Digital Phase Converter

G

gulf0927

Member
Location
Lehigh Valley, PA
Customer bought a 230V 3 phase router (2 HP, 5 A) cheap online. He has a woodshop for hobbies. He also preemptively bought a digital phase converter which appears to be properly rated.

It's small, Vevor is the brand. From what I've researched, it uses digital signal processing to "trick" the circuit into having 3 phases.

Anyone have experience with DSP phase converters?

It's his only piece of 3 phase equipment, and it has inherent overload protection, so I feel mostly comfortable installing it. But just wanted to get a sense of their reliability vs. rotary converters and VFDs. Obviously he made this choice because of cost, as they are cheaper and quieter than rotary setups.
 
gulf0927 said:
...

It's small, Vevor is the brand. From what I've researched, it uses digital signal processing to "trick" the circuit into having 3 phases.
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I think that is rather inaccurate or at least I certainly hope it is. These kinds of units use power electronics to transform power from one type of source to another. DSP is only used to control the power electronics. The load is not 'tricked' into thinking single phase is three phase. The load sees three phase voltage.

But just wanted to get a sense of their reliability vs. rotary converters and VFDs. Obviously he made this choice because of cost, as they are cheaper and quieter than rotary setups.
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In general concept these are like VFDs, not like a rotary phase converter which uses a motor and windings to generate the third phase. The main difference is that a VFD, as the name implies, may be programmed to deliver power at variable frequencies. A phase converter just delivers power at a standard frequency i.e. 60hz in this country.
 
I believe that a digital phase converter only synthesizes a single phase, leaving the two supply legs to simply pass through the the output. In this way they are more like a phase converter than a VFD. A VFD synthesizes all three phases.

-Jonathan
 
ptonsparky said:
Cost?

That size VFD is reasonable, but I have no idea what the OPs customer paid out.
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Possibly this unit

5 HP rating for only $122 is cheap compared to even some the cheap VFD's.

Not sure how well it would work for loads requiring higher starting torque, appears you still need to supply overload protection where a VFD normally will provide that function which may put you back up to similar price range in the end as going with the VFD.
 
winnie said:
I believe that a digital phase converter only synthesizes a single phase, leaving the two supply legs to simply pass through the the output. In this way they are more like a phase converter than a VFD. A VFD synthesizes all three phases.

-Jonathan
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VFD'S are feed with three phase three wires that feed a rectifiers bridge that has two wire DC output that connects to IGBT'S that believe can fire up to 5,000 Hertz to produce a somewhat choppy output. On 480 Volt three phase drives it produces around 665 Volt DC Buss voltage. Surprised they still make noisy MG Phase converters. Only guessing but the other types must be more energy efficient.
 
garbo said:
VFD'S are feed with three phase three wires that feed a rectifiers bridge that has two wire DC output that connects to IGBT'S that believe can fire up to 5,000 Hertz to produce a somewhat choppy output. On 480 Volt three phase drives it produces around 665 Volt DC Buss voltage. Surprised they still make noisy MG Phase converters. Only guessing but the other types must be more energy efficient.
Click to expand...
Not all VFDs require 3 phase power, especially in these small sizes. Which is why they are often used as a phase converter.
 
kwired said:
Possibly this unit

5 HP rating for only $122 is cheap compared to even some the cheap VFD's.

Not sure how well it would work for loads requiring higher starting torque, appears you still need to supply overload protection where a VFD normally will provide that function which may put you back up to similar price range in the end as going with the VFD.
Click to expand...
Overloads for a table router? Isn't that considered short time or intermittent duty according to 430.22(E)? 430.33 allows me to use the breaker as the overload in that case, unless I'm way off here.
 
winnie said:
I believe that a digital phase converter only synthesizes a single phase, leaving the two supply legs to simply pass through the the output. In this way they are more like a phase converter than a VFD. A VFD synthesizes all three phases.

-Jonathan
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If the input in 240V, the two supply lines are 180 degrees out of phase. You can't synthesize another supply and get three phase. In three phase the supply lines are 120 degrees out of phase with another line and 240 degrees out of phase with the other.
 
robertd said:
If the input in 240V, the two supply lines are 180 degrees out of phase. You can't synthesize another supply and get three phase. In three phase the supply lines are 120 degrees out of phase with another line and 240 degrees out of phase with the other.
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Explain please.
IDK, what my 1ph to 3ph VFD is doing. Maybe synthesize is what I dont' understand.
 
robertd said:
If the input in 240V, the two supply lines are 180 degrees out of phase. You can't synthesize another supply and get three phase. In three phase the supply lines are 120 degrees out of phase with another line and 240 degrees out of phase with the other.
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It's not that simple.

If you have two line conductors with a 240V voltage you have a single waveform between them. It is possible to synthesize the third phase of a 240V *delta* with both a rotary or digital phaew converter. It does not matter what the voltage or phase relationship of the synthesized phase is to the neutral of the split phase system if you won't use it, which you typically won't.

Beyond that, it is possible with a rectifier/inverter type VFD or phase converter to produce almost any typical voltage, phasing, or frequency supply you want from a single phase source.
 
The key with synthesizing only the 'third leg' of a three phase system from a single phase system is to remember that phase angles are always relative, not absolute.

Think of the phase angles in a high leg delta service. The 120V A-N voltage is 180 degrees out of phase with the 120V C-N voltage. But the 240V A-B voltage is 120 degrees out of phase with B-C and B-C is 120 degrees out of phase with C-A. The 208V B-N voltage is _90_ degrees out of phase with the A-N voltage.

If you start with normal residential 240V split phase, and you synthesize a third leg, 208V and 90 degrees out of phase from the supplied single phase, you will in essence create a high leg delta system. The L-N phases are unequal (just like in a high leg delta system), but the three phase voltages are perfectly 120 degrees out of phase relative to each other.

This is what a rotary phase converter does, and what I'm pretty sure a cheap digital phase converter does.

-Jonathan
 
winnie said:
If you start with normal residential 240V split phase, and you synthesize a third leg, 208V and 90 degrees out of phase from the supplied single phase, you will in essence create a high leg delta system.
Click to expand...

The above sentence should be 'If you start with a normal residential 240V split phase, and you synthesize a third leg, 208V and 90 degrees out of phase, line to neutral, you will in essence create a high leg delta system.'

-Jonathan
 
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