A mate of mine has bought some huge-mother of a miller for his company (details unknown) and has offered to give me their old miller. Apparently it's desktop mounted and comes with a 1.5hp 3 phase motor.

He reckons it'd be cheaper to to buy a converter (such as those sold in Machine Mart) than refit it with a single-phase motor of the same power.

These converter-thingies are the about £350. http://www.machinemart.co.uk/product.asp?p=010712805&r=2105&g=1 14

Anyone know of a simpler (i.e. cheaper) way of doing it? I have no miller-specifics at the moment, just interested to hear your opiions on phase conversions as there are various types about. Apparently.

Cheers,

Neil

To be honest, you could faff around and maybe lash something together - but a 'proper' converter is so much easier to use.

He's right about converting to single-phase - a motor of equivalent power would be much larger and have capacitors, etc. attached. Best stick with what you've got.

David

BTW: lucky beggar!

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=40003&item=5939411964&rd=1
If you feel ambitious read this site. I've had it in my bookmarks for years and I keep going back to it.
http://www.oldengine.org/members/holland/images/Rotophase/rotophase.htm

All you need is a motor the same size or larger+some caps+a relay or two.

You pretty much start the extra motor on 2 phase with a cap, then use it as a generator to make 3 phase.

Metalwebnews- Phase Converters

Contrary to the 12Volts DC Kills /Is Safe thread.

DONT mess touching the wires on any 3 phase stuff.. It can KILL, or badly burn, or maim etc.

Between each phase (Red / Blue / Yellow) and Neutral there is good old household 240Volts ac. Between any two of the phases ie red to yellow, red to blue, etc there can be as much as 415Volts AC. and can be very nasty even if you are lucky.

I am fairly sure this is correct, about 415v between the phases.
Anyway... Treat 3 Phase with a LOT of respect. ie Just do it right, and if you dont know, or are in the slightest doubt, ask or consult a qualified electrician.

I looked at this before.
Do it yourself 3-phase

Mmmmmm.

David,

After a run of bad luck for myself, wife and 3 kids that was described by my dad as 'Epic', I feel good times are ahead.

The free miller complements a 1995 BMW 525SE Vanos with FSH that was presented to me by a former colleague for being a good mate and generally helpful chap in the face of adversity. It goes up the local hill sideways in second.

I'm not really in a position (i.e. competent) to tackle some of these DIY jobbies and feel sure that my life insurance would be insufficient for my dependants should I do the obvious and fry myself.

I like the idea of a £150 box off EBay provided by a chap who's keen to help (so he says), but looking at his site points me to the fact that I don't know enough about the machine itself just yet.

When it's delivered (in the next week or so - end of term - Huzzah!) I'll get some photo's up and you can all envy me through a visual medium.

Keep those suggestions coming - I'm learning all the time!!!!

Cheers,

Neil.

Neil that £150 jobbie looks a bargain as for the capacitor idea unless your a qualified crazy electrical engineer with a death wish stay away.A capacitor when it goes is like a hand grenade.In saying that a 1.5 hp single phase motor aint that dear in fact half the price of the ebay converter at machine fart
Cheers,
Bob

[Edited on 8/12/04 by splitrivet]

[Edited on 8/12/04 by splitrivet]

Hi Neil

If the motor can be connected in DELTA ( should have a triangle shape on motor rating plate) you can use an AC speed controller like :-http://rswww.com/cgi-bin/bv/browse/Module.jsp?BV_SessionID=@@@@0615231523.1102546135@@@@&BV_EngineID=ccciadddfeheeedcfngcfkmdgkldfik.0&cache ID=ukie&3279999141=3279999141&catoid=-668446111

you may have to cut and past the link its a bit long

These convert 240 single phase to 220 three phase

Adrian

Yup i converted my 3 phase Harrison lathe using this method, and it works a treat, total cost £22 .



Originally posted by The Shootist
All you need is a motor the same size or larger+some caps+a relay or two.

You pretty much start the extra motor on 2 phase with a cap, then use it as a generator to make 3 phase.

Metalwebnews- Phase Converters

quote:

---

Originally posted by The Shootist
All you need is a motor the same size or larger+some caps+a relay or two.

You pretty much start the extra motor on 2 phase with a cap, then use it as a generator to make 3 phase.

Metalwebnews- Phase Converters

---

<snip> Edited out an incorrect statement that was potentially dangerous!

Final word - try this web page for really helpful info:

Power Capacitors

This company are highly regarded in the model engineering world, and will give loads of help if you buy their kit (or look like you will!)

David

Is it me or what, sorry fella's I dont see the point.
After rereading this thread why buy a converter,why buy another 3 phase motor a load of capacitors ,risk your life and take weeks to codge up something inherently dangerous.

WHEN YOU CAN GO OUT AND BUY A SINGLE PHASE BRAND NEW (WITH 12 MNTH GTEE) MOTOR FOR £57 and be up and running in minutes.Not only that you can have the added bonus of sticking the old motor on Ebay and sell it to some idiot trying to make a 3 phase converter.

