Author Topic: (AC power) Converting single-phase into 3 phase: What are my options?  (Read 5997 times)

0 Members and 1 Guest are viewing this topic.

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #25 on: September 22, 2018, 04:27:47 pm »
???

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

VFDs rely on the fact that they are driving a motor to make the circuitry simple and inexpensive.

A decent quality VFD in that power range is a couple hundred bucks.

Show me an inexpensive (somewhere even remotely cost competitive with a VFD) 3-phase-output inverter that takes wall power for an input or with a cost effective power supply to run it from whatever DC input voltage it requires.
 

Offline cvanc

  • Frequent Contributor
  • **
  • Posts: 608
  • Country: us
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #26 on: September 22, 2018, 04:36:44 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.

If there aren't any native three phase loads, why not tie the phases together into a single one?

I've supported these machines for 20 years.  Hell, there isn't enough therapy in the world to get them outta my head  :-DD

I'm 100% certain there are only 120v loads inside, and nothing 3 phase, and nothing 208v (leg-to-leg).

But here's the problem:  People have tried what you suggest before and the internal neutral burns up.  It's not sized for this and does not tolerate it.  What a mess THAT was, and here's why...  the power distribution panel in these things is literally the first assembly installed in the factory, and it's held in by really long bolts coming up from the underside.  If you need to pull it you have to lay the machine on its' back.  It weighs  sixteen hundred pounds.  And it's full of fragile, totally obsolete, delicately aligned optics.  Doing any kind of maintenance on the power distribution panel is the single most difficult task this design has.  It's just a non-starter.

It gets worse.  Before it burned up (it made it for 2 or 3 weeks) the output images had rolling humbars that nobody could figure out.  The power rewiring had done something to screw up the analog front end.  God only knows what.

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.)

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.

Hmmm, this is something that I don't think anyone has tried before but given the history of the internal neutral failing with increased load I have to admit my doubts the box would be OK.  And there's always the hum-bars-in-the-picture thing to worry about...

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.

Oh absolutely, this is very clearly the best and safest answer.  The utility was contacted weeks ago but a response has not come yet.  It remains my best hope but time moves on and we have to come up with an answer.

I've yet to visit the site and the folks there are not technical.  I tried to get them to tell me what's on the poles in the alley but no luck yet.  (I asked for pictures of the poles and they sent photos of the bottoms of the poles where they go into the ground - sigh)

For all I know 3 phase is 30 feet away from them and this is all no big deal to "do the right way".  But it's not an industrial area, so who knows.

Way back when I knew someone with this same issue and they found out the nearest pole with 3 phase on it was over a mile away.  The utility was happy to quote pulling the line to their address, however they wanted 35 grand to do it.  In the end it was decided to give the utility the money but boy did the people who chose to lease that building catch hell.

I really appreciate all of you for engaging in this conversation.  It's never too late for me to learn.  Thank you.
« Last Edit: September 22, 2018, 04:38:53 pm by cvanc »
 
The following users thanked this post: SeanB

Offline Benta

  • Super Contributor
  • ***
  • Posts: 2569
  • Country: de
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #27 on: September 22, 2018, 04:40:02 pm »

A decent quality VFD in that power range is a couple hundred bucks.


I must be living in parallel universe. A 10...15 kVA VFD for a couple hundred bucks? Do show.
 

Offline Brumby

  • Supporter
  • ****
  • Posts: 10193
  • Country: au
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #28 on: September 22, 2018, 04:49:24 pm »
It's pretty clear the only acceptable solution is to provide clean 3 phase power that can handle poorly balanced loads across the phases - which is what the OP asked for in the first place.

To my mind, the motor-generator solution is the simplest.  The sine wave output should be pretty good.

Second up is 3 inverters at 120º phase difference, on a common neutral.

Last is a 3 phase generator set ... but that's a whole new level of noisy.
 
The following users thanked this post: boB

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #29 on: September 22, 2018, 04:59:54 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.

If there aren't any native three phase loads, why not tie the phases together into a single one?

But here's the problem:  People have tried what you suggest before and the internal neutral burns up.

NO!  You *absolutely* cannot do that!

