How can I know if an alternator is more than single phase just by examining
it? Some of the small gas engine ones, like those on lawn and garden
tractors, are single phase. Others on twin motorcycle engines are 3 phase.
What do I look for to tell?

Howdy RB......Typical 3 phase automotive (and many other) alternators
will have 3 leads for output - the 3 resulting combinations of pairs are
each of the 3 phases outputting power. Looking closer at the winding to
lead connections you may see that each winding has a single wire
connecting to the output lead and that somewhere in the bundle you may
also see a 3 lead connection with or without a 4th lead attached - this
will indicate a typical 3 phase WYE connection......should you see 2
winding wires connection to each of the 3 output leads but no other
connection, this would typically indicate a 3 phase DELTA connection.
Each has it's own characteristics requiring more or less windings to
achieve whatever design voltage/current capacity is required. A further
or additional giveaway will be in the rectifier bridge associated with
what you're asking about.....3 phase alternators will typically have at
least 6 diodes and a typical rectifier will use 5 connections 3 for the
AC phases, 1 DC output and the ground connection whereas a single phase
winding (typically a single winding only with 2 leads) may have as
little as 1 diode (halfwave) or as much as 4 diodes in a bridge (this
may just look like a block with 4 terminals on it).

Hope this is a little clearer than mud to ya

Gord

It makes sense. Thanks, Gord.

Am I likely to run across any phase designs other than single and 3 phase
with small engine alternators?

I would think it would be incrementally more expensive to go up in phase
design. What is gained by going to a 3 phase over a single phase
alternator?

RB wrote:
....
I would think it would be incrementally more expensive to go up in phase
design. What is gained by going to a 3 phase over a single phase
alternator?

Polyphase (more than one phase) benefits:

* Smoother DC when rectified. (The more phases, the smoother it gets.)
* 3 phase (and greater) creates own rotating magnetic field in a motor -
does not require start/run caps, etc.
* Deliver same power with lower voltage and smaller conductors than
single phase.

Probably others I've forgotten in the many years since college...

Cheers

--
Matthew Smith
South Australia

In article ,
RB wrote:
How can I know if an alternator is more than single phase just by
examining it? Some of the small gas engine ones, like those on lawn and
garden tractors, are single phase. Others on twin motorcycle engines
are 3 phase. What do I look for to tell?

Certainly on a car type, which is three phase, the connections to the
rectifier pack are easily exposed and counted.

I'd have thought a single phase one rather inefficient for battery
charging purposes - although perhaps ok for direct lighting, etc.

--
*What was the best thing before sliced bread?

Dave Plowman London SW
To e-mail, change noise into sound.

Thanks for all the info.

Where I ran head on into this recently was in trying to get an el cheapo
voltage regulator subsititute for a garden tractor I work on for our church.
The dealer wanted $120 for one, and I can buy a number used ones for approx
$20.

However, what I didn't know about was the fact that some of the motorcycle
and boat stuff is for 3 phase.

And, a 3 phase regulator definitely won't work with a single phase system.

Having finally been made aware of this, I wanted to get a leg up on the
problem to maybe be able to identify what I'm dealing with by sight, rather
than having to tediously go back to manufacturers of engines, regulators,
etc.

You guys have given me enough to probably be able to identify single or 3
phase alternators.

I still have only a partial grasp of how to look at any old regulator and
tell what it was made for.
On those, it may be the only way to find out is to ask the company who made
it, or know for sure what it came off of and ask them the phasing of their
alternator.

The single phase regulator I'm dealing with has six wires, but is for single
phase alt. Two of the wires go to the stator/alt, one to the battery, two
are sensing circuits for low oil pressure and low battery warning lights,
and there is a ground.

The first one I bought was an aftermarket regulator for a Harley, and it has
3 wires. Two to the alternator, and one to the battery. When it didn't
work, I started asking around, and found out many of the twin motorcyles use
3 phase alternators.

Aaah, "the rest of the story"! :^)

What you're seeing here really isn't related to whether it's a 1- or 3-phase alternator. At the most basic level, the
regulators for each type of alternator are the same, assuming the alternator in question produces a DC output. Regardless of
the number of phases, the basic function of the regulator is to sense the DC output voltage, and regulate current supply to
the rotor (armature) to keep the output voltage correct.

The differences between the two regulators you have are more related to 1) details (unrelated to # of phases) in how the
alternators are wired and 2) the fact that the one from the tractor apparently has functions usually not associated with
voltage regulators on small engines, namely the oil & battery warning lights.

Eric Law

"RB" wrote in message ...
Thanks for all the info.

Where I ran head on into this recently was in trying to get an el cheapo
voltage regulator subsititute for a garden tractor I work on for our church.
The dealer wanted $120 for one, and I can buy a number used ones for approx
$20.

However, what I didn't know about was the fact that some of the motorcycle
and boat stuff is for 3 phase.

And, a 3 phase regulator definitely won't work with a single phase system.

Having finally been made aware of this, I wanted to get a leg up on the
problem to maybe be able to identify what I'm dealing with by sight, rather
than having to tediously go back to manufacturers of engines, regulators,
etc.

You guys have given me enough to probably be able to identify single or 3
phase alternators.

I still have only a partial grasp of how to look at any old regulator and
tell what it was made for.
On those, it may be the only way to find out is to ask the company who made
it, or know for sure what it came off of and ask them the phasing of their
alternator.

The single phase regulator I'm dealing with has six wires, but is for single
phase alt. Two of the wires go to the stator/alt, one to the battery, two
are sensing circuits for low oil pressure and low battery warning lights,
and there is a ground.

The first one I bought was an aftermarket regulator for a Harley, and it has
3 wires. Two to the alternator, and one to the battery. When it didn't
work, I started asking around, and found out many of the twin motorcyles use
3 phase alternators.

Hadn't thought of that, but can accept that explanation. For sure the
garden tractor apps are different than the motorcycle and outboard engine
apps.

So why wouldn't the three wire motorcycle regulator work on our tractor when
I simply didn't connect the two warning light leads (left the two leads to
the alternator/stator, and one lead to the battery? Seems it should have,
if it didn't care whether it was looking into a single or 3 phase source????

Well the problem is there are a variety of ways to configure it, it's entirely up to the person(s) who designed the thing.

The stator configuration is not likely to vary very much - the output leads go to an array of diodes. One other lead from
the array is grounded (the negative output from the alternator) and the other lead is brought out as the positive output
terminal.

But the rotor/armature wiring can vary more. It can have only one terminal brought out, with the other connected either to
ground, the positive output from the diodes, or its own set of diodes (common in cars). Or, both terminals can be brought
out and connected to battery/ground/regulator.

Bottom line is you're not likely to get very far without obtaining (and understanding!) wiring diagrams both for the tractor
and the "donor vehicle".

Eric Law

"RB" wrote in message . ..
Hadn't thought of that, but can accept that explanation. For sure the
garden tractor apps are different than the motorcycle and outboard engine
apps.

So why wouldn't the three wire motorcycle regulator work on our tractor when
I simply didn't connect the two warning light leads (left the two leads to
the alternator/stator, and one lead to the battery? Seems it should have,
if it didn't care whether it was looking into a single or 3 phase source????

Thanks for the info. I've saved all on this discussion and am putting it in
my general noteboook on my mechanical stuff.

I haven't seen any different designs (discounting actual DC
generators).....yet