the field coil is getting the most power that it gets (the wire to the field coil goes through just PART of the wire-wound resistor. When the electromagnet gets 13V it pulls the arm down and the field coil gets less power -- the circuit to the field coil is going through the ENTIRE wire-wound resistor.

The voltage is adjustable. The screw through the upright puts more tension or less tension on the spring. You MAY need to turn the screw IN to increase the tension on the spring to make sure the field coil gets more juice. I'm not saying this is recommended because it's a pain to get the tension just right i.e. ride with a meter on and see where the regulator steps the voltage down then turn the screw . . . .

EDIT: But I didn't answer your question. You can't manually close the points because they're closed up and they're closed down.

EDIT AGAIN: My error for using the terms "up" and "down". I did a lot of work with a couple of regulators on my bench. On the motorcycle, left corresponds to my up and right corresponds to my down. Or you can just imagine your regulator on the workbench and my terminology will be impeccable.
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Grinnin screwed with this post 10-24-2012 at 06:40 PM
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Old 10-25-2012, 12:15 PM   #22
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Grinnin... your posts make sense now that I see the rotor, as you said, the field induces the rotor and the rotor induces the stator. I've seen a lot of generators, but not quite like that.

you should be able to put battery power on the field coil with jumpers to bypass the regulator and give you an unregulated output. one field lead to battery plus the other to minus. even the polarity won't matter

points style regulators typically give full field through the closed points. the resistor is in parallel with the points and when system voltage is reached, the points open which puts the resister in series with the field. this will reduce the field's strength.

another way to check the rectifier and the stator is to use a clamp on amp meter if you have one. put the clamp on to the output to the battery (from the rectifier) and set it on AC. run the engine and turn on everything electrical. bad parts will give pulsing DC that the meter reads as AC. There normally is a slight pulsing DC on top of the rectified output but any reading over about 1/2 amp AC is bad.

if you have an Oscope...

normal ripple:


bad diode:


bad stator coil:

Beezer screwed with this post 10-25-2012 at 12:22 PM
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Old 10-25-2012, 01:14 PM   #23
Grinnin
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Originally Posted by Beezer View Post
I've seen a lot of generators, but not quite like that.
It's odd and fascinating, isn't it?

Quote:
Originally Posted by Beezer View Post
points style regulators typically give full field through the closed points. the resistor is in parallel with the points and when system voltage is reached, the points open which puts the resister in series with the field. this will reduce the field's strength.
You're right, the regulator DOES include a short-circuit around the resistor. I either didn't know that or had simply forgotten it.
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Old 10-25-2012, 03:07 PM   #24
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I'll see if I can find a rectifier and try it.
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Old 10-25-2012, 06:14 PM   #25
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It is said many parts are interchangeable with the Gold Wing of the era!
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Old 10-26-2012, 05:12 AM   #26
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Beezer, you say energise the field coil. It has 2 wires, a green and a white? How would one measure the output? Would you need to bypass the regulator system? This type is a very different system. Albeit, it may be a good design. I am not an electronics guy.
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Old 10-26-2012, 08:36 PM   #27
Beezer
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well if you connect the field to the battery. the generator will give full (unregulated) output. the voltage will rise with the RPM if the field coil is good and the stator is good. it could go as high as 40-50 volts so be careful doing this test

the field windings measure in the 4-8 ohms range, whatever color the wires are. I think one is white & the other appears to be green. hook one wire to battery plus and the other to ground.

measure the VOLTAGE as you run the engine. if the output voltage rises with RPM & goes high, then the field and (probably) the stator are good, if not then one of them is bad.... probably the stator if the field measured something like 8 ohms & is not shorted to ground in it's own case/frame. the voltage can go as high as 40 or even more so don't dally at high outputs or the lights will cook

do this test & if it fails it is either the stator or the field windings. if it passes then the problem is the rectifier, the regulator, or the wires to those systems. there are other tests to identify the problem from here.
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Old 10-31-2012, 07:52 AM   #28
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Been dealing with rain issues and a wet floor in me shed. Evan Grist over at Race Tech Electric is trying to work me up a modern solid state volt reg/rectifier unit more specific to this unusual alternator. He said this thread was very helpful.
Hope to conclude this event in a few days.
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Old 11-04-2012, 01:06 AM   #29
Beezer
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kool. as odd as this system seems, the regulator part is pretty straight forward. just about any 12v regulator from an automotive system could be made to work.

did you try bypassing the reg by hooking the field straight to the battery?
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Old 06-18-2013, 02:42 PM   #30
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Winter is over..........

I'm back into it again. Been using the fine 400a lately.
On the 750a, the regulator/ rectifier has been replaced by a solid state unit from Race Tech Electric as well as a good used stator, donated from one of our own here. New battery, just in case, no signs of corrosion anywhere, so far. Still 12.5 max output. I will try replacing the field coil, may be weak?
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