That takes the neutral from carrying 0-30 amperes to carrying the full load of everything in the device (up to 90A in this case.)

That is a common mistake made by people installing a 120-volt inverter system.  You have to go back and re-wire anything that shared a neutral between phases to have their own separate wires.

Quote
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.)

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.

Hmmm, this is something that I don't think anyone has tried before but given the history of the internal neutral failing with increased load I have to admit my doubts the box would be OK.  And there's always the hum-bars-in-the-picture thing to worry about...

That would work from a power standpoint and as long as you keep the phases somewhat balanced, your neutral would be fine since it only carries the difference (unlike just jamming them all together, which absolutely will not work!  Egads!  That is guaranteed to burn up the neutral!  :scared: )

Unfortunately this does not help you if physically cannot get to any of the wiring.

The hum bars would very likely be due to the fact that the neutral was running at 3x its maximum capacity and probably many, many times what it would normally see when running on three phase where it only sees the difference.  This would cause all sorts of havoc and is exactly what I would have expected to see in that ill-fated scenario.  :palm:  There would be severe voltage drop on something that was supposed to be essentially unloaded.

Quote
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.

Oh absolutely, this is very clearly the best and safest answer.  The utility was contacted weeks ago but a response has not come yet.  It remains my best hope but time moves on and we have to come up with an answer.

If it is available and within budget then obviously that is certainly a valid method.  :)

I only say it is "silly" from a cost perspective compared to the minor modifications (if any) required to run it properly on 120-N-120...  i expect it would be cost prohibitive, though I do not know your budget, and like you say, maybe there is 3-phase available right there.  I suspect not, though, since they have a 400 amp panel that is only single phase.  Usually if you have a location that is getting a service of that kind of size, it would be 3-phase by default if it were available nearby.

Every area is different, though!  :)
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #30 on: September 22, 2018, 05:11:42 pm »
I must be living in parallel universe. A 10...15 kVA VFD for a couple hundred bucks? Do show.

Ok, fair enough, probably more like 500-750 bucks for a new one in that power range.  The very common 10 HP-class ones are a couple hundred bucks, plus there is always the used market if cost were an issue.  VFDs are incredibly common units now.

I still doubt you'll find a three-phase inverter or a set of three that is stackable at 120 degrees for anywhere close to what a VFD costs.  180 degrees is a pretty commonly available stacking configuration but 120 is very rare, as are dedicated 3-phase units.  (It could solve the OP's problem, of course, though, if the cost is tolerable.)
 

Offline dmills

  • Super Contributor
  • ***
  • Posts: 1785
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #31 on: September 22, 2018, 05:29:05 pm »
Old Rank cinetel?

Here is a left field idea, grab three big audio amps (I have a certain fondness for old Crown MA5000VZs for this sort of stunt), add suitable signal generator and some wiring, job done.
You can have three phase of almost arbitary waveform and frequency, and could even lock it to an external SPG if chasing black and burst is a thing in your workflow.

Or do it the sensible way, motor inverter (or VFD, don't really matter) and a modest delta-star transformer (to get you the neutral), you can get filters for the outputs of the better sort of inverter drives to make decent sine waves, and the delta-star transformer will provide useful filtering anyway (as well as soaking up any triplen coming back from the scanner).

Regards, Dan.
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #32 on: September 22, 2018, 06:23:06 pm »
Old Rank cinetel?

Here is a left field idea, grab three big audio amps (I have a certain fondness for old Crown MA5000VZs for this sort of stunt), add suitable signal generator and some wiring, job done.
You can have three phase of almost arbitary waveform and frequency, and could even lock it to an external SPG if chasing black and burst is a thing in your workflow.

Heh...  That "left field idea" is not nearly as crazy as you think.  :)

That's exactly what our APS-3720 is based on.  Three modified audio power amplifiers.  :)

The use of a commodity item as a building block allowed us to make them available for a fraction of the cost of similar units.  I originally designed it as a cost effective alternative to using an aircraft APU for testing their door systems in the hangar.  The customer was pleased with the cost-performance ratio and have ordered multiple units since I did the original design.  I think the reason they ordered the most recent one was they sent the one that was in Florida to some military base in The Philippines or something.  :)

This is the original prototype unit, from almost a decade ago:



The back of the rack:





Single phase in operation during testing (things like boiling water in a kettle using 400 Hz power sounds funky.  Like you're on a plane.  :) )



 

Offline dmills

  • Super Contributor
  • ***
  • Posts: 1785
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #33 on: September 22, 2018, 06:37:20 pm »
Yep, that would get it done.
My use case was a US touring band that had specified 120V, but forgot to tell us that they were driving a tonewheel organ and the 60Hz mattered (it usually doesn't much!).

