# Broken Central Pneumatic 21 Gallon - DIY Fix/Improvement



## jefferywdonald (Feb 3, 2021)

Hello everyone, new to the forums here. I've been thinking about making/building my own compressor out of different parts because the one compressor I did have (Central Pneumatic 21 Gallon) wasn't keeping up with my requirements. But seeing how the pump/motor just blew up on me today I figured I would salvage what I can and go from here.

The pump on this unit is ALSO the motor, it's all one piece and probably proprietary to the brand (go figure).

So what I would like to do is buy a motor and a pump separately and mount them to the tank and use the old control switch if possible.

I want to keep this on 120V 20AMP circuit. What's the best option for me here?

I'm going to use the old motor mounts to make a flat platform for the new motor and pump to mount to.

I don't need a ridiculous amount of power or air but maybe just a bump up from the original specs (2.5 HP motor with 4.7 CFM @ 90PSI with a maximum working PSI of 125)

Can someone recommend me a decent pump/motor combo for this 21 gallon tank?


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## stevon (Mar 5, 2019)

jefferywdonald,

You are not going to get a lot of performance improvement possibility staying with 120 VAC. 1.5 HP is the most you can get out of a 20 amp 120 volt circuit. You can only use 80% (16 amps) of the 20 amps available or you will blow the circuit breaker. This is a NEMA code rule for the wire, outlet, plug and circuit breaker rating. If this is a single line to one outlet I would convert it to 240 volt (an Electrician can explain how to do this) but if other outlets are connected (and usually there are) all would be upgraded to 240 volts yikes! The pump in the picture has such a small platform that it is impractical to upgrade motor and/or air pump. What are you doing that requires so much air? sand blasting? Painting cars? 1.5 HP is good to fill tires and blow off stuff for the average homeowner. I would recommend that a separate wire be run with at least 10 gauge wire to a single 240 volt outlet and a 30 amp breaker to start.

Stephen



jefferywdonald said:


> Hello everyone, new to the forums here. I've been thinking about making/building my own compressor out of different parts because the one compressor I did have (Central Pneumatic 21 Gallon) wasn't keeping up with my requirements. But seeing how the pump/motor just blew up on me today I figured I would salvage what I can and go from here.
> 
> The pump on this unit is ALSO the motor, it's all one piece and probably proprietary to the brand (go figure).
> 
> ...


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## B Mann (Feb 14, 2021)

I fall into the same situation at times.... Fix what I have. You have a Harbor Freight unit. Pretty much bottom of the line. A good pump will run you about $200 and up. A new motor, $150 and up. Now depending on a pulley set up, You are looking at a $400 to fix what you have. HF has a few compressors for half that. Mostly 4 cfm. I agree with Stevon. 220 is a good start to get more volume. Building your own is fun, if it is balanced and works, but may cost more than a new unit. 

Guessing you are not close. I have a spare pump I could sell you cheap. What ever you do make sure you have a working pressure relief. Air tanks can be a bomb.


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## stevon (Mar 5, 2019)

jefferywdonald, 

On 12 gauge wire you can run 16 amps at 240 volt. The most you can get out of it is a 3 HP @ 9CFM at 100 psi to run non stop and not overheat the wiring, plug and circuit breaker. With 10 gauge wire you can get a home user type Dewalt DXCMV5048055 5 HP at 22 amps @ 17.0 CFM at 175 psi. Running non stop this would not overheat the wire outlet or breaker on this setup.

I would buy a good used compressor, I bought a Sanborne (store quality) 5HP 2 stage, 60 Gal for $350 with a light duty Italian T29 pump. It's 20 years old and still working fine as a light hobbyist user. I like to fix/rebuild compressors as a fun project but that doesn't mean it is the fastest most practical or the cheapest solution. It all depends on what you are trying to do and how much tools, skills, workshop and time you have. For most, a sale at Lowes, Home Depot, Tractor supply, etc. is the smoothest way to get an air compressor for their needs.

Stephen


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## stevon (Mar 5, 2019)

jefferywdonald, 

I checked my records, I only paid $250 for the used rusty Black Max 2 stage and the guy selling it thought that I was paying too little. He thought he had an IR or Quincy quality compressor (it wasn't) I'm sure it was $299 on sale or for less new at Lowes 20 years ago!

Stephen


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## stevon (Mar 5, 2019)

jefferywdonald,

Hello! I am interested on the finned air tube coming off of the pump. My Sanborn is leaking and I could use it if you are not using it, is $10 a fair offer?

Stephen


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## Derptasic069 (3 mo ago)

Stevon - A 12 AWG circuit (with a 20 amp breaker) will support a continuous 20 amp load, as per NEC. This is a safety requirement, there is no need for "cushion" unless an appliance pulls more start up amps than running. 12 AWG already has a "cushion" built in.


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## stevon (Mar 5, 2019)

Derptasic069,

Good point about startup amps, the 80% rule is explained in great detail below.









The 80% rule and how it is applied to circuits.


In short, these article says that a standard-rated circuit (circuit breaker and wire) can carry 80% of the circuit breaker and conductor current rating. In contr ast, 100...




www.homeownershub.com





Reading it is confusing but in practical use I've found that a compressor type load using a 12gauge wire and 20 amp breaker on a motor load with more than 15FLA eventually trips the breaker and the wires are hot enough not to hold on to. A 15 amp motor load on a 20 amp breaker, 12 gauge wire and a 20 amp rated receptacle/plug is the max amps that setup will support for more than a half hour use. The LRA of a motor (locked rotor amps) or inrush current is 6 to 10 times the FLA listed on an induction motor. So a 20 FLA listed motor under full load at 0 rpm will draw 120 to 200 amps at startup for a second or more until compressor comes up to full speed. Small tank compressors that cycle frequently are prime examples, the distance of the wire run also affects current draw. I use a 240v, 30 amp breaker with 10 gauge wire (40 foot run) to run a 20FLA compressor motor load and have run the compressor at near 70% duty cycle for 6 or more hours. The circuit breaker, wire, dryer type 30 amp receptacle and plug aren't even warm to the touch, no breaker or motor thermal overload trips yet.

Stephen




Derptasic069 said:


> Stevon - A 12 AWG circuit (with a 20 amp breaker) will support a continuous 20 amp load, as per NEC. This is a safety requirement, there is no need for "cushion" unless an appliance pulls more start up amps than running. 12 AWG already has a "cushion" built in.


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