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motor starter #182578 12/03/08 12:26 AM
Joined: Dec 2001
Posts: 444
S
Sandro Offline OP
Member
Ever get those jobs where you think you "know" something can be done, but due to brain cramp, can't figure it out??

With a push button motor starter (1 stop, 1 start. Not a manual button starter but one controlled with coil), connected to a compressor with pressure switch. When the pressure switch opens the circuit and breaks the coil contact, it takes the operator to push the start button again once the pressure drops to get the motor going again.

Argh! the holding contact, I believe there is a way around this..... and can't quite remember how to do this. Wire the pressure switch into the aux contacts?

Work Gear for Electricians and the Trades
Re: motor starter [Re: Sandro] #182579 12/03/08 12:31 AM
Joined: Mar 2004
Posts: 947
T
twh Offline
Member
I think a compressor needs an off-auto switch.

Last edited by twh; 12/03/08 12:34 AM. Reason: changed switch type
Re: motor starter [Re: twh] #182580 12/03/08 12:45 AM
Joined: Jul 2007
Posts: 265
W
wire_twister Offline
Member
You need an off-auto switch, or a locking run push button


Jimmy

Life is tough, Life is tougher when you are stupid
Re: motor starter [Re: wire_twister] #182581 12/03/08 01:31 AM
Joined: Nov 2005
Posts: 820
J
JoeTestingEngr Offline
Member
I don't think I would leave it that way. I would fill the holes with a press-to-test indicator and a momentary-off-on rotary selector switch. The pressure switch should have a pressure and deadband or differential adjustment. The Off position breaks path to N.C. opens on P increase, switch terminals. The momentary, "Hand" position, parallels P-switch, to check operation without bleeding the tank. The N.O. aux switch would be used to drive your indicator. Do you have any E-stops in the mix? You wouldn't need any holding contacts unless you were going to use 2 separate pressure switches in series. In that case, the holding contact is in parallel with the low pressure switch. It helps to think of one as "closes on low pressure", and the other as, "opens on high pressure"
Joe

Re: motor starter [Re: JoeTestingEngr] #182582 12/03/08 01:58 AM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
Member
Seems like someone is trying to defeat a safety device ... to me. If there's a high-pressure cut off switch, it's there for a reason. I'm not about to give advice on defeating it.

If you want the compressor to automatically re-start when the pressure has dropped ... well, that's a normal control problem, and would be solved by adding a pressure switch - not by bypassing an existing one.

I'm real close to locking this thread. Did I understand the request correctly?

Re: motor starter [Re: renosteinke] #182583 12/03/08 03:59 AM
Joined: Jul 2004
Posts: 9,540
G
gfretwell Offline
Member
I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.


Greg Fretwell
Re: motor starter [Re: gfretwell] #182584 12/03/08 09:09 AM
Joined: Dec 2001
Posts: 444
S
Sandro Offline OP
Member
BINGO!!!

Re: motor starter [Re: gfretwell] #182585 12/03/08 09:10 AM
Joined: Dec 2001
Posts: 444
S
Sandro Offline OP
Member
Originally Posted by gfretwell
I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.


BINGO!

Re: motor starter [Re: Sandro] #182589 12/03/08 12:35 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
Member
Thanks for the clarification.

Re: motor starter [Re: renosteinke] #182590 12/03/08 01:27 PM
Joined: Dec 2000
Posts: 4,283
electure Offline
Member
Quote
Argh! the holding contact, I believe there is a way around this.....


Forget the holding contact

You need to bypass the holding contact entirely, and run the coil directly from the pressure differential switch.

A MAINTAINED contact switch can be inserted anywhere in the control circuit to turn it off.



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