Author Topic: Electric Motors  (Read 5269 times)
ggillis
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Electric Motors « on: December 20, 2014, 12:04:44 PM » Author: ggillis
Hi, is anybody on LG into electric motors or collects them?
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Re: Electric Motors « Reply #1 on: December 21, 2014, 01:34:15 AM » Author: DetroitTwoStroke
My dad has a few old motors sitting in the basement. We have a few General Electric 1/3 hp motors and a couple of other types / brands.
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Re: Electric Motors « Reply #2 on: December 21, 2014, 10:02:06 AM » Author: ggillis
Cool, I have a three phase baldor 1/2hp two pole(3600rpm) motor on my forced air furnace with a variable frequency drive converting 1ph to 3ph, and also controlling the speed of the blower.
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Re: Electric Motors « Reply #3 on: December 21, 2014, 10:22:07 AM » Author: funkybulb
I have a small collection of dc brush motors
And large stepper  motors as well.
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Re: Electric Motors « Reply #4 on: December 21, 2014, 08:31:27 PM » Author: themaritimegirl
I've got a few small shaded pole motors, a universal motor, and a synchronous motor. I don't do a darn thing with any of them, but I would like to make a small box fan out of one of the shaded pole motors someday. And maybe someday I'd like to convert the universal motor to brushed DC so I can experiment with using it as a DC generator.
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Re: Electric Motors « Reply #5 on: December 21, 2014, 08:45:02 PM » Author: funkybulb
A universial motor can run on DC
As i have ran many 120 power tools on
Bunch of lead acid batteres..
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Re: Electric Motors « Reply #6 on: December 21, 2014, 08:51:15 PM » Author: themaritimegirl
Yes, but they can't generate it. One or more of the coils have to be re-wired in such a way that the motor becomes a brushed DC motor.
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Re: Electric Motors « Reply #7 on: December 21, 2014, 11:30:58 PM » Author: TheUniversalDave1
Hey Trent, speaking of motors, I watched your video of the Airworks heater teardown, and I thought "hey, I've got about five broken heaters, why don't I use the motors for something?" So, I took out an old Honeywell plastic tower heater and proceeded to beat the crap out of it with a slimline ballast. Since, ya know, it had SECURITY TORX... I got the motor and stuff out and decided it would be cool to make a homemade box fan. Tonight, I took apart (with less violence) a Utilitech heater with a gem of a shaded pole motor. It uses 15 watts (1/50 HP), and moves the perfect amount of air for my project. Which brings me to the question: Could I buy a potentiometer at Radioshack and have infinite speed? Or would running the motor too slow ruin it? The week after Christmas, my dad and I are going to build a wooden frame and stain it and make it look pretty and we're probably going to use the Utilitech motor.
« Last Edit: December 21, 2014, 11:45:48 PM by TheUniversalDave1 » Logged

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Re: Electric Motors « Reply #8 on: December 22, 2014, 03:40:56 PM » Author: themaritimegirl
Yes, you could. You need to make sure you get the right kind of potentiometer, though. You need one that has a high enough resistance so that the motor goes as slow as you want when it's turned all the way down, but not so high that the motor stops completely before there's still quite a way to go down. You also need one rated for enough power that it won't burn up in operation.

You can determine both of these things by putting a light socket in series with the motor, and gathering up a wide range of incandescent light bulbs to test with, starting with 100 watt and going all the way down to the smallest you can find, at least no bigger than 7.5 watt (use something to put a night light in series for the smaller wattages, if required). Wire a multimeter such that it measures the voltage across the light bulb, and use the Kill A Watt to look at current. Start with the biggest bulb - you'll find that the motor runs at full speed and the voltage across the bulb is small. The smaller bulb you go, the higher the voltage across the bulb will be, and the slower the motor will run.

For every light bulb you try with, calculate the power the light bulb consumes. That's the voltage across the bulb times the current. Do this for every light bulb, and then note the one which had the highest power consumption. You want a potentiometer a bit bigger than that. I found with my motor, the biggest light bulb power consumption was about 3.2 watts, so I'd want a 5 watt potentiometer. Such a potentiometer is relatively large and will cost you a few bucks... You probably won't find one at Radio Shack.

For the maximum resistance, just find the smallest light bulb that makes the motor go as slow as you want. Resistance is voltage across the bulb divided by current. A 7.5 watt bulb made my motor spin pretty slowly. It had a resistance of 1800 ohms and some, so I'd be looking for a 2000 ohm pot.

That's pretty much it. You'll find the motor doesn't vary in speed in a linear fashion - It will keep maximum speed pretty well, then all of a sudden "crash" and start declining in speed pretty rapidly. This is because AC frequency determines the speed of induction motors, rather than voltage.

And finally, DON'T use a dimmer. I can confirm they don't work for this, at all.
« Last Edit: December 22, 2014, 03:44:25 PM by TheMaritimeMan » Logged

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Re: Electric Motors « Reply #9 on: December 22, 2014, 04:00:42 PM » Author: TheUniversalDave1
Thanks! I'll try that and we'll see how it turns out. I'll already be wiring a main switch with a fuse on the side of the case, it wouldn't be too hard to add a pot after it's built.
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Re: Electric Motors « Reply #10 on: December 22, 2014, 04:14:58 PM » Author: themaritimegirl
I'll be interested to see how it turns out!
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Re: Electric Motors « Reply #11 on: December 22, 2014, 07:20:15 PM » Author: TheUniversalDave1
I decided that since I have two motors with bladesets, that I'm going to make two box fans. An "Economy" and a "DeLuxe." The "DeLuxe" will have infinite speed and the "Economy" will have just a single pole switch. The motor you saw in the picture will probably go to the "DeLuxe."
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Re: Electric Motors « Reply #12 on: December 22, 2014, 07:34:00 PM » Author: themaritimegirl
Sounds good to me!

Oh Dave, I completely forgot, you could put an appropriate capacitor in parallel with the motor to improve its power factor. If you do that, current goes down and you could use a smaller, cheaper pot. One of the very reasons power factor correction exists.
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Re: Electric Motors « Reply #13 on: December 22, 2014, 09:24:27 PM » Author: TheUniversalDave1
What type of capacitor do you think would be appropriate for a 15 and a 20 watt motor? The motor on the right will be used as the Economy motor since it has a black bladeset and moves less air. It came from a Honeywell "Pro Series" that I had to destroy because it had security torx. It uses 20 watts. The motor on the left came from a Utilitech. It moves more air and uses 15 watts.
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Re: Electric Motors « Reply #14 on: December 22, 2014, 10:32:39 PM » Author: themaritimegirl
You can calculate the proper capacitance. You need the power consumption and the power factor of the motor. Then you can calculate the reactive power, Q,  of the motor using:

Q = P*tan(arccos(Fp))

Where P is the power and Fp is the power factor. arccos is the inverse cos function.

We need a capacitor that will have the same reactive power Q. So, we need to find the reactance, Xc, of the capacitor we need:

Xc = V^2/Q

Where V is the voltage (120).

Now that we have the reactance, we can find the capacitance:

C = 1/(w*Xc)

Where w (Greek letter Omega) is the angular frequency of the AC current, which for 60 Hz is 377.

This can be put into one big equation, which I've attached in a picture. So if we say your 15 watt motor has a 0.5 power factor, we're talking a capacitor of approximately 4.5 μF.
« Last Edit: December 22, 2014, 10:37:16 PM by TheMaritimeMan » Logged

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