We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember George
saying something like:

Thanks for that. It is 1500. rpm. But I am only going to try and use
this 65 Kva alternator because I have it. The only other one I have
is about 5Kva and not strong enough to drive the 3 main motors I have
in my workshop, currently a Herbert Lathe 5 or 7 1/2 HP . A Denbigh
Mill and a low HP pillar drill. I am also thinking of a big welding,
- plasma cutter set. Second hand 3 phase is cheaper as not so many
people have it.

Excellent idea, and one I'm pursuing, trying to find a big 3ph
alternator cheaply locally, as the carriage costs for such a thing are
horrendous. I too have noticed the dirt cheap prices of 3ph kit.


My worst load is the Herbert and I am still able to get it up to speed
if I wait a bit, on a cold morning, using a 3HP. 1 to 3 phase
converter. The sheer weight of the alternator rotating parts will
give a nice start-up capability. I am not all that concerned about
exact frequency stability. A pretty simple AVR will also suffice. In
the future I may use it to charge up inverter batteries for a combined
heat and power set up, running on bio-diesel. It will be neater to
directly couple it so I would prefer to run at 1500. It will go in an
insulated space and so not annoy neighbours, the water being plumbed
in to a hot water tank and central heating. Waste not, want not. I
shall only start it up when I need it.

What do you think?

The CHP setup is the way to go, for sure.

Regarding the engines, the P3 is only 2.3L, which in itself isn't a real
problem, as you won't be pulling out anywhere near the max capacity of
the alternator, but I can't find any figures for the P3 itself. I can
only guess at its output at 1500rpm from my looking into using a VW 2L
road diesel engine for the same purpose. At 1500rpm the VW engine is
producing 100Nm of torque, compared to its peak of 102Nm just 500rpm
higher - in this it's fairly characteristic of diesels, producing a lot
of low down grunt and rapidly running out of steam above that. The power
curve is disappointing for this purpose - at 1500rpm it's only producing
~15kW, rising to ~40kW @4800rpm.
This is why I mentioned the camshaft above - the same engine produced by
VW for stationary power has a different camshaft (indeed, as do all of
them) for plant applications, maximising the breathing for the steady
speed they will be doing.

Anyway, it's like comparing apples and oranges - the P3 is an ancient
design and will probably be less good than the VW, but it's a stationary
engine, so you might be in with a shout and who knows, it might produce
more power at 1500 rpm than the VW.

Regarding the direct coupling - don't fack about, go to a decent power
transmission stockist and tell them what you're up to and what they
recommend. There's a range of couplings you could use and a range of
prices too, but you need to get it right. Fecking dangerous if you
don't.