Author Topic: (AC power) Converting single-phase into 3 phase: What are my options?  (Read 5985 times)

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Offline cvanc

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Hi all-

I need to run a machine that needs 3 phase power in a building that only has single phase.  So I need to manufacture roughly 10KVa of 208v, 3 phase, Wye power.  With a decently clean sine wave as well!  How do I do that?

Here's the details:

INCOMING BUILDING POWER
The building has the usual split 240v single-phase coming in, which becomes a pair of 120v rails in the breaker panel 180° out of phase with each other (in other words, the totally generic typical single-phase power provided here in the U.S.)

THE MACHINE NEEDS
208v Wye 3 phase power; the circuit breaker at the AC inlet inside the machine is 30 amps, but I am told max draw on any leg is never more than 20

THE QUESTION
How do I get 'from here to there'?  In the old days one option was a motor-generator set, which is nothing more than a single phase motor directly driving a 3 phase generator.  I've actually used these in decades past and while they absolutely work they are loud and smelly and hot and did I mention loud?  This approach just doesn't work here; it's an office setting and there will be people in the same room with the machine.  I'd have to mount it outdoors (roof? alley?) and put it in some kind of custom built soundproof, theftproof enclosure.  Ugh!

Surely there's a solid state answer this this kind of problem, but I have no experience in that arena.  I'd like to lean on those who've BTDT to see what might exist and get to a discussion of specific brands of gear that are respectable, or to be avoided.

"Why do I need a clean sine wave?" "Why do I need Wye?"
'Cuz this box is ANALOG and FUSSY, that's why.  And it has like 22 different power supplies inside, some of which are linear and some of which are switchers.  I need to baby it and give it exactly what it expects to receive.  This thing wants Wye with at least a half decent sine wave and I will not even TRY to rock that boat.

I'm all ears folks, I've got maybe 2 weeks to propose a solution so there's a bit of time to kick this around but not a lot.  Thanks so much for any insights you can offer.
« Last Edit: September 22, 2018, 12:11:52 pm by cvanc »
 

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #1 on: September 22, 2018, 12:25:27 pm »
Would it be possible to rewire it for single phase?
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Offline sokoloff

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #2 on: September 22, 2018, 12:33:30 pm »
THE QUESTION
How do I get 'from here to there'?  In the old days one option was a motor-generator set, which is nothing more than a single phase motor directly driving a 3 phase generator.  I've actually used these in decades past and while they absolutely work they are loud and smelly and hot and did I mention loud?  This approach just doesn't work here; it's an office setting and there will be people in the same room with the machine.  I'd have to mount it outdoors (roof? alley?) and put it in some kind of custom built soundproof, theftproof enclosure.  Ugh!

Surely there's a solid state answer this this kind of problem, but I have no experience in that arena.  I'd like to lean on those who've BTDT to see what might exist and get to a discussion of specific brands of gear that are respectable, or to be avoided.
The old solution you describe above is called a rotary phase convertor. The newer, solid state, solution is a variable frequency drive (VFD). I've only used them to drive mill motors where I didn't care (and didn't check) on the cleanliness of the power.

So, look into that, but VFD/variable frequency drive is at least a keyword for you to search on...
 
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Offline Floyo

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #3 on: September 22, 2018, 01:30:23 pm »
If its really fussy about clean power a VFD as is wont cut it, they just output a modulated square wave, and are really geared towards driving motors.
What you could look into is an AC source, they basically create a super clean grid on their outputs, fully programmable in voltage and frequency.
Since their outputs are isolated from the grid they can probably (not standard) be wired in parallel on the primary side, and their outputs in 3 phase.
One brand to look for is Chroma http://www.chromaate.com/product/list/ac_power_source.htm
Edit: here is another https://pacificpower.com/products/afx-series/

Having said that, AC sources are "call us for a quote" levels of pricey ;)

If we had more info on the machine another option could well be possible since, aside from motors, not a lot needs native three phase.
« Last Edit: September 22, 2018, 01:41:07 pm by Floyo »
 
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Offline Jeroen3

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #4 on: September 22, 2018, 01:53:17 pm »
THE QUESTION
In the old days one option was a motor-generator set, which is nothing more than a single phase motor directly driving a 3 phase generator.  I've actually used these in decades past and while they absolutely work they are loud and smelly and hot and did I mention loud?  This approach just doesn't work here; it's an office setting and there will be people in the same room with the machine.  I'd have to mount it outdoors (roof? alley?) and put it in some kind of custom built soundproof, theftproof enclosure.  Ugh!
There won't be a silent solution for this. Either you use a solid state converter, which needs cooling fans. Or you use an rotary converter, which needs cooling fans.
Putting it somewhere else is not that hard, it just requires some work.

