Who knows about VFD's

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I have a 3 phase motor on my compressor. The rotary phase converter is home made. Works just fine.I am interested in replacing the rotary phase converter with a VFD. I have heard they are better efficiently and easier on the motor on the compressor.I could use the other motor for another project if I replace it with a VFD.What do I need to know about VFD's?As long as input an output are OK, I am good to go?As always, thanks a bunch.
Reply:What is the hp of the compressor?In my experience a static convert is a LOT cheaper than a VFD and with a compressor you won't be changing the frequency, variable not needed. A rotary is the most efficient and can handle larger loads but a static or VFD takes a lot less space.Your looking for something like:http://www.grizzly.com/products/Stat...-to-7-HP/G5843The tire shop across the street runs a 10hp on a static-converter. Not sure what the utility has to say about it... because their rules specify only a 7.5hp start on single phase. You have to oversize it appropriately so start. A compressor load can be hard starting unless you have an unloader on the compressor.Hope this helps.
Reply:Originally Posted by Bob WarnerI am interested in replacing the rotary phase converter with a VFD. I have heard they are better efficiently and easier on the motor on the compressor.
Reply:VFDs really help with the speed or the start up of a motor. But they can be a lot cheaper than a phase converter. Look at automation direct, they have several VFDs and some can have 120v input with 480v three phase output. They are pretty easy to set up and will run for a good long time if proper maintenance is done. Hope this helps!!!
Reply:Depends on how big your compressor motor ishttp://www.driveswarehouse.com/is a good place to lookcall them they know their stuffonce you get up to a cretain size motor with single phase input then a RPC works out cheaper, butyou have to have it running for the compressor to workG
Reply:The best way to buy the right VFD for a project is to talk to the VFD manufacturer. Give them the motor size and rating, the line voltage, and the intended load for the motor. They will pick out the right VFD for your application. Some high starting loads require oversize VFDs. Static phase converters are good for fixed loads without high starting currents and are not suitable for high starting or variable level loads. A rotary phase converter or a VFD is best for this. Automation Direct is a good economical source for VFDs.CharleyMiller MM252Miller Bobcat 225NTMiller DialArc HF / DIY Cooler2 Victor O/A TorchsetsMilwaukee 8" Metal SawMilwaukee Dry Cut "Chop" Saw 5 Ton Wallace Gantry Various Grinders, Benders, etc.
Reply:Originally Posted by ohmthisVFDs really help with the speed or the start up of a motor. But they can be a lot cheaper than a phase converter. Look at automation direct, they have several VFDs and some can have 120v input with 480v three phase output. They are pretty easy to set up and will run for a good long time if proper maintenance is done. Hope this helps!!!
Reply:Originally Posted by forhireI'd be interested in finding a good single phase VFD for larger motors in the  5 HP to 10 HP range. Anyone have a model number?
Reply:You'll need  VFD with a rated current higher than motor current and at least 1 analog input for the pressure switch.  http://www.candlepowerforums.com/vb/...d.php?t=260782 He has a simple walk through of what he did to convert his compressor to a VFD.
Reply:Will a 10hp VFD work on a 5hp motor?There is a 10HP VFD on Craigslist locally for $150 but not sure if it will work for my 5HP compressor.Ideas?
Reply:What I would recommend is a 230V 1PH input to 230V 3PH output.If you derate a 3PH VFD by about 2x you can run a 3PH on a single 1PH. All the VFD does is rectify the line in to DC then modulate it to 3PH output from DC. Most (check with the manufacture before obviously) will run happily at 1/2 power on 1PH. So that 10HP VFD if 3PH will run a 5HP motor on 1PH happily.If it is a 1PH input 3PH out then it will also run the 5HP motor happily. If you ever upgrade to a larger compressor it will also run that happily.Using a VFD allows for soft start and stop which will greatly extend the life of the compressor.
Reply:I'd be checking ebay too, seen several VFD's go for way cheap because the seller was too lazy/dumb/whatever to google the model number and post specs on his auction.  Personally I built a 220V rotary because I already had most of the parts.
Reply:thing is... a VFD is just a drive.. not a converter.. unless you're looking into using it in conjunction with your converter and i missed that part... i would stay with a rtotary tho for an input power source as it produces a far finer sinusoidal waveform than anything else, and aren't subjected to the vector distortion (between amperage and voltage) that capacitor-style static converters will tend to develop.as far as a drive, just make sure you know a little about it.. you can oversize it with  no problems, but you must set your parameters accordingly. amperage, speed (under load.. very important of telemechanique drives), IR comp, slip comp and overcurrent cutout are the most important numbers to get correct.depending on the application, you may be able to run whatever's in it.. as well, most let you pick the ramp speed and starting torque (expecially on vector drives) this is important as you don't want to short or too long a start time, obviously.  good luck!http://kawispeed.com/ -moderator and tech deluxewww.myspace.com/trickortrack -cuz i have no life
Reply:Originally Posted by whitehendrix!thing is... a VFD is just a drive.. not a converter..
Reply:i know.. i was a controls engineer for 5 years. i was not aware that it had been mentioned however.. thank you for the correction. just sorta skimmed.. i was tired.http://kawispeed.com/ -moderator and tech deluxewww.myspace.com/trickortrack -cuz i have no life
Reply:I was told one time that if you are going to buy a used VFDmake sure that it comes with the manual so you know how to program the thing.   If one is not available the VFD may be useless
Reply:Most manufacturers of industrial equipment have their manuals available online nowadays (except Caterpillar).
Reply:You will want to talk to your electric utility if you plan on installing a VFD.  They create a lot of harmonics on the line, and it may be necessary for the utility to put you on a separate transformer bank from anyone else.-- This space for rent.  Inquire within.
Reply:well, really you need quite a few VFDs running at once to create enough harmonic distortion to backfeed a neutral or cause excessive noise on the phase(s) 1 running at 50% load ( assuming your 10HP drive on a 5Hp motor..) will create minimal noise. i bet you could barely notice a 20mV ripple (maybe less) with a scope across the line. i have seen where 80 or 120+ drives (vectoring drives and soft-starts included) included will generate noise, but again, this is large-scale.if you decided to run the dynamic converter and source your 3ph. power for the compressor for that, the converter will, in effect be an isolation transformer. using te drive as a means of conversion, still.. the power supplies and IGBT sections are isolated and theres minimal crosstalk, and as well, most of them, if not probably all with jsut a simple 1 motor load probably will barely make a peep on an oscilloscope in the form of transient harminics, multiples included.  line PF should stay the same as well.. or VERY very close.http://kawispeed.com/ -moderator and tech deluxewww.myspace.com/trickortrack -cuz i have no life
Reply:Guess I will keep the RPC attached to the compressor.