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#64268 - 04/03/06 03:26 PM Phase Converter
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
Can any one give me any info. on the operation of phase converters. I have never dealt any in the past, but would like to familarize myself. I saw one the other day that was 240 volt 1 Ph.- 230 V 3 Ph. The way it was connected seemed a little odd, but I am unsure.

I would appreciate any information on connections, how they work, ect.

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#64269 - 04/03/06 04:23 PM Re: Phase Converter
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
Was it a rotary or static type? http://www.phase-a-matic.com/
_________________________
Ron

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#64270 - 04/03/06 04:51 PM Re: Phase Converter
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
Rotary

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#64271 - 04/03/06 05:33 PM Re: Phase Converter
DYNAMITE Offline
Member

Registered: 12/22/03
Posts: 37
Loc: Winkler, MB, Canada
I've experimented with building phase converters. Basically your shifting one phase with capacitors and using the rotating magnetic field in your 3 phase idler motor to create your 3rd leg

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#64272 - 04/03/06 06:19 PM Re: Phase Converter
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
I've always imagined, that it was a single phase motor, with its shaft rigidly connected to the shaft of a three phase generator (motor operating in reverse). When the single phase motor would spin, the three phase motor generator shaft would spin, thus outputting three phase power.
_________________________
Ron

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#64273 - 04/04/06 03:48 AM Re: Phase Converter
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
I built a phase converter of a 3 phase 5 Hp motor which I start up on one phase supply.
It has a ± 5 Kg heavy pulley on the shaft as flywheel which seems to dampen the startcurrent taken from the "load motor" from the lathe.
The Ø terminals are marked R S T. the U V W terminals I have shorted together with the shorting links, this motor was designed for star / delta supply 220/380 Volts. ( Heemaf Hengelo Motor )
I connect 230 Volts 50 Hz to R and Neutral to S
Then around 80 to 120 µF Capacitors across R and T. these caps get switched off after 3 seconds via a timer when the motor is up to speed.
You can experiment with different value of caps and see what works best in your case. They need to be at least 275 Volts RMS or higher rated.
From the motor terminals R S T there is 3Ø 230 Volts available to drive an other 3Ø motor directly to drive a lathe for example. this motor has to be less than 5 Hp.
I can start this circuit with no problems from a 230 Volts 16 Amp supply.
Good luck with the experiment,
Raymond
_________________________
The product of rotation, excitation and flux produces electricty.

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#64274 - 04/04/06 04:47 AM Re: Phase Converter
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Most folks who want 3-phase for domestic use usually have their eye on some tidy secondhand home-workshop machinery! I have a 6kva single to 3-phase motor-generator, using 2 x 3hp single phase motors in tandem driving a commercial alternator in my shop. Always with these 'converting' systems you have to consider the acceptable compromises on complexity, usability and cost.

The best solution of course, is to get a poco supply laid on. Not always possible, and in my case prohibitively expensive, having to deal with a State-owned monopoly.

Ray's system works well, but you have to use a big 'donor' motor, usually twice the size of the biggest 'driving' motor envisaged. Ray mentioned in an earlier post the 'stall at starting' problem he encounterd, although I had not read of this before? For a multi-motor workshop, though, every 'driving' motor in use aids the production of the 3-phase, cascade fashion. IMHO, the biggest problems with this method are the 'pick the right capacitors' connundrum, the complex switchgear for start and the huge donor motor needed to run say a 5hp drive motor- [if less than 5hp is needed, go buy a single-phase motor for the machine.] The 'donor' motor could of course be run up to speed with a fract. hp single-phase 'donkey motor', arranged on a timer.

My system also has a complex start procedure, involving manually running up the s.p.motors in sequence, plus the cost of the twin starters. The 6kva alternator and twin motors alone cost well over US $1000.

Professionally-built rotaries are the best bet if you can afford one- simple to operate and run, with no complex switching arrangements at the converter, and guaranteed to work well if used within the design capacity.

