Adding low voltage control to a 5hp compressor

[slackdaddy1]

I have a 5hp IR T-30 60gal compressor, I put a new WEG 5hp motor and WEG mag starter on it a few years back.
The manual/auto air pressure switch is wired into the WEG Mag starter. The mag starter label states 208-230v coil voltage.
I am moving the compressor into a shed that is ~10 feet from the garage. The shed has a 50amp sub panel.

I would like to be able to control the compressor via a low voltage (18-24v) circuit.
A mech wind timer switch in the garage,, and possibly a "high Temp" sensor on the compressor.

Do they make magnetic starters with contacts rated for 230v - 5hp motors,, but with LV coils? I can not seem to locate any.
I asume I would need one with a small inigrated 18-24v transformer,, or supply my own low voltage seperate of the mag starter.

Or, would it be cheaper to add a "relay" and 18-24v source in series with the air pressure switch, then have my low voltage stuff control that additional relay ?

Anyone have any examples of having LV circuitry control a compressor ?

 

[whateg01]

I would either just add a relay and external controls to control the existing contactor (starter) or add another contactor before the compressor itself.

 

[Sumboodie]

Mag start is usually low amperage 120v for the coils. Uses just 1 leg of the 240v.

Use a 120v/24v contactor, like what a boiler uses.

Quick Amazon search finds one for $22 rated for 20 amps.

That being said, my compressor stayed on for 12 years in a shed ~75ft from the garage. I'd only kill power if I was out of town for a while, also shut water off, water heater, etc then too.

 

[micromind]

There's no limit to the size of motor that can be controlled by 24 volts. I've designed and installed control systems that use the 24DC output of a PLC (Programmable Logic Controller) that started and stopped motors over 1,000HP.

In your case, using a low voltage source (24 AC or DC) to control a relay that in turn, controls the existing starter would very likely be the best way. You'll need to use a relay that can handle 240 volts, plenty available.

The RIBH1C will accept 10 - 30 AC or DC for the coil and the contact will operate your starter. It's enclosed in a plastic case and fits a standard 1/2" knockout hole. You'll need to provide a power supply that's 10 - 30 volts, AC or DC. The coil needs 20mA with dc and 55mA with AC.

Pretty easy to connect, you'll be using 4 of the 6 wires. Cap off the 2 that are not used.

Grainger has them for less than $25, many other places have them too.

 

[slackdaddy1]

Thanks for the affirmation
I'll use a relay/contactor in series with the air switch, making sure it can handle the curent of the mag starter coil and has a 12-24v coil,,

Another thought,,, I guess I need to address the fact that i may be cutting power to the compressor without it "unloading" ?

 

[pcmeiners]

Do they make magnetic starters with contacts rated for 230v - 5hp motors,, but with LV coils? I can not seem to locate any.

Have have a low voltage control on my Quincy, Square D make swapable coils as do most manufacturers. Used 12v for everything but the contactor, as I already have multiple 220 and 120v contactors. The smallest relay in the box below is a 12v relay which controls the contactor.

Pardon Our Interruption...

"Made modification to control my QR 325. Added one dual time delay relay to lock out the power contactor should the compressor run continuously for more the a specified amount of time, so at the moment ,if it runs continuously for more then 1 1/2 hours it shuts down, and locks out until a manual reset, via a latching relay. Each time the compressor powers on by the tank switch it reset the timer .

Second modification involves an added oil pressure switch. The oil switch is a single pole double throw Nason pressure switch, one contact is in the power circuit to the contactor, the other pole goes to a latching relay circuit. . Should the oil pressure drop below 13 lbs, the compressor will lock out until a manual reset. Issue with this circuit I needed to add a time delay of a few seconds, to maintain a circuit as the power is turned on, and the oil pressure builds to >13lbs, or the latching circuit would kick in immediately. Other issues with the circuitry involved reverse flow of power in the circuits, messing up the logic. Next time I do something like this I will give a programmable logic controller a shot, this required too much wiring and space, even though it requires few brain cells to maintain (my main goal). All circuitry is 12vdc, except for the contactor coil which is 240AC

Third part of the circuit involved a dual time delay relay (dpdt) to activate a 12vdc solenoid valve to drain the tank, was $22 total for the valve and delay relay. Added a screen filter before the solenoid valve, and a 1/2" diameter magnesium anode in the same area."

"

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Have to plug the relays, cheap and versatile....

http://www.ebay.com/itm/0-1s-99h-Pr...717543?hash=item2ca92ad4e7:g:xZUAAOSwMtxXwSvD

http://www.ebay.com/itm/DC-12V-0-30...466259?hash=item1a1b239453:g:3DAAAOSwhdRYWnnN

 

[Bert_]

24vac furnace transformer, and a 24vac control relay. Can all be bought under $40

 

[larry4406]

Good info!

