Single phase to 3 phase variable power supply - Page 1
Forum section: electronics / beginners

author: jfphp
author_rank: Regular Contributor
timestamp: May 31, 2023, 03:18:58 pm
content: Hello,I am looking for a power supply from 110V 60 Hz or 220V 50 Hz to three phase variable 50/60 HZ (10V to 60V or more) about 200 W. Any idea ? Thank you

author: HalFoster
author_rank: Frequent Contributor
timestamp: May 31, 2023, 06:39:43 pm
content: The easiest - and by far the cheapest - solution would be to design your own 3 phase oscillator and amplifiers, especially as it would only be for 200 watts or so. A more expensive but also more flexible solution would be to buy three different used AC power supplies from someone such as Elgar, California Instruments etc. - they are available on epay and can, depending on the model, be connected together to supply three phase power. The most expensive solution and, outside of cost, the best would be to purchase a new all-in-one model from someone like Chroma and others - but that would run to the high 3 / low 4 digit price range.Let us know more about what you are trying to accomplish so the responses will be better targeted towards your needs.Hal

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 31, 2023, 10:34:41 pm
content: One option would be to buy a standard motor frequency inverter. You can set limits for output voltage and current and other parameters in these things. Disadvantage is that the outputs are not isolated from the input voltage.Another DIY option is to use some class D audio amplifiers.Also: Is your 200W output power for all phases combined, or for each phase separately?There are also plenty of BLDC motor controllers available, and open source projects for their firmware and that also seems a viable option.

author: Benta
author_rank: Super Contributor
timestamp: May 31, 2023, 10:56:11 pm
content: I think we need to know if this is a DIY project or a search for a suitable box.Also: sine-wave out or pseudo sine-wave?More info needed.

author: johansen
author_rank: Super Contributor
timestamp: June 01, 2023, 02:45:58 am
content: Off the shelf 230v vfd followed by 3x 240v primary 120v secondary transformers. You need an extra inductor on the primary side and a capacitor across the output of the transformer. Connect the 120v outputs in Y and ground the neutral. Program the vfd for whatever output voltage you want, or buy 240v:60v transformers.Another possibility is a 240v:240v transformer on the input of the vfd. You can then LC filter the output. A small 3 phase transformer with a zig zag winding (you will have to make one) can be used to ground the center point of the 3 phases and give you a neutral. The problem with this is that the dc bus of thr vfd will have a square wave impressed on it of plus and minus 170vdc...at the pwm frequemcy of the drive. You cant ground it.a third option is wind 3 additional coils around the cores of 3x 500va 120v variable transformers. Connect the autotransformers in y, with the three additional coils in series, to form a delta tertiary coil. You can now get whatever voltage you want without reprogramming the vfd.You can ground the Y connection of the variable transformers....if the 230v vfd is driven from a floating 230v isolation transformer as described in prior paragraphThe LC filter required to get a sine wave out of a vfd is pretty minimal. 100 feet of 16 awg wire wound on a bobbin approaching that of a standard crispy creme donut, and a 10uf capacitor is acceptable for a 2hp vfd.

author: EPAIII
author_rank: Super Contributor
timestamp: June 01, 2023, 05:38:50 am
content: Would a VVVF (Variable Voltage Variable Frequency) do?https://www.google.com/search?client=firefox-b-1-d&q=VVVFQuote from: jfphp on May 31, 2023, 03:18:58 pm

author: Berni
author_rank: Super Contributor
timestamp: June 01, 2023, 06:33:07 am
content: By far the cheapest solution is going to be buying a off the shelf VFD with single phase inputThey will do the conversion to any freqency 3 phase, as that is there job. But they also have the ability to reduce the output voltage at the same time, since if you run 3 phase induction motors at lower frequencies you have to also lower the AC voltage, otherwise you would saturate the motors windings and eventually have them overheat and catch fire.Tho you have to do some research into what input and output limits they allow. Not all of them are universal input 220/110V and they might not let you reduce the output voltage that low at 50Hz. You can fix that by adding a 3 phase transformer (or three single phase transformers wired together) to the output. This would also give you more current capability on the output since the VFD drives are limited by the number of output amps per phase (so they reach the spec Watts at high output voltages)

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 01, 2023, 06:41:33 am
content: Like often mentioned above, a off the shelf VFD. I bought2 off theserecently, and they work well.HOWEVER: What is your use case? Typical VFW do not generate true sine, not even modified sine, but a PWM approximation. If the primary load is a inductor, like a motor or transformer, no problem. But if you want true sine, like@johansenmentions above, first turn it through a triplet of single 1:1 transformers, or find some pre-owned 3-phase transformer. All of which will make the solution a bit more cumbersome.

