VFD choice?

B

bronchialcircle

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Feb 23, 2016
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Hey everyone, I've got my 2x72 grinder all built except that I need a VFD to control my motor. The motor is Baldor 3hp, 3 phase, 3450 rpm, 8.4 amp, 60hz.
I've looked a fair amount online but I have no experience with VFD's and I'm scared I'll get the wrong one! Does anyone have recommendations for me? I would greatly appreciate it!
The cheaper the better! But I suppose I can deal with something more pricy if needed.
 
You really have two choices, at least that I found, and it comes down to the KBAC and Chinese imports.

I have a very similar setup motor-wise with a 3HP Baldor at 3450RPM and have been very happy with it. I went with the KBAC 29, you can't go any lower as they will not run a 3HP motor.

The down side of the KBACs are the price, they are not cheap and a model 29 runs about 400$ last I checked. The alternative is a Chinese model with the most popular probably being a Teco.

I did a lot of reading up and found three downsides to the cheaper route. Enclosure, reliability and support were all lacking on the import models. I don't know if you can get a NEMA 4X enclosure for a Teco so most guys build their own, but it needs to be enclosed. I did my research on industrial sites where I figured there were more in use and the biggest complaints I found were they did not last and when they tried to get them warranty repaired they had issues with support. The upside is they are much cheaper than a KBAC.

I've had to call KBAC support twice and both times my call was immediately transferred to a technician who was friendly, spoke English and solved my problem on the phone. The instructions were good and it has been a trooper for almost two years now.

In closing if that 400$ price tag doesn't scare you away its a no brainer in my eyes. Conversely I know there are guys on here who use Teco's and have not had issues with them. I personally will only run KBACs on my grinders but I am not above getting a Teco to run a saw or other three phase tool that I don't rely on as much or I know will not get coated in metal dust.

Good luck!

-Clint
 
KB electronics, in a NEMA 4X enclosure. Here's the thing, a VF drive built to be in a NEMA 4X enclosure is designed to be in an unvented sealed box. So everything that needs to be cooled is attached to a heat sink that is part of the enclosure. The drive is designed for continuous duty at room temperature. Clean the heat sink once in a while. Take a drive that requires active or passive cooling and put it into a sealed box, and it will overheat because the air in the box will get hot. Leave the drive open to the air, and it won't overheat, but will eventually be killed by dust.

We have 2 wood lathes in the shop. One made by a major manufacturer who saved a few bucks by using a passively cooled drive and putting it in a mostly sealed box that we still have to clean the dust out of occasionally. Load the lathe heavily or run it slowly and the drive eventually overheats and shuts down the lathe for about 1/2 hour to cool. $7,000 lathe...wish I had known, and when I have to replace the drive on this lathe, I will buy a KBAC NEMA 4X. The other lathe we upgraded to variable speed and that manufacturer sent an open drive with the inverter grade motor. I bought a KBAC drive to put on instead. We have not overheated the drive yet on that lathe.

FWIW the 2X72 grinder in the shop has a DC motor and a KB DC drive. I think KB has the best ratio of cost to quality that you'll find for a NEMA 4X drive.
 
They both said what I would have.

If you wanted to keep it cheap, then 2 hp would hae been the way to go.

Not only is the 3 hp box more than the 2 hp box, you will pay much more for

breakers, wiring to gt the power to the vfd.
 
Yep, KBAC drives are the industry standard for grinders. I just ordered one yesterday for a grinder I'm building, and am very much looking forward to getting it.

Ebay has pretty good prices on them, though they don't come stock with a line voltage power switch. Electric Motor Wholesale is probably the next best price, and you can chose add on switches and what not.
 
Please allow me to toss in a different view. For general hobby use (like myself) where the grinder will get perhaps 10 hr/wk or so of use, and it's not "end of world" if grinder ever goes down, the Chinese VFD does offer a viable VFD. For $116 shipped (last time I checked) for the 3hp VFD is a good budget item. Of course, it is an open frame with internal fan for cooling. Either put in enclosure with filter over inlet (air blowing out prevents dust from getting at outlet), or do as I did and put filters over the inlet and clean from time to time.

With that said, were I considering a full time knifemaker situation, I'd sure spend the extra $300 or so for the KBAC NEMA 4X drive.

Ken H>
 
Just to add to Ken's post, I do have a Chinese VFD to run 3 phase power to my knee mill and surface grinder. I use it quite regularly and often for extended periods, and have had zero issues with it. I just mounted it inside a cabinet on the wall next to my machines to keep the dust out and drilled a couple of holes in the bottom of the cabinet for air circulation. It's a very high value for the money, and I'd buy one again in a heart beat.

The reason I went with a KBAC for my new grinder build was convenience more than anything. This way I don't have to wire an external switch and pot control, or build a new enclosure, worry about dust/filters, etc... and since I don't dust collection system at the moment, this was a concern.
 
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