Noodle
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| posted on 8/12/04 at 09:34 PM |
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3 phase
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
Your sort make me sick
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David Jenkins
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| posted on 8/12/04 at 09:44 PM |
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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!
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Peteff
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| posted on 8/12/04 at 09:48 PM |
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Try on ebay
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
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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The Shootist
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 posted on 8/12/04 at 09:53 PM |
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You can make a rotary converter ...
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
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wilkingj
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| posted on 8/12/04 at 09:59 PM |
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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. 
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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drmike54
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| posted on 8/12/04 at 10:01 PM |
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I looked at this before.
Do it yourself 3-phase
Started Welding the chassis!!!!
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Noodle
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| posted on 8/12/04 at 10:17 PM |
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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.
Your sort make me sick
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splitrivet
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| posted on 8/12/04 at 10:32 PM |
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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]
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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ady8077
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| posted on 8/12/04 at 10:58 PM |
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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
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Wadders
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| posted on 8/12/04 at 11:55 PM |
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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
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David Jenkins
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| posted on 9/12/04 at 08:28 AM |
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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
I just KNEW a USA poster would suggest that! Trouble is, in Europe houses don't get 2-phase supplies (i.e. 2 of 110v) - we just get a single
phase of 230v. THIS METHOD WILL NOT WORK. (pardon my shouting).
<snip> Edited out an incorrect statement that was potentially dangerous!
A warning on 3-phase convertors - their size has to be matched to the machine's motors, but a milling machine often has several different motors
of varying sizes. You may have to drive what's called a 'pilot motor' to keep a stable supply for all the different motors - a
pilot motor is just a spare 3-phase motor that sits running with no load, somewhere safe. It doesn't take much current, but it does ensure a
good 3-phase supply.
This sounds expensive, but you can get old 3-phase motors and switchgear really cheap. The advantage of keeping the machine's 3-phase motors is
that they are a lot more powerful for their size.
David
[Edited on 9/12/04 by David Jenkins]
[Edited on 10/12/04 by David Jenkins]
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David Jenkins
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| posted on 9/12/04 at 08:33 AM |
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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
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splitrivet
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| posted on 9/12/04 at 12:41 PM |
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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]
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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David Jenkins
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| posted on 9/12/04 at 02:51 PM |
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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
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splitrivet
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| posted on 9/12/04 at 03:11 PM |
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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 used to be a Werewolf but I'm alright nowwoooooooooooooo
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David Jenkins
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| posted on 9/12/04 at 03:25 PM |
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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
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splitrivet
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| posted on 9/12/04 at 03:33 PM |
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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 used to be a Werewolf but I'm alright nowwoooooooooooooo
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The Shootist
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 posted on 9/12/04 at 03:59 PM |
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Ooooops....sorry.
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.
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David Jenkins
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| posted on 9/12/04 at 04:08 PM |
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quote:
Originally posted by splitrivet
Oh so 550 foot pounds per second is different now then.
That's not the way they specify it these days - now they say 1 HP = 768W. So, the motor's taking 3 Amps at 240v, let's call that
768W input, so that's a 1HP motor.
Trouble is, that doesn't equate to the power on the motor spindle, as you describe. I have an old 1HP single-phase motor at home that plated
for 4 Amp input power, so 1KW roughly by their rules.
David
(I'm bored now)
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splitrivet
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| posted on 9/12/04 at 05:32 PM |
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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
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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James
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| posted on 9/12/04 at 06:13 PM |
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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]
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PaulBuz
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| posted on 9/12/04 at 06:25 PM |
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3 phase motors
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]
ATB
Paul
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splitrivet
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| posted on 9/12/04 at 07:19 PM |
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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]
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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David Jenkins
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| posted on 9/12/04 at 08:46 PM |
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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]
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MikeR
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| posted on 9/12/04 at 11:05 PM |
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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?
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