Phase Converter

Phase Technologies Phase Perfect PT-355 Phase Converter

Large motors run more efficiently and last longer on three phase (3Ø) power than on single a.k.a. split phase power. We’re way the heck out at the end of the power line and it would cost $85,000 to bring in 3Ø power for our butcher shop. Not happening.

The solution is to either run the machinery inefficiently on single phase or to get a three phase converter. Since the equipment is rather expensive I don’t want to shorten its life, or make it noisier than necessary which also happens with 1Ø power.

Three phase converters come in several varieties. The rotary phase converters have been around for a long time but are in efficient and not as cheap as they appear since you have to essentially buy twice as much power as the rating of the equipment.

Digital phase converters are newer and more expensive. Doing the math I discovered that the digital phase converter’s increased efficiency meant that it will pay for the higher cost vs the cheap rotary phase converter within in one to two years. After that it starts saving us money every month. I like that.

Digital phase converters also produce cleaner power which is better for the motors and they’re quieter, although not silent. Interestingly, their buzz is high enough pitched that not everyone can hear it. Both Will and I could quite clearly when I powered our new unit up. It works. It’s not going in the office. Good thing we built a dry mechanical room for it!

Now for the tricky part. The phase converter arrived and we took it indoors. I went to open it but couldn’t figure out how. Now I’m very good at puzzles so this was unusual. And there were no instructions on how to open it. After a bit of unproductive pondering I called the company and spoke with tech support. Turns out you have to use an unusually large allen wrench inside a hidden spot within the door bumper. And where were the instructions for how to do this? Inside the machine, where else! You can see the manual there on the far side after I got it open. Cute.

Well, it works. We got it hooked up to our single phase also known as “split phase” power which really should be called two phase power in my book and out the other side of the phase converter flowed three phase power. Nice!

Outdoors: 74°F/44°F Sunny
Tiny Cottage: 66°F/64°F

Daily Spark:
I to Will: Do you have a vise?
Will: No, but I would like to learn to smoke.
(She was talking about a clamp for metal working. He was talking about makin’ bacon.)

About Walter Jeffries

Tinker, Tailor...
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7 Responses to Phase Converter

  1. james says:

    What would you call the 2 phase that was used in the early 1900’s

    • That is also two phase. I just don’t like calling the two phase that we have one phase which is what is commonly done. There is also a single (one) phase that is truly just one phase. The single phase produces 120V AC between a ground and a live wire and was common in the past and is still common in many rural areas that have not been upgraded. The miss-nommered single phase also known as split phase (two phase) we have that is now common in rural and residential areas has a single ground and two life legs that are 180° out of phase with each other producing 120V AC between either leg and ground or 240V AC from leg to leg. Thus what we have is truly two phase even though they call it one phase, split phase or single phase. I suspect this inappropriate naming is the result of the historical fact that there was the other form of two phase long ago, and still used in very limited circumstances, which had two legs plus ground but was only 120° out of phase rather than the full 180° out of phase – that has positives and negatives, if you’ll excuse the pun. I’m sure none of that will faze an electrician. :)

  2. Ed Allison says:

    Walter, I imagine that the digital phase converter is also more easily damaged by lightning strikes or surges. I know you’ve said that up on the mountain, you have had those kind of issues before. Does the converter have built in surge protection? If not, how will you protect it and are you protected (replacement costs) in the event of issue?

    • Aye, lightning is something we live with. I design our electric systems from the power mains to the fencing to antennas to deal with the reality of lightning on the mountain. Very good grounding, avoiding cross overs, bubbles of protection, surge suppression at many levels and disconnects during the worst storms – all part of keeping equipment up and running.

      The other thing we do is redundancy. Having multiple systems that are the same. Two 15 joule fence energizers rather than one 30 joule energizer for example. Like wise the phase converter is such that we might get a second one later and then divide our loads between them. That way if either dies the other can take over the full load while we fix the dead one.

  3. Dan Moore says:


    I’ve used variable frequency drives (VFDs) for three phase power for large shop tools like lathes and mills before. Wonderful technology. However now I have to put in something like what you are doing for our delivery truck we just bought. It has a Diesel engine to drive the cooler on the truck to keep our meat frozen but can also be plugged in. It requires 30 amps of 3 phase 240 volt. I sized all the VFDs in the past based on the horse power of the motor but I’m not sure to to size this digital phase converter. HP or based off the 30 amp load. You are powering multiple devices so I know you had to do some math to figure out what size unit to get. Can you share how you sized it and where you purchased yours?

    Thank you for sharing.


    • With the digital phase converter (DPC) it wasn’t necessary to oversize. That is part of what made the rotary phase converters more expensive than they appear at first – they must be over sized. Give the people at Phase Technologies a call. They are very helpful. I peppered them with dozens of detailed questions and they patiently answered them all, reviewing my diagrams, etc.

      What I did was make a spreadsheet chart of all of our equipment and what would be used when – some things never run together, some things might, some things often will. This let me calculate my maximum loads, starting loads, running loads, etc. Using that I then picked the PT-380, PT-355 or PT-330 as likely candidates for our application. The technician at Phase Perfect suggested the PT-355 would be able to handle the load fine. I’m setting things up so that if we need to we can add a second PT-355 later which will give us more power and redundancy. They can run in parallel for more power or they can each power a separate 3Ø breaker panel.

      Figure up your loads. Basically, 1 HP = 745.7 Watts and from there you just use standard electricity power math. Watch the startup draw for motors. See here for a discussion of HP to Amps conversion.

  4. Patrick says:

    @Dan: Make sure the converter is capable of handlng generator power at the same time as the startup issues with refers.

    Generators typically have lousy harmonic distortion, and all the digital units will clean that up to some extent. But some converters might have longevity/warranty issues because a wide THD (over 5%) might cause some pulses out of range, which could lower lifespan or even result in tripped circuits.

    Plenty of inverter/converter systems will work, but don’t forget to ask the manufacturer specifically. It would help to know the THD of your genset when you call, or at least the specific model number so they can look it up if they have questions.

    I’ve seen 3-phase converters fry in a week after working for years – they died the week the backup gens were used after a storm. The irony is the generators kept the store cold during the hurricane, but then some things went bad anyway because some converters died right about the time the main power came on. Expensive lesson.

    If they are specified for mobile conversion, they should be ok.

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