Compressor pressure switch wiring?

Iron-Iceberg · Sep 28, 2008

I just got a new 5 hp motor, mag starter and pressure switch for an old IR compressor of mine. But Im having problems wiring the pressure switch.
The compressor pumps up and shuts off but will not restart even if the pressure drops to 0. I have to hit the button on the mag starter to get it to kick in again.

The mag starter has 2 wires coming from it to the pressure switch.
The pressure switch has 4 lugs, 2 that read MOTOR and 2 that read LINE.
I tried wiring it with one wire to the MOTOR and one to LINE. And it pumps up but will not restart.
And also one wire to one of the MOTOR lugs and one to the other MOTOR lug. Nothing at all this way.
The pressure switch is a Furnas/Hubbel

Any ideas? This is driving me nuts. I need some air, compressed air that is. :lol_hitti

W-Cummins · Sep 28, 2008

The pressure switch is not the problem, it sounds like the mag starter is not wired correctly. What is the coil voltage on the contactor? Any way, in a compressor application the contactor coil is wired in series with the pressure switch. One side to the pressure switch line terminal ( from an allways hot, line in, from the starter ) and the other wire to the pressure switch motor terminal conects to the contactor coil. The other side of contactor coil is to the grounded conductor if it's a 120v coil or to the other line in hot if it's a 220V coil. So that when the pressure switch is closed ( low pressure) current flows to the coil on the contactor and the compressor runs until the pressure builds up and opens the contacts of the pressure switch, then the current is cut to the coil and the mag contactor opens and turns off the motor....

William...

dwilliams35 · Sep 28, 2008

Which "button" on the mag starter are you talking about? If you're talking about the overloads, you've either got motor problems or you bought the wrong overloads: they may be five horse overloads, but at a different voltage. If you're talking about the litle "button" that you can push in and force the coil in, then I'd say your coil is bad or the voltage may be wrong: it doesn't have enough uumph to pull in the coil, but will hold it in once it's engaged. Once it's released by the pressure switch transitioning, it won't pull the coil in the next time. A lot of compressors have a dual-voltage coil: make sure you've got the jumpers installed right for your voltage.

BigChevy80 · Sep 28, 2008

You only need to use one side of the pressure switch. If the trigger coil is a 240v coil, it has one side directly connected to one leg of the 240v feed and the other leg loops through the pressure switch.

So you would connect one side of the trigger coil directly to one leg in the magnetic starter box. Then run a jumper from the other leg to the "line" side of the pressure switch. Run another jumper from the "motor" lug of the pressure switch back to the other side of the trigger coil.

Also make sure both sides of the trigger coil are being powered by the side of the magnetic starter that is always hot (the side the power comes in from the service panel). If its powered from the other side, it would cause the circuit to be "self latching" which would cause the problem you are describing.

dwilliams35 · Sep 28, 2008

BigChevy80 said:
You only need to use one side of the pressure switch. If the trigger coil is a 240v coil, it has one side directly connected to one leg of the 240v feed and the other leg loops through the pressure switch.

So you would connect one side of the trigger coil directly to one leg in the magnetic starter box. Then run a jumper from the other leg to the "line" side of the pressure switch. Run another jumper from the "motor" lug of the pressure switch back to the other side of the trigger coil.

Also make sure both sides of the trigger coil are being powered by the side of the magnetic starter that is always hot (the side the power comes in from the service panel). If its powered from the other side, it would cause the circuit to be "self latching" which would cause the problem you are describing.

He did say it would turn off on its own: that wouldn't happen if the coil was powered on the wrong side.

Iron-Iceberg · Sep 28, 2008

The mag starter is a Siemens WS5 model here is a picture of the wiring and this is how I wired it.

Iron-Iceberg · Sep 28, 2008

I'm not an electrical guy but I guess that it is 110v by just coming off one line (L1) from the circuit breaker, and the other wire #3 on the wiring directions is to engage the coil when the pressure switch says so.
The button on the front of the mag stater is a reset button. It is not the button on the coil. If I push that then it will kick on if the pressure is low enough.

It does turn off if the pressure gets up to about 130 psi, it just will not restart on its own even after it drains down to 0 psi.

