Thread: replacing three phase motor with single phase

Not difficult - no real traps except use a Capacitor start single phase motor.
Match the HP and the nominal RPM

Don't use a brush motor, too bloody noisy and rough.
Cap starts, good just like Bob said, and watch your fingers.

Are you sure you don't already have 3 phase? I found that I already had it and I was told that this is not uncommon. Apparently older electric ranges used 3 phase. My house is dated around 1969.

To get the same efficiency out of the bandsaw you are better to get a larger single phase motor than the original 3 phase unit. If it has a 1hp motor you are better with 1 1/2 or 2hp in single phase. If the motor is 3hp or larger in 3 phase then you may be in trouble as the largest single phase motor you can run of a domestic supply is 3hp and you had better have a good supply as the starting currents on these motors is fairly high. In some older homes you can see the lights dim everytime someone starts a 3hp single phase motor.

[QUOTE=rev]I am thinkink of buying a cheap but solid three phase bandsaw and replacing the motor with a single phase one. QUOTE]

Perhaps an inverter for your 3 phase motor,to run of single phase .May avoid a bit of work making new motor fitting to machine.
Regards ,Bela

Thanks for all the tips.

Unfortunately, I do not have 3 phase wired to the house - had an electrician check that.

I didn't know about the loss of efficiency and the need for a larger motor in single phase. Why is that?

I also don't know anything about the inverters mentioned. Are they costly? Are they easy to wire in? Do they cause any loss of power from the motor? I thought inverters were designed to run 240V AC appliances from batteries.:confused:

Thanks again for the ideas.

I've done this with several pieces of machinery. My 12" SCM jointer now runs a 3hp 1ph motor that's not a capacitor start. If the machine is not under load when started you don't need a cap start motor.
A bandsaw motor is usually under load due to the blade tension & friction (width of blade) so a cap start motor will be required.
3hp IS NOT the largest single phase motor you can get, it's 5.5hp BUT start-up load for a motor this size is REALLY extreme. You'll need @ least 40²mm main electrical supply line CLOSE to the distro point.

Originally Posted by rev

Thanks for all the tips.
I also don't know anything about the inverters mentioned. Are they costly? Are they easy to wire in? Do they cause any loss of power from the motor? I thought inverters were designed to run 240V AC appliances from batteries.:confused:
Thanks again for the ideas.

There are all sort of inverters .For your application it may be ok, if the price of the saw is low.I had quotes for motor and inwerter for A$300.
There are quite a few companies in the Melbourne yellow pages selling this system.Suggest you research how cost effective this solution may be for you.
Feel free to contact me .
Regards ,Bela

How does the startup load compare from single to 3 phase motors. Do the 3ph draw as much current on startup.

Just musing with a comparison for large single phase as compared to a comparable 3 phase running via a phase converter. I seem to remember something about 3 phase having lower start loadings; as with the way they are wound; the next phase acts as a "magnet" to continually draw the commutator forward.

If this is the case; it may be viable for those of us with heavily loaded lines to invest in a phase converter to run multiple 3 phase motors.

Ken

Originally Posted by Toggy

How does the startup load compare from single to 3 phase motors. Do the 3ph draw as much current on startup.

Just musing with a comparison for large single phase as compared to a comparable 3 phase running via a phase converter. I seem to remember something about 3 phase having lower start loadings; as with the way they are wound; the next phase acts as a "magnet" to continually draw the commutator forward.

If this is the case; it may be viable for those of us with heavily loaded lines to invest in a phase converter to run multiple 3 phase motors.

Ken

The way I understad it is that 3 phase requires less power initially as the three polls act in a push/pull motion, this is the reason that they don´t need a capacitor to start them. They also tend to have better torque than their single phase counterparts due to the three poles spinning the motor.

If I´m wrong then I´ll gladly be corrected but that´s the way it was discribed to me.

I checked my old uni textbooks and you are both correct. An induction motor requires a rotating magnetic field. With a single phase motor, you cannot get start a rotating field, just one that pulses back and forth. Hence, the single phase motor needs some way to get it started. Once going, single phase is OK to keep it turning (although a 3ph motor will have less "slip" and better torque). To start the 1 ph motor, a second winding, using the same supply, but at a slightly different phase, is used. There are a number of methods to obtain the phase shift in the so-called "starting winding" of a 1 ph machine.

A capacitor in series with the starting winding can be used to get the phase shift. The more start-up torque required - the larger the cap, you may need to use two, one can be switched out once the motor is up to speed.

Alternately, the starting winding may be of a different thickness wire with a different impedance to get the phase shift. The starting torque for the second method is about 1.5 times the full load torque.

Clear as mud?? :confused:

Rev,

I replaced a 3-phase with a single-phase motor about 6 months ago. Apart from matching power and RPM, be careful about matching the shaft size - you don't want to have to replace the pulley at the same time! I initially tried Hare and Forbes
Hare_Forbes
who had a few motors - in my case the right RPM/HP but wrong shaft size. In the end, I went direct to a company called CMG:
CMG
and was able to match RPM/HP/shaft size... plus they have detailed lists of their motors, sizes, performance data etc. on their website ("CW" motors). In the end, the hardest part was removing the pulley from the old motor...

You might also be lucky like me and convince them to offer you a trade price

Hope this is of help,
NWB

What is the cost of a single Phase motor eg 2, 3 HP?

Rev,

Have a look at the thread below but be careful to read the whole thing as there are a few minor description errors at the start. Fossil is one of those natural engineers that our society needs more of.

http://www.woodworkforums.ubeaut.com...ighlight=phase



You may find that the three phase motor can be re-configured in the terminal box and with a phase converter could be used as is. I have never done it but it appears plenty of others have successfully. Everytime I by something second hand for the right size motor I end up fix the equipment and then won't strip the motor of it.

Cheers,

Blackout