208 to 480 3 ph vfd? is there such a thing

Hi I tried a search and nothing , the sites I've looked at don't seem
to help either.
Does some one make a 208 3ph to 480 3ph vfd.
thanks jim
2 hp.

Your going to need a step up transformer...

drylakemachine said:

Hi I tried a search and nothing , the sites I've looked at don't seem
to help either.
Does some one make a 208 3ph to 480 3ph vfd.
thanks jim
2 hp.

Click to expand...

VFDs can only REDUCE the effective motor voltage, but are limited by the supply voltage as to the maximum output. In other words, 208V input, 0-208V output: 480V input, 0-480V output. They cannot create voltage from thin air (otherwise they would have solved the worlds energy crisis years ago). That is why you get a transformer ahead of the drive, you step the voltage up ahead of it, then buy a 480V rated drive.

But first, confirm that your motor is not already wound as "dual voltage", ie 230/460V, many small motors are. If so, many of those are fine with a 208V input.

Note: there are very small drives that APPEAR to increase the voltage, because they take in 115V single phase and put out 230V 3 phase. But those use a special board on the front-end called a "voltage doubler" circuit. You will notice however that these stop at about 1HP 230V, because the board is expensive and beyond that size, it is far cheaper to just use a transformer.

The general type you want DO exist. But practical considerations limit them to 120V input and 240V output, at HP ratings up to maybe 1.5 or 2 HP.

A 480V motor is generally a higher power motor, unless it HAD TO be 480 due to the main machine motors being 480. At higher power the usual voltage doubler type power supplies are just not practical. You'd be getting into PF corrected inverter input types, of which tehre are very few. Maybe none at that level.

I'd probably use a transformer to get the voltage, and use a 480 drive, figuring a derated drive is fairly cheap, and everything works without oddities then, as motor is coupled direct to drive.

FWIW Drives Direct - Digital Phase Converters - Home Page has 220 1ph to 415 3ph drives in the 1 to 3 hp range. They are proud of them and the 3hp is 420 english pounds plus shipping. This sort of drive is available
outside the US as this is a common problem in parts of the world with 220V residential and 415 or higher industrial power. In the US previous advice to use a transformer is likely to be cheaper and makes the possibile use of a 'used' 440v primary VFD, which can be pretty cheap, offsetting the cost of the transformer, as JST suggests.

How about just getting a 3ph 208 to 480 transformer and running it backwards?

Jraef said:

VFDs can only REDUCE the effective motor voltage, but are limited by the supply voltage as to the maximum output. In other words, 208V input, 0-208V output: 480V input, 0-480V output. They cannot create voltage from thin air (otherwise they would have solved the worlds energy crisis years ago). That is why you get a transformer ahead of the drive, you step the voltage up ahead of it, then buy a 480V rated drive.

Click to expand...

Yes and no. Before the AC input voltage is fed to the output it is rectified to DC then the DC is chopped up at high frequency by a bunch of IGBT's and fed out to whatever load you are driving. You can't create amperage from thin air but you can use a buck-boost circuit to increase voltage by quite a bit, of course Watts = V*A so if you double voltage from a given source you effectively cut your amps at that higher voltage in half.

That said, when AC is rectified to DC and smoothed thru capacitors inside a VFD the peak AC RMS voltage is about 1.414*RMS average voltage, so for a 208v input the max output you'll get is ~294VDC. Definitely not enough to power a 480V motor but enough to give a pretty wide range of adjustability to whatever motor or application you may be running.

Whew.

you have 3ph, buy a 208->460v transformer then use any of a dozen std 460 vfd drives.

Knowing 208 gets multipiled by 1.14 to make higher dc bus voltage is of no value to you: that then can only make same ac output as input; no free lunch - forget you heard 294vdc....

That said, if you DO insist on 200 something ac in and 400 something out, you CAN BUY IT FROM AN ENGLISH COMPANY - google harder to find them. They do the voltage doubler input trick and do go high in hp. but you will pay 4-5x the going rate, it wont be supported in the usa, and when it breaks you will be SOL.

mike_kilroy said:

Whew.

you have 3ph, buy a 208->460v transformer then use any of a dozen std 460 vfd drives.

Knowing 208 gets multipiled by 1.14 to make higher dc bus voltage is of no value to you: that then can only make same ac output as input; no free lunch - forget you heard 294vdc....

Click to expand...

