On Thu, 21 Mar 2019 11:35:14 +0000
T i m wrote:

I'm pretty sure it's a very basic unit and so likely (then?) only a
very simple alternator with some basic voltage regulation?

I get that (therefore) it wouldn't put out as much (electrical) power
at low revs but I wasn't really interested in that at the time, just
that it could tickover before being used to do something real (like
charge a car battery as a form of boost charger).

If it's a simple alternator it has to run at 3000 RPM to produce 50 Hz
output - no reason for it to run at any other speed. It's not smart
smart enough to idle until something starts drawing current, although
there may be a manual switch to do that.