Thanks for the help guys.

Charles (in GA) · Sep 28, 2008

The mag starter has 2 wires coming from it to the pressure switch.
The pressure switch has 4 lugs, 2 that read MOTOR and 2 that read LINE.
I tried wiring it with one wire to the MOTOR and one to LINE.

The above statement is correct.

My Square D starter is functionally the same. On mine L1 goes to the pressure switch, then the pressure switch returns to one side of the coil (both of which are physically located directly behind the L1/L2 terminals, but in no way connected to them). From the other coil terminal the red wire goes to the thermal overload switch which is directly behind M1 but not connected to it from the other terminal of the thermal overload switch, the red wire makes its way back up to L2, completing the circuit.

This is how you show it in your diagram except that the overload should be drawn off to the side, it in no way involves M1. It sits behind M1 because the thermal heater is in the M1 supply. The heater causes the overload to trip if it gets too hot, simulating an overheated motor. What may be happening is your heater is tripping the overload. hitting the button is the normal cure for this, it resets the the overload switch closed, so the coil circuit is complete again. Your pump is not shutting off because the pressure switch is opening, but rather it is shutting off because the thermal overload switch is opening. You need a heater element better matched to your motor size/amp load. These are replaceable. The heat element is located directly above the M1 terminal and is a metal strip looking device supplying M1.

If you take the cover off the pressure switch you can confirm this, as you will see the compressor shut off, but the pressure switch mechanism will not be opening up.

Charles

Aceman · Sep 28, 2008

I agree, it sounds like your overloads(heaters) are undersized. Find the full load current on your motor nameplate and multiply it by 115%, this is your required overload size.

It would be a good idea to double check the size of your starter also, make sure it's rated for a 5hp single phase 230v motor. It's usually written on the side of the starter.

Iron-Iceberg · Sep 30, 2008

Charles and Aceman are the winners. I checked the pressure switch and it didn't even move.
The overload is a 28 amp and the motor is rated at 23 amps

The problem is that when I just checked the amperage with a meter its shows that the motor is drawing 25 amps at around 30 psi and 29-30 at around 115 psi of course then the overload kicks.

Now my question is how to fix this. Do I need a different pulley to slow down the pump? And let the motor not work as hard?

This is a 5hp Baldor motor that spins at 1750 rpms. That is the same as the original 5hp 3 phase motor.

Charles (in GA) · Sep 30, 2008

Make sure you have the right amps rating here. You are looking for the FLC or FLA number on the name plate, for the voltage you are running it at. Some motors have amps listed for 208V, 230V, 240V, which the motor will run on without a problem, but the amps are different, so be sure you have the right numbers for the volts you have. Is the motor compressor rated? They do make "compressor rated" motors, I really don't know the differences however.

Charles

MXtras · Sep 30, 2008

I believe the compressor rated motors are made to handle far higher starting current inrush than a standard motor - to supply the required torque to get to work at low RPM.

For future reference - I have come to learn that Charles knows of what he speaks about electrical matters. I have never seen Charles post inadequate or incorrect info. If he's unsure of specifics, he states so.

Thanks, Charles.

Scott

MXtras · Sep 30, 2008

Iron-Iceberg said:
Charles and Aceman are the winners. I checked the pressure switch and it didn't even move.
The overload is a 28 amp and the motor is rated at 23 amps

The problem is that when I just checked the amperage with a meter its shows that the motor is drawing 25 amps at around 30 psi and 29-30 at around 115 psi of course then the overload kicks.

Now my question is how to fix this. Do I need a different pulley to slow down the pump? And let the motor not work as hard?

This is a 5hp Baldor motor that spins at 1750 rpms. That is the same as the original 5hp 3 phase motor.

Sound like you might be seeing the effects of a voltage drop (thereby kicking the amps up to "compensate")? What size feed to you have supplying this motor?

Scott

Iron-Iceberg · Sep 30, 2008

Here are the #s on the motor.

And I am running it on 15' of 8 Gage wire, cord. On a 60amp breaker from a 100 amp sub panel.

