Rectify 3-phase Question

I have the spindle drive motor out of a Toshiba CD-ROM drive that has a rotor that's a steel cup with a magnetized ring inside, I would guess it has multiple poles. This fits over a laminated stator of 9 arms, each arm having a coil of wire. There are three pads for the wires from the stator. I'm not sure how the stator is wired, maybe three sets of three arms in series? There are also three Hall effect sensors(?) there, too.

I have a red LED soldered across two of the pads, and when I give the rotor a real good spin, the LED lights up brightly. I can measure the DC resistance of about 3 ohms between each pad and they're all equal so I would say that this indicates the windings are equal, i.e. they are not center tapped. What I'd like to do is rectify the AC output of the three pads, but how? Should I use 6 diodes like the alternator in a car has? Or treat it as a center tapped winding?

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Watson A.Name - "Watt Sun
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Yes indeed.

These alone make disassembly of old floppies worthwhile, too.

This is a good strategy. Of course, the low output voltage might be problematic for some, but you have a god deal of experience with electronics so you can probably visualize at least three ways to do this effectively. Pick two points and call them minus and plus. Pick a third and call it common. From each winding, take one wire and run it to the common point. Take the other and put a pair of diodes on it- cathode from one, anode from the other. The other ends of the diodes go to the two plus or minus points like this: flying anodes go to the minus wire, flying cathodes go to the plus wire. Any capacitor would then go from plus to minus for full voltage, or you have the option of using half voltages from the coil common to either the plus or the minus. This gives you bipolar supply capability, or you can just ignore it. Of course, if you don't mind the excess drop, you can use a bridge rectifier on each lead and common all the plus outputs and also common all the minus outputs, but this is really wasteful. And, use some Schottky rectifiers for the best output overall. They are pretty common on old modem cards and other computer cards as surface mount devices.

Cheers!

Chip Shults My robotics, space and CGI web page -

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Reply to
Sir Charles W. Shults III

Hi Watt Sun,

Three phase bridge rectifier.

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Put a cap on the output and have fun. If you want more voltage use a ?Voltage Doubler?.

Jay

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Reply to
happyhobit

In article , snipped-for-privacy@OVEcfl.THISrr.com mentioned...

have

the

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the

Perhaps I didn't make it clear enough. There are only three pads for all the windings. I think this means they're connected as a wye or "Y", not Delta, because I see only three wires coming from the coils down to the pads. From your description above, it seems that you're describing how to connect three separate windings, i.e. six leads. If I connect any winding wire to another, I'd get a short. At the bottom of this web page there is a schematic of an alternator stator and rectifier bridge. I believe that's the way the windings are connected on this spindle motor, and I'm guessing that's the way I should connect the six diodes, as shown in this schematic.

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I bought a bunch of 1N5818 schottky rectifiers, so no problem there. I haven't had much success in IDing the surface mount diodes or transistors from PC boards. Some of the three terminal devices on PCBs are marked diodes, even tho they're in a transistor package. That's enough to mess with your mind. I'm still trying to ID some smt transistors, but the lists I've found don't show them. And this is even tho the PCBs are from the mid-'90s -- five or ten years old. Thanks.

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Watson A.Name - "Watt Sun

In article , snipped-for-privacy@wideopenwest.com mentioned...

Yeah, I guess that's the same as the one at the bottom of this URL. After I looked at it, it looks like they left out a connection dot or two.

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The other way I thought might be okay would be to treat the third leg as a center tap. Does this make sense? (view with courier font)

+-------------------------->|----+---------o | D1 | +--CCCC--+ | \ winding 3 | winding 1 \ || + | filter cap o---CCCC--+---||-----+ Winding 2 / | || | / | | +--CCCC--+ +----------)---------o | D2 | +------------------------->|-----+

Thanks.

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Watson A.Name - "Watt Sun

Google Groups can't resolve the proper address, so I'll post here in the thread.

Yes, you are correct and that excellent drawing shows it well (a lot of photos & graphics for a dial-up connection). The in-phase winding outputs upward thru its diode in the upper group and the return current from the out-of-phase windings goes down thru their diodes in the lower group.

Reply to
JeffM
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Reply to
happyhobit

Hi Watt Sun,

(Fat fingered that one)

Nice text drawing.

The only drawback, I can see, is that it?s half-wave. You lose half the power, or maybe half of two thirds. Half wave on two phases.

It would be interesting to do it both ways and see how much difference in power output is.

Jay

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Reply to
happyhobit

I still think the Delco print contains all the ideas you need. Center-tapped is not necessary, in fact the voltage in that 3rd winding will buck what you get from the other 2. You will also lose the 3-phase advantage and get a lumpier DC. ....... | . | . | . | . | Va-b = 1.732 * Va

Reply to
JeffM

In article , jeffm snipped-for-privacy@email.com mentioned...

  1. > You will also lose the 3-phase advantage and get a lumpier DC.

Yeah, I would think that the center tapped wouldn't be a good as the full wave. But the full wave has an additional diode drop per leg. At these low voltages, that might be more important. Thanks.

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Watson A.Name - "Watt Sun

Have you considered making the bridge out of six LEDs, and putting a resistor between the + and _ outputs to set the current? You should get more light, and waste less cranking energy getting light.

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Michael A. Terrell

Well, right now I'm still using just a single LED, no resistor, nothing else. Can't get much more efficient than that. But I thought that it might be a good idea to use the rectifiers if I put a big cap on the output to store up a bit of muscle power. I was thinking maybe a couple 1F caps might help... ;-)

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