Its ~1.414 (well, square root of 2 if you care to get specific) and thats why I followed it up with "Definitely not enough to power a 480V motor" some people's reading comprehension on here really needs work. You can produce 294VAC 3ph output from that DC bus using a chopper driver and IGBT's, just not at anywhere near the amperage your input power is capable of.

I have a dumb question. It is REALLY common for 3 phase motors to accept multiple voltages based on how the wires are terminated on the motor.

Are you sure you can't re-wire the motor to accomplish what you are after.

Sorry if I am misinterpreting the scenario.

greenbuggy said:

Its ~1.414 (well, square root of 2 if you care to get specific) and thats why I followed it up with "Definitely not enough to power a 480V motor" some people's reading comprehension on here really needs work. You can produce 294VAC 3ph output from that DC bus using a chopper driver and IGBT's, just not at anywhere near the amperage your input power is capable of.

Click to expand...

I thought that is what you were saying. No, you cannot get 294vac out. I am on cell phone now so someone else can enlighten you.

mike_kilroy said:

I thought that is what you were saying. No, you cannot get 294vac out. I am on cell phone now so someone else can enlighten you.

Click to expand...

Yes, yes you can, and I've measured on the CNC power supply I built, and you do in fact get a DC bus voltage of ~1.414*ac input voltage provided you have capacitors behind the rectifier. This DC bus voltage is higher than the AC input voltage (RMS Avg). Is it practical/economical to do so in order to run a different size motor? Probably not.

Basic Power Supply Rectification Tutorial

Edit: Just checked the VFD on my cold saw for shits & giggles. DC Bus voltage 367 volts, no load. Lathe VFD, 368 volts no load. Coming off a 240V outlet measured at 252.7 volts, no load.

I am pretty sure Invertek (the English (ok , Welsh) company I know about) do not go above about 1.1 kW for doubler models standard. They are well represented in the US, both directly and as OEM models, so you can't be referring to them.

As far as voltage.... better figure on more like 1.35x for peak voltage. That takes several things into account.

BUT....

Standard VFDs can't get the RMS above the input, and in fact can't get it up TO the input voltage, without some "harmonic injection", which to you may as well be called "distortion of the waveform". The sine peak is always just out of reach,, because to duplicate the input, you have to nullify the diode drops, and the voltage drops in the IGBTs, and the effect of the "deadtime" between pulses, and the maximum duty cycle limits, and so forth....

Now, if you add a boost stage at the input, which allows you also to correct the very nasty power factor of a rectifier, then you can get virtually any voltage you would like, AND a power factor corrected input.

Want 480VAC from a 230V input? No problem, boost to a 700V bus, and off you go. Input current may get a bit ridiculous, but you knew that, right?

Problem is, those drives are uncommon so far, and cost considerably more.

JST said:

I am pretty sure Invertek (the English (ok , Welsh) company I know about) do not go above about 1.1 kW for doubler models standard.

Problem is, those drives are uncommon so far, and cost considerably more.

Click to expand...

I dont recall the mfgr i was thinking of, but simple google search found:

egohttp://stores.ebay.co.uk/drivesdirectinvertersltd_W0QQ_fsubZ5

upto and including 20hp models shown on ebay - like $4k US.

eplexus said:

How about just getting a 3ph 208 to 480 transformer and running it backwards?

Click to expand...

This is what I've done... except not three phase. I've got a drill running that concept, but rather than three-phase into the VFD, I'm putting 240 single phase into the secondary of a 3kva 480:240 dry transformer, and sending the resulting 480 single phase out to two of the three terminasl of an A-B 1305 BA06A, feeding a 3hp motor through a toothed-belt drive to the spindle. I limited the output to about 2.5hp.

I rescued the transformer from a scrapyard, it was mounted on a post underneath a large (about 150' tall x 4' diameter) overhead sign pole... cost me about $15...

DaveKamp said:

This is what I've done... except not three phase. I've got a drill running that concept, but rather than three-phase into the VFD, I'm putting 240 single phase into the secondary of a 3kva 480:240 dry transformer, and sending the resulting 480 single phase out to two of the three terminasl of an A-B 1305 BA06A, feeding a 3hp motor through a toothed-belt drive to the spindle. I limited the output to about 2.5hp.

I rescued the transformer from a scrapyard, it was mounted on a post underneath a large (about 150' tall x 4' diameter) overhead sign pole... cost me about $15...

Click to expand...

The main reason most people use a VFD is to convert one source to another. A 3ph 480-208 transformer will do the conversion for a couple hundred bucks.