If you cannot rewire the machine, and it definitely needs a clean power source, then I think the rotary converter in some other room is the only way.

An office usually has a server room with AC. How about there?

Did you check if the building connection capacity large enough?
 
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Offline cvanc

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #5 on: September 22, 2018, 02:03:27 pm »
Would it be possible to rewire it for single phase?

No.  The machine is old and was super expensive back in the day and it's failure-prone and hard to get parts for and fragile.  Plus, any problems it has going forward will be my problem, so no internal modifications of any kind will be done, period.

If its really fussy about clean power a VFD as is wont cut it, they just output a modulated square wave, and are really geared towards driving motors.
What you could look into is an AC source, they basically create a super clean grid on their outputs, fully programmable in voltage and frequency.

I don't need some perfect super-low distortion sine wave but I sure don't want a coarsely stepped square wave.  I was hoping to find products that live in the middle ground between those extremes but maybe 'slightly distorted sine wave generators' don't exist?

If we had more info on the machine another option could well be possible since, aside from motors, not a lot needs native three phase.

Please see above, no internal modifications allowed, we have to treat it like a black box and accept it as it is.

Having said that, AC sources are "call us for a quote" levels of pricey ;)

I was afraid of that.

Thanks for your insights; much appreciated.
 

Offline cvanc

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #6 on: September 22, 2018, 02:11:13 pm »
If you cannot rewire the machine, and it definitely needs a clean power source, then I think the rotary converter in some other room is the only way.

You may well be right.  On the positive side, every now and then you can get a good used one ridiculously cheap on eBay (shipping can be $$$, though).

Did you check if the building connection capacity large enough?

Plenty, I've got two panels.  One has a 400a main and the other has a 200a main.  Both are currently fairly lightly loaded, especially the 400a one.
 

Offline langwadt

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #7 on: September 22, 2018, 02:16:14 pm »
Would it be possible to rewire it for single phase?

No.  The machine is old and was super expensive back in the day and it's failure-prone and hard to get parts for and fragile.  Plus, any problems it has going forward will be my problem, so no internal modifications of any kind will be done, period.

If its really fussy about clean power a VFD as is wont cut it, they just output a modulated square wave, and are really geared towards driving motors.
What you could look into is an AC source, they basically create a super clean grid on their outputs, fully programmable in voltage and frequency.

I don't need some perfect super-low distortion sine wave but I sure don't want a coarsely stepped square wave.  I was hoping to find products that live in the middle ground between those extremes but maybe 'slightly distorted sine wave generators' don't exist?


VFD outputs pwm but once it is "filtered" by the motor it is a pretty  good approximation of a sine wave

https://youtu.be/U71WrUihzO0

 
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Online drussell

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #8 on: September 22, 2018, 02:21:10 pm »
THE MACHINE NEEDS
208v Wye 3 phase power; the circuit breaker at the AC inlet inside the machine is 30 amps, but I am told max draw on any leg is never more than 20

What kind of machine is it?

If there is just one motor, a VFD is definitely the way to go.  They are readily available, inexpensive lego-type pieces these days.  It gets much trickier if the equipment has tons of different motors, etc. thus to make a realistic recommendation, we need to know exactly what it is you're needing to power...  :)
 
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Offline Benta

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #9 on: September 22, 2018, 02:24:50 pm »
I'd go for a 15 kVA AC inverter with line filters. It doesn't need to be a VFD, a simple inverter will do the trick.
 
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Offline capt bullshot

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #10 on: September 22, 2018, 02:26:24 pm »
A VFD rated for 10 kVA (kW) output usually has a 3-phase input. At least here in Europe.
One can add a sine filter to the VFD to get a decent sine wave output voltage.
There's one caveat: The VFDs output doesn't have a neutral, so if your unit requires a neutral, this can't work.
Safety devices hinder evolution
 
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Offline Floyo

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #11 on: September 22, 2018, 02:31:15 pm »
I don't know of any "slightly distorted" options off the shelf, other than what's already been mentioned. A VFD with a filter could possibly work, but the filter also needs to account for the common mode voltage generated by the drive.
Another option could be (which is I think what Benta is suggesting) a solar inverter capable of islanding mode, but that'd need a DC input.
 
