gas to electric conversion

[Mike(NEOhio)]

I have a homebuilt compressor with a three cylinder Speedair pump, 13 CFM I think. I use it for sandblasting. Powered with an old Wisconsin BKN, 7.5 hp but kind of worn and the small gas tank requires frequent refills. I would like to put a little more power to it. Will a 5 hp single phase motor; be a good option? I always heard to replace electric with gas takes more than double the hp.

 

[Dusty MI]

I've always heard that to go electric from gas, a gas engine needed to be twice the hp.

 

[wore out]

I have a homebuilt compressor with a three cylinder Speedair pump, 13 CFM I think. I use it for sandblasting. Powered with an old Wisconsin BKN, 7.5 hp but kind of worn and the small gas tank requires frequent refills. I would like to put a little more power to it. Will a 5 hp single phase motor; be a good option? I always heard to replace electric with gas takes more than double the hp.

My 18 cfm 2-stage 180 psi compressor is run by a 5 HP, 22 Amp motor.

 

[BarnyardEngineering]

5HP is plenty, but be aware that the way an engine powered air compressor works is different from the way an electric motor powered air compressor works:

An engine compressor has an unloader valve that opens when operating pressure is reached in the tank, and idles down the engine.

An electric compressor shuts off when operating pressure is reached in the tank.

An electric motor on an engine style compressor would never shut off, and never get a chance to cool down. Compressor motors are usually not rated for continuous duty. If you only use the compressor occasionally for short periods of time you could probably get away with a cheap compressor duty motor, but ideally you want a constant/continuous duty motor for this application.

 

[Ultradog MN]

I have a homebuilt compressor with a three cylinder Speedair pump, 13 CFM I think. I use it for sandblasting. Powered with an old Wisconsin BKN, 7.5 hp but kind of worn and the small gas tank requires frequent refills. I would like to put a little more power to it. Will a 5 hp single phase motor; be a good option? I always heard to replace electric with gas takes more than double the hp.

It would be easy enough to put one of these on it.

https://www.amazon.com/Pressure-Switch-Single-Phase-Compressors/dp/B00V52Q1HI

 

[cwtech]

Most compressors use a pressure switch to operate a magnetic starter or starter relay. ...The pressure switch does not carry the motor's amperage.

The pressure switch which Ultradog linked to has a current rating of 1 amp. .....This is satisfactory to operate a starter, but not to carry the motor's running or starting amp draw.

The proper pressure switch will also include an unloader to relieve any head pressure in the compressor for easier starting. ...Some compressors have a mechanical unloader but most do not.

 

[Mike(NEOhio)]

I'm eyeing a 5 hp electric on ebay. I'd use it a lot more if I didn't have to drag it outside, put up with the noise and keep refueling I was pretty sure it would be enough and not to worry, guys. I know the difference between controlling gas and electrics.

 

[TerryfromSWIowa]

Most compressors use a pressure switch to operate a magnetic starter or starter relay. ...The pressure switch does not carry the motor's amperage.

The pressure switch which Ultradog linked to has a current rating of 1 amp. .....This is satisfactory to operate a starter, but not to carry the motor's running or starting amp draw.

The proper pressure switch will also include an unloader to relieve any head pressure in the compressor for easier starting. ...Some compressors have a mechanical unloader but most do not.

I beg to differ, a 220 volt compressor pressure switch is marked line and motor.

 

[buickanddeere]

7.5HP is a consideration .
Are you looking at 3450rpm motors ?

 

[Buffalo Pete]

Careful on your motor selection. Unless your compressor has an unloading valve, starting is really hard. Verify your RPM needed of the compressor, and gauge the motor speed and pulley size accordingly. Suggest stopping by a motor shop. Explain your situation. See what they recommend. They often will have rebuilt motors available at better than new prices.

 

[Loosehandle]

I have a homebuilt compressor with a three cylinder Speedair pump, 13 CFM I think. I use it for sandblasting. Powered with an old Wisconsin BKN, 7.5 hp but kind of worn and the small gas tank requires frequent refills. I would like to put a little more power to it. Will a 5 hp single phase motor; be a good option? I always heard to replace electric with gas takes more than double the hp.

Be careful a lot of electric motors are falsely rated these days

 

[ss55]

I have a homebuilt compressor with a three cylinder Speedair pump, 13 CFM I think. I use it for sandblasting. Powered with an old Wisconsin BKN, 7.5 hp but kind of worn and the small gas tank requires frequent refills. I would like to put a little more power to it. Will a 5 hp single phase motor; be a good option? I always heard to replace electric with gas takes more than double the hp.

Besides checking with an electric motor shop, I would also check with an air compressor shop. They can help you size your electric motor, what controls will be needed, and what your engine powered compressor is currently worth. You might be able to sell your old compressor and buy a new one for less than converting the old one to electric. One thing to consider is how old is the tank on the engine compressor?

 

[zuhnc]

I replaced a 5 HP Honda engine with a 2HP, 220V electric motor. Wheelbarrow-type Emglo compressor. Needed something I could run in the shop, rather than have to drag it outside for air. 1740 RPM electric motor, I did have to adjust motor pulley size for proper compressor operation. Also lengthened the discharge tubing from compressor to tank; the pressure switch unloader closed before the motor could come up to speed, causing tripped breakers. Motor never came off the start windings. Also had to install an in-tank check valve for the stop/start operation. Installed additional components for continuous-run operation, as well. zuhnc

 

[Texasmark]

Be careful a lot of electric motors are falsely rated these days

Yeah......they use "Locked Rotor" amps x "Unloaded" line voltage to calculate HP. Well my way of thinking is that if you have a locked rotor, all you have across line is the DC resistance of the circuit, not that plus the "Reactance" of the running Counter EMF field. These would be lowering the current draw and allowing the line voltage to rise when in normal operation.