I would not recommend the present generation of 'solid state' devices on the market for any 'big-power' requirement- they don't produce true 3 phase, there are usually motor-size limitations, [ often the advertising blurb does not point out that a 10hp unit is required for a 5hp drive]. You are also limited to a 'one drive at a time approach',[ though that's not a real problem in a one-man shop ] and they do not 'like' aluminum bodied motors, for some reason. Anyone know why?


Alan

Paragraphs added.

ps. Ray, any idea what amps are needed to run-up a donor motor? I have a big, [it must weigh best part of 150lb, I drag it round the shop ], old English Electric 1950's 7.5hp 3000rpm [50hz] 3-ph motor, c/w grease-nipples [i] here that I use as a manually-rotated turntable for routing stair's goosenecks and wreaths. Might be a good larf if it wouldn't mean plunging the whole commune into darkness!

[This message has been edited by Alan Belson (edited 04-04-2006).]

[This message has been edited by Alan Belson (edited 04-04-2006).]
_________________________
Wood work but can't!

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#64275 - 04/04/06 12:39 PM Re: Phase Converter
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
Alan, thanks for your addition to this interesting topic.

The start up current for my 5 Hp motor is around 25 to 30 Amps for about 1 second, then quickly decreasing to 8 Amps for another second and settling up to 4 Amps at 0.6 PF lag. ( 1500 RPM 4 pole ).
The cost of the motor was nil, so was the old contactor I use and the electro mechanical timer which I had in my "spare" junk area of my workshop.
You can probably source a second hand 3Ø motor for less than $50 bucks.

What Alan said with more motors running of it will stabilise the 3Ø supply created.
A bit of trial and error is required to work out what's best.
I have tried other 3Ø motors with cap start on single phase and they all seem to work well. (1500 and 3000 RPM motors).
The actual 3Ø "converter" motor runs very smooth on 1Ø and doesn't have the typical humm as 1Ø motors seem to have probably because of the higher weight of armature and pulley.

Alan, to avoid tripping i use 3 metres of 1 mm² or 1.5 mm² TPS as feed cable, Its a bit thin but doesn't overheat also with longer running periods of the converter. I also fitted an hour meter to monitor "3Ø running time".
If a very big motor needs to be started up I would make some primary resisitors in the motor feed, just to control the current.
I have done this on a 30 Hp 3Ø motor in The Netherlands which i ran of a 3Ø 16 Amps supply driving a rotary saw.
_________________________
The product of rotation, excitation and flux produces electricty.

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#64276 - 04/05/06 03:29 AM Re: Phase Converter
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
http://www.electrical-contractor.net/ubb/Forum7/000234.html

I know the above [2003] post by 'Hillbillysawmiller' has been quoted several times recently in parallel threads on this topic, but it's a most impressive commercial use of the 'big motor' method.
With a 200A single-phase supply, HBSM was (is?) running a variety of big wood-mill machines. Starting a 25HP 3-ph. donor with a small single-phase donkey, he then runs up a 40HP 3-phase saw with a 10hp 3-phase donkey-motor, switching it in to his 'main' once up to speed, so is he using a 'donor' as a power source? He has a 20HP resaw, 10HP blower and a variety of 7.5 and 5hp motors on auxilliary machines too. Interestingly, HBSM made several points- that 'capacitor starting' drew big peak start-amperes, which was why he went for donkey-starting; that a colleague sawyer had been 'shut down by the poco' when using a rotary-converter, as this had seriously affected supply volts for several miles around; and that he had little or no problems with voltage drop on the supply side or with switching-in motors once up to rpm.
One nagging doubt I have is; are the 3-phase donor[s] 1- or 2-phasing?- a recipe for motor overheating?

Alan

Moderator, the URL is correct, ?

[This message has been edited by Alan Belson (edited 04-05-2006).]
_________________________
Wood work but can't!

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#64277 - 04/05/06 08:28 AM Re: Phase Converter
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
If you are just trying to power a small machine, the easiest way is to use a VFD. Input single phase and output 3 phase with the added advantages of soft start and speed control. Most drives are suitable for this application, but you need to size the drive at about 150% of the motor horsepower.
Don
_________________________
Don(resqcapt19)

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