Guys,
Some of us sometimes require 3 phase power supply to test or run small 3 phase motors or equipment in areas where there is no 3 phase supply like in our homes. The solution is to use variable frequency drives. Variable frequency drives may have single or 3 phase inputs. The electronics convert the AC to DC then chops it back to AC to the desired frequency for speed control. This is the main purpose of this device.
Competition and cheap electronics have made the prices of these devices very affordable nowadays.
I have offered this advice to a friend who is planning to put up a small ice plant in his backyard!
Re: How to get 3 Phase from Single Phase Supply
How much are they now? I helped build one before and they are not simple animals, so I doubt if they are worth their cost if you only want to test 3 phase motors from time-to-time.
I've seen and read of these much simpler circuits that use capacitors and inductors. Try searching the internet, or looking in local industrial supplies. I once saw one of these devices running a Bridgeport vertical mill. It was doing production runs so I suppose it is good enough for long term use.
Re: How to get 3 Phase from Single Phase Supply
If I remember right a VFD for a 1/2 hp motor sells for 15K. Its a taiwan made unit.
Re: How to get 3 Phase from Single Phase Supply
Laos na pala what I used to see. A single phase motor running a three phase generator.
Re: How to get 3 Phase from Single Phase Supply
valenzuela mac arthur hi-way, you can buy a single phase motor converter, output is three phase, cheaper kasi surplus, 1,000/ hp ang dating price
Re: How to get 3 Phase from Single Phase Supply
paapano ang schematic ng VFD?
ang normal namin ginawa kasi is to make the 3-phase motor to run on single phase line (not the other way around o pareho lang ito?) using a capacitor (malaki itong capacitor)....but i forgot the schematic nito...then to start the motor we use a push button switch (starter push button switch ng oto).
Re: How to get 3 Phase from Single Phase Supply
Ang VFD ay isang device na plug and play. Highly electronic. OK ito kung gusto mo ng instant three phase. Wala ng modification or anything duon sa three phase machine mo. Hindi kita masasagot regarding the schematics. Alam ko, and AC ay kinokonvert to DC tapos chop chopin para maging AC ulit at a desired frequency. Nakakagawa ito ng three phase kahit single phase ang pasok.
Re: How to get 3 Phase from Single Phase Supply
I'm at odds whether to recommend home brewing a VFD or not. I remember when we were developing a 1 hp unit and I would literally runaway from the thing. But hey if you want to just be careful.
Here is a short description of the circuit: Diodes convert your 220V AC into 300V DC. The 300VDC feeds 6 electronic switches arranged into 3 sets of 2 switches connected in series. Each pair is connected across the DC bus with each corresponding to one of the 3 phases to be generated. The 3 wires from the motor are each connected to a center node of each of the pairs. Now by turning the switches on and off in particular patterns the motor will be fed 3 phase AC.
The electronic switches can be BJT, MOSFETS, IGBT or even SCR. Most modern medium power units will use either MOSFET or IGBTs. High power units will most likely use SCRs. For the homebrewer I strongly recommend MOSTFETs or IGBTs which are easier to work with though a bit more expensive.
The pattern that you feed the switches is a whole field in itself. A simple pattern might be ok for non-prolonged use. The story with the patterns are the harmonics and how they affect the motor. Ever heard of the warning "don't pull your electric fan into a square wave UPS"? Same thing. A good starting point for designing the pattern generator is to draw the waveforms of each phase and to note what phase is on and in what polarity and what is off as time varies. The modern way is to use PWM (pulse width modulation) but unless you want to muddle your brain with tons of math, I'd say a filtered square wave is the way to go. Not as efficient but easier on the brain.
If still want to know more, just ask and I'll do my best to answer.
Re: How to get 3 Phase from Single Phase Supply
I once tried to build a circuit to get a 50 hz sine wave using a function generator in order to run a turntable. Couldn't get the thing to run properly as the motor became noisy as hell. I gave up on the plan.
Re: How to get 3 Phase from Single Phase Supply
You were probably hearing the 3rd harmonic. One way to remedy this is to use a standard flourescent ballast in series with a capacitor across the load. The ballast and the capacitor form a low pass filter. Sorry I don't remember the values but you could do it trial and error. Just remember to use non-polar capacitors rated for at least 220 volts.
Re: How to get 3 Phase from Single Phase Supply
This is very high tech stuff. Just buy the chinese made industrial VFD's which because of competition is priced reasonably. Unless you guys really want to experiment or live up to your name "DIYer)
Re: How to get 3 Phase from Single Phase Supply
Even if a VFD cost the same as the thing the backyard machine shops use, I go with the thing. Unless you really need the variable speed ability, I would not recommend it.
VFD's have their place. I'm told they are wonderful for running all sorts of impeller equipment (A/C, compressors, fans, blowers, water pumps, etc.) and easily pay for themselves from the gains in efficiency.
Tatoski is right, only the most dedicated DIYer or one who's life's dream is to be an electronics designer should try doing his own VFD. If you need one, buying is the better choice. DIY whatever it drives instead.