Apparently we were the ONLY venue on that tour where the thing was in tune!

Regards, Dan.
 
The following users thanked this post: drussell

Offline duak

  • Super Contributor
  • ***
  • Posts: 1009
  • Country: ca
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #34 on: September 22, 2018, 06:52:57 pm »
I would look in to a Phase Perfect converter: http://www.phasetechnologies.com/products/phase-perfect-240v/overview

These things take the center tapped single phase AC in and generate a third phase using a rectifier, bulk capacitor and PWM driver with output filters.  The FP websire has papers describing how it works.  I don't believe the input neutral can be used as the neutral for the output wye so you would also need an isolating delta-wye transformer to re-reference the load neutral.

These things are expensive though.  Another way is to get a big 3 phase motor, a few times the size of the load to act as a rotary phase converter.  Most 3 phase motors in North America are wound with 6 windings that can be connected in parallel for 208-230 V or series for 440-460 V.  As a balanced wye converter, three windings would be connected in a wye with the neutral brought out for the secondary or load.  The other three windings are usually connected as a wye already.  Two of these windings are driven directly from the single phase lines while the third is driven by a phase shift capacitor from one of the lines.  An additional capacitor may be needed to get the motor up to speed.  By taking advantage of the two sets of windings, the motor can serve double duty by also acting as an isolating transformer.  Most of the noise is from the cooling fan.  A good motor, especially 1200 or 900 RPM, is quite quiet.

Cheers,
 
 
The following users thanked this post: schmitt trigger

Offline edpalmer42

  • Super Contributor
  • ***
  • Posts: 1808
  • Country: ca
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #35 on: September 22, 2018, 07:02:26 pm »
Just for comparison, I've heard of one brand of rotary converter, AmericanRotary.com .  They have prices on their web site.  It looks like their AD-15 model (21 amps) would do the job.  Price is $1649.

If you wanted to rewire the unit, but can't due to the overloaded neutral, is there any way that you could replace the existing neutral with a bigger one?  It doesn't have to be pretty - I'm talking drills, hole saws, hammer & chisel, dynamite - you get the idea.  Maybe run the new neutral external to the machine, but inside a conduit for protection.  You just want to get from the point where the power connects to the other end of the neutral cable.

Ed
 

Offline Beamin

  • Super Contributor
  • ***
  • Posts: 1438
  • Country: us
  • If you think my Boobs are big you should see my ba
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #36 on: September 22, 2018, 09:33:22 pm »
Is this some sort of milling machine with CNC and motor controllers? Hence all the different power supplies? IF you have money to spend on this MrCarlsons lab of youtube fame  has a real business doing/making power supplies for CNC machines. Hes out of Canada. and has a website.
Max characters: 300; characters remaining: 191
Images in your signature must be no greater than 500x25 pixels
 

Online IanB

  • Super Contributor
  • ***
  • Posts: 9732
  • Country: us
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #37 on: September 22, 2018, 09:51:50 pm »
Is this some sort of milling machine with CNC and motor controllers? Hence all the different power supplies?

No it isn't. Why not read the thread instead of doing a drive-by posting?  ::)
I'm not an EE--what am I doing here?
 

Offline cvanc

  • Frequent Contributor
  • **
  • Posts: 608
  • Country: us
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #38 on: September 22, 2018, 10:59:19 pm »
Again, thank you everybody.

