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I have a Selmi plus and need to move to a facility where running a 3 phase line is a costly endeavor.i,ve been told I can get a phase converter or possibly switch the motor. Anyone have thoughts or more importantly experience with this?

Tags: 3, Selmi, chocolate, equipment, phase

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There are two different type of converters. One is cheaper and VERY loud and puts out a lot of heat. Can't remember much more, but do your research before buying.

Before you go down the path of 'synthesizing' 3 phase power from a single phase source, the first thing you should do is contact Selmi and find out how much it would cost to convert the machine for single phase operation.  I found a Selmi Plus user manual online, and it shows a couple of three phase motors...but most of the machine is using single phase power.  Any heating element can be reconnected for single phase operation, and the control circuits use 24V derived from a single phase converter/transformer (it is not clear to me from the manual if the control is 24V DC or AC).

It may be that Selmi has already designed for an internal single to 3 phase converter to run the motors.

Failing this, there are several approaches to producing 3 phase from single phase; however these all have their issues.

The cleanest (and most expensive) way to produce 3 phase is a 'motor generator set.  This is as simple as it sounds.  You have a single phase motor that runs off your single phase supply, and drives a generator which produces 3 phase power.  This is not really a likely option, but I mention it for background.

A very common mechanical approach is something called a 'rotary phase converter'.  This is simply a 3 phase motor with two of its terminals connected to your single phase line.  A special starter triggers this motor to turn, and the third terminal of the motor _generates_ the 3rd terminal of the three phase supply.   The benefit of the rotary phase converter is that you get clean sinusoidal output, and only part of the power is actually passing through the converter; for a load that only has a portion of 3 phase loading, the bulk of the power can come directly from the single phase supply.

The downside of this is that the output may not be well balanced, which can cause heating issues in motors.  Also you have a spinning machine which means mechanical noise, and the need for bearing maintenance.

The final approach is something called a VSD or inverter.  These are actually used to control motor speed, but can also be used to convert single phase to 3 phase power.  They work by taking their supply power, converting it to DC, and then using electronics to convert the DC to 3 phase AC.  The output AC can have arbitrary frequency and voltage, which gives you the ability to control the speed of a three phase motor.

These devices are relatively inexpensive, and have no moving parts.  The downside is that the output AC is rich in electrical noise and harmonics.  These units are really meant to drive _motors_, not general purpose 3 phase loads.  You would almost certainly need additional filtering between the VSD and the Selmi.  Because these units are really meant to drive motors, the 'cleanest' approach is an internal VSD that only drives the motors, leaving the rest of the Selmi using single phase power directly.

(A quick aside: if you have a two terminal AC supply, then it is 'single phase'.  If you have 3 terminals, then it is 'three phase'.  To see why, draw two points on a piece of paper, and connect them with get a single connecting line.  Now draw three points and connect them with get 3 connecting lines.  Since a circuit requires a closed path between the supply terminals, a pair of supply terminals gives you one phase but 3 terminals give you 3 different paths.)


I am in the process of buying a new tempering machine.

I got a quote from Selmi of 700 euros extra to order the Selmi plus in Single phase rather than 3 phase in January.

Melanie - 

Your headline is misleading: you don't need to convert from 3-phase to single phase at all. Any 3-phase supply automatically includes single-phase power - it's all in how you take the power off the panel (the number of breakers and wires; single-phase 220V will use three wires and three breakers and 3-phases uses four wires and four breakers).

If the Selmi Plus a 3-phase machine and you're moving to location where there is only single-phase power, then you need a ROTARY phase converter because of the variable nature of the load (e.g., the compressor cycling on and off). I suggest you contact American Rotary ( You are going to want to purchase their 10HP (AD10-S) converter. I don't remember the price and I have never quoted shipping to Hawaii. We have several people running these on changing loads with FBM machines for well over a year without any problem. What is a problem is if you order one that's too small. Then some of the issues that John mention may crop up.

From my experience, it is NOT possible to convert a machine that has been shipped from the factory at one electrical configuration to another electrical configuration in the field -- cost effectively, or at all. Even if you could it would require many hours in the hands of an experienced (on Selmi equipment specifically) electrician. In my experience, it is much cheaper to change the external power supplying the machine than to change the power inside the machine.

VSDs will not work for this application because of the control electronics of your machine. If you were directly driving just the motors, maybe. But you're not - the electronics of the Selmi are. You'd need to attach the VSD to the CPU in the Selmi and that's not an option.

Another option for the rotary phase converter is to power a panel instead of directly power a machine. This way you can wire and power more than one 3-phase machine off the same converter. If the combined load is to great (you trip the circuit breaker) then it's easy to switch between the two at the panel. Plus the electrical inspectors prefer this method over running long cords.

Thanks Clay that's what I needed the actual phase converter. Weighing the cost of that vs pulling the 3 phase in from the panel on the main bldg.

I forgot, there is one additional option: a 'static phase converter'.  This is electrically similar to a VSD set to fixed frequency with all of the necessary filtering to run a generic three phase load.

Anywhere a rotary converter can be used, a static phase converter can be used. 

If in Clay's experience the rotary converter mentioned works with the machine, then that will very likely be the cheapest approach.

However you just added a significant detail.  You said that there is 3 phase at the main building where you are located.

What voltage is your Selmi rated for, and what voltage is actually being supplied to your location (both at the main panel and in the space where the machine will be located).


Jonathan -

We looked into static phase converters as they tend to be less expensive. However, they are not good in situations where the load varies considerably - in the case of a tempering machine, where the cooling compressor kicks in. Now if it were just a melter where the load was more or less constant - then you could use the static converter.

And to add to my last question: is the voltage in the location that you are moving to 120/240V or 120/208V.

Is the selmi set up for 208V 240V or 480V three phase?

208 and 240 often get confused or are (mistakenly) considered the same thing.

480V is what you would find in a modern industrial facility

240V is what you might find in an old industrial facility

208/120V is what you would find in an office/light industrial facility, because it is a three phase system that gives 120V directly for receptacles and the like.


The voltages on the Selmi and FBM machines and others are going to be 208~240VAC 60Hz -- that's 220V +/- 10% -- either single or three phase.

FBM handles single-phase power by putting inverters on the motors that need to run in reverse plus changing out components that handle the input voltage from the wall. Some internal components are 60Hz specific. Given what Louise said about Selmi charging €700 to support single phase they are probably doing the same thing.

The reason for my question about the exact supply voltage in the new location is that 208V 'single phase' is really two phases of a three phase supply, whereas 240V single phase is a true single phase.

If you have 208V from two legs of a three phase supply, then you can use a transformer to generate the third leg.


Which is why I always recommend that my potential FBM customers get an electrician involved to know exactly what the customer has to work with. 

Hey Melanie, I've been running my Selmi Plus off a Phase Perfect digital phase converter for two years with no issues.  Here's their website:  Don't know how their prices compare to other brands because I bought mine used.  You should have your electrician help you pick out the model that suits your needs.


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