Anyone else using a voltage step-up (boost) VFD to run 575v motors?

[tinwacker]

I've recently noticed that cheap Asian VFDs sold on AliExpress or Amazon can now be purchased with voltage step-up or boost capability. Typically they are advertised as 220v single phase input/380v 3-phase output. Here's an example of one that I've recently purchased and tested.



The reason I purchased it was to experiment to see if it would work to run a 12" pedestal grinder with a 3 phase, 550v, 2 hp motor that I purchased surplus from City of Ottawa municipal works main garage. It's a 1940's vintage Ford-Smith grinder weighing about 400 lbs.


It turns out that the VFD worked even better than I expected. It actually has the capability to double the input voltage and go well beyond the listed 380v output. In my case, my 240v main voltage actually usually measures about 248 volts and the 3-phase output from the VFD measures about 485 - 500 volts when set for 60 Hz speed. This starts and runs the 550v grinder motor no problem. I can push a chunk of metal pretty much as hard as I can against the grinding wheel and it doesn't slow down in the slightest.

Here's a picture of the VFD, just temporarily installed for testing. I'm going to need to put it into an enclosure to protect it against grinding dust (and also to make it safe, since as can be seen the terminal strips are not covered and are pretty close to the run/stop buttons.)


So my question is just to find out if anyone else has been using these 380v boost VFDs? Has your experience been the same as mine in that they can actually double the input voltage? And also wondering if a more modern 575v motor could be successfully run at voltage in the 485 - 500 volt range. I have a bandsaw and a slot mortiser with 575v motors that I was looking for replacement motors for, but these cheap VFDs seem like a really economical alternative if the motors would run OK on a slightly reduced voltage.

And they seem crazy-cheap right now. I've got another one on the way from China for testing. It's a 7.5 kW unit for only $126! That seems like a bargain to me.


Thanks, Tom

 

[Martin w]

This would be especially handy when switching from resin bond wheels to CBN or Diamond for rpm and surface feet per minute..
Tom, do you know if these would be CSA approved at all?
Martin

 

[Tom Kitta]

I have almost identical grinder - I think grinder is identical but the pedestal is different. Good to know its from 1940s. Are you sure its 550v? Mine is set at 480v or at least it runs fine on 480v and starts slowly and is weak at 240v.

Yeah I have another Baldor at 3hp - this one is like 5hp - and both are more or less fully capable of removing metal no matter how hard you push the metal in. I got mine like 5 years ago, maybe more - for like next to nothing.

 

[slow-poke]

I would be very surprised if that device has CSA approval. Most of these (everyone I have looked at) have a smattering of approval like icons for example CE that are meaningless. FYI anyone can self certify and apply a CE mark, the problem is that most the CE marked devices from some countries have not been tested to any standard.

I worked in electronic product commercialization and was asked countless times what certifications do you want stamped on the product?

Some of this equipment is safe and some of it is downright dangerous, use a good fuse;-)

 

[Canadium]

If I'm not mistaken the general rule of thumb is that a motor should not be run at voltages beyond +/- 10% of motors rated voltage. Otherwise the life of the motor will be reduced.

How to specify motor voltage for better performance and longer life

Know the difference between motor and transformer voltage.

www.piprocessinstrumentation.com

 

[Tom Kitta]

I would be very surprised if that device has CSA approval. Most of these (everyone I have looked at) have a smattering of approval like icons for example CE that are meaningless. FYI anyone can self certify and apply a CE mark, the problem is that most the CE marked devices from some countries have not been tested to any standard.

I worked in electronic product commercialization and was asked countless times what certifications do you want stamped on the product?

Some of this equipment is safe and some of it is downright dangerous, use a good fuse;-)

Intertek is the cheapest - this is why a lot of China has it.

Most machines / equipment are not CSA approved - I think there was a discussion here on the forum how much it costs - I think it was few hundred CAD +++ depending on what it is. It is certainly important if machine / equipment is used commercially.

 

[YotaBota]

Some of this equipment is safe and some of it is downright dangerous, use a good fuse;-)

I think I remember reading/hearing that if a fire/damage to the house can be traced back to a non conforming device your insurance may be void.

 

[slow-poke]

Intertek is the cheapest - this is why a lot of China has it.

Most machines / equipment are not CSA approved - I think there was a discussion here on the forum how much it costs - I think it was few hundred CAD +++ depending on what it is. It is certainly important if machine / equipment is used commercially.

Correct you can have CSA or other approved safety agency come do a "special inspection" and apply a CSA sticker. Applicable for low volume (<100 devices). Have not had one for quite a while, last one was $330

 

[Ironman]

If I'm not mistaken the general rule of thumb is that a motor should not be run at voltages beyond +/- 10% of motors rated voltage. Otherwise the life of the motor will be reduced.

How to specify motor voltage for better performance and longer life

Know the difference between motor and transformer voltage.

www.piprocessinstrumentation.com

I was told 20% +- rated voltage and I took the sparky at his word and ran 440 motors on 525 3ph. There were no abnormal heat issues, and the other 600volt motor on 525 got a bit hot so we had a water hose dribbling on it to cool it. TEFC motor and at lower voltage the amps go up.
Industrial users tend to beat them and put them away wet.

 

[Tom Kitta]

I run motors at 50% of rated voltage and they did not overheat - they were just super anemic. I think at 50% voltage the actual power was like 1/3 or less of rated. I think the life comment has to do a lot with heat generated. I.e. running motors at incorrect voltage will produce heat and that heat will kill that motor faster. This may not apply to a lot of hobby use which is not even a tiny fraction of industrial use.

 

[mbond]

This has been discussed before, so you can search the archives. AC induction motors can operate at a wide range of input voltages and frequencies. This is a function of the design of this type of motor, but the further away from the nominal values, the less accurate the values on the name plate.

The maximum voltage is determined by the quality of the insulation. The minimum voltage is determined by the needed power and thermal limits. Frequency changes the speed of rotation and has to be in a range sufficient to overcome internal resistance & inertia without exceeding the bearing capacity. For motors with power factor balancing capacitors, the frequency is more important because they need to be switched on / off at the right speed.

AC induction motors produce power only while under load, so for a grinder that's during startup. Once the wheels are spinning, the load is much less. So if it starts okay, then its fine

 

[tinwacker]

Thanks for all the answers - very helpful. As others have guessed, the VFDs shown in my posting are not CSA approved; they just have the meaningless CE stamp. But I've done my own personal risk assessment and for my personal situation, they are fit-for-purpose. They will only be used for hobby use, in a stand-alone building on my rural property, and only operated by me, standing directly in front of the machine while it is running, and all other times will be isolated from electrical supply by a proper approved 2-pole switch.

Finding these inexpensive step-up voltage VFDs that get "close enough" to the necessary 575 volts is a real game-changer for me as a hobbyist. Quite often, well-made, commercial-grade but obsolete 3-phase, 575v machines of all sorts sell for really cheap around here. And now I think that I can power them up with a simple all-in-one solution, and get adequate performance.

Thanks, Tom

 

[Proxule]

Nice choice in beer my friend, Very nice!

 

[Dan Dubeau]

It's an interesting solution. I'm currently batting O fer on Import VFD's and don't want to take another pitch though.

I've always wanted one of those big old pedestal grinders, or even better a toolbit grinder. No idea where I'd put it though. They pop up every so often for cheap enough prices to make me consider buying one just because.