Is it possible to convert 3phase motor to run 240v?

[TonyWarrington]

I have been considering buying a second hand pillar drill - something like a Meddings. Most however seem to be 3Phase systems I have been told that it is possible to rewire to run on household mains supply.
Is this feasible and if so are there any draw backs to be aware of.

 

[Spark123]

You'll need an inverter or a 3 phase supply to do it properly, or buy a single phase motor.

 

[TonyWarrington]

Thanks Spark123. I would guess then that the better option would be to look for a single phase motor of similar speed rating if I decide to go this route.

 

[tim west]

An invertor is a way of running a three phase motor from a single phase supply but a cheaper method is that a three phase motor with two accessible terminals per winding can be wired to work as a single phase motor by using two of the windings as running windings and the third winding as a starting winding with a capacitor and switch(usually a centrifugal type but could also be driven from a Tachometer)which disconnects the start winding once started and the motor runs on the other two windings.
In olden days before health and safety rightly put stop to such a practice, simple wound motors could be started by hand by twisting the shaft and then very quickly standing back

some smaller motors including those on small drilling machines could even run on a permanently connected capacitor start winding ie no switch.

 

[TonyWarrington]

Thanks Tim interesting stuff.

 

[TicklyT]

An invertor is a way of running a three phase motor from a single phase supply but a cheaper method is that a three phase motor with two accessible terminals per winding can be wired to work as a single phase motor by using two of the windings as running windings and the third winding as a starting winding with a capacitor and switch(usually a centrifugal type but could also be driven from a Tachometer)which disconnects the start winding once started and the motor runs on the other two windings.
In olden days before health and safety rightly put stop to such a practice, simple wound motors could be started by hand by twisting the shaft and then very quickly standing back

some smaller motors including those on small drilling machines could even run on a permanently connected capacitor start winding ie no switch.

Just OOI Tim, how well would a 3ph motor run on a single phase? would it run at it's rated speed and output?
I imagine using 2 windings at 120 degrees could end up with a lot of tortional vibration.
That would explain why a toolmaker I know always favoured a pillar drill with apparently longer than necessary flat belt drives to the spindle to soak up those vibes!

I think I would go for a 3 phase converter. You can choose the spindle speed by changing the converter output frequency instead of messing about with drive belts and cone pulleys.

 

[breezer]

Just OOI Tim, how well would a 3ph motor run on a single phase? would it run at it's rated speed and output?

it cant, it was designed to run on 3 phase

 

[tim west]

Possibly because of the advent of invertor technology they dont teach this old method of conversion anymore but it is possible, we achieved it when I was at college all those years ago

heres a link showing the principle and another involving a starter or idling motor but im talking about the capacitor method shown later on in the article, remember I said you can run a small motor with the capacitor permanently connected I forget the limit now but i think it was on motors up to 0.75hp? :

http://www.metalwebnews.com/howto/phase-converter/phase-converter.html

Of course if moneys not a problem then i would suggest an invertor as they can give you far greater control over speed both ramp up and running.

 

[Spark123]

Does it not end up underpowered? I mean where you would normally have 415v you'd only have 240v? I suppose a delta setup would still give 240v per coil, then only the differences in phase angles to contend with.

 

[tim west]

The methods depend on motor sizes and application, if big then the idling motor approach is used this acts as a starter motor initially then converts to a generator that energises the start winding this synchronised setup (if applied properly) allows the motor to run smoothly at higher loads.

A similar but opposite parallel setup used to be used for exciting a coil in a generator to increase output, these days done with electronic control systems.

the smaller motor setup leaves the capacitor inline so the rotating field is still maintained through all three windings

 

[RickH]

......
some smaller motors including those on small drilling machines could even run on a permanently connected capacitor start winding ie no switch.

If you want to know more about how to wire up capacitor start or capacitor tun 3PH motors for 1PH use .... a cgood couple of good books are:
Electric Motors - Jim Cox
Electric Motors in Home workshop - Jim Cox

Both are form Workshop Practise Series ... very cheap paperback books, full of useful information.
I bought mine on Amazon.

 

[Spark123]

The original post is now over a year old

I found this a good read too http://www.allaboutcircuits.com/vol_2/chpt_13/9.html