Best word of the thread so far?  "Dynamite"  :-+
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 19839
  • Country: nl
    • NCT Developments
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #39 on: September 22, 2018, 11:45:27 pm »
At 10kVa getting 3 phase power to the machine is the best option. 10kVa translates to around 100A @110V single phase.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline 6PTsocket

  • Regular Contributor
  • *
  • Posts: 212
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #40 on: September 23, 2018, 12:12:51 am »
That was my thought, too. The original was 3 phase to spread the load but the OP wants to run it on single phase that has to carry the whole load. I see no advantage to splitting the source into 3 phases that all have to come from his single phase source that must supply all the power.
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.

Sent from my SM-G900V using Tapatalk

 

Online IanB

  • Super Contributor
  • ***
  • Posts: 9732
  • Country: us
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #41 on: September 23, 2018, 12:40:26 am »
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.
That was my thought, too. The original was 3 phase to spread the load but the OP wants to run it on single phase that has to carry the whole load. I see no advantage to splitting the source into 3 phases that all have to come from his single phase source that must supply all the power.

Another drive-by posting.

Because if you tie all the phases together the neutral will burn out. See higher up the thread where this was discussed.

Quote
Sent from my SM-G900V using Tapatalk

Why do we care about this? Please tidy up your litter and don't keep dropping it everywhere.
I'm not an EE--what am I doing here?
 

Offline BrianHG

  • Super Contributor
  • ***
  • Posts: 4327
  • Country: ca
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #42 on: September 23, 2018, 02:37:14 am »
Build your own 1 phase to 3 phase rotary converter.  You will have your true real 3 phase sine wave, but, of course, you will hear an AC motor spinning all the time:  Note that other youtube videos include schematics and tests and what to avoid...


« Last Edit: September 23, 2018, 02:46:19 am by BrianHG »
__________
BrianHG.
 

Offline richard.cs

  • Frequent Contributor
  • **
  • Posts: 837
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #43 on: September 23, 2018, 09:28:47 am »
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.

Hmmm, this is something that I don't think anyone has tried before but given the history of the internal neutral failing with increased load I have to admit my doubts the box would be OK.  And there's always the hum-bars-in-the-picture thing to worry about...
If all the phases were equally loaded then the neutral current would equal the line current, so unless the neutral is smaller than the line conductors this would be fine. If they're unequal and you pick the highest loaded one to be on the opposite phase then the neutral current is lower. The only condition where the neutral current is higher is if you pick the wrong one, perhaps because the phase balance is time varying.

In terms of hum bars you would have to try it and see but at least it's not damaging to do so. Depends entirely what the pickup mechanism is as to if it cancels when phased like this or not. I suspect it'll be better than with all on one phase but perhaps worse than in three phase. There has to be some such effect on 3 phase because the balance is never perfect, just weak enough not to see.
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #44 on: September 23, 2018, 09:30:16 am »
Build your own 1 phase to 3 phase rotary converter.  You will have your true real 3 phase sine wave, but, of course, you will hear an AC motor spinning all the time:  Note that other youtube videos include schematics and tests and what to avoid...

A rotary converter would certainly work, however, for the power level that the OP needs it is going to have to be one seriously big honkin' motor, especially to handle the horrible power factor that is likely to be presented by a bunch of capacitor-input rectifiers in all those power supplies without the wave tops getting so smashed that it looks more like a square wave.  :) 

Edit:  After more thought, I don't believe a rotary converter would ever be able to be made to work correctly in this case, especially since the loads are not static.  There would great imbalance between the phases to begin with that would be unlikely to be able to be compensated for with the capacitor arrangement, certainly not always stable with varying loads on each phase.  I do believe a motor-generator set would work, if appropriately sized, but I think the single-motor converter is out.

That will not fulfill his "low noise, somewhat sinusoidal" requirement.  :)

The motor will also make some interesting noises with power being drawn only at the peaks of the wave, especially when the phases are going to be randomly imbalanced and the imbalance is going to be changing during operation.

Remember, we're talking about needing about 20 amps per phase, all being drawn through DC supplies with (presumably non-power factor correcting) rectifier inputs.  I expect the peak currents to be very high, and only at the tops of the waves and that is probably why it has a 30 amp supply, even though the average power stays down below 20 amps.

<story mode on>
My first appreciation of just how much power factor actually meant in practice was a similar issue 15 or 20 years ago that I had just really never thought through, even though I had built dozens of different and all manner of power supplies and such before in my lifetime.  It took sticking my scope on there to see what was going on before the light bulb above my head finally came on.

