Build your own VFD?

[tgrandahl]

Hi there,
This is my first post on this form but i have been reeding on here for quite awhile as i am in the middle of building (slowly) a cnc router. I recently picked up a 7.5hp colombo spindle, its 460v and im told is a 4 pole configuration. I cant confirm that yet as i wont receive it until later this week. The problem that this presents is that i will need 460v 3phase at 600hz to get my 18,000 rpm. From looking around different websites and the bay i realize that 600hz is rather high and most VFD's require/prefer 3phase to begin with.

So it seems like im supposed to get a rotary phase converter connected to high frequency VFD. That sounds very expensive and wasteful, most VFD's are just going to rectify that three phase to 460volts DC so that phase converter could just be a transformer or voltage doubling circuit + rectifier + cap. Then generate the sign wave and use some igbt's to drive the spindle.

Now i know a lot of what i just said can be really quite complicated, especially generating and controlling the correct waveforms. Its just something i have been thinking about and wondering if anyone has attempted before. Any comments/ideas?

Tyler

[CountZero]

I would look at used from ebay first. If you are dead set on rolling your own check out renesas M16C cpu offerings, the often include timers designed for threephase generation. I think they have an appnote with code examples too.

Oh this solves the waveform generation, driving the IGBT's and the rest of the highvoltage stuff is another matter... not easily homebrewed safely without experience.

[Al_The_Man]

You are probabally going to find there is alot of time and agravation involved in trying to build your own.
What I would do first, is see if you can find a manufacturer that allows their 460v 7.5hp VFD to operate on 1phase, usually the cut off is around 5hp.
This way you would just need a 240/460 1 ph transformer, and the 460VFD's are cheaper on ebay than the 240v models.
Check with SEW, WEG, Square D, Mitsubishi.
What made you buy a 460 model?
Al.

[tgrandahl]

Countzereo, That renesas M16C sounds great do you have any experience working with these?

Al, i have been thinking about / hoping that i can take a route like that as i have seen a few that might fit the bill, but most all drives only run up to 400hz and these are considered "high frequency". I have found a few that run higher but they are rated at 1000hz and cost quite a bit more. Is there a way to rewire the motor to run as a two pole?

Its 460vots because there was not other option i got an awesome deal on the spindle, or so i think. I also knew that bumping the voltage up should not be that big of a problem.

thanks guys

[JRaef]

2 things going on here.

1) You want to feed a VFD with 1 phase power and get 3 phase out of it. You can do that with almost any VFD now. Under 5HP you can do 230V drives without derating because they are designed up-front for that capability. At 480V, all you need to do is double the size of the VFD for the motor. 2 reasons for this; the front end components were sized based on a 3 phase input current, so since the 1 phase current will be greater by the sq. rt. of 3 (1.732), the drive must be rated for at least that much current. The rule of thumb says to double however because you must also have enough extra capacitance to smooth out the additional ripple caused by the 1 phase input. The only caveat to applying 1 phase input after the current rating is dealt with is that there are a few brands that have input phase loss protection built-in, most of which can be defeated in programming, but fewer still that cannot. Only those that cannot be defeated are unusable on a 1 phase input. Just be sure to ask before signing the check.

2) You want a 600Hz output. While most VFDs stop at 400Hz, there are a few that go higher.

The Siemens Micro Master 440 (MM440) Series goes up to 650Hz output and will not trip on input phase loss. Just buy a 15HP drive and you are good to go. http://www.sea.siemens.com/drivesbu/...chures/440.pdf

[Al_The_Man]

I have never understood the reasoning behind doubling the VFD size when going to 460 1ph for the same size motor as the current is approx half, and the power supply components are capacity sized for current.
So by going to half current the size requirement doubles??
Al.

[DennisCNC]

^^ To make more money!

[oliver9866]

Hi, everyfriend:
glad to offer you our cnc routers here. we professionlly manufacture cnc routers. and if you want DIY cnc routers, we also can offer you spare parts, like spindles, stepper motors, microdivision drivers, controlling card, power supply, linear guideway, dust collector, holddown system. etc. welcome to contact me for your demands. thanks. waiting your reply. welcome.
Email: oliver9866@gmail.com MSN: oliver9866@hotmail.com
Shandong ITOP technology co.,ltd.

[oliver9866]

Hi, everyfriend:
glad to offer you our cnc routers here. we professionlly manufacture cnc routers. and if you want DIY cnc routers, we also can offer you spare parts, like spindles, stepper motors, microdivision drivers, controlling card, power supply, linear guideway, dust collector, holddown system. etc. welcome to contact me for your demands. thanks. waiting your reply. welcome.
Email: oliver9866@gmail.com MSN: oliver9866@hotmail.com
Shandong ITOP technology co.,ltd.