Performance Data: L1410T

Product Nameplate Data :
Rated Output 5 HP Hertz 60 NEMA Nom. Eff. 82.5
Volts 230 Phase 1 Power Factor 87
Full Load Amps 23 NEMA Design Code L Service Factor 1.15
Speed 1725 LR KVA Code G Rating - Duty 40C AMB-CONT

(Typical performance - Not guaranteed values)
General Characterstics at 230 V, 60 Hz, 5 HP

Full Load Torque 15 LB-FT Starting Current 140 Amps
Start Configuration DOL No-Load Current 8.4 Amps
Break Down Torque 34 LB-FT Line-line Resistance @ 25° C 0.45 Ohms
Pull-Up Torque 28 LB-FT Temperature Rise, C @ FL (in deg) 90
Locked-Roter Torque 41 LB-FT Temp. Rise @ S.F. Load (in deg) 110
Load Characteristics at 230 V, 60 Hz , 5 HP

% of Rated Load 25 50 75 100 125 150 S.F.
Power Factor 60 78 86 89 91 91 90
Efficiency 67.2 79.2 82.7 83 81.5 78.5 82.1
Speed (rpm) 1786 1772 1756 1739 1718 1691 1726
Line Amperes 10.1 13.2 17.2 21.9 27.4 34 25.2

If you cant read this here is the web page I got the info from.
www.baldor.com/products/perfdata.as...ase=1&hp=5&winding=36WGW849&rating=40CMB-CONT

Iron-Iceberg · Sep 30, 2008

Oh and I checked the voltage at the end of the cord and it was 240v.
Just checked the voltage at the mag starter its running 233v and drawing 30a at about 80psi running.

Charles (in GA) · Sep 30, 2008

Does sound like a smaller motor pulley might be in order to unload the motor some. Just a guess, unless something is wrong with the motor.

Charles

Aceman · Sep 30, 2008

Iron-Iceberg said:
The problem is that when I just checked the amperage with a meter its shows that the motor is drawing 25 amps at around 30 psi and 29-30 at around 115 psi of course then the overload kicks.

Now my question is how to fix this. Do I need a different pulley to slow down the pump? And let the motor not work as hard?

You definitely need to gear that motor down. Ideally, you want the motor to max out at nameplate amps(23) when the pump is at the end of the cycle and is done filling the tank. It's alright to go an amp or two over right at the end of the cycle, but you should try to keep it at 23 amps or less.

Iron-Iceberg · Oct 1, 2008

Thanks for all the help guys. At least we know the problem now.

The motor pulley is around 5" dia. and the pump is about 17" dia.
What size should I go to on the motor and where is a good place to get a pulley for a 1 1/8" shaft.

Aceman · Oct 1, 2008

Iron-Iceberg said:
The motor pulley is around 5" dia. and the pump is about 17" dia.
What size should I go to on the motor and where is a good place to get a pulley for a 1 1/8" shaft.

Can't help you with that, maybe you find an online calculator to help you. I know how I'd probably do it, the expensive way, trial and error.

You might be able to get pulleys at Napa, I know they sell v-belts.

Iron-Iceberg · Oct 2, 2008

I thought Id give you guys and update. Im doing it the Aceman, ie expensive way. LOL
The local shop had a 3.75" pulley on the shelf so we went with that and the motor is drawing around 17 amps all the way from 0 psi to 150psi, now but it is pumping up kinda slow.
I think Ill will try a 4.25" next and go with that.

Thanks again for all the help.

slowtwitch · Mar 26, 2009

I know that this is an older thread, but, if your still looking for pulleys, try here.....
http://www.surpluscenter.com/

pete

primosoup · Nov 7, 2009

I know this is an old post...but I think the real problem was that he thought the heater B28 reflected the amperage limit i.e. 28 amps....but it doesn't..its rated at 17.7 to 20.6 amps. The reason I know is that I had the same problem, only I had B25's in my magnetic starter. So..I installed B32's in it (rating 20.7-23.1 amps) and my 5 hp motor..putting out 22 amps @ 125psi...works flawlessly. Truth is..I almost did the pulley swap myself....Hope this helps someone in the future, Dave (primosoup).

Compressor pressure switch wiring?

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