Sine wave output VFD
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  1. #1
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    Default Sine wave output VFD

    I want to put VFDs on a few machines I'm working on, namely a blower that I want to throttle to maintain constant pressure despite filter clogging and baffles opening and closing. It will be a quiet, low speed large diameter airfoil type blower, and I really don't want to listen to VFD whine in the motor the whole time it's running.

    Sine wave output inverters are common and affordable in various consumer products where noise is an issue. Is anyone aware of a line of commercial VFDs that produce sine wave output in the 2-10hp range?

    I am aware of line reactors but those can whine on their own and an output stage designed for sine wave output is going to be cleaner, easier, and smaller than adding filters.

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    Not sure what you are asking for here........ Almost every VFD is "sine wave", the pulses add up to a decent sine wave when "integrated" by the motor inductance and/or inductors added.

    A "real" sine wave unit (analog) will be many times larger and also less powerful, most likely. We had a unit that took up about 8 rack spaces, and put out around 6A or 8A at 230V.

    Try setting the pulse frequency very high and accepting the increased losses. That will be cheaper in the long term.

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    As JST commented, search for "carrier frequency" in your VFD manual, this is changeable.
    One of my VFDs is settable from 750Hz to 16KHz. The issue is if you use a very long wire from the VFD to the motor, you may trip the circuit breaker using the higher frequency. That's really an industrial issue where the motors are remote to the power control room.

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    Quote Originally Posted by JST View Post
    Not sure what you are asking for here........ Almost every VFD is "sine wave", the pulses add up to a decent sine wave when "integrated" by the motor inductance and/or inductors added.

    A "real" sine wave unit (analog) will be many times larger and also less powerful, most likely. We had a unit that took up about 8 rack spaces, and put out around 6A or 8A at 230V.

    Try setting the pulse frequency very high and accepting the increased losses. That will be cheaper in the long term.
    Specifically I want 0-60hz without harmonics.

    That seems strange to me considering how small the circuit boards are on inverter generators. I guess quiet motor drives in industrial applications aren't an area with enough demand to warrant the development. Or maybe line filters work well enough. I'll have to price some out and see how big they are.

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    Set the switching frequency above 8-12 kHz and you won’t hear drive, load reactor, or motor operating from 0-60Hz.

    We have done lots of fan / blower apps just like you describe for cooling glass molds with constantly changing operational conditions. Cold days operating at 35Hz with only a few mold cavities running to hot days with all cavities running pulling 400+hp to keep things cool.

    Adaptive mold cooling with centralized plant data | Applied Motion Systems

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    Quote Originally Posted by motion guru View Post
    Set the switching frequency above 8-12 kHz and you won’t hear drive, load reactor, or motor operating from 0-60Hz.

    We have done lots of fan / blower apps just like you describe for cooling glass molds with constantly changing operational conditions. Cold days operating at 35Hz with only a few mold cavities running to hot days with all cavities running pulling 400+hp to keep things cool.

    Adaptive mold cooling with centralized plant data | Applied Motion Systems
    Unfortunately I'm still young and can tell when someone left a machine on because I can hear the CRT whine from across the shop.

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    Quote Originally Posted by Strostkovy View Post
    Unfortunately I'm still young and can tell when someone left a machine on because I can hear the CRT whine from across the shop.
    Possibly the correct hammer for this nail, isn't an AC motor run via VFD. Alternate suggestion: dc motor with a dc motor drive.

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    You cannot get zero harmonics from a PWM-type inverter. Domestic type inverters generally just throw some filtering at it; I am not sure of the specific specification they achieve.

    Use a proper line filter, a low switching frequency, and ensure all your screened cable is terminated perfectly.

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    The domestic inverters with filters meet the FCC regulations (or are supposed to), which normally are pretty strict. Much more so than is reasonable for use with a motor and short wires.

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    Quote Originally Posted by Strostkovy View Post
    Specifically I want 0-60hz without harmonics.

    That seems strange to me considering how small the circuit boards are on inverter generators. I guess quiet motor drives in industrial applications aren't an area with enough demand to warrant the development. Or maybe line filters work well enough. I'll have to price some out and see how big they are.
    LOL! What JST said.

    C&W was sending a Lorraine off to scrap around 1985. Crystal-controlled to 60 Hz. Pure sine wave. VERY!

    About 11U tall and 85 lbs Avoir. I snatched it up for ten bucks, saved them the scrap run, ran a 42U rack with triple S-100 units off it for years with four marine-RV deep-discharge Gould gelled electrolytic batteries to get the telco-standard neg 48 VDC.

    Good for three days, no utility-mains power. But that was only for the 60 Hz sync-sensitive drives.

    The REST of the S-100 gear used DC, "eventually" so it was easier to provide.

    @ 85 lbs avoir and a whole, munificent FIVE Mike-Foxtrot AMPS of my very own 120 VAC?

    That was ALL it was gonna do! Our telco sites had multiple ROWS of Lorraine inverters, 42U tall!

    And THAT in an environment where most things ran off the neg-48 (nominal). Actual float is much higher.



    Just hang a TCi "Sine Guard" class dv/dt filter on any decent VFD (inverter" gen set, or solar system "Inverter") and clean-up the pseudo-sine wave by "enough" to call it good.

    That will be cleaner than the average UPS, or the raggedy-ass wave-form some of those "inverter" gen sets produce, too, BTW.

