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Air compressor: buy a 3-ph and convert to 1-ph??

Spencer in NH

Stainless
Joined
Jan 22, 2007
Location
Southern New Hampshire
I have been offered an Ingersol-Rand 5HP 3-phase aircompressor for $500. I need a 1-phase machine. I am thinking of converting by swapping motors, or using a dedicated VFD. Is this worth it, or should I pass and keep looking for a deal on a 1-phase unit.

There is no emergency, I am getting along on a Sears "6"HP unit (6HP, sure!), but I know that (as ARB has predicted) I am going to eventually kill it.
 
Maybe.

What's the age of the compressor?

What's the CFM?

Is it a single stage or a two stage? The two stage is much more energy efficient.

I'd check www.surpluscenter.com to see how much it would cost for a single-phase motor.
 
I bought a used Curtis 5HP 2 stage compressor with vertical 80 gal. tank with a junk 3PH motor. I installed a NOS Baldor 5HP 3450 RPM single phase motor and sized a new motor pulley to get the pump RPM right. I also installed a NOS motor starter with correct heaters for the overloads. Everything was bought used or surplus, so it cost much less than a new one. It has been running fine for over 25 years. A cheap VFD was not a possibility back then, but it certainly would be now.

You can probably find your best deal on a single phase motor or a 5HP VFD on eBay.

Is the I-R brand sometimes found on low-end compressors? Be sure it is one of the good ones for that price.

Larry
 
Sometimes I lean toward VFD and sometimes the RPC I built, however, this time, if it requires 5HP (maybe up to 7-1/2) or less, I'd go with 1Ph. It's just a compressor and 240V single phase has fine starting torque and little complication on the retro-fit. You can probably even adapt the motor starter with no more than some wire swapping, possibly a different coil. If the coil takes 2 of the 3Ph, (assuming 240V) leads, heck 240V single phase will give you that.

Haunt "motors" on ebay and steal a nice single phase.

If it takes a "big" motor, disregard above. In that case, I'd opt for the RPC, because a compressor has no need for variable speed and the RPC can built for less than the cost of a "big" VFD and be used for additional machines though not necessarily at the same time.

No, I won't say something lame like, "just my opinion", of course that's my opinion!:)

Bob
 
Spencer,

I was looking at the same thing with my Saylor Beale. I decided it was cheaper to buy a new 5 HP single phase motor. When air comprssors start there is a large current draw. When talking to RPC providers I was told to buy a 15 HP RPC to over come the start up current. I assume a VFD would have the same requirement. A single phase motor was cheaper than these large converters.

Hope that helps,
neilca
 
I have been offered an Ingersol-Rand 5HP 3-phase aircompressor for $500. I need a 1-phase machine. I am thinking of converting by swapping motors, or using a dedicated VFD. Is this worth it, or should I pass and keep looking for a deal on a 1-phase unit.

There is no emergency, I am getting along on a Sears "6"HP unit (6HP, sure!), but I know that (as ARB has predicted) I am going to eventually kill it.

Here (Norway) the 5 HP Ingersoll Rand compressors has an automatic star/delta switch, and when the motor goes in to delta mode, a valve close, then the compressor starts to load the tank. The timer here is adjustabel, and if you make it satrt by using a capasitor, it may be possible to run it on single phase. The motor is normaly big enough.
You will probably need nearly 30 sec delay on the timer.

dsk
 
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