Air compressor motor amps

[WranglerX]

From a slight different perspective from a welding site I visit the generator should should have about 50% more wattage capability than runtime wattage requirement of "welder" to take care of initial surge for when initial striking an arc... Of course this is a welder application, BUT I suspect the same theory may apply with start surge requirement for air compressor motor....

So if a welder requires 120 volt at 20 amp, that is 2400 watts at 120 volts so any generator should be capable of supplying 3600 watts (includes 50% factor) ....

Going on that theory if your air compressor requires 15 amp as normal run, then it would be 1800 watts, and with addition 50% factor then generator should be capable of 2700 watts (surge).....A limiting factor may be circuit breaker and receptacle on generator output panel....

I personally use a 7500 watt generator running a 120V MIG welder that requires about 24 amps running full tilt weld (2880 watts) and with 50% factor added in that is 4320 watts... My only issue was the 120 volt 30 amp receptacle on generator was a 3 prong twist lock plug/receptacle and have to convert it to 2 prong w/ground adapter cord to match that on welder (remember this a 120 volt 140 amp MIG welder) .... And yes the welder requires a 30 amp breaker and appropriate wire size when on shop power...

THE main limiting factor of generator is, can the rotating mass of generator (flywheel/armature) maintain the output level of power without severely bogging down from excessive load and causing severe voltage drop and lose frequency stability.... ,

IF you chose to ignore this post its ok.... It was just put up for perspective....

 

[bigtiller]

You guys and the video have convinced me. I am not going to try to power it with my little generators. And it possibly won't be happy with my big EU7000iS Honda either.

I think I will use this $50 compressor as a power plant for a pneumatic bench & floor broom in the tractor shed.

Thanks for the education.

 

[SPYDERLK]

From a slight different perspective from a welding site I visit the generator should should have about 50% more wattage capability than runtime wattage requirement of "welder" to take care of initial surge for when initial striking an arc... Of course this is a welder application, BUT I suspect the same theory may apply with start surge requirement for air compressor motor....

So if a welder requires 120 volt at 20 amp, that is 2400 watts at 120 volts so any generator should be capable of supplying 3600 watts (includes 50% factor) ....

Going on that theory if your air compressor requires 15 amp as normal run, then it would be 1800 watts, and with addition 50% factor then generator should be capable of 2700 watts (surge).....A limiting factor may be circuit breaker and receptacle on generator output panel....

I personally use a 7500 watt generator running a 120V MIG welder that requires about 24 amps running full tilt weld (2880 watts) and with 50% factor added in that is 4320 watts... My only issue was the 120 volt 30 amp receptacle on generator was a 3 prong twist lock plug/receptacle and have to convert it to 2 prong w/ground adapter cord to match that on welder (remember this a 120 volt 140 amp MIG welder) .... And yes the welder requires a 30 amp breaker and appropriate wire size when on shop power...

THE main limiting factor of generator is, can the rotating mass of generator (flywheel/armature) maintain the output level of power without severely bogging down from excessive load and causing severe voltage drop and lose frequency stability.... ,

IF you chose to ignore this post its ok.... It was just put up for perspective....

It is a 120V x 102A = 12,040W surge at motor start. It is brief at that level, but the V output of a small genny buckles virtually instantly.

 

[jigs_n_fixtures]

Yes, that is why I added the volume, the compressor isn't working against tank pressure until after the motor has started and is running in it's low current state.

Add the extra current from the start and have it working agains pressure at the same time and my generator could not supply sufficient current.

They often use compression fittings, so you just need two more, cut the line and install the extra volume inline.

Just a thought. But the increased air volume in the line doesn't need to be inline. You could tee of and add a section of pipe to provide the extra volume. I'd hook a balloon on the outlet from the compressor and turn it over five times by hand, then add that volume to the discharge line.

 

[jwmorris]

This is the compressor I was talking about earlier.

This early 1900's Curtis compressor is another way to have low amp start.

Note lack of capacitors on motor.

The pully does not spin the compressor shaft until it is up to speed, then the counter weights engage the pump.

 

[WinterDeere]

This early 1900's Curtis compressor is another way to have low amp start.

Note lack of capacitors on motor.

Nice old motor, I have had many. Note that lack of a modern bubble housing on top of the motor does not mean it lacks a start capacitor, as many old motors bury them inside the base casting.

But yeah, a lot of old compressors used repusion-induction motors (type RI), which engage brushes and act as a DC/Universal motor during startup phase. Look thru either end bell housing to see if you can spot a commutator and brushes. Type RI motors usually have no start capacitor. They provide higher starting torque, necessary on old compressors starting against a load without modern unloader valves, but they also draw a pretty high current during startup phase.

 

[Mike1955]

You guys and the video have convinced me. I am not going to try to power it with my little generators. And it possibly won't be happy with my big EU7000iS Honda either.