I plan to install an electronic ball valve to also shut off the tank.

 

[OccupantRJ]

My compressor setup is 240 volt. I used a relay to override the electric through the pressure switch, and control that relay from the front door of my shop with a different color light switch as I enter or leave. By overriding the pressure switch it should have nothing to do with unloading the compressor because it would be the same as if the pressure switch stopped it. The control function can also be done when you turn the lights on if you use a relay with a 120v coil.
If you prefer low voltage control then use a transformer and a relay with a low voltage coil.

 

[Bad Habit]

Just did a similar set up but used a 120v Smart Switch to control a contactor feeding the compressor. Have it set up to turn on at the compressor, also can hit my shop light switch twice to turn it on, or use the Smartthings app on my phone. Then have it set up to turn off with the shop lights. More nerdy than most

 

[Shoreline_]

IC330-300L-22-AD28, Contactor, 300A, 3 Pole, Aux: 2NO/2NC, Coil: 24-28VAC/DC

www.factorymation.com

This should work for you.

 

[OccupantRJ]

IC330-300L-22-AD28, Contactor, 300A, 3 Pole, Aux: 2NO/2NC, Coil: 24-28VAC/DC

www.factorymation.com

This should work for you.

And cheap too!

 

[slackdaddy1]

My compressor setup is 240 volt. I used a relay to override the electric through the pressure switch, and control that relay from the front door of my shop with a different color light switch as I enter or leave. By overriding the pressure switch it should have nothing to do with unloading the compressor because it would be the same as if the pressure switch stopped it. The control function can also be done when you turn the lights on if you use a relay with a 120v coil.
If you prefer low voltage control then use a transformer and a relay with a low voltage coil.

I have a 1/8" copper line from the cylinder head to my pressure switch,
Looking closely at my pressure switch,, if I flip the manual lever to "off" , it pushes up on a pin valve and bleeds off that line,,
Also, when the diaphragm opens the contacts (when the tank hits the high cut off),, a tab hits the bleed valve open.

So interrupting the circuit from the air switch to the Magnetic starter contactor,, would not bleed the cylinder off.
That said,, if I cut the compressor off via the remote switch,, I would not be starting the compressor right back up anytime soon,,, So I imagine the cylinder would bleed off the pressure past the piston rings after a few minutes? 30 minutes?

 

[Shoreline_]

I have a 1/8" copper line from the cylinder head to my pressure switch,
Looking closely at my pressure switch,, if I flip the manual lever to "off" , it pushes up on a pin valve and bleeds off that line,,
Also, when the diaphragm opens the contacts (when the tank hits the high cut off),, a tab hits the bleed valve open.

So interrupting the circuit from the air switch to the Magnetic starter contactor,, would not bleed the cylinder off.
That said,, if I cut the compressor off via the remote switch,, I would not be starting the compressor right back up anytime soon,,, So I imagine the cylinder would bleed off the pressure past the piston rings after a few minutes? 30 minutes?

If the pressure switch reaches it cut out pressure it will release the discharge line when it turns off. Or you can manually do it. What scenario youll run into is if you turn off the power from the disconnect mid cycle and leave the pressure switch in the auto position. Then itll start loaded.

 

[loganb]

I just covered a similar project I did for mine...though I took a slightly simpler approach and made the outlet providing power relay controlled

Details below, couple posts farther down has the links for the things used

Post in thread '3rd time's a charm with a 3 car workshop' https://www.garagejournal.com/forum...rm-with-a-3-car-workshop.461763/post-11218702

 

[slackdaddy1]

If the pressure switch reaches it cut out pressure it will release the discharge line when it turns off. Or you can manually do it. What scenario youll run into is if you turn off the power from the disconnect mid cycle and leave the pressure switch in the auto position. Then itll start loaded.

That is what I was eluding to above,, If I were to cut the power while it was running, mid cycle,, It would leave the cylinder "loaded"

Question is,, how long does it take for the cylinder to naturally bleed down (leak past the piston rings) ??
Because, it I cut the power,, it is 99.99% that I am walking out of the shop for the night, or at least an hour or 2

 

[Shoreline_]

That is what I was eluding to above,, If I were to cut the power while it was running, mid cycle,, It would leave the cylinder "loaded"

Question is,, how long does it take for the cylinder to naturally bleed down (leak past the piston rings) ??
Because, it I cut the power,, it is 99.99% that I am walking out of the shop for the night, or at least an hour or 2

Not sure but you could always wire in a 120v n.o. solenoid valve since I assume you dont have the centrifugal unloader variety of the t30. You can get a chinese one pretty cheap on ebay.