# Is there a down side to using a VFD?



## rogee (Apr 15, 2013)

In reading the above Sticky posts over numerous times, it seems that the RFCs are over kill for the needs of one machine in my one man hobby shop, while the use of static converter could be asking for more problems than I probably am able to handle at a later date. Seems the VFD has been given mostly good revues, Other than expense is there a down side to it's use?  Might it be more complicated to wire,  will the average village Idiot like myself be able to follow the instructions?


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## Kennyd (Apr 15, 2013)

In my opinion?  No, no downside if the motor is under 3 horsepower.

Wiring is easy plenty of help here if you need it.


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## stupoty (Apr 15, 2013)

rogee said:


> In reading the above Sticky posts over numerous times, it seems that the RFCs are over kill for the needs of one machine in my one man hobby shop, while the use of static converter could be asking for more problems than I probably am able to handle at a later date. Seems the VFD has been given mostly good revues, Other than expense is there a down side to it's use?  Might it be more complicated to wire,  will the average village Idiot like myself be able to follow the instructions?




The vfd i use on my mill has a 1 page manual writen in chinglish,
 (i say that with humorous affection for peoples translation skills not zenophobia, you should see my chinease skills, omg it's bad :jester

it has conectors for single phase in labled "phase, neutral, earth"

the output is 4 connectors labled "p1, p2, p3 and earth"

their are remote control conectors under a seperate low voltage cover that can be used for switches to be conected to start/stop the speed can be selected via the rotory knob on the vfd if you don't nead local speed control at the machine.

if the spindle spins the wrong way swap any 2 phases on the 3 phase side.

Check the voltages that the 3 phase motor can run on, many motors can be rewired in the terminal box(change jumper/connectors) to run with different supply voltages, most of the cheeper vfd's i have come across  don't change the supply voltage.  So single phase in at x volts will become 3 phase out at x volts

all fairly basic to connect, most vfd's have advanced fetures in adition to the basic like electronic brake that may require extra configuration, for a lot of users they will never be used. 

but if you are confident in wireing a multiple switch lighting circuit or simmilar and following simple diagrams it shouldn't be out of the reach of most peoples skills.

If your unsure I would imaging any competant electrician should be able to fit the wireing quite quickly for you.

to be honest it's got to be simpler than a static convertor to set up.

I have heard that some older motors don't like the way they make the 3 phases and might run a little hotter than normal but a static convertor would make the motors hotter than normal any how and stress them more.

or as other people have said previously swap the motor for a single phase unit.

although i do find the speed ramp up/down to be nice to the mechanics of machinery, kind of eliminates that ka-chunk sound i get with the single phase stuff when power is switched in.

Hope that helps,

Stuart


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## November X-ray (Apr 15, 2013)

Other than cost, there really is no downside and nowadays the VFD has gotten really affordable compared to several years ago. My first experience with them was about 12 years ago when we used VFDs to drive two 3500 HP motors. Those were the size of an ocean container and liquid cooled but what they could do was amazing by running the motors anywhere between 150 RPM to 1500 RPM with full torque at any of these speeds. 

As mentioned above, 3 phase 3HP or less motors are perfect for the Hobby Machinist!

Good Luck!


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## cdhknives (Apr 15, 2013)

Reliability...it is another potential point of failure.


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## cross thread (Apr 15, 2013)

About 20 years ago I was using a RFC to power two 2hp motors and a 5hp motor. 2hp motors were on mills. 5hp motor was on a lathe .
Mills ran ok . Lathe with it's high / low electric did not work well at all.  
Worst thing though was I would forget to shut off the compressor , but I would shut off the RFC. So when the comp. automatically started 
it would flicker the lights in the house, that was my tip off to run , by the time I got there the comp. motor was toast.
. Some type of clever wiring would fix that, I think. I just wrote a note on my panel box. TURN OFF COMP.


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## CluelessNewB (Apr 15, 2013)

The only down side is they are addictive.  I started out with one on a wood shaper, then another for a wood jointer, then the metal lathe and the latest on a disc/belt sander.


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## stupoty (Apr 15, 2013)

cdhknives said:


> Reliability...it is another potential point of failure.



This could be a potential issue, especialy if your work shop is left for long periods, bugs(creepy crawlys) and condensation are probably the worst problems you may face.  I personaly keep mine powered 24/7 to try to prevent condensation and to zap any bugs before the make a new home in it.

Alough i've seen some terible wireing damage on motors and hvac and plastic water pipes from rodents so theirs always going to be some chance of failure I guess?

Still the carbonised milliepede between the live and earth of a plug socket has to be one of the funniest i've come accross(probably not for the millepede though :jester.


Stuart


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## 8ntsane (Apr 15, 2013)

While VFDs are popular, and I run my machines on VFDs, there is nothing wrong with using a RPC. The phase converter
will power several machines, and VFDs are used to power just one machine, though some guys have wired them to work on two machines. The RPC is reliable, and even the most simple home brew jobs work very well. The RPC wont give you vari-speed, braking and such, and only you could say if you need it. The only thing I don't like about RPCs is the extra noise of the RPC running in the back ground. My shop is connected to my home, and the RPC was not making the wife happy. So the change to VFD was made. If you use a low RPM 3 phase motor for your RPC, it does make a big difference.
I have built several and found the 1200 rpm motors are very quiet. Just keep in mind, the faster the motor spins, usually means more noise. I think if I had a VFD crap out, I would rig up a RPC to get up and running again. Used 3-phase motors are sold cheap on craigslist , kijiji . If your machine is already wired up, and you don't want to do a total rewire job, the RPC would be easyer for you.Providing you can live without the bells and whistles the VFDs have.


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## Ray C (Apr 15, 2013)

Some machines (like the ones that have dual speed motors controlled with drum switches) are harder to rewire and without using a different motor, you'll lose one of the two speeds.
They must be used with care with older motors since older motors relied on a minimum RPM for cooling.
Older motors were balanced for a fixed speed so running faster or slower sometimes caused vibration.
If you had a machine that has other electronics, you can't simply snip-off the plug and wire it into a VFD because, the other electronics might not be able to run at speeds other than 60 Hz.

This along with what everyone else has mentioned those are some additional down-sides.

Electrically, VFD's are fine and produce good looking power.  I looked at the waveform with an oscilloscope and it was a nice healthy sine wave and the phase cross-overs were on the money.  120[SUP]o[/SUP] apart -exactly the way it's supposed to be.

Ray


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