No Voltage Regulation?

[Hans]

Ok, next electrical conundrum.

My little '71 Yamaha AS3 has electrical issues.  Following through the electrics, I see that there is no voltage regulation.  There is a rectifier, but that is all it does... AC to DC.  The manual says do not attempt to run the bike without a battery because up to 400V from the Alternator may course through the system and fry stuff.  Does this sound right for a bike of this simplicity and vintage.  Is the battery providing the voltage regulation? Ideas?

[stevecrout]

I'm no expert but there's a couple of things that come to mind.  The battery is only used to store the generated electricity but nothing else.
the generating system on your bike is probably using permanent magnet/alternating/stator system and will have a series of diodes used to convert the AC current to DC. There also needs to be a regulator that will dump excess current  when the battery becomes fully charged or if the voltage produced reaches 14.5 volts. The rectifier you mention may actually be both the AC to DC converter and a built in solid state regulator but probably more like just the regulator with a big heat sink
It sounds like you are missing one of several things in your system.  If the permanent magnets housed in the flywheel are weak or dead there won't be any electricity produced when the magnets are passed by the field coils. If the diodes housed in the coil body are burnt or otherwise out of service the voltage produced won't be converted from AC to DC and returned to the battery. The manual is correct in suggesting you don't run the bike without the battery in place as it completes the circuit necessary for the package to function.

It sounds like starting with the stator to make sure there are no breaks in the windings then checking the strength of the magnets on the flywheel then checking the diode board to ensure they aren't burnt should cover most of the issues found. The diode checks will need to know the values and if the diodes are exposed they should be written right on the case.

See if that gets you any closer to Nirvana.
There are several shops in town (One on Massey comes to mind) that can test your equipment for you.
Good Luck!

[Hans]

One would think, but I have the wiring diagram for the bike and the schematic from the service manual, and I don't see it unless they've conveniently skipped a step.  There is also a somewhat ominous warming about 400v blowing through the system.

[Dennis]

I swiped this off the Web.  I see that this diagram identifies what should be a regulator/rectifier as only "rectifier." 



I bit of googling found this interesting post.  If you scroll down, the writer says that 1981 did not have a regulator.  Later models had a resistor.  Hmm.

http://www.aircooledrdclub.com/smf/index.php?topic=27776.25;wap2

A similar question has been asked on the Web regarding outboard motors.  Short answer, small engines with batteries do come without a regulator.

http://www.ybw.com/forums/archive/index.php/t-285843.html

Back to Yamahas, and the reference to later model Yamahas having a resistor.  This is what they look like:



Peace, Amps & Ohms, Dennis

[Theo]

Ok, next electrical conundrum.

My little '71 Yamaha AS3 has electrical issues.  Following through the electrics, I see that there is no voltage regulation.  There is a rectifier, but that is all it does... AC to DC.  The manual says do not attempt to run the bike without a battery because up to 400V from the Alternator may course through the system and fry stuff.  Does this sound right for a bike of this simplicity and vintage.  Is the battery providing the voltage regulation? Ideas?

Not having a voltage regulator is unusual and I admit I have not before encountered such a system. However, I suppose if the generator output is quite carefully balanced to meet the needs of the simple electrical circuit of this bike (lights and ignition), then it could function satisfactorily.   The battery may be able to absorb the small amount of excess current generated without harm thus providing some degree of "regulation".

I guess my question is: What electrical issues do you have?  Clearly, a battery must be used to power the ignition system.  The charging system is single phase AC so that means 4 diodes in the rectifier (full wave rectification; easily tested but, use the diode test function on your multimeter - not the ohmmeter), and the rest of the charging system should be diagnosable by simple inspection with a multimeter.

But back to my question - what is the problem?

Ted

[Hans]

Seems like it is not charging well...

Symptoms have me perplexed. 

New fully charged battery.

Headlight DIM on battery only, engine off.  Better when engine on.  Brakelight bright.
Turnsignals won't blink unless substantial RPM's are on.
Go for a half hour ride with the headlight on, it starts to sputter and die out
Ride some more with headlight off it picks up again.

[Hans]

more info.....

headlight actually not much brighter with rpm's.  Checked with voltmeter, volts go up from 12 to 12.6 across the battery.  Multimeter not sturdy enough to check amps.
turn signals need 4000 rpm to blink.
checked the rectifier.  It has continuity in the right directions, but lots of ohms. Actually doesn't make my $10 Crappy Tire multimeter go beep.  Shows 600 ohms through each diode.
Engine drops 100rpm a idle when I turn the headlight on.

[Theo]

Couple of thoughts:
1. your circuit info mentions the rectifier grounding at the "shaft".  Without seeing the actual part, I am guessing the shaft might be the mounting bolt for the rectifier assembly.  Inspect it for any corrosion/rust/tightness.  Then test for voltage drop across it's connections - this might be a little tricky - I could help if you have trouble.
2. The circuit diagram also seems to show that the headlight portion of the generator is switched in and out to supply power for the headlight.  Those windings appear to add current capacity to the main stator winding to help supply power for the whole bike.  If the switching mechanism has failed, that may explain why the battery runs down with the headlamp on.  Check the integrity of the switch module connecting those yellow and green wires.

It's not easy to follow the diagrams.  Maybe it's my aging eyes, but they don't seem entirely consistent with each other on a couple of points.

Maybe you need a shop night.  We could negotiate an evening - I don't drink much beer.  ...and I have multimeters with plenty of current reading capacity.

Ted

[Hans]

Thanks Ted, I'll probably need to take you up on that.  Yes, the ground of the rectifier is the mount (shaft).  I have good continuity through that to the frame.  I am going to look at one more thing, I may have replaced the bulb with a 55/65 watt bulb instead of the asked for 35watt at some point.

[Theo]

That could be enough to account for what you're experiencing.
Keep us posted.
T.

[Kaw-meister]

It seems that your bike has a factory setup of rectifier and resistor, does this mean that you could not bring it into the new millennium by converting it to a regulator style charging system...only because you want to ride it.

[Theo]

That seems like a good idea, Paul, and shouldn't be hard to do.  It crossed my mind also - I suppose it depends if you want to keep it pure original or not.

The question of the headlamp bulb would still need to be resolved as, regulator or not, the generator doesn't seem to produce enough to run the lighting system and keep the battery charged.

T.

[Hans]

so, I'm pretty convinced that the main issue is 2 fold.  The bulb is too high of a wattage, so I need to find a 35watt bulb.  Also, with the engine off there is 12.4 volts at the battery and 10.8 at the headlight.  With the engine running and revved up, got over 12 volts at the headlight.  It think the loss is at the headlight switch.  I took it partially apart and poked around with my multimeter and got 11.8 on one side of the switch and 10.8 on the other.  So, I'll give that a good cleaning.  Hopefully with these 2 things I'll have a charging system that charges with the headlight on.  Also replace the turn signal flasher with a new universal one.  Turn signals work all the time now.

[Dennis]

Turn signals work all the time now.

I hate when that happens.  I only want my turn signal to work when I'm turning.