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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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  #1  
Old 04-18-2008, 11:23 PM
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Default DC to 3 phase inverter for hard drive motor

This probably seems to simple to the rest of you, but...

I have removed the spindle motor from a couple of hard drives. I think these are three phase motors. I want to run them off of a simple battery. I think what I need is a circuit that inverts DC to 3 phase to run this, with some kind of speed controlling variable resistor.

I did a few searches on the Internaughty and in this forum, but everyone seems to be in love with stepper motors, which I always thought was the motor that controlled the heads.

So, anyway, I have two types of motors. One with three leads and one with four. By playing around with wires and a battery. I can get the motor to jump back and forth by jumping any two of the connectors, one after another. This is why I think it's a 3 phase.

I am working with the Elentco 500-in-1 electronics kit for components and breadboard. Can someone help me with a simple circuit diagram or other information to get me going?

Appreciate it.

Last edited by lostowl05661; 04-18-2008 at 11:24 PM. Reason: typos
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Old 04-19-2008, 12:04 AM
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Well, do you have a Schmitt-input IC that has at least 3 inverters? Something like a CMOS 4093, 40106?

If they are indeed 3-phase motors (I don't know, never took one apart) the one with three leads is probably a Delta wound motor; the windings are connected like an equilateral triangle with the three leads coming from the "points" of the triangle. Using an Ohmmeter, the resistance between one pair of leads will be approximately the same as between any other pair of leads.

If the 4-lead motor is 3-phase, it's likely wound in a wye ("Y")configuration. In a wye, there is one phase connected to each "tip" of the "Y", and neutral is connected to the center. Perhaps not so obviously, the neutral line is the one that has the least resistance to the other three phases. It won't be zero Ohms, though.
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Old 04-19-2008, 12:16 AM
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I've done a bit of searching, but can't find a list of what parts are included in your 500-in-1 kit. If you post it, that would help a great deal in figuring out what might be built from what you have.
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Old 04-19-2008, 01:03 AM
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I don't know what a Schmitt-input IC is. Sorry, I am on lab 38 out of 500. Oscillators. I looked on Wikipedia and saw the circuit diagrams for a 3 phase inverter ( but I don't understand why none of the transister base's are connected). I was hoping this was a standard kind of thing where a few transisters, resistors and capacitors would get me spinning.

For theory, I understand the 3 phase uses three single phase AC currents offset by a certain amount, and that to do this you need to use transistors and diodes to create the AC. I am hoping to learn a bit more with this side project.

The 500-in-1 kit has the usual smattering of resisters, capacitors, transistors, diodes etc.

For IC, it has the following:
High Speed CMOS IC
74HC76
74HC00
74HC191
74HC4028
74HC4511
74HC02

Timer IC 555

Audio Power Amplifier 546

Operational Amplifier 324
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Old 04-19-2008, 01:09 AM
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Quote:
Originally Posted by SgtWookie View Post
If they are indeed 3-phase motors (I don't know, never took one apart) the one with three leads is probably a Delta wound motor

If the 4-lead motor is 3-phase, it's likely wound in a wye ("Y")configuration. In a wye, there is one phase connected to each "tip" of the "Y", and neutral is connected to the center.
that is what I thought as well. i'll check with the the ohm meter as you suggested.
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Old 04-19-2008, 01:19 AM
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Yep, one is delta and one is star. The three prong one has a resistance of 2.8 ohms between the prongs. The four lead one has 1.3 between the fat leads and .8 to between the skinny lead and any of the fat ones. So, that means the skinny is the neutral, right? Interestingly (to me) the delta motor has tactile cogging and the star doesn't.

Thanks for your prompt reply. I am a computer administrator, etc, and I know how annoying it is when people ask questions without RTFMing, and I try not to do it. However, I am kind of reaching a mental block about reading any more about 3 phase, single phase, AC/DC, induction brushes and toilet paper. I learn best by doing, so I'd like to cobble up a circuit and try to figure it out after wards.

BTW, the IC idea, is the circuit too complicate to do with transistors, capacitors and resistors? I'd help me understand it better if I can see the circuit that way. From what I've read though, it's starting to seem like what I want to do isn't that simple at all....
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Old 04-19-2008, 01:40 AM
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Well, sure you can do it without IC's - but the IC's have built-in functions that remove the necessity of having to do a lot of wiring.

OK, let's go with the 324 opamp.

What kind of transistors do you have, and in what quantity?
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Old 04-19-2008, 01:48 AM
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Wait a minute!
Look in your manual, in book 2
Section 6) "More About Oscillation"
Experiment #320, "Three Phase Oscillator", page 37?

Scan and post it.

Might as well start with something that you KNOW you have parts for.

Basically, from that circuit it will be a matter of using three transistors driven by each of the three phase outputs. You might be able to use the wye-wound version with V+ being fed to the neutral, the collectors of three NPN transistors tied to one each of the phases, their emitters tied to ground, and bases connected to the 3-phase outputs via resistors, say 20k each. It depends upon your transistors, and how the circuit is configured that is generating the three phases.
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Last edited by SgtWookie; 04-19-2008 at 01:52 AM.
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Old 04-19-2008, 02:36 AM
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OK, threw together a 3-phase generator using an LM324. See the attached.

It's output frequency is about 19.2kHz, which is way too fast for your motors. But I did it that way so that it would be easier for you to see the pseudo-sine wave output.

If R5 through R7 are removed, the outputs become square waves and the frequency drops to around 250Hz, which should work fine with your motors. However, the opamp alone won't likely have enough current to drive the motors.

Note that R4 sets the voltage level for the + inputs of all three opamps. This is to allow adjustment for the duty cycle of the outputs; I wanted 50%. In this simulation, I wasn't worried about getting it exact; ballpark was enough. It really needs a 0.1uF cap to ground to eliminate noise.

Note that there should be a 0.1uF (100nF) bypass cap across the supply pins. This goes for just about any IC.
Attached Images
File Type: png 3-phaseLM324.PNG (77.2 KB, 668 views)
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Old 04-19-2008, 10:35 AM
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Quote:
Originally Posted by SgtWookie View Post
Wait a minute!
Look in your manual, in book 2
Section 6) "More About Oscillation"
Experiment #320, "Three Phase Oscillator", page 37?

Scan and post it.

Might as well start with something that you KNOW you have parts for.
.
Sarge, you rawkith mightily. I looked through the book for inverters in the table of contents, I totally blocked on the oscillator doing essentially the same thing. (or exactly the same thing).

Thanks for the second post. I can't wait to study it.

here is the page you quoted from book two.

http://www.viciousbunny.net/images/3phaseOscillator.jpg I think you are right. I'm going to skip to this experiment for now, and also examine your diagram. Thanks for you help.
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