Compressor Help

Honest John Back Room » Motoring discussion
View Threaded
Sun 23 Apr 2006 19:56
Compressor Help - thomp1983
Hi the motor on my air compressor has given up the ghost, it is a single phase 0.75bhp 1750rpm motor, i have been offered a single phase 0.5bhp 2850 motor, i know i can gear down the rpm through using different size pulleys, my question is will using a underpowered motor just mean that it will take longer to fill the receiver or is there something else involved? it has a 200ltr receiver so i don't think it's going to run out on me during use just take longer to fill

cheers
chris
Reply | Report as offensive | Link
Mon 24 Apr 2006 00:21
Compressor Help - martint123
I've fixed two compressors in the last year by replacing the capacitor. They seem to get hot and fail. The ratings of them seem similar for similar sized motors and I proved the first compressor one failed by teporarily using one from the pressure washer motor.

Warning. Don't play if you don't know your electrons.

Martin
Reply | Report as offensive | Link
Mon 24 Apr 2006 08:44
Compressor Help - L'escargot
Gearing down from 2850 RPM to 1750 RPM will reduce the torque capability at the compressor proportionally, i.e. it will reduce it to 61% of the motor's capability. So the maximum pressure capability of the compressor will be reduced. On top of that it's only 0.5 hp compared to the original 0.75 hp. So you lose two ways. My guess is the the 0.5 hp motor won't generate as high a pressure. It may not even reach the governor pressure. It may just stall. Without knowing the power/torque characteristics of the motor and compressor it's impossible to be specific.
--
L\'escargot.
Reply | Report as offensive | Link
Mon 24 Apr 2006 09:21
Compressor Help - IanJohnson
Doesn't gearing down increase the torque output?

Power = torque x speed ?

Would agree that you need to check that the motor could reach the governor pressure - if it can it will take longer

With the smaller motor can it produce compressed air at the right pressure at the same rate as you use it? Lower power would indicate delivery rate of 2/3 of the old motor.
Reply | Report as offensive | Link
Mon 24 Apr 2006 10:28
Compressor Help - L'escargot
Doesn't gearing down increase the torque output?


Oops, my mistake.
--
L\'escargot.
Reply | Report as offensive | Link
Mon 24 Apr 2006 10:30
Compressor Help - Peter D
The motor may well stall or at least get very hot before the max pressure switch is satisfied gearing down will help but mat still not be man enaough for the job. I am surprised that it only had a .75 hp motor. Machine mart have some decent replacement motors. Regards Peter
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide