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#182578 - 12/03/08 01:26 AM motor starter  
Sandro  Offline
Member
Joined: Dec 2001
Posts: 444
Stoney Creek, ON, Canada
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

#182579 - 12/03/08 01:31 AM Re: motor starter [Re: Sandro]  
twh  Offline
Member
Joined: Mar 2004
Posts: 916
Regina, Sask.
I think a compressor needs an off-auto switch.

Last edited by twh; 12/03/08 01:34 AM. Reason: changed switch type

#182580 - 12/03/08 01:45 AM Re: motor starter [Re: twh]  
wire_twister  Offline
Member
Joined: Jul 2007
Posts: 265
Georgia USA
You need an off-auto switch, or a locking run push button


Jimmy

Life is tough, Life is tougher when you are stupid

#182581 - 12/03/08 02:31 AM Re: motor starter [Re: wire_twister]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 785
Chicago, Il.
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


#182582 - 12/03/08 02:58 AM Re: motor starter [Re: JoeTestingEngr]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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?


#182583 - 12/03/08 04:59 AM Re: motor starter [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.


Greg Fretwell

#182584 - 12/03/08 10:09 AM Re: motor starter [Re: gfretwell]  
Sandro  Offline
Member
Joined: Dec 2001
Posts: 444
Stoney Creek, ON, Canada
BINGO!!!


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


BINGO!


#182589 - 12/03/08 01:35 PM Re: motor starter [Re: Sandro]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Thanks for the clarification.


#182590 - 12/03/08 02:27 PM Re: motor starter [Re: renosteinke]  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,260
Fullerton, CA USA
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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