I think I will use this $50 compressor as a power plant for a pneumatic bench & floor broom in the tractor shed.

Thanks for the education.

Never know till you try it. Hook it up and see. The generator has a breaker and it can be reset if it trips. I believe you may have overthought this one

 

[WranglerX]

It is a 120V x 102A = 12,040W surge at motor start. It is brief at that level, but the V output of a small genny buckles virtually instantly.

IF this was a issue, then circuit breakers ( shop or generator) would trip every time compressor starts up, it is so brief the breakers probably does not have time to react.... THis is where the 50% over factor comes in when using genney.....

 

[WinterDeere]

IF this was a issue, then circuit breakers ( shop or generator) would trip every time compressor starts up, it is so brief the breakers probably does not have time to react.... THis is where the 50% over factor comes in when using genney.....

Nope. Residential breakers have two trip mechanisms, thermal and magnetic. The thermal trip mechansim is slow, designed to heat up and trip the breaker faster than your wiring can heat up and melt its insulation, whereas the magnetic trip mechanism is your fast short-circuit protection.

The standard magnetic trip on any 15 or 20A residential breaker I've ever seen is 10,000 amps, so you're not going to trip that on motor start.

Thermal trip follows a time/temperature curve, the harder you push it, the faster it will trip. I'd need to dig up some tables, but I suspect something like 2 minutes at 120% rating is probaby in the ballpark. A 20A residential panel breaker can easily handle 50A inrush for a second or three, without tripping, no sweat.

I have no idea how those little push-button breakers on generators are configured. I'm speaking only of standard residential panel breakers.

 

[WinterDeere]

It is a 120V x 102A = 12,040W surge at motor start. It is brief at that level, but the V output of a small genny buckles virtually instantly.

Depends on type, and if mechanical, then the mass of the rotating assembly. Get a big flywheel moving, and even if it's constant-current rating is low, it'll punch right thru any momentary strain.

 

[SPYDERLK]

It is a 120V x 102A = 12,040W surge at motor start. It is brief at that level, but the V output of a small genny buckles virtually instantly.

IF this was a issue, then circuit breakers ( shop or generator) would trip every time compressor starts up, it is so brief the breakers probably does not have time to react.... THis is where the 50% over factor comes in when using genney.....

It is. Standard breakers will hold for a 1 second or more at a current of 5x rating. The key is that the locked rotor current is very brief (as stated previously) because a hard voltage source will kick the system into motion and the current will decline to within the nominal working range of the motor. - - A little gen is a hard source only up to its power rating, E x I = W. Afterward voltage, E, subsides quickly. At even twice the power rating the effect is virtually instantaneous; the voltage output buckles preventing the torque needed to reach system operating speed. It hums and trips its output breaker. -- The genny would start the motor alone fine ... just not a system that builds resistance quickly as it is put into motion. Count on a 400%+ overfactor when starting such system.

 

[SPYDERLK]

Depends on type, and if mechanical, then the mass of the rotating assembly. Get a big flywheel moving, and even if it's constant-current rating is low, it'll punch right thru any momentary strain.

You are talking a limitation in the prime mover [engine] to sustain startup. So yes there, IF the gen capacity is well above what the engine can provide. A gen capable of the max startup demand will not buckle - it will just subside fairly linearly as it slows.

Usually Engine/Gen sets are pretty close matched so a flywheel would have little effect.

 

[BlueKnife]

I bought a used Coleman 20 gallon air compressor and need help with the amperage requirements for powering it with a generator. Can you see on the label how many amps are required at start-up and run?

It looks to me that it wants 102 amps at start-up. Is that possible?

Is this going to regularly run on the generator or is that just a temporary thing? If it's something that's going to happen often, I'd be converting it to gas engine powered. Way more efficient than running a generator.

 

[bigtiller]

Is this going to regularly run on the generator or is that just a temporary thing? If it's something that's going to happen often, I'd be converting it to gas engine powered. Way more efficient than running a generator.

Someday, in 2027 I may build about 1200' of fence using mostly steel T posts and beat them into the ground with a pneumatic post pounder.

But with my age and the order of importance around here, puts that fun time near the bottom of the list. So if it happens, it probably will be a younger man doing it with his own tools.

 

[WranglerX]

Someday, in 2027 I may build about 1200' of fence using mostly steel T posts and beat them into the ground with a pneumatic post pounder.

But with my age and the order of importance around here, puts that fun time near the bottom of the list. So if it happens, it probably will be a younger man doing it with his own tools.

Think you are going to need bigger air compressor......

 

[bigtiller]

Think you are going to need bigger air compressor......

and some younger muscles

 

[WinterDeere]

Think you are going to need bigger air compressor......

I heard rumor that was actually an un-planned or un-written line, and that Scheider just improvised it, on the spot.