Ive been reading more about IMAG stuff, as i spotted a motor in a barn arround here, and the owner told me that it had been sitting there for four years, and, when he got arround to it, he was going to scrap it....
Anyhow, its a 5hp, 3ph Brook motor.
Ive read that anything over about 3kw is generally Delta rather than Star config, so only easily configured to 3ph generation.
Which is fine for me, as ill be wanting to rectify to DC for feed to a grid tied inverter (and the ripple from 3ph will be much less than 1ph)
...but
my inverter (SMA 2500) can be configured to present different loads at different input voltages, to give a exponential response suitable for a wind turbine
...anyhow, this 'feature' can also be used with an engine driving the generator, so that the rpm of the engine can be varied also - so at lower rpms, the voltage from the generator will fall, and the inverter will present less load, and, hence, the engine will not stall etc.
so that's all well and good so far, and this is completely achievable, as Dick Jotec has been proving for some time now.
...however
Dick has a permenant magnet alternator, which, of course, does not require excitation.
Im trying to do the same, on the cheap, with an old motor, that will require excitation before it starts to generate.
(remember, as the output is recitified to DC and then fed to an inverter, there will be no current to sync to)
So, this is where im unsure, and would like someone with better knowledge than me to clarify -
Say, if i configure the gearing of the induction motor to run at
- rpm, if i drop the rpm by, say 37%, will i still be able to get the motor to excite, and generate? And what will likly happen to voltage?
And then if i raise it by 37%, what then?
The engine that i have will run at about 300 - 650rpm, so, what im thinking of doing is setting up the gearing at, say, 475rpm, and then running at between 300 and 650rpm (hence the 37% margin either way)
Thanks, Julian
