1200mm Rotor/Stator Air Gap

[adaml]

Dear All,
I had a go at building a Piggott 1200mm/4' machine - a learning process more than anything as usually play with motor conversions.  I have it all together and running.  Question is - I don't really understand air gaps.  I note in the booklet 1.5mm is stated.  Is this a standard gap to aim for?  If I open the gap I guess it will spin up better but performance will drop off.  If I close the gap too much then it could stall or suffer start up issues.  I realise it is a trade off.  I have seen 8.5A closed in 4.1m/s wind, 12V system obviously.  Re-reading the "instructions" max output is 20A, again realise this is in perfect conditions with spot on construction methods.
Any advice/suggestions would, as ever, be very welcome.

[Flux]

Air gap technically is the gap in the magnetic circuit. That machine is single rotor and what you are describing is mechanical clearance between rotor and stator. That gap is indeed a compromise

If you open the gap it will need to spin faster to reach cut in, so light wind performance may be compromised. With the gap at minimum, it won't compromise start up in any way, it will just reach cut in in lower wind speed. If your circuit resistance is very low you may stall the blades in higher winds and compromise high wind performance .

Unless you have very short and heavy cables i wouldn't expect much stalling on the 12v version . Try reducing the gap and see what happens, if it is worse try opening it, the gap will make a lot of difference.

With a small machine you are not doing too badly to see 8.5A. It will most likely do 20A in a high wind at 12v, depending on the furling, but don't expect this sort of output on normal days, it will take well over 30mph to get that sort of current and that won't happen often.

Any output over 10A under normal conditions is probably fairly good going for a 4ft machine.

Flux