Hi Tim,

Roylowenthal is quite right in stating that your engine will happily
run this alternator.
If you plan to use it for welding, the alternator will take
appreciably more than its normal horse power.
This is because you'll have some 22V to 30V at the arc point, at
nearly 100 Amps.
You can then expect the alternator to take something like 3000W to
4000W of shaft power.

Your 12HP engine ought to be able to deliver 12*746 = 8942 Watts.
So you should find that your engine can spin the fully loaded
alternator quite nicely :) .

Here's hoping you'll be able to share some pics of your new machine
with us.

Best wishes,
Steve McAmptramp.

--- In Amptramp@yahoogroup s.com, "roylowenthal" <roylowenthal@ ...>
wrote:
>
> The basic unit conversion is 746 watts/horsepower.
>
> 100 amps @ 12 v = 1200 watts (actually, 15 v is more realistic, so
> 1500 watts)
>
> 1500 watts / 746 watts/hp = 2 hp
>
> Allowing for real world inefficiency, you've got plenty of engine
for
> a bigger alternator or for the engine to be loafing while it runs a
> 100 amp one.
>
> Roy
>
> --- In Amptramp@yahoogroup s.com, "timowens3k" <timowens3k@ > wrote:
> >
> > Good day all. This is my first real post and I hope I am not being
> > redundant on this question. I have an extra riding lawn mower
with a
> > 12hp vertical shaft motor. I am thinking about picking up a 100
amp
> > alternator at the local pull-a-part. Would this be to big for the
> > engine? If so, what size would you recommend?
> >
>