Generator won't power compressor....ideas?

[Raspy]

Wouldn't that Compressor check valve be in the compressor itself PRIOR to the copper tube that was to be lengthened....per suggestion? Once the air is pushed out of the compressor it goes thru the copper line and into the tank. I can't see how LENGTHENING this tube will help anything without de-pressurizing that tube. What am I missing?

There are various ways to do this, but the most common, and certainly on larger compressors, is to have a check valve at the tank where the delivery line enters the tank. Then the line can be depressurized at shutoff. It's the hiss you hear when they stop. The pressure switch often has a vent to the outside that opens when the high limit pressure is reached and the switch opens. This clears the delivery line and prepares the compressor for the next start. There is also a check valve in the compressor on the output port feeding the delivery line. The compressor feeds air through it's check valve into the delivery line. When that pressure is higher than the tank pressure, the air flows into the tank. On the intake stroke the air is stopped at the exhaust port and cannot re-enter the compressor. But during unload, the air in the cylinder can flow out the check and out to atmosphere through the unloader.

So, if you increase the volume of the delivery line the compressor, on it's first compression stroke, won't build as high of pressure in the delivery line and therefore starts with less resistance. Increasing length increases volume. Or it could be a larger diameter, but then you'd have to adapt it at each end to the existing fittings. Longer is simpler. It's good idea, if that is the problem. You just need more power and changing the voltage is the easiest way and the best way for your generator. Do that first.

There's no need to over think the electrical wiring in the motor either. Simply read the wiring diagram in or on the motor and follow that. Forget all this deep electrical theory and the "bone" you might get thrown, or the book you have to go read. Sheesh. Just get more watts to the compressor motor from your source. Re-wire to 240 volts, use the appropriate feed wires, and try it out. Probably two number twelve wires and a ground is all it needs.

,

 

[Boeing]

John,
Thanks for the clairification.......I don't THINK that I have a check valve AT THE TANK. Where can I get one, it sounds like an excellent idea.
With a check valve, a longer coiled tube and 240V it ought to run great.
I am sure that it already has one or even TWO start capacitors....there are two covered "humps" on the top of the motor.
Thanks again, Rob

 

[Qapla]

...I am sure that it already has one or even TWO start capacitors....there are two covered "humps" on the top of the motor.

One of those is probably a "run" capacitor and the other is the "start" capacitor.

Also, most compressors I have dealt with have some sort of unloading built in. This is to relieve the force needed to start the motor and compressor before beginning to pressurize the tank. However, when running on a generator or a long electrical run sometimes the compressor needs a little more relief, thus the longer supply from the head to the tank.

 

[Boeing]

Are there larger or more powerful start capacitors? If I have a pressure relief valve somewhere should I just add this longer coiled tube?

 

[tshep]

I don't want to add confusion but...

Apparently you have some control circuits (and thus wiring and devices) that are made to be operated at 120 volts (as exists).
If you change motor only to 240, they will still be 120 circuits. You will need that neutral!
Wire all 4 wires in new cord and plug, move old motor neutral feed to new other hot leg feed as directed in motor cover for 240 changeover - leave other devices on original neutral - add chassis ground if needed.
(Or you could verify every wire and device is 240 rated - we already know they are 120 rated - sleeping dogs,etc)

This is the fix - step one and 99.9% probability last step. Forget add-on unloaders, hard start etc - fix the current flow!

 

[Boeing]

Guys, I can't say THANK YOU enough.........
I don't get back to Va. for about a month but I have the ducks in order now.

 

[pat32rf]

The only devices MIGHT be pilot lights and magnetic hold-in contactors, neither which are likely to be found on a portable compressor. Anything else in the circuit such as pressure switches will operate OK on 240V. Just change the plug to a 240V unit, and motor connections to 240V and you should be good to go, leaving the 110v genny outlets free for lighting, skil saws etc

 

[jenkinsph]

I don't want to add confusion but...

Apparently you have some control circuits (and thus wiring and devices) that are made to be operated at 120 volts (as exists).
If you change motor only to 240, they will still be 120 circuits. You will need that neutral!
Wire all 4 wires in new cord and plug, move old motor neutral feed to new other hot leg feed as directed in motor cover for 240 changeover - leave other devices on original neutral - add chassis ground if needed.
(Or you could verify every wire and device is 240 rated - we already know they are 120 rated - sleeping dogs,etc)

This is the fix - step one and 99.9% probability last step. Forget add-on unloaders, hard start etc - fix the current flow!

No offense but you are adding to the confusion, this is a simple motor hookup to a pressure switch. There are no lights bells whistles or other diagnostic circuits to deal with.

 

[BertZegers]

Hope to make this clear and simple.

The power (HP) mentioned on a electric motor is mechanical power on the shaft. This is what is available for driving something. 24 hours a day 365 days a year. This is what the mechanical engineer needs to know.

The amps and voltage on a motor is what the electricien wants to know.

The formula for a single fase motor: Watts (Power)=Volts*Amps*power factor* efficiency.

This means for a single fase 4 HP motor = 3000wats on 230 volt: 3000=230*amps*0.8*0.9 Amps =3000/165.6=18.1 Amps
This means for a single fase 4 HP motor = 3000wats on 115 volt: 3000=115*amps*0.8*0.9 Amps =3000/82.8 =36.2 Amps

So If you connect to 115 or 230 volts, the mechanical output of the motor is the same.

If you want to know the power of a 1 phase motor: HP= volts*amps*power factor*efficiency/750
for example 230Volt*18.1Amps*0.8PF*0.9E/750=4 HP

If you connect to a 115/230 generator, then wire for 230 volts.

The correct numbers for power factor and efficiency you should find on the motor data shield.

 

[Raspy]

Bert,

I'm afraid you are missing he point. The "4 HP" number is bogus. It's not a 4 hp motor. That is an exaggerated advertising claim.

The specs say it is 115V and 16A.

The question here is how to get it to start, not whether the motor output is the same on 120 as it is on 240. We all know it is the same.

It seems clear that it is much more likely to start on 240 volts than 120 volts from the generator because of the generator design and the wire size.

No need to re-invent the wheel or delve into electrical theory here. Just give the thing more starting watts and that's it. The generator can do that if the compressor is hooked up to, and wired for 240 volts.