1ph vs 3ph

TBoomz

Ron
User
Can a 1ph motor work as well as a 3ph at similar HP?
I have a heavy BS, belt driven by a 3HP 3PH motor.

I also have a 3HP 1PH motor. Will this motor push as hard as the 3PH or would I need to get a higher HP [e.g. 5HP] to match the (3HP) 3PH in strength? They both turn at same rpm.

I ask b/c, I just found out that the motor on the RAS I'm trying to sell has, a 3hp 1ph motor. If I can jerry-rig it to run my BS [belt drive] could it have enuff power to turn the heavy wheels w/out burning out? The way the BS is set up, I can introduce slack to the drive belts.
So, am think'n...slack the belt. spin lower wheel. turn on motor. ease slack off till motor catches. Use saw. .... Do-able? Or asking too much of motor.
 

Oka

Oka
Corporate Member
3 hp is 3 hp, doesn't matter if it is 1 or 3 phase as far as hp. Torque will be smoother on a 3 phase motor. 3 phase supply delivers power more steady, and at a more constant rate. Also, with 3-phase power, the 3-phase power supplies are more efficient. A 3-phase power supply can transmit three times as much power as a single-phase power supply, while only needing one additional wire (using 3 hot wires instead of 2). in higher hp 3-phase will be cheaper because the amp requirement will be lower thus you can use smaller gauge less costly wire. Hope thast helps.
 

JimD

Jim
Senior User
I agree with Oka although I would say the benefits he cites for 3 phase are in my opinion minor. Most of us do not have 3 phase power available to our homes. But fortunately a 1 phase motor will still power our equipment just fine. 3 phase is in my opinion only for very large motors in industrial applications.
 

junquecol

Bruce
User
Can a 1ph motor work as well as a 3ph at similar HP?
I have a heavy BS, belt driven by a 3HP 3PH motor.

I also have a 3HP 1PH motor. Will this motor push as hard as the 3PH or would I need to get a higher HP [e.g. 5HP] to match the (3HP) 3PH in strength? They both turn at same rpm.

I ask b/c, I just found out that the motor on the RAS I'm trying to sell has, a 3hp 1ph motor. If I can jerry-rig it to run my BS [belt drive] could it have enuff power to turn the heavy wheels w/out burning out? The way the BS is set up, I can introduce slack to the drive belts.
So, am think'n...slack the belt. spin lower wheel. turn on motor. ease slack off till motor catches. Use saw. .... Do-able? Or asking too much of motor.
That's Sear's (Emerson) 3 HP, which has absolutely nothing to do with reality. Most likely closer to 1.0 HP, than 3.0 HP. Does RAS only run on 220 only? It would have to run on 220 to be 3.0 HP. No standard 110 volt plug is large enough for 3 HP.
 

Woodmolds

Tony
User
"The 3-phase power supplies are more efficient. "
"3-phase will be cheaper because the amp requirement will be lower thus you can use smaller gauge less costly wire. "


These are the main points for me.
I have several small HP 3PH motors that I run daily. Table saw 5HP, Bandsaw 2HP, CNC router 3HP
Even my power feeders are 3PH.

Tony
 

bob vaughan

Bob Vaughan
Senior User
There may be some 'gotcha' details involved.
There could be a problem resulting who's rating the motors. Look at amperage and motor frame size. A three HP 3 Phase motor will draw around 8 to 9 amps at 240 volts. A single phase 3 HP motor will draw 14 to 15 amps at 240 volts. A good three HP single motor will be a 145T or 182T frame motor. If it is a 56 frame motor, its likely a compressor duty ( run for 3 minutes, cool down for 15).

I have a vacuum cleaner that I plug into a wall socket that says it has a 6 HP motor on it. That should tell you something about some people's motor ratings. That's even more egregious than anything Sears ever fantasized.
 
  • Haha
Reactions: Oka

Oka

Oka
Corporate Member
Bob -I have a vacuum cleaner that I plug into a wall socket that says it has a 6 HP motor on it.- :rolleyes: :D That should tell you something about some people's motor ratings. That's even more egregious than anything Sears ever fantasized.

This has always been my amusement in home stuff " 5 amp 120 2 hp motor !".... uh huh .......

Bob brings up another point the duty cycle on alot of motors in single phase are low ergo the 56 frame compressor type. Just depends on how much work you are going to put the motor under.
 
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tvrgeek

tvrgeek
User
3 phase motors are easily reversible. Single phase are not.
3 phase motors work well with electronic speed controllers. Single phase do not.
3 Phase is not usually available residential. More often industrial. You can buy electronic converters* but to get three phase, you still need a big 220 supply.
The voltage of a 3 phase varies. 208 is common, ( gives 120 phase to neutral) so is 480.
An IEC rated 3 HP is a 3HP. Do not confuse these with brush type motors that if you read the fine print, "equivalent"

*Big advantage. Back in the old days, we only had motor-generators.
 

nn4jw

Jim
Senior User
I only encountered 3-phase in the Navy back in the 60's. Aircraft and ship board used it because of all the analog syncro-servo mechanisms in fire control and analog computer equipment. We're talking before digital computers, big and heavy equipment, a lot of vacuum tubes and such. Don't know if it's still prevalent with today's military equipment or not. I would suspect not so much in today's digital age but maybe still in heavy applications. The motor generators were big and heavy.

For a home shop I just don't see it as really necessary even though people seem to convince themselves there's enough advantage to justify the expense involved. Industrial is a whole other thing with different demands.
 

Brantnative

Jeff
Corporate Member
Another related advantage of three phase is you can get full amps at a longer distance if you don't downsize the wire size. We run everything 3 phase 480 volts, even a little 0.5 amp motor, in our pilot plant because we're a long way from the mains.
 

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