Thread: What "HP" to replace 3phase to single phase

Can't say for definite, but, the original 1/2 Hp single phase motor on my drill press died after doing some heavy drilling of thick steel. I replaced it with a 1Hp single phase and its been able to cope with what ever I put in the press
I hope this helps

Gooday 1 HP Is 1 HP regardless of phase

Ok, I guess that makes sense. Just the HP I need to look at regardless of the phase.
I just browsing on the net, 3 phase has better starting torque comparing to single phase at the same power rating as it has 3 pushes on one REV vs 1 in single phase

Jackaroo

Originally Posted by jackaroo

3 phase has better starting torque comparing to single phase at the same power rating as it has 3 pushes on one REV vs 1 in single phase

Jackaroo

As a drill press isn't normally started under load, it doesn't matter if starting torque is less.
In a second or so after switch-on, torque will be the same as a similar power 3 phase motor.
Jordan

my taiwanese drill press ( about 20 years old) has a 3\4 hp single phase, it will handle most things ive tried till the belts start slipping

I have swapped a number of motors for pedestal drills. The most drama I find is the shaft diameter to pulley size. Most new motors are based on a metric frame, and the diameter also depends on the motor rating. Some of the chinese drills have motors with non standard sizes and I have had to get the pulleys bored out to suit.
The local brand CMG motors are still available with imperial size shafts (CW series) which are great to fit onto older waldown drills etc.
Make sure to get a quality motor if it is single phase, as the cheaper models are not reliable with their capacitors.
Peter

Hi Peter,

Its the Waldown I am replacing, most of the 1hp has 3/4" shaft. Where did you get your motor from?

Jackaroo

Jack,
Don't tell anyone, but I got mine from Hairyforbes.
The prices are very reasonable at the moment:
https://www.machineryhouse.com.au/Pr...stockCode=E050
Considering the list prices from CMG are $405 (1 HP) and $526 for 2HP.
And the BS frame bolts straight on.

Another problem that I found with the el-cheapo motors, was the vibration. This is caused by "poling", where the magnetic field ( 4 poles, 1450 rpm) is uneven. The motor tends to accelerate and slowdown for each revolution. Caused by fabrication standards.
One drill I had was so bad, that I could not keep the steel vise still.
Peter

Thanks Peter, I'll pay them a visit over the weekend or so.

Jackaroo

Maybe motors have got more expensive but 5 ish years ago I got a 3hp 2900rpm motor from western electric for $210... They have since closed I think though.

It is not so much the hp that you need to compare, but the torque. If it is not already on the motor nameplate, have a look on the motor manufacturer web sites for the torque that your motor has, then get a single phase motor with the same torque

Hi Jackaroo and all,
I think that if I were in the position of needing to power a 3 phase pedestal drill with single phase, I would consider an inverter drive, (a v.f.d. or v.s.d. depending on which school you went to) instead of changing the motor out. It will mean that you will have the advantage of smoother running, and superior starting torque of 3 phase together with a wide speed range should this be useful to you, and if in the future you have 3 phase available, it will be simple to change back. Your existing motor will hopefully be a dual voltage unit and will be easily converted from 414v 3 phase to 240v 3 phase by swapping the links over in the cable terminating box on the motor. Even if there is no provision for quick changing from star to delta wiring by swapping the links over a motor rewind shop will usually be able to dig the appropriate wires out and do the change over for you, without charging an arm and a leg, but most 3ph. motors of low power ratings have the links available.
Inverter drives have many desirable features like programable acceleration from rest and ditto with deceleration, electronic braking just to name a few, and 1/2 h.p. units are around $300 brand new on eBay so the cost may be even lower than a motor change especially if machining work and new taper lock pulleys are involved. If you have numerous 3ph machines to run, then a rotary phase converter would be well worth considering. I.I.R.C. Fossil who frequents these forums wrote up his adventures in home brewing such a unit, and a search should yield results. I will post a couple of links on vfds, - I have no connection with any of the sites, nor am I an electrician, so please get other opinions from those with more knowledge and experience than yours truly. Good luck,
Rob


Australian Baldor - Products - AC Controls - KBVF - ac Inverter Drive - Chassis Mount



KB VSD VFD AC Drive .37 KW output 240V AC 7amp IN NEW* - eBay Other Electronics Modules, Electronic Modules, Kits, Electrical, Business, Industrial. (end time 25-Feb-10 21:59:52 AEDST)

Thanks for the links Rob.

Have a look here at how to build a Phase Converter for a motor