We had installed a (for the time) fancy new inverter/charger system at a friend's off-grid cabin so there could be power without having a noisy generator running.  (A Trace Engineering DR series with 6 x GC2 batteries, IIRC).  The original generator that was at the cabin was the Honda (EX?)3500 workhorse that had been there for years.  The inverter supplier had indicated to my friend's dad that charging would be slow with such a generator, which it was, so he had already planned to buy a larger unit.

The next spring, they took up a new 6500 Honda but, of course, it didn't charge any faster either.  (Humorously enough, I calculated later that the old one was actually faster, and they are even in the example charge rates for various generators in the Trace manual, though Trace didn't do a very good job of explaining why, power factor, etc. and basically just said "you will need a much larger generator than you think")  The cabin owners were a bit dismayed, of course, but knew I would be coming out in the summer anyway.

At Trace's suggestion, I brought a nice big motor-run capacitor and wired it right across the generator output to help with the PF.  I also parallelled in a second 10ga cable to the inverter/charger from the generator shed to reduce the impedance of the feed line.  I had even brought a little PC-based scope with me (fortuitous choice) just in case and did various basic tests before I finally built a danger-divider using some resistors I happened to have in my laptop bag and put the scope right on the mains (scope and laptop floating, just in case I did something stupid) to see what was really going on.  When I saw just how bad the waveform really was, I knew exactly what the problem was.  Well, I already knew what the problem was but not the magnitude of the problem!  The charger was only drawing current from the part of the wave that was above the equivalent battery level since it was a smart, but relatively standard, non-PFC charger circuit.  The average voltage was being held correctly by the poor Honda but there is just no way it could supply all that power just on the peaks.  I knew it would be a bit clipped, that was expected, but I wasn't expecting the wave to me THAT mashed.

The next morning I was sitting on the steps of the generator shed, pondering the manual for the Honda when I came across the schematic and another lightbulb-over-the-head moment struck me.  Eureka!  Another friend (who is an electrical engineer) stumbled out that way, probably to re-tap the keg for a breakfast brew (we're at the fishing cabin remember, don't judge :) ) and I said, "Hmmm, Dös, take a look at this, what if I take this winding, flip it over and jam it on this one, that should work, right?"  He basically said, "Hmm, yeah, that should work, just don't get it backwards and burn out the windings.  LOL"

The 6500 generator has two separate windings which make up the two sides of the 240 volt output.  The 120 plugs are just distributed half on each side, so in effect our charger was only running on a 3250 watt generator winding.  The old 3500 Honda had a switch for 120/240 volt which used both halves when in 120 mode to actually supply more current than the 6500 could.

Anyway, I opened up the control panel, took off the winding wires, re-jiggered it so they were both in phase and connected together, buttoned it back up and fired her up.  The voltage gauge now only read 120, of course, but it only took a moment before Dös was out there sayin' "Dude, you gotta come check this out!"  I went into the cabin to the inverter and, sure enough, the inverter/charger was hummin' like it had never hummed before.  Dös said "Wow, that's impressive," when he felt the cables.  He was working for Nortel at the time and they have some giant honkin' 48 volt rectifiers and battery banks but he was impressed that our 00 or 000 cable running to the batteries was actually getting warm.  :) 

Essentially, I had (more than) doubled our charge rate by doubling up the 120 at the expense of the ability of the generator to do 240 volts.  (Since we had only ever used 240 once before, to run my giant compressor during a cabin expansion the previous year, that wasn't an issue.)

