Air compressor motor amps

[bigtiller]

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?

 

[SPYDERLK]

Yes. Locked rotor Amps are stated as 102. That is very brief, but it takes a good sized gen to hold voltage to nominal and it drops immediately, foiling startup. This drop means no torque. The compressor loads almost immediately as it spins up and it stalls. If your tank is dead empty ... maybe, but I think you are going to need at least a 10KW to start it otherwise -- and NOT an inverter gen because they want a balanced load to actually give their nominal rating.

 

[404nouser]

Yes it says locked rotor is 102.
But a 20A breaker should hold for it.
The way inductive loads pull power is different than resistive loads.
I would much prefer a breaker tripping than letting a motor pull LRA for more than a couple of seconds.

 

[MichiganIron]

Yes it says locked rotor is 102.
But a 20A breaker should hold for it.
The way inductive loads pull power is different than resistive loads.
I would much prefer a breaker tripping than letting a motor pull LRA for more than a couple of seconds.

Compressor motors are usually capacitor start motors. The start capacitor provides the locked rotor amperage for 1-2 seconds so the motor can provide the necessary starting torque in a compressor application. The capacitor shuts off 1-2 seconds after start up (at rpm) and the motor runs on the rated run amperage under load. This allows a 120v compressor motor to start up and run off a 20amp circuit.

 

[RandyT]

LRA is 102 but motor tag states volts 120 amps 15 hz 60 just below the top of the tag. The issue with trying to run it off a generator is most outlets on gensets are limited to 15 amp breakers with no delay. So it doesn't matter is most cases how big the generator is rated the outlets are the limiting factor.

 

[404nouser]

On a DC supply a capacitor will supply voltage stability to reduce voltage sag from a surge in supply or load.
An AC system uses a capacitor to delay the wave to supply a second waveform thus providing the ability to start rotation from a standstill on a single phase motor.
After the motor is rotating a single phase will keep it going

 

[34Willys]

There should be 1 or 2 humps on the housing where the capacitors are located.
Have you plugged it in to house power and tested? I wouldn't use a generator for the first run.

Patrick

 

[caver]

220-221 whatever it takes.

 

[WinterDeere]

I just love watching electrical threads on this forum.

Listen to 404nouser, he sounds like he actually knows his stuff. The capacitors have nothing to do with supplying LRA, nor do you even care what LRA is, it's a mostly-useless number for the end user.

A single-phase motor is like a bicycle with one pedal. As 404nouser already implied, the capacitor provides some phase shift to the current applied to a secondary winding, temporarily adding that all-necessary second pedal to get the first off bottom-dead center. Once rotating, it can be switched out, as is the norm on most inexpensive "capacitor start induction run" motors. You can ride a bicycle with one pedal, as momentum carries it past the bottom-dead center "stall point", it's only starting them without a second pedal that's a real problem.

All intersting, but none of this has anything to do with your original question of running the compressor off a generator. Your biggest problem with this motor is that it's only a 120V single-voltage motor, with no option to reconfigure for 240V. Attaching this load to any split-phase 240V generator is going to load one leg very heavily, which will cause neutral to "float" in that direction, and cause output voltage on that leg to drop accordingly. This is not good.

 

[bigtiller]

I was hoping to run it on my Honda 2200 inverter generator but it sounds like that's a no-go.

Would I be able to run it by connecting the jumper wire to both the 2200 and the 2000 watt generators? That would produce 4200 watts.

Would that be enough power for the 20 amp plugin on the 2200 genny to run it with no worries?

 

[SPYDERLK]

I was hoping to run it on my Honda 2200 inverter generator but it sounds like that's a no-go.

Would I be able to run it by connecting the jumper wire to both the 2200 and the 2000 watt generators? That would produce 4200 watts.

Would that be enough power for the 20 amp plugin on the 2200 genny to run it with no worries?

The gens would have to be phase matched. Its not likely this pair can be. And even if they could be, they, together, still would not supply anywhere near the required startup surge.

 

[bigtiller]

The gens would have to be phase matched. Its not likely this pair can be. And even if they could be, they, together, still would not supply anywhere near the required startup surge.

My dealer said they will and the following from the internet....

Yes, a Honda EU2200i and a Honda EU2000i generator can be phase-matched and run in parallel to combine their power output, provided the EU2000i model falls within a specific, newer serial number range. This setup allows you to achieve higher power output (up to 3,400 watts rated/4,200 watts maximum) without needing two of the exact same model.

