jemjack
Civil/Environmental
- Jul 25, 2011
- 17
I have a high pressure compressor for filling air cylinders for diving, and a little while ago I asked about 5 hp motors for it, and got many helpful replies from you , thanks very much. I did have a mental block, as when I read the blurb a bit more carefully I saw that it really only required a 4 hp motor. Sorry about that.
The compressor at startup runs very freely and in the past I was using it with a 3 hp motor which worked well but after 40 minutes or so the motor got very hot, so I had to stop it. As time went on the motor would cut out after less and less time until it would only run for 15 minutes which was not enough time to fill a bottle, and I felt that soon I would burn out the motor! I had it connected through a DOL and it was this that cut out, presumably because the amperage rose to high?
I have just bought a new 4hp motor 220 volts ( I live in Spain) single phase 3000 rpm, which is the required motor for this compressor. Also new DOL for it.
The compressor is supposed to run at 1300 rpm but my pulleys are letting it run at rather less, So to my reckoning it should not need 4 hp to drive it!
All connected up and when I press the green button it starts up and runs for about 5 seconds or so and blows the 25 amp fuse at the mains. By the sound of the motor, it is up to the speed that it will run at, i.e. it has stopped accelerating, but has not tripped out the centrifugal switch . This is the problem . which I would very much like some help on please.
The motor runs at 2900 rpm when it has nothing attached to it, the voltage is 215 volts and the centrifugal trips out with no problem.
When the compressor is attached to it by the belt and pulleys the motor runs up to 1950 rpm but the centrifugal switch does not trip out at this speed. The amperage is way off the scale of my meter which only reads up to 50 amps the voltage drops to 180 volts. and the compressor is running at 725 rpm. The pulley ratio is 1: 2.76 I realize that this is so because the started windings are still in circuit.
So it would seem to me that
1 the motor is not producing 4 hp or
2 the centrifugal switch should trip out , then the voltage would rise, and the currant would drop to somewhere around 20 amps. and the motor would produce more power, and accelerate to somewhere near 2800 rpm
3 Or am I missing something here.
I have no way of having 3 phase, the cables from motor to meter are heavy duty about 6 mm so there should be no volt drop in them at 20 amps or so. The start windings have a 400 µf condenser and the windings have a resistance of about .7? and the running windings have a 60 µf condenser and the windings are about 1.9 ?.
Any help or advice would be very gratefully received,
Best wishes
Jemjack
The compressor at startup runs very freely and in the past I was using it with a 3 hp motor which worked well but after 40 minutes or so the motor got very hot, so I had to stop it. As time went on the motor would cut out after less and less time until it would only run for 15 minutes which was not enough time to fill a bottle, and I felt that soon I would burn out the motor! I had it connected through a DOL and it was this that cut out, presumably because the amperage rose to high?
I have just bought a new 4hp motor 220 volts ( I live in Spain) single phase 3000 rpm, which is the required motor for this compressor. Also new DOL for it.
The compressor is supposed to run at 1300 rpm but my pulleys are letting it run at rather less, So to my reckoning it should not need 4 hp to drive it!
All connected up and when I press the green button it starts up and runs for about 5 seconds or so and blows the 25 amp fuse at the mains. By the sound of the motor, it is up to the speed that it will run at, i.e. it has stopped accelerating, but has not tripped out the centrifugal switch . This is the problem . which I would very much like some help on please.
The motor runs at 2900 rpm when it has nothing attached to it, the voltage is 215 volts and the centrifugal trips out with no problem.
When the compressor is attached to it by the belt and pulleys the motor runs up to 1950 rpm but the centrifugal switch does not trip out at this speed. The amperage is way off the scale of my meter which only reads up to 50 amps the voltage drops to 180 volts. and the compressor is running at 725 rpm. The pulley ratio is 1: 2.76 I realize that this is so because the started windings are still in circuit.
So it would seem to me that
1 the motor is not producing 4 hp or
2 the centrifugal switch should trip out , then the voltage would rise, and the currant would drop to somewhere around 20 amps. and the motor would produce more power, and accelerate to somewhere near 2800 rpm
3 Or am I missing something here.
I have no way of having 3 phase, the cables from motor to meter are heavy duty about 6 mm so there should be no volt drop in them at 20 amps or so. The start windings have a 400 µf condenser and the windings have a resistance of about .7? and the running windings have a 60 µf condenser and the windings are about 1.9 ?.
Any help or advice would be very gratefully received,
Best wishes
Jemjack