DIY Air Compressor Magnetic Starter Switch

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DIY Air Compressor Magnetic Starter Switch

Post by jtsmith » Thu Sep 01, 2016 11:12 am

OK here goes.
My Porter cable c7550 5hp 80 gallon compressor developed a stuck on pressure switch and blew the safety valve. Scared a stain out of me to say the least.
I did get it to turn off, however it then would not turn back on until I actually got in there and pried the contacts apart. This is where my daily education begins.

There is a measly 26A rating on the contacts. Seems they are all made like that. Hmmm. the new ones with the same part number are actually rated 12 A. This will not do for a 5hp 32Amp compressor. I am positive this draws at least 35 amps when starting. What were they thinking? Upon talking with an air compressor specialist, I found that a pressure switch is good enough for the standard homeowner. They replace very few under warranty, and hope they do fail out of warranty to trash a compressor and force you to buy expensive pump parts, or a motor.

Well, to be fair this has lasted abut 8 years of pretty good use, (sandblasting at 10+CFM) but I still do not like the idea of replacing it with another 26A switch. Sometimes I take a blasting rig out to the back 40 and do some tank blasting. Can you imagine the carnage it would cause if that stuck on when I was way out there, unable to hear it?

Enter the Magnetic starter.
A fancy term for a thermal overload protected high current relay. Add to this, a little DIY wiring.

I just happen to have 3, Tyco 40A double pole 240v relays with 240v coil voltage I swiped out of a 27kw 3 circuit tankless water heater. I know the relays are in good working order. They look something like this.
The number on the label is M2100-20U6999L

This is the expensive part inside a mag starter unit. I will have 2 spares.



I am going to use an adjustable 28-40A thermal overload relay as protection. Scored on ebay for 25.00 shipped (below)


This will enable the use of a new low current pressure switch. Think of it as a protected relay. Which is what it is.

Of course it will need a power switch to the mag starter unit, and a box.

I know i can just go out and buy a magnetic starter, for around 125.00 however it would be more rewarding to make use of something I already have, and DIY.

I am 100% certain This will make my air compressor way safer that it's present state.

I'm all ears.
You oughtta see what's in my garage, man is she hot!

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Re: DIY Air Compressor Magnetic Starter Switch

Post by diaz8911 » Mon Oct 07, 2019 10:28 pm


Interested in purchasing the 2 spare Air Compressor Magnetic Starter Switch M2100-20U6999L. Please provide cost per switch and method payment. Have a Paypal account if you do accept.

Thank you.

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