author: jfphp
author_rank: Regular Contributor
timestamp: June 01, 2023, 09:11:08 am
content: Thank you to all who answered. My problem is tricky : on a military diesel generator with electric starter, the 24V batteries are charged by a separate system : there is a dedicated 3 phase 3 X 36V winding (!) in the alternator, winding converted to 27V DC by a board with a current limit of 7A and the apparition of the charger's 27V starts a complex sequence with several relays involved enabling instrument panel, fuel solenoid... and finaly the 220V output. Access to this board is very difficult and the noise and vibration near the disesel engine do not help. My purpose is to test outside the generator the charger board : it outputs 23V with the 3 phases checked at the input and is of the switching model. The last but not the least : all the components of the board are glued like a multiplier in a HV tube oscilloscope power supply. Of course impossible to buy a spare board or to get the schematics diagram. Finaly I will have to build a new board but I am not familiar with design and realisation. I was unable to find such a commercial power supply (36V 3 phase AC to 28V DC). Sorry for the long story...

author: Berni
author_rank: Super Contributor
timestamp: June 01, 2023, 10:40:13 am
content: It is simple to build such supply that makes 3 phase 36V AC into 28V DC.You just use a 3 phase rectifier to turn the 36V AC into 50V DC (or into 62V DC in case you don't have a neutral wire and have to run from interphase). Then you use a DC/DC converter module to turn that into 28V DC. For charging lead acid batteries the easy trick is to google for DC/DC converters designed for running LED lighting. Those have both voltage and current limited output. So when connected to a battery they nicely provide constant current, then go into constant voltage once the battery is full.If you have trouble finding a DC/DC fit for the job you can also run the 3 phase trough a capacitor doubler circuit to get 120V DC and that should run most AC/DC modules just fine.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 01, 2023, 10:56:43 am
content: Quote from: jfphp on June 01, 2023, 09:11:08 amSo is it your intent to test and rebuild *original*. To keep in some sort of preserved state. Or do you simply want the charging to work.If the later, indeed as per@Bernisimply rebuilding the charging board with off the shelf components may be easy: 3-phase rectifier, DC/DC converter, and some modern smart monitored Led-Acid battery charger circuit.But if you want to keep original, and indeed want a test bench for your 36V 7Amp 3 phase:I think I would start with a 230V VFD, and then run it through 3 transformers to both make it into a proper sine, as well as step down to 36V (and maybe also provide isolation from the grid)BTW: do check if the 36V is 36V peak, or 36V rms, and whether it is star or delta, so you get the correct transformers. Unfortunately 36V is not very common off the shelf but maybe you can get some that have both 12V and 24V windings.EDIT: also, thinking even simpler:You can probably simply component test the charging board *without* needing all 3 phases. CHances are good the whole things starts with a 3-phase rectifier anyway, in which case you can just run and check the board with a single 36V AC power supply. If the first stage is indeed just a hextet of dioded, there is no real need for all 3 phases, except maybe the resulting voltage will be a little waivy, but even if that turns out to be important, you could temporary hook up a beefy capacitor.You could even simply inject a good 40~50-ish Volt DC , right at the input of the rectifier, and it would pass right through and supply roughtly the same DC current as the recifier would, for testing the rest of the components. Maybe 3 or 4 small lead-acid batteries

author: johansen
author_rank: Super Contributor
timestamp: June 03, 2023, 05:37:01 am
content: Older battery chargers really did sometimes use half wave scr control.I dont understand why l 36vac is needed to charge 24vdc battery..but yes you should be able to test this with a 36vac single phase supply.As other noticed, yes you need a transformer to use a vfd to get 3 phase. But the transformer does not make a clean sine waveAn additional LC filter does.The transformer is needed to get rid of the 170vdc common mode pwm problem.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 03, 2023, 06:24:46 am
content: Quote from: johansen on June 03, 2023, 05:37:01 amI did not know that.Some searchand it showed up indeed.So anyway, while the single phase or even DC (still think it is likely it starts with a rectifier) is probably the real option, some remarks on the 3 phase suggestions:QuoteYou were the first to mention it, no need to be shy.Anyway: Theoretically yes. But practically, would the inductance of the transformer itself (resistance to change)combined with some load, not practically do the same?Not sure about that, just my gut feeling. But, adding some motor starter caps to the transformers secondary side would probably not hurt.QuoteA bit of a principle stance, because Idothink the transformer is needed for step down & isolation from mains & above sine correction (if it happens)But the common mode seems not a reason to use a transformer. As long as no part of the battery or vehicle references mains ground, the sudden PWM polarity shift does not really matter does it?(also, 324Vdc in 230V area's)

author: johansen
author_rank: Super Contributor
timestamp: June 03, 2023, 04:27:49 pm
content: If you can isolate everything well enough then you dont need an isolation transformer, but you will need differential oscope probes for every measurement.Yes you can use the leakage inductance of the transformer as the L and just put a capacitor on the secondary.It may not work well and the transformer may get warm, but it can work.

author: BeBuLamar
author_rank: Super Contributor
timestamp: June 04, 2023, 01:08:33 pm
content: Perhaps get another good alternator and run it with a variable speed motor.