A picked up a TIG welder from a guy on CL for next to nothing because it was powered by 480 1ph. Got a 480-240 1ph transformer, and Bob's your uncle, I'm welding Tig.

Eric

JST said:

I am pretty sure Invertek (the English (ok , Welsh) company I know about) do not go above about 1.1 kW for doubler models standard. They are well represented in the US, both directly and as OEM models, so you can't be referring to them.

As far as voltage.... better figure on more like 1.35x for peak voltage. That takes several things into account.

BUT....

Standard VFDs can't get the RMS above the input, and in fact can't get it up TO the input voltage, without some "harmonic injection", which to you may as well be called "distortion of the waveform". The sine peak is always just out of reach,, because to duplicate the input, you have to nullify the diode drops, and the voltage drops in the IGBTs, and the effect of the "deadtime" between pulses, and the maximum duty cycle limits, and so forth....

Now, if you add a boost stage at the input, which allows you also to correct the very nasty power factor of a rectifier, then you can get virtually any voltage you would like, AND a power factor corrected input.

Want 480VAC from a 230V input? No problem, boost to a 700V bus, and off you go. Input current may get a bit ridiculous, but you knew that, right?

Problem is, those drives are uncommon so far, and cost considerably more.

Click to expand...

As I said

Jraef said:

... But those use a special board on the front-end called a "voltage doubler" circuit. You will notice however that these stop at about 1HP 230V, because the board is expensive and beyond that size, it is far cheaper to just use a transformer.

Click to expand...

"Voltage doubler" / "boost stage", same thing. The point is that just because it can be done, does not make it economically viable, so that's why you do not see it.

By the way, I now see on that "Drives Direct UK" website a drive having the ability to boost 230V 1 phase input to 400V 3 phase output. From what I saw, they are basically just a distributor for Teco, who has no such product, so they must be modifying them internally to add the voltage doubler circuit. I cannot imagine Teco being willing to support that, so if you are outside of the UK, good luck.

I am also very familiar with Invertek drives, which by the way can be bought here under the names Bardac and Anacon. They have no such drive that will boost 230 to 415 or 480 or anything. But I see a marketing glitch on their website which may lead people to believe they do. There is a landing page for their single phase input drives saying they offer 115V or 230V single phase inputs, then it says somewhere below that the motor voltage is 480V. But when you take it a step further to actually create a part number, it then tells you that the output voltage is 230V in both cases, just like everyone else, there is no option for a 480V output. If you use the kW sizing selector they made the same error, saying that the motor Voltahe is 415V when in fact when you try to select and buy one, there is no option for a 415V output, only 240V. Most likely this is a copy-paste error from a different web page, done by a graphics person who has no clue.

Jraef said:

As I said

"Voltage doubler" / "boost stage", same thing. The point is that just because it can be done, does not make it economically viable, so that's why you do not see it.

By the way, I now see on that "Drives Direct UK" website a drive having the ability to boost 230V 1 phase input to 400V 3 phase output. From what I saw, they are basically just a distributor for Teco, who has no such product, so they must be modifying them internally to add the voltage doubler circuit. I cannot imagine Teco being willing to support that, so if you are outside of the UK, good luck.

Click to expand...

Same info I have had. I heard that 'someone' in UK was buying the drive and modifying the DC bus to double - must be those DrivesDirect.uk guys then. I heard they make the voltage doubler by modifying the series caps on the dc bus by using the center of them for ac input instead; most of the doubler circuit is already there doing it this way. Not something I would offer an industrial customer or someone who wanted any USA support.

Jraef said:

As I said

"Voltage doubler" / "boost stage", same thing. The point is that just because it can be done, does not make it economically viable, so that's why you do not see it.

Click to expand...

Entirely different things..... Not remotely the same. And economically, it may make sense. You do not see the doubler for two reasons....

1) Not so many people need it (but Invertek DO make it)

2) The power factor stinks. But it IS the cheapest way.

Doubler.... A connection of capacitors with the rectifier to shuttle charge in such as way as to charge two capacitors each the the lower voltage, but place them in series to supply the load, thus supplying nearly double voltage. The power factor absolutely stinks.

Boost stage.... A circuit employing a "switch" (Mosfet or IGBT typically) and an inductor to achieve any desired final voltage. It is possible to control the power factor such that a load requiring several HP draws current approximating the performance of a resistor within a few milliamps out of several tens of amperes.

You will start to see the boost stage more often as requirements on power factor become more stringent, especially in europe.