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Shopmade 20" Bandsaw #2: The Motor and Driver

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Blog entry by William Shelley posted 05-24-2014 08:04 PM 1698 reads 0 times favorited 5 comments Add to Favorites Watch
« Part 1: The Frame Part 2 of Shopmade 20" Bandsaw series Part 3: Base construction and frame finish work »

A bandsaw would not be much use without something to make the wheels spin. EBay to the rescue.

Lincoln Electric 3-phase 1 horsepower 1140rpm 208/230VAC TEFC induction motor

I picked this up for about $100 including shipping. It has a 5/8” shaft with keyway, and it’s in fair condition. It was ‘refurbished’ by the seller which basically means they painted it. There is some physical damage to the mounting frame which may have happened during shipping. It weighs about 36lbs. This is a six-pole motor which means it has extra windings inside (more copper and iron = heavier). But a six-pole motor is much better for what I am using it for because with the motor only spinning at 1140rpm, my pulley ratio is 2:1 instead of 3:1 or 6:1, if I were using a 1725rpm (4-pole) or 3450rpm (2-pole) motor, respectively.

I don’t have 3-phase service in my shop, but that doesn’t matter. To power the motor, I am using a Square D VSD07 U18 P20 Variable Frequency Driver, which is a device that rectifies a 60hz AC input into DC, then uses a technique called pulse-width modulation to output a new 3-phase AC sine wave with a variable frequency.

Since an induction motor’s speed is a direct relationship between the frequency of the AC sine wave, a VFD unit can be used to run a motor faster or slower than it’s nameplate rating. You do lose a little bit of power when running a motor too far over or under it’s rated speed, but I’m not sure exactly how that’s calculated.

Electronics

The other electronics pictured are a Seimens circuit breaker, some terminal blocks, and a LS Metasol magnetic contactor, as well as a 24VDC power supply which will be used to run indicator lights and some other stuff.

-- Woodworking from an engineer's perspective



5 comments so far

View Tim Royal 's profile

Tim Royal

203 posts in 952 days


#1 posted 06-02-2014 06:58 PM

Very slick! I have often thought 3 phase conversion would open the door to better motors and more flexibility for the money. This is the first I had heard of this Square D modulator and when I looked it up and saw the price I hope you are able to run more than one motor from it!!! Nice build underway.

-- -Tim Royal... Always reminded of this when I see the amazing work LJ's do (I have no choice but to be humble!), "Pride makes us artificial and humility makes us real." -Thomas Merton

View William Shelley's profile

William Shelley

150 posts in 935 days


#2 posted 06-02-2014 07:14 PM

@Tim – They are really handy because they inherently provide a lot of features that would otherwise require separate parts. I have mine configured for soft-start over 3 seconds, as well as “Ramp-to-stop” over 6 seconds… effectively the VFD will reverse the direction of the motor to apply braking when the stop command is sent.

EDIT: You might be able to run multiple tools from one unit by feeding several 3ph outlets or something, but you’d need a much larger unit for that to really be effective. Mostly they are used per-machine.

They aren’t that cheap but I got lucky and got this stuff for free from my workplace…

-- Woodworking from an engineer's perspective

View William Shelley's profile

William Shelley

150 posts in 935 days


#3 posted 06-02-2014 07:20 PM

This is a generic/unbranded unit from china, please don’t take it as an endorsement… I personally would go with a known-brand unit with a reputable source, but this is an example of something that could run multiple 3ph motors simultaneously in a small shop. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130803713199&ssPageName=STRK:MESE:IT&tfrom=130804566139&tpos=unknow&ttype=price&talgo=origal

-- Woodworking from an engineer's perspective

View Tim Royal 's profile

Tim Royal

203 posts in 952 days


#4 posted 06-03-2014 12:41 AM

Free is always good! Nice score!!!

-- -Tim Royal... Always reminded of this when I see the amazing work LJ's do (I have no choice but to be humble!), "Pride makes us artificial and humility makes us real." -Thomas Merton

View TheFridge's profile

TheFridge

5765 posts in 951 days


#5 posted 06-03-2014 12:49 AM

Damn. Tried to run some 3 ph motors faster for a job but the damn Siemens vfds weren’t capable. Good to know that SqD makes vfds that will

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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