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Discussion Starter #1
I have a Quincy model 325 12 that I purchased and it has had the older 3 phase motor replaced with a 5 HP single phase motor that has 3 capacitors on it. It also has no pressure switch on it. What pressure switch should I go with ? Do I need any type of magnetic starter ? Tried posting pics but I can't seem to find them on my computer. Thx Dave
 

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This is an older 5 hp meaning probably equivalent to a 10 hp today. This is the only pic I have, I tried several times yesterday to upload pics but can't get them onto my computer. There is no name plate on the motor. May have been lost when it was rebuilt. Sorry this is all I have. The guy I bought this Quincy from had the compressor checked out and had a shop swap out the 3 phase motor for this single phase motor. It supposedly ran when he got it back but drew to much power from his limited Electric. 100 A service to a 3000 sq ft home... Thx Dave
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I also have a new pressure switch from a Ridgid air compressor I used for work, would I be able to use that ?
 

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Well they are capacitors that help start a motor, they store electric energy that helps create torque when the motor starts. The motor you linked to has capacitors and it is a single phase motor. I have not seen capacitors on a 3 phase motor. These are found on most single phase motors, some are start capacitors and some are run capacitors.
So back to my original question do I need I need a magnetic starter ? I just did research on Google for this and found a video from Compressor-source.com explaining why/when you need a magnetic starter. In my case I still need the pressure switch, but it will now be connected to the starter to turn on the motor. Thx Guys.
 

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wannaBelkhuntin

The capacitors shift the phases to get more torque during startup and used also when running as well. I would think that the 100 amp service could be a problem in starting this compressor motor. The 5 HP startup LRA (locked rotor) is greater than 100 amps, even without the other household loads.

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If you only have two wires to connect power to, you are looking at a single phase motor in most cases. But without a nameplate you don't know at what voltage, full load amps and other information. I would talk to an electric motor rebuilder and see if they can help identify what you have.

Stephen

Well they are capacitors that help start a motor, they store electric energy that helps create torque when the motor starts. The motor you linked to has capacitors and it is a single phase motor. I have not seen capacitors on a 3 phase motor. These are found on most single phase motors, some are start capacitors and some are run capacitors.
So back to my original question do I need I need a magnetic starter ? I just did research on Google for this and found a video from Compressor-source.com explaining why/when you need a magnetic starter. In my case I still need the pressure switch, but it will now be connected to the starter to turn on the motor. Thx Guys.
 

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wannaBelkhuntin,

You might want to consider putting a belt guard on your compressor as well for safety concerns, the fan motion can suck in stuff. At least make sure there is no physical access to compressor if you run it this way for other people, kids, cats, dogs etc.

Stephen
 

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wannaBelkhuntin,

You might want to consider putting a belt guard on your compressor as well for safety concerns, the fan motion can suck in stuff. At least make sure there is no physical access to compressor if you run it this way for other people, kids, cats, dogs etc.

Stephen
Well first off the 100 amp service was for the PREVIOUS owner, as I previously said his service could NOT handle this compressor. As far as the motor being single or 3 phase, the previous owner had the original 3 phase removed and had a single phase 5 HP motor replacing it.
As far as the guard is concerned this compressor is going to be mounted on a platform outside of my garage and then enclosed so there will be no random access to it.
So after all of that can you offer any assistance on my ORIGINAL questions ???
 

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look in to a motor drive...
that will help with the ramp up and lower the in rush.
the better units have a pressure sensor.

yea an digital un loader is a must on these larger units..
that will help on lockup and super hard starting..
they can be set to freewheel the compressor for a min or so to let the fly wheel come up to speed.
then connect the output to the directional check valve to the tank.

seek out a local motor service place.. they can help you on the motor drive as well as all of the other electrical parts.
 

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Discussion Starter #11
So what is this locked rotor chart ? Is this similar to start up amperage vs running amperage ???
I know the original owner mentioned this set up drawing 37 Amps, I would have to guess that was at start up.
 

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well you need the tag off the motor to see the real motor data.

reach out to the former owner..
see if you can find where the motor was purchased from.
and what date..
then contact that vendor for maybe a receipt of what was purchased..
maybe then you will have a make and model of the motor and can look up specs.

we need to know the current to get a HD pressure switch...
yea depending on the motor a contactor might be needed in a start box
and then use a basic pressure switch to control the relay.
try this link below for the parts;
click here for the air compressor parts page
 

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wannaBelkhuntin,

Sorry about getting side tracked, I would recommend using a magnetic starter as your pressure switch contacts will not be able to handle the LRA or "inrush" current of a 5 HP motor. To control a "remote type" magnetic starter you could use almost any pressure switch. Just make sure that the magnetic starter is rated for the HP of your motor and that it has the remote control feature. There are cheaper magnetic starters that are manual start only, don't buy one of those

Stephen
 

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wannaBelkhuntin,

The LRA chart shows just how much power is needed when switch is turned on with an electric motor load. It displays based on electric motor HP, how much power is drawn just before the rotor starts to turn. The rule of thumb is that RLA is 6 times the full load running amps. that's why you would need a 30HP+ gas generator to start this compressor. 37 amps was drawing too much power for this motor, probably voltage drop was so bad that motor was almost stalling and drawing so much power. I'd be curious to see what voltage he was drawing 37 amps! at that current it would soon overheat anyways

Stephen

So what is this locked rotor chart ? Is this similar to start up amperage vs running amperage ???
I know the original owner mentioned this set up drawing 37 Amps, I would have to guess that was at start up.
 

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wannabelkhuntin,

Looking closer at the motor pictured it may be more than 5 HP, 7.5 HP to 10 HP is my guess

Stephen
 

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Discussion Starter #18
I have no reason not to believe the person I bought it from. Based on physical size yes it is big, but I had an even older compressor with an even bigger 5 HP motor so size doesn't concern me. I have a newer Coleman compressor in my shop now and the 5 HP motor is half the size of this one. So I am ordering the parts listed above for it. The worst that can happen is the contacts on the starter take a crap sooner. The POS Coleman in my shop now operates off the pressure switch. Thx again guys
 

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wannabelkhuntin,

Sounds like you have things sorted out. The POS Coleman 5 HP is probably a "bogus" or "peak" 5HP motor drawing only 15amps FLA @ 230volts or in layman's terms an actual 3HP output. The contacts on the pressure regulator can handle a 15 amp, 3HP output motor. 20 amps or more at 230 volts is what a real 5 HP electric motor would draw. Keep us posted on how you make out, have fun!

Stephen
 
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