Variable speed motor drive for your tools ...

Ian Gillis

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...not quite ready for prime time?

I tried to scam Greg Cook into finding the answers for me, but he's too busy gloating today ;)

The idea was to use a variable frequency drive (VFD) with 110vac single phase input to run a 3 phase motor (huff puff) and provide things like variable speed and soft start.

The answer that Greg and I both found, is that you can buy the VFD's all over the place, but they're pricey - starting price on new units around $400.

Well, that's fine for those who don't mind tripling the price of their drill press or whatever to get speed control, but it's more than I want to blow on a luxury item.

I decided to investigate an alternate route - DC motors. The site that really set me on my way is a How-To by a guy who adapted an exercise treadmill motor to his Taig mini-lathe. Everything you need, including part No's is there, so I could stop here.

But while Greg was waxing his latest restoration, I soldiered on and got updated links for the major components. Read the above link for clues on how to put it together.

Motor

Speed Control 1
Speed Control 2

Cooling Fan

Depending on the speed controller you choose, you're looking at $75-85 (+ shipping)

You'll need to spec out a pulley.

The problem from my point of view is that you need to shop in at least 3 different places to benefit from these "savings". Then when you get all the bits, you'll need to have a bit of electrical savvy to put it all together.

Anyone know of a more convenient way of doing this ??

[apologies to Greg ;)]
 
Ian,
I'm not sure were you came up with the $400 price for a VFD. That's a bit high, actually that's REALLY high for a 110v input/1hp 3ph output VFD. The prices on VFDs has dropped incredibly in the last few years. You can pick up a brand new 110v input/1hp 3ph output VFD from Factorymation for $120. http://www.factorymation.com/s.nl/it.A/id.193/.f. You can find used ones on fleebay and such for a lot less. Used 3 phase motors are a dime a dozen, the market is flooded with them. I payed $25 for a 2hp/3ph that had never been installed. Check the used machinery dealers and scrap yards or the local want adds.

Refitting your DP with a like framed 3ph motor is going to be a lot easier than trying to rig up a mount and such for a DC motor which will require quite a bit more effort and ingenuity. Just from a time and aggravation standpoint the VFD/3ph setup will be a lot quicker and cleaner.

The electrical are not difficult. Other than the main power feed, everything Else is low voltage. You can get real fancy and costly using the remote station control boxes from the manufacturer or go bargain basement on the control switches and use simple toggle & potomiter switches from Radioshack.

Mike
 
Mike, I'm glad you chimed in here, as I was thinking of loading a container full of VFD and shipping them to the US, they are cheap here, used, or slightly used, or even new, cheap.

Cheers!
 
Actually Stu, they're cheap here too. You just have to spend some time finding them and know were to look. VFDs and 3 phase power are still mostly found in the commercial/industrial realm here. For the hobbyist it can be a bit daunting to venture into the commercial/industrial market place. The commercial/industrial supply places can be a bit harsh with newbies wasting their time and looking to get educated on THEIR dime. As long as you educate yourself beforehand and talk intelligently you'll have no problem though.

Maybe Don Baer will chime in on this thread to lend some of his expertise and give us some of the pluses and minuses to DC vs. AC motors and VFDs???

BTW, how much did you say it would cost to ship a container of used VFDs form Tokyo to Hampton Roads?:D :D :D If we could figure out how to get them converted to 110/240v 60hz we'd be in business!

Mike

Mike, I'm glad you chimed in here, as I was thinking of loading a container full of VFD and shipping them to the US, they are cheap here, used, or slightly used, or even new, cheap.

Cheers!
 
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I paid $35 for my last VFD. Then I turn around and fried it. :eek: But there is no reason to pay $400. Just check EBay and you can find one for under $150. as Mike said.

I have set up a DC motor and it works. I found all my parts at the Liquidation Center(?). That doesn't sound right but they had the motor and control for about $150 but you never know what they will have in stock.

Jeff
 
Well, I'm glad to hear this. It's what I expected when I first started searching, but Google searches (and I did plenty) kept leading me to something in the $375 range. I searched online surplus places - and fleaBay too. From what Greg said, it sounds like his results were the same.

Anyway, thanks for that link, Mike. Could anyone who has a cheap VFD please post the make and model No of theirs ?

The 3 phase/VFD solution beats the heck out of DC for me. Much less fiddling around with motor mounts.

