Compressor 3hp motor DOL starter question

[styleruk]

the direct on line contactor should come with or you should fit the correct sized overload for the motor it's controlling. You should not have any need for that that thermal overload switch as well.
I'm assuming your current set up would start the compressor automatically as the pressure drops bellow as cetain threshold? This should be run through the controls for the starter so a simple DOL starter will not work as you require it.

I don't quite understand everything you say there.
You say the DOL Starter I'm getting should have a thermal overload switch?
this is the one I'm getting
So I could check that out.
The confusing bit you say is that the DOL will not work as I require. I run the switch for the motor from the pressure sensor, then that sensor is powered from the DOL. When the pressure drops, the pressure switch powers the motor. the pressure switch will be live as long as the DOL starter is switched on.

 

[David Prosser]

That starter has an overload relay inside which can be set between 10-16A.
With the DOL starter you have selected stop/start of the motor is controlled by pushing the buttons on the front of the starter. Your set up should have the pressure switch stopping and starting the motor via the DOL contactor and overload the pressure switch should not have the motor running current through it.

 

[styleruk]

That starter has an overload relay inside which can be set between 10-16A.
With the DOL starter you have selected stop/start of the motor is controlled by pushing the buttons on the front of the starter. Your set up should have the pressure switch stopping and starting the motor via the DOL contactor and overload the pressure switch should not have the motor running current through it.

So you are saying, I should have power going to the DOL, then to the pressure switch, back to the DOL then the motor. That really does not make any sense to me. Is that what you mean? In other words, the last thing before the motor should be the DOL?
If that is the case, then I should mount the DOL onto the frame of the compressor.
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So you are saying, I should have power going to the DOL, then to the pressure switch, back to the DOL then the motor. That really does not make any sense to me. Is that what you mean? In other words, the last thing before the motor should be the DOL?
If that is the case, then I should mount the DOL onto the frame of the compressor.

Maybe if I put power through to the pressure switch, then to the starter, then the motor. But then, when the pressure switch wants to start the compressor again will the DOL reset to off? Or will it stay on?

 

[Lucien Nunes]

I can't stop to answer fully but there is confusion going on between a starter with a contactor i.e. relay, which is controlled by the pressure switch and takes the motor load itself, and a mechanically latching pushbutton switch with thermal overload which is what I think is in the link. The latter is normal for compressors of this size where the pressure switch is rated for the motor current, since the electrical latching of a contactor isn't needed and can't be used if under pressure switch control.

 

[David Prosser]

the starter is a big switch designed to take the motor current what operates this big switch is a little switch, in your case the pressure switch.

If you're not clear on how to connect them up correctly why not ask your brothers mate to have a look. Or just buy a prebuilt unit big enough for what you need. Try Atlas Copco they make good compressors with everything built in.

 

[styleruk]

the starter is a big switch designed to take the motor current what operates this big switch is a little switch, in your case the pressure switch.

If you're not clear on how to connect them up correctly why not ask your brothers mate to have a look. Or just buy a prebuilt unit big enough for what you need. Try Atlas Copco they make good compressors with everything built in.

I have asked exactly that to be sure I get the best I can. Sure, I can spend over £1k for a built unit that has a receiver this size but I would rather renovate my 1960 classic compressor tank to suit everything else in my garage for £300.
I'm not using it for professional usage, it's for now and then and I suppose I could buy a cheap smaller compressor for less and save my time learning, but when this one is finished (and I'm in no hurry), it'll see me out. Plus, I enjoy the small challenge.
I'm rebuilding a classic car in between, so it's a nice distraction during this lock down period.
But thanks to all for the advice so far, I'm slowing going up the right path. I'll post a picture when it's done.

 

[DPG]

I have asked exactly that to be sure I get the best I can. Sure, I can spend over £1k for a built unit that has a receiver this size but I would rather renovate my 1960 classic compressor tank to suit everything else in my garage for £300.
I'm not using it for professional usage, it's for now and then and I suppose I could buy a cheap smaller compressor for less and save my time learning, but when this one is finished (and I'm in no hurry), it'll see me out. Plus, I enjoy the small challenge.
I'm rebuilding a classic car in between, so it's a nice distraction during this lock down period.
But thanks to all for the advice so far, I'm slowing going up the right path. I'll post a picture when it's done.

What car are you working on?

 

[styleruk]

What car are you working on?

Singer Gazelle. Nothing exotic, but a good work horse practical classic. Finished a ton of welding with her, she is now in patchy grey primer here and there, but the crap all-in-one compressor that was bolted to my receiver was just not up to the job of spraying. So I'm upgrading that, it will look more original with a twin cylinder on top. Just renovated an old 2 post lift that I got for a favour, it was rusty as hell but now smells of grease and hammerite. I recently learned a lot about hydrolic lifts and can now lift the old girl up to work on her. It's the same with that, I could have spent a couple of grand on a lift, but would rather spend the evenings figuring it out myself and trying to fix something that is fundamentally better quality.

 

[DPG]

Sounds interesting. Post some pictures if you get chance.

 

[David Prosser]

My mistake miss read the original post and got mixed up thinking you were using a 32A motor. I don't think you will need that DOL starter and overload relay if the pressure switch is a decent one that's rated for 16A you could just use a 2 pole motor protection circuit breaker. These are suitable for motor disconnection as well as overload protection.