Sorry for ranting guys but this is stupid.

Love and kisses.
Bob

[Edited on 9/12/04 by splitrivet]

Err... 'cos if you buy an equivalent power single-phase motor you'll find that it's 50% larger than the original 3-phase one - and it probably won't fit. It certainly won't have the same starting power.

Also, if you buy a 3-phase large mill, it will have 3 or 4 motors to replace, with motors that also will not fit.

So there....

David

A motor of that size 1.5 horse Cap start not having enough start torque are you having a laugh David,have you seen the application re sizing surely this is the easiest/cheapest option.

OK if its some new fangled micro 3 phase motor fair enough but its probably as old as the hills
Cheers,
Bob

[Edited on 9/12/04 by splitrivet]

I could give you a long (and boring) diatribe about the way they calculated HP then and the way they do it now, but I can't be arsed...

DJ

Oh so 550 foot pounds per second is different now then.

Please dont bore me with a load of indians trying to lose weight tho.

Cheers mate,
Bob , me smiley doofers not working otherwise I'd put a load of em here

[Edited on 9/12/04 by splitrivet]

I forget that though you guys have 220v or so at the plug, it's not the same as the 220v we have at the breaker box.

Start torque and surge control are the advantages of a rotary converter. Solid state converters usually cause a de-rating of the driven motor.

quote:

---

Originally posted by splitrivet
Oh so 550 foot pounds per second is different now then.

---

Thats how Ive always worked it so did the old guy who taught me and so did the college I went to donkeys ago.

How did they work it in your day then get a field full of hosses the electric motor in question (or should I say in your case beam engine)then call in Isaac Newton and let em all slug it out.

Yours lovingly,
Bob.
PS Your not as bored as I am

Guy at work is selling this:

----------------------------------------------------
Transwave 3hp single to three phase static converter

3hp max total (multi-motor) load, 2hp max single motor load, 0.5hp minimum load.

Very good condition - can be seen working.

Reason for sale - got a bigger machine and so bought a bigger Transwave converter.

£200
----------------------------------------------------

I'm considering buying it as there's a good chance I'll end up with a lathe from work not too far in the future.
I don't really understand the description so does i sound like it'd do the job/be a good deal?

Cheers,
James

[Edited on 9/12/04 by James]

David
just to say if you put 240v single phase on any one winding of a 3 phase motor, NOTHING will happen..Even if you do spin it with a rope.
However what you describe would start a motor if you had 2 phases on it (415VAC)
the motor would then continue to run for a short period untill it burnt out 2 of its windings.
It is possible to run a 3 phase motor on a single phase supply using capacitors.....however the torque is vastly reduced & no good for the application we are talking about.
Best bet would be to either convert to single phase motor or as has been suggested run a 3 phase motor with the windings connected in delta from an inverter

[Edited on 9/12/04 by PaulBuz]

Its ok if youve got a few 3 phase applications James not that you can run more than one at a time,just reread your post and you can with that item.

But if its just one item you'd get a lot of change out of £200 for a single phase motor.

Burn out pretty quick Paul with one phase gone and there'll be no torque to speak of,not enough to start owt anyroad in my experience.

Cheers,
Bob

[Edited on 9/12/04 by splitrivet]

[Edited on 9/12/04 by splitrivet]

If you want a few ideas about running 3-phase motors from 1 phase, try this book:

Electric Motors, by Jim Cox
ISBN 0 85242 914 2

It's a fair bit of hassle though, and he recommends buying a converter.

Splitrivet - you might like to see what he says about the difference between the input power and output power... perhaps you'll understand it then.

PaulBuz - sorry, you're absolutely correct - that'll teach me not to quote from memory. You can do it on one phase but you need capacitors to give a dummy second phase, but that requires some rewiring. Described by one author as "suitable for running at half power, with occasional bursts to full power". May suit this purpose, though. I've snipped out my original description, in case someone tries it!

DJ

[Edited on 10/12/04 by David Jenkins]

folks, i know nothing about electricity or motors so i felt perfectly qualified to provide the idiot question here.......

what would happen if you took a powerful single phase motor, connected it to a 3 phase motor and ran the single phase motor. Wouldn't the 3 phase motor generate electricity?

You may have to feed a little bit of power into the windings to get the magnetic field started (or there may be enough residual magnetism), but then it would work. No idea how effective or efficient it would be.

This is the principle used in some convertors (and 3-phase enerators, of course). Voltage and frequency control would be an issue though. Not a cheap and easy option in the long run!

rgds,

David

[Edited on 10/12/04 by David Jenkins]

Ive no need to read a book about motors David spent 18 years servicing and repairing motor driven equipment (as a refigeration engineer).
Cheers,
Bob

Fair enough - we'll keep to our own opinions, shall we?

The thread's been answered by assorted people anyway.

regards,

David