 

[404nouser]

Inverter generators are great for fuel efficiency, reduced noise, reduced weight, and the computer in them normally allows for easy parallel options.
But for this load they are less than ideal.
Turn off eco mode to try.

If you're planned load is resistive loads and switching power supplies then inverter generators and inverters are great.
But heavy inductive loads prefer the heavy rotating mass of a traditional style production.

 

[404nouser]

Before someone says regular generators make modified sine wave, they don't that term is for cheap inverters.

 

[sd455dan]

I have run into this with Off grid home power, but a larger 240 Volt 6 HP compressor that pulls 114 amps. This is a video of just how different ratings can be and how High Frequency versus low frequency Inverters respond to unbalanced 120 Volt loads.

In the video a 6800 watt rated Low frequency Inverter was able to start a slightly smaller similar 120 V compressor while powering multiple other loads, where a 12000 watt Hi frequency inverter shut down trying to start just the compressor.

If the Hondas are paralleled and have the same unbalanced line capabilities as the Schneider output circuitry it may work. You need a lot of single leg short term surge capability of about 10000 watts

 

[RandyT]

I was hoping to run it on my Honda 2200 inverter generator but it sounds like that's a no-go.

Would I be able to run it by connecting the jumper wire to both the 2200 and the 2000 watt generators? That would produce 4200 watts.

Would that be enough power for the 20 amp plugin on the 2200 genny to run it with no worries?

In your case the combines output of both generator is irrelevant because your limiting factor will be the 2400 watt or 20 amp rating of the outlet. Most generators are instant blow breakers not slow or delayed blow like household outlets in some cases.

The max output of the 2200 is 2200 watt (18.3 amp)max with a 1800 watt (15 amp) run so by itself would be maxed out and would need input from the second generator and both would be running at about 50 percent capacity just for the run amperage. I suspect that the start surge amperage of that 15 amp motor would exceed the combined surge wattage of both generators if you did get past the 20 amp outlet.

And this information brings up another point were the outlet is breakered higher than the rated output of the single generator so the outlet won't protect you from overloading the windings of the armature and letting the factory smoke out.

 

[jwmorris]

The first test should be tank empty, can the generator run the compressor from 0-125 psi (or wherever it is set)?

If not, there is no need to go any further. Not enough power.

The next hurtle will be, can it start back up from ~80 psi tank pressure and air back up to 125?

That is where I ran into problems.

The line going from the compressor to the check valve/unloader has insufficient volume, so the compressor is trying to push against pressure while the motor is still in "start" mode and the generator could not provide enough power.

I took that little line and added a section of 2x4 aluminum box tube in the line so there was enough volume where the motor could spin up to "run" mode before the compressor had to fight against in tank pressure and everything worked because the current draw at start up was minimized.

Different compressor but basically where the red box is.

It does, hiss longer when it shuts off, as there is a greater volume of air to bleed off but as long as it works, I can live with that.

 

[WinterDeere]

I suspect the total "unloader volume" in most home-scale compressors is literally just the volume of the usually copper hard line that runs from the compressor head to the unloader valve mounted at the tank. The OP's compressor is pretty tiny, that might just be a 3/8" ID line 12 inches long, so total unpressurized volume might be a scant single stroke of the compressor piston.

If this were me, I'd be shopping for a replacement motor, or even easier... a complete replacement compressor, that can be configured 240 volts. The other option, but generally less useful for other applications, is to find an odd 120V-only generator.

And like 404nouser already said, rotating mass is your friend. Some generators actually have a heavy flywheel, which you'll notice by greater than usual disparity between peak and average load ratings, and that would be ideal for this type of load if the flywheel were actually heavy enough to really matter. But I suspect most portable genny's don't have much flywheel, as it would create a portability challenge.

An inverter generator in this application is not only wasted cost, but counterproductive.

 

[jwmorris]

I suspect the total "unloader volume" in most home-scale compressors is literally just the volume of the usually copper hard line that runs from the compressor head to the unloader valve mounted at the tank. The OP's compressor is pretty tiny, that might just be a 3/8" ID line 12 inches long, so total unpressurized volume might be a scant single stroke of the compressor piston.

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.

 

[WinterDeere]

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.

That's a good idea. It wastes a little energy and fuel charging and then unloading that extra volume with each compressor cycle, and I guess you could experience a momentary pressure drop if usage his high and the added volume causes a delay in adding suppy to the main tank. But these are likely small prices to pay, when you just need the thing to work.