Compressor repower: single phase vs. RPC
 

Single phase. Why would anyone chose a 3 phase motor versus single if
they have to run a converter? And if you have 3 phase, you don't need
the converter. Don't forget to make the motor pulley slightly smaller.

Ignoramus6689 wrote:

I am a sucker for lightly fixing old stuff.

I have a 2 HP 3 phase Speedaire compressor that I bought for resale
purposes.

I also have the following:

1) all stuff for making an RPC with a 7.5 HP idler (cost about $33)

OR

2) A single phase 2 HP motor that I bought today for $10.

So, I can repower my compressor in two ways:

A) Keep it 3 phase and build an RPC for it, sans enclosure. Sell it as
"2 HP Speedaire compressor with 7.5HP phase converter". Sell 2 HP
single phase motor separately.

B) Repower it with a 2 HP single phase motor and sell as "2HP single
phase speedaire compressor". Throw away the 2 HP 3 phase motor.

Both A and B will likely take me about an hour, unless I have to make
adapter plates.

The question is, which route will bring me more $$$.

i

Oops, I thought the original motor was 3hp. Do verify that both 3 phase
and single are the same speeds, a lot of older 3 phase are 1750, smaller
single phase tend to be 3450 rpm.

Smaller pulley on the motor cuts down the required starting torque,
runpower requirements, lets it run cooler and quieter. Cuts down the
air output as well. :(

Ignoramus6689 wrote:

On Tue, 09 Aug 2005 14:41:00 GMT, RoyJ wrote:

Single phase. Why would anyone chose a 3 phase motor versus single if
they have to run a converter?


Well, my thought was, it would be nice for someone to get a nice shop
setup: a phase converter plus a compressor, all running, in a single
package local pickup deal.


And if you have 3 phase, you don't need the converter. Don't forget
to make the motor pulley slightly smaller.


Thanks. Converting the compressor to single phase should, hopefully,
be easy. Conceptually it is easy, I just should not screw up the
contactor coil wiring. In the worst case, I would need to make some
adapter plate for the motor, but I have some barstock for that, taps
etc. I will check it tonight.

Why should I reduce the pulley diameter of both motors are 2 HP rated?

Thank you!

i


Ignoramus6689 wrote:


I am a sucker for lightly fixing old stuff.

I have a 2 HP 3 phase Speedaire compressor that I bought for resale
purposes.

I also have the following:

1) all stuff for making an RPC with a 7.5 HP idler (cost about $33)

OR

2) A single phase 2 HP motor that I bought today for $10.

So, I can repower my compressor in two ways:

A) Keep it 3 phase and build an RPC for it, sans enclosure. Sell it as
"2 HP Speedaire compressor with 7.5HP phase converter". Sell 2 HP
single phase motor separately.

B) Repower it with a 2 HP single phase motor and sell as "2HP single
phase speedaire compressor". Throw away the 2 HP 3 phase motor.

Both A and B will likely take me about an hour, unless I have to make
adapter plates.

The question is, which route will bring me more $$$.

i

"Ignoramus6689" wrote in message
.. .
On Tue, 09 Aug 2005 15:51:56 GMT, RoyJ wrote:
Oops, I thought the original motor was 3hp. Do verify that both 3 phase
and single are the same speeds, a lot of older 3 phase are 1750, smaller
single phase tend to be 3450 rpm.

I believe, but not 100% sure, that both motors are 1750 rpm or there
about. I hope that they have the same frame. The old 2 HP has a 145T
frame.

Smaller pulley on the motor cuts down the required starting torque,
runpower requirements, lets it run cooler and quieter. Cuts down the
air output as well. :(

I figure, if I replace a 2 HP motor with a 2 HP motor, I can as well
keep the pulley if the shafts match. A marginally better life
expectancy does not matter too much on a relatively cheap used
compressor. Now, if the shafts do not match, I will buy a slightly
smaller pulley from McMaster.

i

I

I'd advise you to save your money and not change the pulley. The start
up torque is always low with a properly adjusted compressor. The pulley/HP
ratio can be compensated for by setting the cut off pressure lower. Your
mileage will vary.

Jerry

Ignoramus6689 wrote:
I am a sucker for lightly fixing old stuff.

I have a 2 HP 3 phase Speedaire compressor that I bought for resale
purposes.

I also have the following:

1) all stuff for making an RPC with a 7.5 HP idler (cost about $33)

OR

2) A single phase 2 HP motor that I bought today for $10.

So, I can repower my compressor in two ways:

A) Keep it 3 phase and build an RPC for it, sans enclosure. Sell it as
"2 HP Speedaire compressor with 7.5HP phase converter". Sell 2 HP
single phase motor separately.

B) Repower it with a 2 HP single phase motor and sell as "2HP single
phase speedaire compressor". Throw away the 2 HP 3 phase motor.

Don't throw away a good motor. You can be sure you'll want it - or know
someone who wants it - just next week if you do!

Chris

I have gone from 440 3hp 3 phase on an old Quincy to 220 5hp single phase,
running the air pump faster to get more air. It was plenty expensive for me
because the mag switch on it wasn't beefy enough so I had to upgrade it. That
cost maybe $300. But if I had to sell it now (fat chance) it would be MUCH
easier to sell. Face it -- most guys are woodworkers or auto freaks, neither of
whom are very into making 3 phase power.

GWE

Ignoramus6689 wrote:

I am a sucker for lightly fixing old stuff.

I have a 2 HP 3 phase Speedaire compressor that I bought for resale
purposes.

I also have the following:

1) all stuff for making an RPC with a 7.5 HP idler (cost about $33)

OR

2) A single phase 2 HP motor that I bought today for $10.

So, I can repower my compressor in two ways:

A) Keep it 3 phase and build an RPC for it, sans enclosure. Sell it as
"2 HP Speedaire compressor with 7.5HP phase converter". Sell 2 HP
single phase motor separately.

B) Repower it with a 2 HP single phase motor and sell as "2HP single
phase speedaire compressor". Throw away the 2 HP 3 phase motor.

Both A and B will likely take me about an hour, unless I have to make
adapter plates.

The question is, which route will bring me more $$$.

i