'75 Suzuki A100 Electrical

Discussion in '2 smokers' started by MotoActionADV, Mar 14, 2015.

  1. MotoActionADV

    MotoActionADV Level 16 wizard

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    Hey guys,

    Trying to get my 1975 A100 sorted before taking it for its inspection. All seems well except for the electrical side of things. The headlight is very very dim only when the engine is running and off when the engine is off.

    From what I can tell from the wiring schematic of an earlier model (http://smokeriders.com/diagrams/Suzuki/Singles/A-100A_dis.gif) there are 3 coils: one provides current for the spark plug, one goes through a rectifier (and presumably the rectifier has some sort of regulator built in) to charge the battery, do the signal lights and do the instrument lights, and the final coil powers the headlight (and has a regulator).

    Well, I took the regulator out to look at (and forgot I had taken it out) and started the bike. The headlight lit up fully! This makes me believe that the regulator is busted. At this point I had not found the schematic yet and I assumed that the regulator was a simple zener shunt across the headlight, so I ordered a new 50W 6.2V zener (still not here). That was me making the assumption that the regulator came after a rectifier. Now looking at the diagram, it seems like the headlights must be A/C since I see nowhere where the current is rectified before going to the headlight (the rectifier is on the other circuit) This would imply that the regulator must be an A/C voltage regulator instead of a simple zener (perhaps it is 2 zeners in series but facing different directions - it still just must be a shunt to ground though as there are only 2 wires and 1 goes to ground).

    Is anyone familiar with this system who might have some ideas? I'm not entirely familiar with how the magneto works - will running the bike without the regulator burn out the headlight and if so does anyone know what is actually in that regulator? I saw a schematic for the similar ax100 here: http://www.cmelectronica.com.ar/wiring-diagram/imagenes/suzuki-ax100.jpg and it has no regulator - but the current for the headlight seems to come from the half point of the coil which I suppose would make it less.

    Thanks!
    #1
  2. Beezer

    Beezer Long timer Supporter

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    looks like the headlight is on the regulator, but not rectified (so its AC). I'm looking at the Green wire that comes off hi/lo switch & goes into a connector with 2 other wires... one to the regulator, the other to the coil. the regulator is simply grounding out whatever is over system voltage. might be just a Zener diode... it might be something else. funny thing about a zener is that it is still a diode... it blocks current in one direction, but it passes current freely in the other at any voltage over biasing (about 0.7v). hooked in parallel like that in an AC system, half of what the generator makes goes straight to ground. the other half is whats lighting the light.

    there are ways to make it more efficient but you have to get into the coils. I've done it on my old bikes long ago.

    yes, the other diagram shows a different lighting coil. many of the old enduro 2x bikes did not regulate the headlight because AC has a self regulating tendency as RPM increases. running without the regulator will shorten the life of the light for sure.... can't say how much. maybe one ride.

    did you check the old regulator? see if it tests like a diode

    the magneto is an independent system & doesn't care about any of the lighting.
    #2
  3. Beezer

    Beezer Long timer Supporter

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    just had another thought.... since the headlight is on it's own coil all alone, you could insert a rectifier and make it DC pretty easy. the AC input to the rectifier would be the green wire and the frame. the DC out would go to the Hi/Lo switch and the 3rd pin of the socket for the bulb. so, remove the "ground" from the socket & insulate it to the rectifier. then ya got full wave DC. put the zener across the output to regulate

    10 amp rectifier.....

    http://www.mouser.com/Semiconductor...tifiers/Bridge-Rectifiers/_/N-ax1mf?P=1z0wapt

    edit: 'doh... I meant rectifier.... I changed it
    #3
  4. MotoActionADV

    MotoActionADV Level 16 wizard

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    Ok, that makes sense. So what I have now (once I replace the regulator) essentially is a regulator that is regulating my output between -0.7V and approximately the zener voltage.

    I like your idea of using a rectifier to make this more efficient.
    #4
  5. MotoActionADV

    MotoActionADV Level 16 wizard

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    Bought a Haynes Manual and it contains yet another wiring diagram for the '75 A100. Very interestingly, it doesn't include a regulator for the headlight circuit - but it does specify which coil to run the headlight off of.

    The Haynes manual is from the UK though and my bike is Canadian so I suspect that is where the difference comes in. Canadian model also only has off/on ignition positions instead off/day/night. I think the reason there is even a difference is that at that time daylight running lights were mandatory in Canada and not in the UK (so essentially, the Canadian bike is in night mode all the time)


    Haynes A100M Diagram: https://drive.google.com/file/d/0B6unED4Kz3KmZEFvS1Q3d0Y0TUE/view?usp=sharing
    #5