Charge rate was now solved but I was still never able to properly equalize the batteries with that set-up.  You just couldn't get the battery voltage high enough to really do it, even after many hours of running at full charge.  PFC control chips were just starting to become a thing so I started drawing up plans to make a PFC'd battery charger but in the years since, they ended up added a solar panel setup which keeps the batteries fully topped up, even when nobody is there for 95% of the year so it has become less of an issue and I never built the PFC charger.
</story mode off>

My point is, you're likely to need a WAY bigger motor than you expect if you go this route.  That is where an electronic solution may well become more practical than the mechanical one.  Phase imbalance becomes irrelevant and any design with feedback will at least do its best to keep the waveshape correct within the limitations of the wiring impedance, etc.
« Last Edit: September 23, 2018, 09:17:07 pm by drussell »
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1468
  • Country: ca
  • Hardcore Geek
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #45 on: September 23, 2018, 09:39:05 am »
If all the phases were equally loaded then the neutral current would equal the line current, so unless the neutral is smaller than the line conductors this would be fine. If they're unequal and you pick the highest loaded one to be on the opposite phase then the neutral current is lower. The only condition where the neutral current is higher is if you pick the wrong one, perhaps because the phase balance is time varying.

Unfortunately it is time varying, depending on the operation of the machine at the time.

The OP also states that any re-wiring to re-balance is impossible since it is located in the bottom of the 1600 pound machine, so that's a non-started also, supposedly.

If the OP can get to at least enough wiring to move a couple of the right supplies to another phase to re-balance onto 2 phases instead of 3, everything would work great.  I have never seen the machine, obviously, but if there is any way that can be done, even having to add external wiring right to an external junction box or something, it would make everything so much simpler and less expensive than any other solution.

I can't fathom how it wouldn't be possible, even if the OP cannot get to the main distribution inside the unit.  If it is possible to get to a couple of the supplies that are on ANY one phase, the necessary minor re-balance should be possible... 

...but then again, I have not seen the actual machine....   :popcorn:
 

Offline BrianHG

  • Super Contributor
  • ***
  • Posts: 4327
  • Country: ca
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #46 on: September 23, 2018, 10:27:16 am »
Though it would be big, looking at your current requirements, and this one is completely out of my area of expertise, what about a https://en.wikipedia.org/wiki/Scott-T_transformer, or, maybe use one of these in reverse http://transformer.sikes-elec.com/Transformer/Three-phase-to-single-phase-transformer .
« Last Edit: September 23, 2018, 10:32:15 am by BrianHG »
__________
BrianHG.
 

Offline BrianHG

  • Super Contributor
  • ***
  • Posts: 4327
  • Country: ca
__________
BrianHG.
 

Offline Floyo

  • Regular Contributor
  • *
  • Posts: 90
  • Country: nl
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #48 on: September 23, 2018, 10:41:43 am »
That scott T transformer is meant for four wire 2 phase networks, running at 90 degrees, not the 180degree split phase system.
This system 90 degree system is oldschool, and not (really?) used any more because you need four wires for two phases instead three wires for three phases with the 120 degree system, which is more efficient cabling wise.

The other option also wont work, you don't magically get the required phase shifts.

Interestingly the Phase Perfect converters mentioned by duak use a principle similar to the scott T transformer by electronically generating a phase that is 90 degrees out of phase with the split phase supply, so the line line voltages end up 120 degrees apart with the right voltage, but the line-neutral voltage of the generated phase is higher than 120V, and thus this wont work for the OP (unless using a delta-star transformer). The white paper has a decent summary of the issues presented in this thread http://www.phasetechnologies.com/downloads/products/phase-perfect/phasewhitepaper.pdf
 
The following users thanked this post: drussell

Offline Fryguy

  • Regular Contributor
  • *
  • Posts: 53
  • Country: de
Re: (AC power) Converting single-phase into 3 phase: What are my options?
« Reply #49 on: September 23, 2018, 01:11:28 pm »
Hi there ,

I'd go for the 3phase powerline installed to the building by the power company .

cvanc has to come up with a solution in less than 2 weeks and i don't think the proper rewiring of the machine for 2 or 1 phase operation can be done in this timeframe due to the complexity of the existing installation inside the machine and the problem of accessing it and moving this really big , heavy and fragile heap around without crashing it .

The rotary converter seems to be out of the question because of size / weight and noise issues .

Gluing the 3 phases together to 1 phase is a nice idea - i wonder how big the current impulse will be when you turn on 2 dozen big power supplies at the same time . . .  :bullshit:  and i'm not sure this nice setup with the 3 audio power amps will be able to handel the startup current either ( that is where the rotary converter will work pretty good ) :-//

Well - these are my thoughts so far .

May the forces of evil get confused on their way to your home !
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf