Howdy Tim,

Yes, that information is missing from the site, as it's a somewhat
unusual approach that I took for my air compressor.
My alternators deliver about 70V when operating into an open circuit.
The 60V DC compressor motor was fed directly from this source, through
a Mosfet switching circuit.
You shouldn't try to use a relay for this, as the high DC voltage will
create an arc when the relay opens. Destruction of the relay will take
about 3 seconds, once the arc begins!

To get around this problem, you could drive your alternator's exciter
circuit via the compressor's pressure switch. When the pressure reaches
the 'cutoff' point, the exciter is also cut off.
This will let the alternator drive the compressor safely, and
automatically.

You could have a manual switch in the system to select between the
compressor and the welding loads. That way, they don't interfere with
each other.
The same switch would also select between drive sources for the
exciter, to maintain control over the alternator.

As you have a reasonably big engine, you might like to opt for 2
alternators instead of just one.
One can be used to maintain the battery and run the compressor, while
the other supplies the welding current.
The compressor driver can be a relatively modest alternator of some 30
to 40 Amps rating.

Though the DC from the alternator will happily run most power tools and
lights, you do run the risk of destroying the tools. The motors are
generally happy to run on DC, as they are usually compound wound -
brush types. On the other hand, the tool's trigger switch can be a
problem.
When you release the power tool's switch, an arc can occur. This will
rapidly cook the switche's contacts.
The way around this, is to have a separate control for the alternator's
exciter.
You'd cut the exciter current a moment before you turn off the tool.
This permits perfect control of the power source, while eliminating the
risk of switch failure.

A word of caution - DC at 110V is dangerous. Much more so than AC of
the same voltage.
Contact is likely to be lethal, so please take the greatest of care
with this power source.

Talking of voltage regulation, this may be accomplished in one of two
ways:
1) Varying the DC 12V current to the exciter,
2) Varying the engine's speed.

The best method is to keep the engine speed constant and vary the DC
feed to the exciter.
You can use electronic means for this, or you may elect to use a
rheostat.
The rheostat will need to have a power rating of about 60watts - and a
resistance range of 0 to about 40 Ohms.
This needs to be wired in series with the exciter, between Battery
positive and exciter positive. Battery negative and Exciter negative
are then connected through the machine frame.
A 10 amp switch will be needed also, so you can turn off the exciter
when selecting loads, or when you are not using the machine.

There are more complex ways of doing all of this. Mine is controlled by
a home made computer that manages all of the electrical transactions
that occur during operation.
Before implementing this approach, I killed two car batteries by
accidentally leaving the exciters on.
It's ok though, I gave the batteries a proper Christian burial ;) .

To sum it all up, I would suggest that you put 2 alternators on the
machine. 1 at 140A and 1 at about 40A. The 40A one will supply high DC
volts for appliance loads - as well as battery charging current via a
switchable regulator. The 140A one will supply lower voltages for
welding loads. Naturally, you could add a third one, for battery
charging, while the other 2 are dedicated to their separate tasks.
Hmmm, it's getting complicated, but you'll find that it's worth the
effort :) .


I hope this has been helpful. There are lots of related points to
cover, but I think you are already going in the right direction.
Please do feel free to set up a picture / file folder to show us how
you are getting along with this great project.



Best wishes,
Steve McAmptramp.



--- In Amptramp@yahoogroups.com, "timowens3k" <timowens3k@...> wrote:
>
> I have been thinking about my 12 hp craftsman motor. I think I know
> where I can get a 140 amp alternator. I may be able to scrounge up a
> York air condition compressor. I was planning on wiring up a couple of
> 110 volt receptacles to run a few power tools and lights. I looked
> through the Files and photos section and maybe I missed it somewhere.
> Your air compressor is ran by a 60 volt dc motor. Did you just plug
> this into a receptacle that comes off the Amptramp? I am wanting to do
> something like that with mine. I have a small 20 gallon air tank that
> would be mounted with the dc motor and compressor. I would not need
> the air all the time. Could you give me a brief description of how you
> wired the motor into the Amptramp? Or would it be (for my purpose)
> just as simple as plugging the dc motor into one of my receptacles.
> Forgive me if I missed this information. I hope this all makes
> sense...
>