Needing VFD Suggestions - 1Ph to 3Ph

sparkie said:

Hah, my boss got his master's in CO. I have seen a lot of the work those boys do and it has always been pretty nice. I know he is damn good at what he does.

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Anymore, I just tell people that I'm a handyman. What they don't know, won't occupy my weekends... ;>

We do single to 3 phase conversion with drives on a regular basis. The utilities want to charge an arm and a leg to run 3 phase power to the rural locations, so the small to medium farms, sawmills, etc. have to decide how to run their equipment. Irrigation for example is a big deal here in the flat-lands... We've done up to 300hp with single phase feed!

One solution, especially cost-efficient when you have multiple loads, is to use a big DC power supply for a DC bus, then feed the individual VFD's from there.

On smaller, single motor applications, de-rating a drive is more convenient and cost effective. As jref stated, the drives run hot, depending on how hard you push them. So, investing in a much larger drive will help it's life expectancy. Regardless, the de-rate will seem excessive, until you consider the ripple current going on in the capacitors. Don't think you can just add a few capacitors, either, the rectifiers likely will not handle it.

For example, I just did a quick look-up on Control Techniques. For a 25a (3ph) load, you would need a 61a drive. The next frame size would be much better, and give you a little overload capability... A 132a frame size 8 would allow 38a.

As you can see from the shocked responses from the rest of the world, we, in the US, are way behind. IMO, our residential power supply should be 208Y120. This would give use 3 phase to efficiently run our appliances, and single phase for our lights and convenience items.

You can use a rotary phase converter. There are millions in operation. Be prepared, however for the poor efficiency, power surges, noise, and much larger incoming supply required to start the converter. The LRA of a 5hp converter is likely 300-500a.

Static converters are used routinely for light duty loads, like Mills, Fans, etc. They work by using the motor as it's own converter, thus de-rating the motor itself. So, for example if the lift you are working on is rated for 5 tons, don't plan on more than 2-3 tons of real work.

It is always best to get a single phase VFD of the right voltage range if you know you're going to run it on one phase. Running a 3-phase or a drive meant for a different voltage will require de-rating and finding out how to turn off the phase monitor faults. In the case of voltage difference, it might simply not be allowed, or you have to figure out how to set the target DC bus voltage or disable the associated faults.

I'm mostly a servo guy, but on two of the platforms I use, the VFD of choice is the Schneider-Electric Altivar 32, either native or re-branded as the B&R P74. I would imagine this drive is not very cost effective for something simple, we use them because you can fit a lot of them side by side and communicate to them with the native drive communication protocol.

I know a few people that used to rave about ABB VFDs for discrete IO control for their performance and inexpensiveness, but that's been a decade ago and product lines change.

I just wanted to thank everybody for the information on this topic. You have shed a TON of insight for me and I will soon be delivering him the solution.

Why not buy a VFD rated 240V single phase input 5hp. They are out there and are economical. No need to derate if the VFD is built for the single phase input.

I think you will find the rotary phase converter unacceptable. The third phase is often not properly formed or positioned and the motor will run hotter than normal.