air compressor

[farmbj]

My starter box burned up and was wanting to put another one on do you need a special one or can you make any one work of the same voltage I have 240 and how do you wore the pressure switch to it also it is a 7 1/2 hrs

 

[Russ from MN]

I think you need qualified help.

 

[drsportster]

My starter box burned up and was wanting to put another one on do you need a special one or can you make any one work of the same voltage I have 240 and how do you wore the pressure switch to it also it is a 7 1/2 hrs

Goes by amperage used

 

[Mule Meat]

7 1/2 hrs and I still have no clue as to what you are asking.

 

[Red Dave]

My starter box burned up and was wanting to put another one on do you need a special one or can you make any one work of the same voltage I have 240 and how do you wore the pressure switch to it also it is a 7 1/2 hrs

I'm going to make a leap here and assume that you mean 7 1/2 horsepower compressor.
There are several ways that the pressure switch could be wired to the starter box.
If you have a name brand compressor, it is likely the manufacturer can supply a direct replacement, if not there are aftermarket options that should work just fine.

This isn't rocket science, but I get the impression from your question that you aren't very familiar with electrical equipment and wiring. To keep you safe and to protect your equipment, with all respect I recommend that you have a qualified electrician replace the starter. There are places where it is OK to "do-it-yourself" to save money. Electricity isn't one of those places.

 

[john in la]

A starter box is rated by the HP of the motor and if it is 1 or 3 phase.
Or as drsportster said amperage used.
In other words a starter box for a 5 HP motor will not work on a 10 HP motor and a starter box for a 10 HP motor will not protect a 5 HP motor.

Mule Meat
Think of a starter box for a compressor as a starter relay for your cars starter.
The pressure switch now takes the place of the key.
So high amps goes to the starter box and directly to the motor by passing the pressure switch.
The pressure switch only tells the starter box when to cut on and off.
This saves the contacts in the pressure switch as they can not handle high amps.
Reason if you buy a big compressor at a box store you constantly burning up pressure switches.
They do not include the starter box to keep the price lower.

​

 

[wp6529]

7 1/2 hp implies three phase since that is an unusual size for single phase motors but common for three phase motors. That also means phase rotation needs to be correct or you will destroy the compressor. I've seen a nice 10 hp compressor destroyed because someone hooked it up with the wrong rotation and ran it with the resulting zero oil pressure until it siezed.

 

[Dusty MI]

Starters are magnetic relays that turn the motors on and off, and come in different sizes.

 

[MF294-4]

I have a 7 1/2 hp motor on my compressor. Not what I needed but it replaced a 5 hp 3ph and it was cheap.

 

[Steve@Advance]

My starter box burned up and was wanting to put another one on do you need a special one or can you make any one work of the same voltage I have 240 and how do you wore the pressure switch to it also it is a 7 1/2 hrs

Hopefully there would be enough left of the old starter to identify it.

For one to burn up beyond use is rare, usually a single component failed, like the coil, or the contacts, or a heater, which can be replaced as opposed to starting over from scratch. A good magnetic starter is very expensive!

Hint, if the starter is mounted on the compressor, now would be a good time to mount it on the wall. Vibrations from the compressor tend to shake the components and wire connections loose.

 

[38 Sears Roebuck]

I'm going to make a leap here and assume that you mean 7 1/2 horsepower compressor.
There are several ways that the pressure switch could be wired to the starter box.
If you have a name brand compressor, it is likely the manufacturer can supply a direct replacement, if not there are aftermarket options that should work just fine.

This isn't rocket science, but I get the impression from your question that you aren't very familiar with electrical equipment and wiring. To keep you safe and to protect your equipment, with all respect I recommend that you have a qualified electrician replace the starter. There are places where it is OK to "do-it-yourself" to save money. Electricity isn't one of those places.

Agreed

 

[Fixingfarmer]

A starter box is rated by the HP of the motor and if it is 1 or 3 phase.
Or as drsportster said amperage used.
In other words a starter box for a 5 HP motor will not work on a 10 HP motor and a starter box for a 10 HP motor will not protect a 5 HP motor.

Mule Meat
Think of a starter box for a compressor as a starter relay for your cars starter.
The pressure switch now takes the place of the key.
So high amps goes to the starter box and directly to the motor by passing the pressure switch.
The pressure switch only tells the starter box when to cut on and off.
This saves the contacts in the pressure switch as they can not handle high amps.
Reason if you buy a big compressor at a box store you constantly burning up pressure switches.
They do not include the starter box to keep the price lower.

​

It’s possible he might have a 7.5 hp single phase motor I know those cheap orange compressors that the auto parts stores are selling now have a WEN motor on them with a big black box holding the starting capacitors. We have one. When they were building the shop at the coop the electrician didn’t believe me said it was a weird one so we went and looked at mine that’s what it was at least what the tag says. Saw one at the local car guru getting delivered the other day. Like everything else I suppose a horse power isn’t what it used to be

 

[buickanddeere]

If the compressor motor was three phase . A VFD could take care of the stop/starting . With a simple low current signal from a pressure switch

 

[Geo-TH,In]

7 1/2 hp implies three phase since that is an unusual size for single phase motors but common for three phase motors. That also means phase rotation needs to be correct or you will destroy the compressor. I've seen a nice 10 hp compressor destroyed because someone hooked it up with the wrong rotation and ran it with the resulting zero oil pressure until it siezed.

I agree 7.5 hp is likely to be 3 phase.
Is what he is calling a starter box really a 3 phase converter, VFD, with a 3 phase motor starter, contactor, relay or what ever you want to call it?
Without posting pictures of the motor plate and starter box, we are just guessing.

 

[Jim.ME]

I agree 7.5 hp is likely to be 3 phase.
Is what he is calling a starter box really a 3 phase converter, VFD, with a 3 phase motor starter, contactor, relay or what ever you want to call it?
Without posting pictures of the motor plate and starter box, we are just guessing.

It will be interesting to see if he returns. He joined at 10:00 AM Sunday, started 4 threads, and was last seen at 10:23 AM Sunday. Hopefully he is ok.

 

[farmbj]

It will be interesting to see if he returns. He joined at 10:00 AM Sunday, started 4 threads, and was last seen at 10:23 AM Sunday. Hopefully he is ok.

Appreciate the fact that you noticed i wasn't active
Was dealing with some health issue but back on track .

 

[farmbj]

7 1/2 hrs and I still have no clue as to what you are asking.

I was thinking of using a three phase compressor and will need a contactor/motor starter with three poles in order to break all three power legs going to the motor. The starter will need to have a coil voltage equal to whatever i use as a control voltage in order to pull the contacts in .
I am right on this ?

 

[farmbj]

I agree 7.5 hp is likely to be 3 phase.
Is what he is calling a starter box really a 3 phase converter, VFD, with a 3 phase motor starter, contactor, relay or what ever you want to call it?
Without posting pictures of the motor plate and starter box, we are just guessing.

It burned up was because of age probably because its over 40 yrs old and now i realize I need a starter box with a coil that will switch it on when the pressure switch activates it

 

[farmbj]

Thanks to everyone as I can already see there is a wealth of knowledge here

 

[kencombs]

I have a 7 1/2 hp motor on my compressor. Not what I needed but it replaced a 5 hp 3ph and it was cheap.

Not common, but not that rare. What is rare is any single phase motor over 5hp to be cheap! Lots of them on eBay right now, cheapest is a Vevor at around 400+shipping up to 2 grand for the best ones.