Inexpensive Digital Converters

I.RonMann

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So has :anyone: tried out the compact single phase to three phase digital converters avail. online for $100.00 to $200.00? Fully programmable, upwards of 1.5 kw/7A and supposedly a better 3ph source. Just wondering.
 
Do you have a link to share?
The only digital converters I have seen are made by Phase Perfect and are well over $200.
Disclosure: I have never seen one in person, only on-line images.

My understanding of the digital converters is that they use the two 240V legs and add a third "generated" leg similar to how a rotary phase converter works.
The digital converters do it all with solid state devices instead of rotating machines.

Terry S.
 
if you are referring to any of the VFDs (Variable Frequency Drivers) on the market, then yes- many of us here use them, me included.

I run my 3 phase lathe off of a single phase 110 outlet with a VFD, and it runs great. no stalling, not starved for power - runs like a champ.
 
Do you have a link to share?
The only digital converters I have seen are made by Phase Perfect and are well over $200.
Disclosure: I have never seen one in person, only on-line images.

My understanding of the digital converters is that they use the two 240V legs and add a third "generated" leg similar to how a rotary phase converter works.
The digital converters do it all with solid state devices instead of rotating machines.

Terry S.

Yes there are quite a number of them to choose from: http://www.alibaba.com/product-gs/843685060/220V_frequency_converter_single_phase_to.html / http://www.alibaba.com/product-gs/910627369/CE_Approved_Energy_saving_Small_Size.html / http://www.alibaba.com/product-gs/713969075/S900_E_Single_Phase_To_Three.html From these links you can check out the number of converters avail. :thumbsup: And the explanations go something like:Three phase induction motors may operate adequately on an unbalanced supply if not heavily loaded. This allows various imperfect techniques to be used. A single-phase motor can drive a three-phase generator, which will produce a high-quality three-phase source but with high cost for apparatus. Several methods exist to run three-phase motors from a single-phase supply, these can in general be classified as:

  • Electronic means of creating three phase where the incoming power is rectified, and the three phase power is synthesized with electronics. Power electronic devices directly produce a three-phase waveform from single-phase power, using a rectifier and inverter combination. This also offers the advantage of variable frequency.

  • A digital phase converter uses a rectifier and inverter to create a single voltage with power electronics, which is added to the two legs of the single-phase source to create three-phase power. Unlike a phase converting VFD, it cannot vary the frequency and motor speed since it generates only one leg which must match the voltage and frequency of the single-phase supply. It does have the advantage of a sine-wave output voltage and excellent voltage balance between the phases.

  • Rotary phase converters constructed from a three-phase electric motor or generator "idler". These normally require some kind of starting aid and capacitors to improve phase balance and power factor. This is a two motor solution. One motor is not connected to a load and produces the three phase power, the second motor driving the load runs on the power produced.

  • Static conversion techniques in which the motor is run at less than full efficiency mainly on two of the legs of the three phase motor. Current is sometimes injected into the third leg with a capacitor or transformer arrangements that provide imperfect phase shift. In these systems the motor must be derated. A digital phase converter creates a three phase power supply from a single phase supply. A digital signal processor (DSP) is used to control power electronic devices to generate a third voltage, which along with the single-voltage from the supply creates a balanced three-phase power supply.
    AC power from the utility is converted to DC, then back to AC. The power switching devices used in this process are insulated gate bipolar transistors (IGBT).
    In one type of digital phase converter the input rectifier consists of IGBTs in series with inductors. The IGBTs are controlled by software in the DSP to draw current from the single-phase line in a sinusoidal fashion, charging capacitors on a constant voltage DC bus. Because the incoming current is sinusoidal, there are no significant harmonics generated back onto the line as there are with the rectifiers found in most VFDs. The controlled rectifier input allows power factor correction.
    The output inverter consists of IGBTs that draw on the power of the DC bus to create an AC voltage. A voltage created by power switching devices like IGBTs is not sinusoidal. It is a pulse-width modulated (PWM) waveform very high in harmonic distortion. This PWM voltage is then passed through an inductor/capacitor filter system that produces a sine wave voltage with less than 3% total harmonic distortion (standards for computer grade power allow up to 5% THD). By contrast, VFDs generate a PWM voltage that limits their versatility and makes them unsuitable for many applications. Software in the DSP continually monitors and adjusts this generated voltage to produce a balanced three-phase output at all times. It also provides protective functions by shutting down in case of utility over-voltage and under-voltage or a fault. With the ability to adjust to changing conditions and maintain voltage balance, a digital phase converter can safely and efficiently operate virtually any type of three-phase equipment. :drink2::machinists::drink2:
 
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