Colin,
I'm really confused. If you already know so much about alternators, why ask
your question to the group in the first place? Glenn has expressed very
valid concerns when equiping an engine with an alternator. It appears that
you have out engineered yourself. If you need to spin your alternator 8k rpm
to get it to perform, you have clearly chosen the wrong alternator. Go out
and buy a proper large magnet Leese-Neville industrial grade alternator and
spin the thing acording to OEM instructions. Problem solved.
Steve

"CS" wrote in message
ups.com...

Glenn Ashmore wrote:

Look at the LN curve I've posted - it is not as stated above. Full
output is at 5000 alt rpm and it then levels out.

That is what I meant about "OP's choice of alternators may not be the
best
". That particular alternator has a relatively slow slope up to full
power.

My engine can deliver up to 20kW at engine idle according to the makers
engine manual - more than enough for the 2 - 3 kW taken by the
alternator. Torque will also not be an issue with dual belts.

Off which end? My Yanmar can handle a lot of torque off the back end but
the front crankshaft bearings are not designed to handle a lot of side
load.
Double belts will stop the slippage but a double pulley extends the
center
of load further from the bearing increasing the leverage of the side
load.

Off the front crankshaft and or a PTO shaft. The engine is an 8 litre
6 cyl natural aspirated 160 Hp engine which weights 1000kg and is a
proper industrial marine engine as used by fishing vessels - not a
bleeding micky mouse Yanmar engine designed for pleasure yachts. I
have done a certain amount of research and I am amazed by the complete
rubbish being spouted about alternators.