# Rotary Phase Converter Questions



## bosephus (Apr 25, 2016)

Here is a questionable question for those who know more then I . 

  can I use a 230v to 460v step up transformer  in front of a 460v  motor to make a 460v rotary phase converter . 

and to further muddy the waters , can I also use a step down transformer  after the phase converter to run both 230v and 460v motors off of the same phase converter 

to my brain it seems to be a fairly sound concept ...


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## Chipper5783 (Apr 25, 2016)

I suppose you could do that.  It seems you will have one more piece of equipment than you need to.  Is there some reason that you must use the 460v motor?  Can you reconnect it to 230v?

How about you run the 230v phase converter right off your utility power - from there you can power the 230v machines - no transformer at all.  To run you 460v machines, you just need the one transformer.

This is exactly what I have done.  I run the 230v phase converter on its own 2 pole breaker.  From there I power a few 240v 3 phase machines.  I also feed a 240-600v 3 phase transformer - and supply a couple 600v machines.

Has been working well for 5 years.


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## bosephus (Apr 26, 2016)

chipper

Your way does make more sense , but the idea was born out of necessity.    I am trying to help a friend get some wood working equipment powered up and the only motor he has available to use as the idler is a dedicated 460v  that the local motor shop says is not wound to be a dual voltage motor .
and with the exception of a contactor we have everything on hand to build it .


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## Chipper5783 (Apr 26, 2016)

How large a converter are you needing to build (HP of the largest intended load)?  Unless you are buying new, motors are much easier to come by than transformers.  To find a good used 230V, 5HP motor for your idler, should not be difficult.  I felt I was very fortunate to have been able to land a good used 240-600 3 phase transformer (small decent little motors I have come across many).


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## bosephus (Apr 27, 2016)

The idler we are going to use is 40 hp  and the largest motor it is starting is 20 hp.   
he already has the transformer that came out of the shop with the machines. 

I understand that this might not be the ideal set up ,  but it gets him powered up without spending any real money ..    everything is already on hand except a magnetic contactor for the pony motor


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## strantor (Apr 27, 2016)

You realize you that you will need a minimum of 125A circuit for this? Any place I've been that had 125A circuits in the walls, had 3 phase supply. Just hoping you don't plan to run this off your home dryer plug; it will likely consume more power than the average 2 story house with all the lights on, in a Texas summer with the AC on and all the windows and fridge wide open. And the microwave running.


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## bosephus (Apr 30, 2016)

Well there's  nothing like having your intelligence insulted .


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## 4GSR (Apr 30, 2016)

Nothing like upsetting your neighbors when you kick in that 40 HP motor and everything in the house for four blocks away dim for a fraction of a second.  Anything like me, I updated my entrance panel to 200 Amp, and I asked the electric company why they did n't run a new service entrance cable to the house that would handle 200 amps.  Thier answer was, the old 2 ga cable will handle it!  Well, that was 10 years ago, the cable has been spliced three times for various reasons, and it is slowly getting longer and smaller in gage size from all of the heat it gets.  In another couple of years, it will almost touch the ground!  Can't wait to get a 300 amp Syncrowave welder tied in, kick in the HF on a piece of aluminum plate and toast that service entrance cable.  Maybe that will convince them I need a 0000 cable run!


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## strantor (May 1, 2016)

bosephus said:


> Well there's  nothing like having your intelligence insulted .


Sorry if I offended. 
Thing about insulting someone's intelligence from across the Web is, you don't know what their intelligence  (rather their knowledge ) is. 

Most people don't have a good concept of physics. 
Most people don't realize that a king size snickers bar contains more stored Energy than a stick of dynamite.
Most people don't realize that hard braking a 4,500lb car from 80mph to 0 dissipates more heat Energy into their brake disks over a span of 6 seconds than a 120V/15A space heater dissipates into a room over a span of 14 hours -and a heater that big is apt to pop a breaker if anyone turns on a light.

....aaand most people don't realize that starting a 40hp electric motor draws more instantaneous current than 2,000 60W bulbs would draw.

So often the only way to make the point is to provide an example. Sometimes people take the example the wrong way. And I have a habit of causing people to take it the wrong way. Just not good with words I guess. Sorry.


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## bosephus (May 10, 2016)

Whew ... finally have everything wired up and working .  On the first try even ... well I have to be honest it took two tries . the first attempt was with a 1.5 hp pony motor to start the idler and it just didn't have enough muscle to get the big motor up to speed .   But a quick upgrade to a three horse and things went a lot better .   
The 40 horse power idler seems to be balanced fairly well on the generated leg and all the machines start up very easily .


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## FOMOGO (May 10, 2016)

Congrats on the startup. Now to totally enjoy your success, you need to throw the main switch and do your very best mad scientist Bwaaa Haaaaa Haaaa. Mike


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## Keith Foor (May 10, 2016)

Curious, did you look at the current draw on the 220 single phase side once you had the idler motor up and running?


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## bosephus (May 11, 2016)

Keith 
I seen your question last night and it made me curious .  

with no load the idler pulls just a smidge over 4 amps .  
We have the pony motor wired up on a separate circuit and with the idler spun up to speed before switching on the power it pulls 16 Amps for about 5 seconds on start up .

If we switch the power on at the same time as the pony it spikes up over 60 amps


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## Keith Foor (May 11, 2016)

I have built a number of RPC's and modified ones built by others to get them to work right.  Idle current is a good indicator of how well the converter was designed and if the L1-L2 and L1-L3 capacitors are of a good value.  An RPC is a tuned circuit of sorts.  It actually 'rings' if it's designed right and the idle current is very low.  With what you described you were doing you have a LOT of inductance to tune to a point that it will 'ring'.  With those current draw numbers, it seems that you hit the sweet spot.  I am also going to assume at this point that your leg to leg voltages on the RPC are within 10 volts of each other as well under no load.  I would advise you to verify the leg to leg with a full expected load as well to be safe.  One things that RPC's can do when the capacitance isn't correct is develop a high leg on L3.  You can see 500 or more volts under no load or during a load transition on to off.  Just something to keep in mind if you are running anything that's electronic on the 3 phase power.


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