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Online drussell

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #12 on: September 22, 2018, 02:34:49 pm »
A VFD rated for 10 kVA (kW) output usually has a 3-phase input.

The vast majority of VFDs a just rectified inputs to get the main DC rail input.  Yes, larger ones have a three phase rectifier available but virtually every one will allow you to use just two of them from a regular single-phase 240 volt input.  You just leave the third one disconnected.  Sometimes there is a setting or a jumper to disable any phase-loss detection from being triggered by the (intentionally) missing input phase.

This application is very common.
 
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Offline cvanc

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #13 on: September 22, 2018, 02:42:35 pm »
What kind of machine is it?

A motion picture film scanner.

If there is just one motor, a VFD is definitely the way to go.

Everybody, please lose all thought of motors.  There aren't any motors.  (well, there are, but they all run on DC)

What it has, internally, is about two dozen single phase (120v) power supplies of wildly varying types, power levels, and vendors, all poorly distributed across the three hot phases, and all returning to a single shared neutral.  This is why it has to be Wye power (5 wires: 3 hots, one PE, and a real copper neutral).  Any 3 phase topology that does not have a real copper neutral at the midpoint of the 3 legs will not work.  Plus they did a bad job distributing the load around the circle and even at idle the neutral current is several amps.  So Wye it is.

This is why I really, really can't consider internal changes.  It's a black box for the purposes of this discussion.  Thank you all for your suggestions and ideas.
 

Offline Floyo

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #14 on: September 22, 2018, 02:46:52 pm »
If there aren't any native three phase loads, why not tie the phases together into a single one?
Otherwise so far only the AC source option remains, it has a real neutral.
 
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Offline Benta

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #15 on: September 22, 2018, 02:50:07 pm »
Why do you guys keep talking about VFDs?
The OP needs a simple 3-phase fixed-frequency inverter. They're off-the shelf parts, the line filters as well. And yes, there are types with neutral for a wye connection.
The input rectifiers can be 3-phase, split-phase or even single-phase depending on model.
There's nothing magical about this.
 

Online Ian.M

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #16 on: September 22, 2018, 02:52:21 pm »
If you are *100%* certain there are no PSUs inside it with 208v phase to phase input or three phase input, then it should run with all phases strapped in parallel externally and fed 120V, 60A.

How you get that 120V 60A is a different matter - I suspect a transformer off a 240V 30A split phase feed would be the best option.
 

Online drussell

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #17 on: September 22, 2018, 03:02:05 pm »
Well, if it isn't a motor load, VFD is out.  You would need some kind of three phase inverter, not the nice simple, cheap VFD.

Personally, since all the loads are 120, I would open it up and re-wire the one third of the stuff that is on the blue phase to be half on the black, half on the red and be done with it.  Easy peasy, re-wired for 240.  (120-N-120, with neutral, that is, of course, not really 240.)

I could build you one of our APS-3720s, I'm in the process of building another one anyway (a variable frequency model, they're using it for 3-phase 400 Hz) for an aircraft company that builds specialized stuff for C-130s for the US military but they're about $5000, though a fixed frequency version at 60 Hz, maybe sans some of the metering, of one could potentially be a bit less expensive, I suppose.  :)
 

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #18 on: September 22, 2018, 03:03:51 pm »
If you are *100%* certain there are no PSUs inside it with 208v phase to phase input or three phase input, then it should run with all phases strapped in parallel externally and fed 120V, 60A.

Except that he would have to beef up the neutral internally since everything would now go through the neutral instead of just the difference left over that didn't cancel between the three phases.
 

Online schmitt trigger

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #19 on: September 22, 2018, 03:08:19 pm »
What Floyo and Ian are suggesting is THE best option.
I would go one step further and tie 2 inputs to one phase and the remaining input to the other phase. And the neutral where it belongs of course.

This will work because the line to neutral voltage in a 208v Wye is 120v. Exactly the same as in 240v split phase.
 
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Offline SeanB

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #20 on: September 22, 2018, 03:18:48 pm »
You have a 120VAC split phase supply, which then gives you 2 hot wires and a neutral. Thus simply take the highest loaded phase and connect the one hot to that, and tie the other 2 to the other phase. Breaker at 40A, double pole, and the only neutral current will be the difference again, and as it is not a balanced load anyway it has a beefy enough neutral. Nothing in there is actually 3 phase, and even stuff that is 207VAC and across phases will generally be happy with 240VAC anyway.

No need for anything other than a look to be absolutely sure the thing has no 3 phase motors ( 3 phase motors run via an inverter or VFD will be happy here anyway, on 208V and 240V they get about the same DC  bus voltage anyway) DOL, just regular mystery 120VAC supplies, and the switchers will be happy at 120-240VAC in most cases, and linears anyway will be 120VAC or have a primary tap changer if they are critical in any way.
 

Offline tpowell1830

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #21 on: September 22, 2018, 03:39:33 pm »
Having had to deal with putting a machine shop with 3 phase motors in a garage that only had single phase power (the 240 VAC phase are 180° apart, not 120°) and 3 phase was not available in the area, we used the rotary converter method as Jeroen3 suggested. In your setting this will not work, since it is loud and you don't get the common neutral.

You are left with a very expensive option as was suggested, or you have to call the power company to install a 3 phase transformer at your shop, if you have 3 phase available in your area. In my area, getting 3 phase transformer installed is not very expensive if you use it for a large portion of your power requirements. You do not have that, since you only need it for this single device.

Tough predicament, but my first move would be to call the power company and tell them your needs and see what they can do to get your 3 phase power. If deemed too expensive or not available, then you only have the other 2 options; i.e. one very loud and the other very expensive. Granted, the power company option may be fairly expensive after having to get a separate 3 phase panel and the wiring required as well, but you would then have the 3 phase available from that point on in case 1. You added another of these machine or 2. you added other 3 phase equipment. The upside with this option is that the 3 phase transformer side would be true 3 phases at 120° with a common neutral and the transformer would be maintained by the power company plus no noise.

Hope this helps...
« Last Edit: September 22, 2018, 03:42:16 pm by tpowell1830 »
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Online drussell

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #22 on: September 22, 2018, 04:14:37 pm »
Installing 3-phase power would be silly overkill in this instance.  cvanc simply needs to double and triple check that everything really is 120 volt and then supply it from both sides of the available split 240.

As suggested multiple times above, this can be as simple as wiring two of the phases to one side, provided that the imbalance doesnt't cause an overloaded neutral, though that is unlikely as long as it is on both sides of the 240, not just all on a single 120 (which would be silly anyway.) 

If the imbalance will be huge or the OP wants to run from a smaller breaker, I really can't see why it would be too difficult to move even just a couple of the supplies from one phase to the other to balance things out, even if he doesn't want to move everything from the third phase.

I still think it would be pretty easy to move everything from the blue phase (or whatever one was easiest) over to the other two, but surely it can't be too difficult to just strap two of them together at the supply and move just a couple of the supplies from the now more heavily loaded "double side" over to the other phase.

I can't see why that would be very difficult.

Of course, I haven't seen any photos of the actual unit's internal horror show either, though.  :)
 
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Offline Benta

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #23 on: September 22, 2018, 04:19:18 pm »
Well, if it isn't a motor load, VFD is out.  You would need some kind of three phase inverter, not the nice simple, cheap VFD.


???

Huh? An inverter is simpler than a VFD.   :-//
 

Offline tpowell1830

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Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #24 on: September 22, 2018, 04:27:24 pm »
Installing 3-phase power would be silly overkill in this instance.  cvanc simply needs to double and triple check that everything really is 120 volt and then supply it from both sides of the available split 240.

As suggested multiple times above, this can be as simple as wiring two of the phases to one side, provided that the imbalance doesnt't cause an overloaded neutral, though that is unlikely as long as it is on both sides of the 240, not just all on a single 120 (which would be silly anyway.) 

If the imbalance will be huge or the OP wants to run from a smaller breaker, I really can't see why it would be too difficult to move even just a couple of the supplies from one phase to the other to balance things out, even if he doesn't want to move everything from the third phase.

I still think it would be pretty easy to move everything from the blue phase (or whatever one was easiest) over to the other two, but surely it can't be too difficult to just strap two of them together at the supply and move just a couple of the supplies from the now more heavily loaded "double side" over to the other phase.

I can't see why that would be very difficult.

Of course, I haven't seen any photos of the actual unit's internal horror show either, though.  :)

As far as installing 3 phase power being silly, I don't think you actually read his post. He is saying that the internals of his device is a black box and he is not going to modify it to balance any loads or re-arrange the internals in any way because it is very sensitive. In other words, he doesn't want to modify the stuff in the box.

I stand by my advice to get 3 phase power if within his cost structure, as I clearly implied. If getting 3 phase power is not within his cost structure then he may ignore my post entirely, up to him. It would still be appropriate to call the power company to see what they can do for him.
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