Reply To: Pulley calculation un relable websites and actual speeds

[BikepeteParticipant @bikepete]

Ah – if the inverter shows 50 Hz not 50 %, then I think I know what's going on.

50 Hz is 100% of normal mains frequency, so it will turn a two pole motor at around 2820 rpm like it says on the motor nameplate. Which with a 1:7 pulley reduction would give 403 rpm.

So when you had the inverter set at 100 Hz, thinking it was 100% of 'normal speed', your motor was actually whizzing round at approx twice normal speed i.e. 5640 rpm! Giving you the 800ish rpm output, after the 1:7 reduction.

That is quite possibly dangerously fast for a standard motor. Might be an idea to look at configuring your inverter so it can't go above say 60 Hz.

Perhaps someone else can double check my workings, though. I'm no longer quite sure what you measured – any chance you could specify when you quote rpm figures as above whether they are at the motor (i.e. input) or at the output (i.e. the output shaft after the pulley reduction)? And can you confirm if your inverter figures are Hz or percent?

Edit again – if the inverter shows 442 rpm (i.e. motor shaft input), and you are getting 800 rpm output after your gearing, then your pulleys are stepping up the speed 2:1! This is very strange if the pulley sizes are 1 inch and 7 inches. And what I wrote above is probably not the case.

Don't suppose you could post a picture of the set-up in case that clarifies anything? 

Edited By Bikepete on 30/08/2017 19:07:24

Edited By Bikepete on 30/08/2017 19:23:16

Edited By Bikepete on 30/08/2017 19:30:26