I'm glad I found out more about the DC option, though. That treadmill motor could be handy for lots of things. And I've seen treadmills go dirt cheap at auctions. And they have their own inverter/contoller built in... If I ever get motivated to built a mortiser or something (unlikely) I might revisit this.

Thanks all :wave:
Ian G
 
From motor theory, you could use a VFD to drive a single phase motor (just use one phase of the three phase output). I never hear about people doing this, so maybe there's some reason it won't work. My expertise is in communications and not motors.

If anyone has used a VFD to drive a single phase motor, please post. If it will work, you could use your existing single phase induction motor.

Mike
 
From motor theory, you could use a VFD to drive a single phase motor (just use one phase of the three phase output). I never hear about people doing this, so maybe there's some reason it won't work.

Mike

Hi Mike

This has come up before. The reason that 3 phase motors are preferred is that they don't have start coils, capacitors or centrifugal switches like single phase motors do. These extra features are not compatable with low speed operation - the start capacitor or winding will stick in start position due to low rpm and burn up.

Well, that's my civilian take on it anyway ;)
 
Ok, OK....I've been View attachment 4797 into posting.... :D

Thanks for the link....those are cheaper than what we've found so far...but still! By the time you get a decent motor, and the controller, you've invested a good chunk of change.

Here's a used motor listed on craigslist...

http://seattle.craigslist.org/see/tls/277931220.html

I sure would like to see some real bargain motors and FVDs.... I'll try to find a surplus place around Seattle, too.
 
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Fortunately for us there isn't much of a market for used 3ph motors. Businesses don't buy used, they buy new cuz the bean counters would freak out if you brought them a PO for a "used" motor from the junk yard:D Most hobbyists get all freaked out over 3ph too and swap out the 3ph motor for a single phase. Unless you go with a cheap chiwaneeze motor it usually costs more for a new quality motor than it would cost for a VFD to run the 3ph. Kinda silly huh?:huh:

Check the scrap yards, used machinery dealers and motor shops. Scrap yards often have a stack of them sitting around or scrounge one out of a derelict machine. If it's been sitting outside for a while or even well worn, a new set of bearings are cheap and easy to replace. 3ph motors are simple animals, there are no centrifugal switches, no start capacitors, no run capacitors, just plain old motor. Not much to go wrong with them as long as the insulation and windings are good. Check the local woodworking stores too, some have a bulletin board were you can post want adds or there might just be a add for a used 3ph motor.


Greg, $100 isn't a bad deal for a 3hp motor, but I'll bet you can talk him down to say $25 to $50 in a few weeks when he can't get rid of it. I did exactly that on a 2hp for my lathe, got a never used motor still in the box for $25. He was happy to get rid of it:p On the other hand, 3hp is probably a bit stout for a drill press unless you got a real monster there:D Most hobby level DP are in the 1/2hp to 1hp range.

Mike
 
Hi Guys,
I post a few ciomments for now since I am fried between starting a new job (I just got off work) and closing on the new house. I promise to post a more detailed thread later but in short here is the analysys. An Just for those who don't know me I have over 30 years applying variable speed drives to industrial machines. Both DC and AC.

First remember two things
1. HP = Torquex RPM /K (The Kis 63025 if your using in.lb. or 5252 if your using ft.lb.)

2. For the most part the only machine that is in a woodworking shop that can benefit from constant HP is a lathe.

DC Moter and their controlers are constant torque devices. (at leats in the smaller <10 HP size)

AC Motors and controllers provide constant torque from 0-base speed (1750 or 3450 RPM's ) and some model can provide contants HP abve base speed.

as a rule of thumb except for lathes eitehr one will work equally as well.

AS for why VFD's aren't applied to 1 phase motors as someone else mentioned 1 Phase motors have starting windings, starting caps and cyntrifical swithches which stay into the cyrcuit until the motor reached 2/3 of base speed. The motors will burn up if they stay below 2/3 speed for very long so a VFD on a 1 phase motor is kinda useless as a variable speed device.
 
Hi Mike

This has come up before. The reason that 3 phase motors are preferred is that they don't have start coils, capacitors or centrifugal switches like single phase motors do. These extra features are not compatable with low speed operation - the start capacitor or winding will stick in start position due to low rpm and burn up.

Well, that's my civilian take on it anyway ;)
Good point - I forgot that the starting switch is centrifugally operated and would "connect" at low RPM. Thanks for pointing that out.

Mike
 
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