On 28/06/2020 20:15, David wrote:
On Sun, 28 Jun 2020 19:36:10 +0100, nothanks wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...ble-Fan-Speed-
Controller-Hydroponics/252403438896
work?

I used S&P units - not cheap but they are fan manufacturers.


Cheers


Dave R


Are they VFDs, phase controllers or ???? (Google hasn't been helpful)