voltage regulator query

I am asking for help in getting educated in voltage regulators for small gas engines. Here, I'm speaking of the kind that have a starter unit separate from the alternator.

I'm getting all sorts of mixed signals as to what will or won't work with my

17hp garden tractor.

My dealer wants $100 for a new one, and I'm reasonably sure I can get by with much less money out of pocket than that.

Ebay has maybe 20 pages of voltage regulators.

My contention is:

  1. HP---engines or roughly the same hp should have charging systems scaled accordingly. Is this more or less true?

  1. That a 12v regulator is a 12v regulator, is a 12v regulator, as this refers to output dc voltage.

  2. That the size (amp rating) of voltage regulator matters only insofar as your need to provide a given max charge rate to the battery---i.e., we can use a bigger of smaller regulator than the system design/spec rate, and all it does, if the one we choose to use is smaller, is restrict the rate the battery will charge up.

I think I could use just about any of these that match up roughly to the amp rating I need, the 12v rating, single phase alternator (most small engine garden tractor ones are single phase), and 3 wires out of the voltage regulator.

I understand the 3 wire thing is standard for simple circuits. Two leads go to the alternator ac output, and one goes to the battery.

If the case isn't grounded, then a 4th wire is needed for a ground.

So, my garden tractor is specified to have a 20 amp system. Any reason that just about any 3 wire, 20 amp, 12v alternator wouldn't work with my engine?

So, there are my perceptions and ignorance. Now, please set me straight.

Reply to
RB
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On Fri, 25 Mar 2005 11:44:03 -0600, "RB" put finger to keyboard and composed:

I would offer advice, as I've actually built regulators for mining equipment, but I've never seen an alternator that had an AC output. All have had internal rectifier diodes (which would be cooled by the alternator's fan). Does your regulator provide the rectification?

The alternator may have a floating field, a grounded field, or a field that is tied high. You will need a different type of regulator for each configuration.

Do you have a wiring diagram for the tractor?

- Franc Zabkar

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Reply to
Franc Zabkar

amp

Are you sure? Most auto ones are 3 phase. Anyway, even an old auto one could be cobbled to work. It's a matter of physical fit mainly.

N
Reply to
NSM

engine

could

He's right, most small engine alternators are single phase, they're nothing but a coil mounted near the flywheel to get their energy from the magneto magnet.

Reply to
James Sweet

nothing

OK. I've seen those as a sort of magneto. Do they have a diode rectifier?

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N
Reply to
NSM

}}} but I've never seen an alternator that had an AC output. All have had internal rectifier diodes (which would be cooled by the alternator's fan). Does your regulator provide the rectification? {{{

Right you are. Most of the bigger ones (cars & trucks, etc), have DC output. And yes, they have internal recifier networks.

The small gas engine ones use a simple one that brings AC out. The voltage regulator unit is actually dual function. It has a rectifier network, and then, somehow, purports to regulate. I think the regulation is mostly a figment of someone's imagination, as there doesn' seem to be anything in most of 'em except a resistor or two. Anyway, it does purport to regulate the recitified DC it produces.

}}} they're nothing but a coil mounted near the flywheel to get their energy from the magneto magnet. {{{

This is close to the truth, but still misleading. The magneto he speaks of is simply a ring of magnets glued around in a ring on the face of the flywheel which rotates past a stator coil to get ac. When we say magneto, we normally are thinking of the thing that helps make the spark for firing. This alternator is a form of magneto, but is different not the normal ignition magneto.

Reply to
RB

On Sun, 27 Mar 2005 12:57:50 -0600, "RB" put finger to keyboard and composed:

I could imagine a regulator consisting of two pulse width modulated SCRs with some minor support components. The switching noise wouldn't be that serious in a tractor.

- Franc Zabkar

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Reply to
Franc Zabkar

{{{

DC

voltage

network, and

mostly a

anything in

regulate

magneto

speaks of

the

magneto,

firing.

normal

I am wondering if you have a john deere 317 mower tractor? these came out with a kohler 2 cylinder air-cooled engine or a 2 cyl onan air-cooled. either engine has approx. 12 charging coils mounted stationary inside the flywheel and output alternating current at approx. 13-14.5 volts. this ac voltage brought out via 2 wires to a connector plug which goes to the rectifier ( voltage regulator ). the (vr) has 3 wires -2 ac in & 1 dc out. this goes to a plug which carries an ignition, lights, electric p. t. o. clutch (some models) & the charging voltage back to the instrument panel. check all plug connectors ( at vr , main harness &the plug coming out of the flywheel area.) if the engine is a kohler, the part # from john deere is AM

106357 which is $42. good luck. Jim
Reply to
Jim

The ones I've seen use the same magnets used for the ignition magneto, the coil is just mounted in a different location around the circumference. That's certainly not to say other types aren't in use, most of the small engines I've worked on didn't have any sort of charging system at all so I don't have a lot of experiene there.

Reply to
James Sweet

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