Soft starter for reciprocating air compressor
Soft starter for reciprocating air compressor
(OP)
Can it be possible to have a soft starter on reciprocating compressor having 15 hp motor?
The control of the compressor motor is on pressure switch.
The control of the compressor motor is on pressure switch.





RE: Soft starter for reciprocating air compressor
You need to make sure it's protected from ever short cycling.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Soft starter for reciprocating air compressor
I'm curious though as to why you would question it? Did someone tell you that it couldn't work?
RE: Soft starter for reciprocating air compressor
13 Loadless starting
Positive acting, governor-type centrifugal unloader assures longer motor life by allowing the compressor to start unloaded every time.
RE: Soft starter for reciprocating air compressor
I know the smoke comes pouring out of our compressor within about 3/4 second if we try to start it unloaded.
I bet gkarsandas has a compressor that is dimming the lights every start and is trying to mitigate that.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Soft starter for reciprocating air compressor
Yes compressor motor has to starts at low set point pressure.
Seeking your advice.
RE: Soft starter for reciprocating air compressor
Easily the biggest killer of compressors, the world over, is a failed unloader. The small innocuous device will allow connecting rods to bend and break, crankshafts to snap, motors to smoke, contactors to remove themselves from walls, and production to stop.
With a properly working unloader, starting a compressor motor is nearly trivial. The motor only has to spin up the flywheel inertia. With a malfunctioning unloader... Most compressors remain stalled until something lets go.
It sounds to me like your unloader is not doing its job.
The SS starts its cycle but since the compressor is improperly loaded the motor can not even begin to shove the pistons into a cylinder already filled with pressurized air. So the the SS continues to ramp the power, (big humming), while the motor's torque builds thru the start cycle. At some point you get lucky and the piston is forced thru Top Dead Center,(TDC), the inertia built up after that TDC is enough to carry the system thru the next compression stroke and so the compressor continues to run.
Your unloader is bad. You must fix it. The very next humming start could easily be the last one that motor will ever manage.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Soft starter for reciprocating air compressor
On the other hand, if the load has a very high break-away torque or has very high torque on the first compression stroke (as in a compressor without unloading), that high torque sets the softness of the start. So, for example, if the motor requires all its overload torque just to get past that first compression stroke, you can buy a softstarter but you won't be doing any softstarting. You will have to set the softstarter for full starting torque and immediate ramp up to speed. That would be the same as an ordinary magnetic starter and a good example of how to waste money!
RE: Soft starter for reciprocating air compressor
So, in a nutshell, it's a fairly useless soft-starter that gives other good soft-starters that do control all 3 phases a bad name.
If you properly install (proper programming is necessary too) a good soft-starter that motor will start as smooth as smooth.
RE: Soft starter for reciprocating air compressor
The compressors sounds as if it has stalled. If it has an unloader it needs to be fixed. If it doesn't I wouldn't use a soft-start.
I start some reciprocating pumps without an unloader and don't have any trouble
RE: Soft starter for reciprocating air compressor
By the way don't keep starting it this way, it's highly unlikely that those bypass contacts are rated for DOL starting.
RE: Soft starter for reciprocating air compressor
OK, if it struggles for about 1/3 rotation or so and then blasts up to full speed it is the unloader. gkarsandas's description of the start basically said the motor made a huge noise for a few seconds and then starts so maybe gkarsandas can describe the start a little better. The 2-phase controller noise isn't real nice and saying it then starts doesn't at all describe how, ie full voltage, nice ramp, struggles for the first compression stroke.
The easiest way to check the unloader is to turn off the power and try rotating the pump by hand. The unloader will allow it to rotate pretty easily.
RE: Soft starter for reciprocating air compressor
Mike Halloran
Pembroke Pines, FL, USA