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Variable Frequency Drives  Rate Topic 
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 Posted: Tue Aug 20th, 2019 05:37 pm
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Jim Humphrey
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Hi All,
I've been talking with Terry Fisher about Veritys fans, and the topic of VFDs came up.  He has one he uses on the 230/250 V, 50 cycle fans, and I've started looking for a VFD that would let me use the proper 50 cycles on the Veritys I got from Doug Wendel at Fan Fair as well as a couple of Emerson fans that run on 25 cycles and 133 cycles respectively (unless they've been rewound for 60 cycles, I don't really know yet).  I can provide 120 V, 60 cycle single phase and 230/250 V, 60 cycle single phase to a VFD through my step up transformer.

So, I would need a VFD that covers at least the 50 cycle through 133 cycle range.  I've seen some of those advertised, but their outputs are 3 phase.   I'm not sure, but that seems to me like it might be a problem, since I think all our old fans are single phase.  But this is getting into an area of technology and science that is beyond me.

Could someone give me some further info on selecting a VFD, and what specs I should be looking for, and maybe a manufacturer/model that would work for this application?

I'd appreciate any help here.  Thanks.

Jim

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 Posted: Sat Aug 24th, 2019 12:54 pm
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Mark Olson
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A VFD is an inverter.

While you may find a single phase VFD, there is a reason that they are rarely offered for sale.
Single phase motors are not meant to be run at speeds other than the line frequency they are designed for, particularly the
starting windings, switches, or related starting components. Knowing that your fan is designed for 133 hz or 50 hz, you
could conceivably build a device to run the fan at its design frequency.

First, look into what an inverter is. It converts D.C. power into A.C. power. Computer uninterruptible power supplies are
inverters. They have batteries in them that charge during normal power conditions and the batteries supply power to the
inverter during outages to allow computer systems to be safely shut down. Inverters are also commonly found in mobile use
for running A.C. appliances, equipment, or tools off of vehicle batteries where line power is not available.

With this in mind, two readily available potential sources of inverters exist, and you may even have one in your possession already.
The inverter for mobile power could be fitted with a line A.C. to 12 volt D.C. power supply (of the right power rating) and
The computer UPS already has the D.C. supply built in.

The real trick to this scheme is going to be changing the frequency at which either of these inverters run. Typically, the
frequency is determined by the resistor capacitor value in a multivibrator driver circuit which drives transistors, that in turn,
drive the mosfets (power final devices), which drive the primary of the step up transformer connected to your fan.
The exact frequency circuit type would need to be determined in order to modify it, but it is certainly doable.

I have a UPS laying around here that i will investigate at some point....
The mobile inverters are cheap at the import tool store, I may buy one of those and look inside of it.

Do you know an electronics whiz near you? Most any radio man should be able to help you.

Let us know if you pursue this possible avenue and how it works out.


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 Posted: Sat Aug 24th, 2019 12:58 pm
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Russ Huber
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http://www.afcaforum.com/view_topic.php?id=14866&forum_id=1&highlight=KBDA-24D

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 Posted: Sat Aug 24th, 2019 01:56 pm
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Jim Humphrey
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Mark, Russ,
Thanks for the info and the link, guys.  Once again, proof that things always seem simple to someone like me who doesn't really understand diddly about the subject.  How hard can it be, right?  I just don't want to damage something because of my ignorance!

Jim

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 Posted: Sat Aug 24th, 2019 02:03 pm
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Russ Huber
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Jim Humphrey wrote: Mark, Russ,
I just don't want to damage something because of my ignorance!

Jim

You're far from ignorant.  :D

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 Posted: Sun Aug 25th, 2019 12:56 pm
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David Hoatson
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It seems like modifying a battery backup UPS so you can control the frequency would work. If you can find a model that allows this. 
Or, combine a 120 volt to 12VDC power supply with a European 220v, 50 HZ inverter like this:



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 Posted: Sun Aug 25th, 2019 01:55 pm
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Jim Humphrey
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OK, but guys, I think there are people right now running fans on frequencies other than 60 Hz using VFDs.  I see VFDs advertised that use 120V 60Hz input and provide variable voltages and cycles at 230 V and 400 cycles or more.  Here's one on the Bay https://www.ebay.com/itm/SCHNEIDER-ELECTRIC-Variable-Frequency-Drive-1-HP-230VAC-ATV12H075M2/293200024147?epid=3012060466&hash=item4444155253:g:Qk8AAOSwGVRdWGed with 240 V 50/60 cycle input and 230 V at 10 to 400 Hz output.  This isn't one I'd select because I'd like to just plug into 120 V and get a range of voltages and cycles on the output side, but they pretty much all say 3 phase output.  But I don't want to just run a VFD if there are problems that need to be fixed with a UPS or other methods to make the system right.

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 Posted: Mon Aug 26th, 2019 01:44 pm
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Dan Miley
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Good DC-to-AC inverters produce a pure sine wave like the waveform that comes out of a wall outlet.  Cheaper ones (most of them) produce a squared-off "modified sine wave" output that can be damaging to some electrical devices, particularly motors.
https://www.lifewire.com/pure-sine-wave-inverters-534758

Personally I'd only use a pure sine wave inverter on an AC motor but a modified sine wave unit might be OK.



Last edited on Mon Aug 26th, 2019 01:57 pm by Dan Miley

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 Posted: Mon Aug 26th, 2019 05:02 pm
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Jim Humphrey
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Good points Dan.  I'm not really planning to do any extensive running of fans that need a different number of cycles than what's readily available.  Actually, I'd be satisfied if they would run without overheating and with enough power to at least appear to be operating correctly.  But any fan in my collection has to run, and I know there are ways to crutch even the 133 cycle fan so it will sort of run, but putting it on actual 133 cycle, even if it's modified sine wave, is preferable.  I'm going to grab a VFD and have at it. Thanks guys.
Jim

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 Posted: Mon Aug 26th, 2019 05:45 pm
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Dan Miley
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Jim, will that Schneider VFD really do what you want? As far as I can tell from the spec sheet, it is intended to run and control the speed of a 3 phase motor that has a speed sensor that feeds back into the controller connected to the VFD. See the docs here:
https://www.schneider-electric.com/en/product/ATV12H075M2/variable-speed-drive-atv12---0.75kw---1hp---200..240v---1ph---with-heat-sink/

Maybe it will do what you want but I’m an EE with some motor experience and that’s not obvious to me. If it will do the job for you, go for it and I will have learned something. 

Mark Olson’s knowledgeable post above suggests that a standard inverter could be hacked to alter the output frequency. That’s an interesting idea. As Mark says, the inverter has some type of frequency generator inside that switches the MOSFET transistors on and off to create the positive and negative swings of the output waveform.

Maybe using something like an Arduino processor with the right electrical interface to replace the internal frequency generator could make this happen.  This is an example but might not be big enough to start up and run a fan.  Some of the output components could be upsized. 
http://www.bristolwatch.com/ele/arduino_power_inverter.htm

Last edited on Mon Aug 26th, 2019 06:04 pm by Dan Miley

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 Posted: Mon Aug 26th, 2019 06:00 pm
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Jim Humphrey
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Hi Dan,
No, I wasn't considering the specific VFD I mentioned, I was just looking for a quick example of a VFD with a wide range of frequency outputs, but the rest of the info for this particular VFD are way beyond my knowledge and pay grade.  Rather, I'll be looking for a VFD that others seem to have used to good effect with their fans.  I don't want to be breaking new ground or pushing the envelope!

Jim

Last edited on Mon Aug 26th, 2019 06:01 pm by Jim Humphrey

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