    TANSTAAFL

    You want true "rotating power" class as to clean sine-wave?

    There's a TCi Sine-Guard on my 10 HP Phase-Perfect. Under a hunded bucks.

    And then? - it hits a 27 KVA EGS/Hevi-Duty 1:1 3-Phase Delta-> Wye "drive isolation" transformer. About $400. Plus freight & liftgate delivery.

    You want REALLY clean sine-wave?

    The Marathon head on my MEP-803a NATO gen set does that.

    But cheaply?

    Only because I NEED standby/emergency power anyway.

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    My solution for the inverter and sinewave filter that feeds my workshop is to house it, along with the computers, network switch etc. in an enclosure made from 1" MDF. It has a cooling fan on a thermostat pulling air through a filter for temperature control. The enclosure removes most of the noise from everything even without any additional sound absorbing matting inside.

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    Quote Originally Posted by Mark Rand View Post
    My solution for the inverter and sinewave filter that feeds my workshop is to house it, along with the computers, network switch etc. in an enclosure made from 1" MDF. It has a cooling fan on a thermostat pulling air through a filter for temperature control. The enclosure removes most of the noise from everything even without any additional sound absorbing matting inside.
    I'm deef. So "Acoustic" noise was not my issue. EMI/RFI "and more".... rather.

    If non-metallic housings? My electricals, starting with the cable router off the ISP, all live in well-Earthed "Faraday cages" regardless. LAN is Gig-E over Copper. WiFi is for guest use, only, firewalled and throttled.

    Copper roofer's flashing & solder.

    Filters of all tribes do the rest.

    Sig C, MIL-SPEC, spooky folk, Telco Central Office, PABX, private networks, UPS, mainframe, data center, & outside plant guy, eventually a Cable & Wireless pensioner?

    Old stuff. Very!

    Done deal. No problems.

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    Just a note on using high carrier frequencies. It increases the switching rate of the transistors, which thereby increases the switching LOSSES in the transistors. So responsible VFD mfrs will instruct you to de-rate the VFD by a certain percentage when using carrier frequencies over a certain level, usually 4kHz. So for example I'm looking at one that says if I want to use 16kHz as the carrier frequency, I must de-rate the drive amps by 50%. So be careful and RTFM.

    There was a VFD mfr in Sweden a few years ago who made claim to being the only VFD with a true "sine wave" output, called NSK. They never made it here to the US because they didn't want to get UL listing. Basically though, they built in what's called a "sine wave filter" into each drive, whether you really needed it or not, and it increased the price of their drives by over 50% compared to others on the market. Turned out, almost nobody really needed it when they had to pay extra for it. NSK got out of the VFD business altogether.

    You can buy sine wave filters for any drive now from companies like TCI, MTE, Schaeffer and others, the same people that make and sell reactors. The thing is, in some cases they cost almost as much as the VFD itself, so you have to REALLY want it. I do recommend them for people connecting VFDs to old irreplaceable motors that were never designed to run on VFDs. The filter mfrs do tout that one of the benefits is the elimination of the motor whine, it's just a hard sell to add one just for that alone.

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    Quote Originally Posted by Jraef View Post
    I do recommend them for people connecting VFDs to old irreplaceable motors that were never designed to run on VFDs. The filter mfrs do tout that one of the benefits is the elimination of the motor whine, it's just a hard sell to add one just for that alone.
    It WAS a "hard sell".. until one could find all sorts of capacity MFE, GE-FANUC, or (Emerson) TCi Sine-Guards like new .. or even ACTUALLY "NOS", never even been connected the first-time.... for about $70 bucks each on average.

    Irony? I no longer OWN a VFD for the shop at all!

    Mine are on the Phase-Perfect. Which is already CLOSE to "perfect". Lotta IRON in a P-P compared to a VFD. Not all that hard to filter well at a fixed frequency, y'see.

    But a P-P has been known to suffer a partial fail. So I decided the goods were worth an ounce (or many POUNDS!) worth of extra prevention "just in case".

    Upstream feed gets fat chokes, too... and "not only".

    Anal about all that?

    Guilty as charged!

    But if a career in weapons systems, uber-reliable telco and data center environments ever learnt you only ONE damned thing of lasting value?

    "Shit happens!"


    Routine as afternoon thermal air-mass thunderstorms and near-miss lightning strikes all part of Northern Virginia's environment. "Lo these many millenia" .... already.

    Count on that much!

    It can get comical. In eyeshot of the tallest feature in a dozen miles.. a coms tower a previous life had me familiar with. Pentagon to Vint Hill Farms coms traffic. And MAGNET for direct lightning strikes.

    Back of the glass wall of the conference room is another all-glass building.
    The reflection off it suddenly goes from innocent blue sky and cheery bright sunshine to solid BLACK so bad it is scary!

    Munchkin from London Head Office trying to "sell" Metcalf's folly ten-base T is shocked!

    "My GOD, what is that!"

    As legions of his acolytes stream up and down the hallways speading the daily word:

    "Storm coming!" "Save your work, power-down and unplug your PC!"


    "That, Kamal, is why MY staff are on TCNS-100 mbps ARCNET COAX!"

    "We have work to do. It does not have TIME to pause!"

    And pause we did never... fiber-optics, ferro-resonant Best "FerrUPS", (now Eaton..) decent Diesels, and massive telco-routine battery bank in the mix as well.

    "Anal"?

    Got the dam' JOB done!



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