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Forum Index : Windmills : minimill
| Author | Message | ||||
| Guests Guest  Joined: 01/10/2003 Location: Posts: 52 |
Hey I have a few questions for those of you that have constructed mini mills. I am using a stepper motor out of an old inkjet but have a few issues. mine is a 4 wire motor. 1. how do you tell which lead is which? i hooked the the motor up to a drill and tried every possible combination of the wires w/ a multimeter (testing for voltage) and still couldnt tell the positive/ground wires. the multimeter voltage was jumping all over the place and never got about .01mv. (digital multimeter) 2. How did you attach your blades to the motor? Mine only has a very small aluminum wheel around it. I got the smallest bolts that i could find but i have some doubts about being able to drill the holes in the wheel b/c it is so small. Alternative methods of hooking the blades up? |
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| drew Newbie  Joined: 16/04/2006 Location: United StatesPosts: 3 |
some details i forgot to add: i know the motor works b/c i took it out of a working (but junk) printer i play to use the windmill to light some LED's..if that makes a difference with the wiring, are the zeners and such still necessary? |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Hi Drew Sounds like you have your multimeter set to measure DC volts. Steppers make AC volts, and this wont register on a meter set to DC. Switch the meter to AC and try again. To convery the AC to DC you need a rectifier. But if you only want to light LED's, they are a diode ( Light Emitting Diode ) anyway so you can connect them straight up. There is no default methode of attaching the blades, its a case of creative junk pile searching. My little stepper had a aluminium flange that was big enough to drill a couple of holes into. If the end of your aluminium wheel is nice and flat, you could try to glue a flat disc to the wheel. Pre dril the disk to suit your propeller before gluing to the little aluminium wheel. Use some 24hr epoxy. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| RossW Guru  Joined: 25/02/2006 Location: AustraliaPosts: 495 |
I agree with the diagnosis here. The other thing you MAY be able to tell it from is just measuring resistance. If it's 4 wire, you probably only have 2 coils (well, more than two but wired in parallel). Won't help you with the phase though.
Word of caution here. Depending on the voltage being produced, if
you connect the LED directly to the output, you run a high chance of
destroying the LED due to the REVERSE voltage. LEDs have a fairly low
reverse breakdown voltage and they don't like it. Easy answer: run *TWO* LEDs, back-to-back, so one will conduct on
the negative half cycle (thus protecting the other from reverse
voltage), and vice versa.
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| drew Newbie Joined: 16/04/2006 Location: United StatesPosts: 3 |
Thanks for the replies. What do you mean by back to back, just wire them in series? So if i test the leads of the motor for AC it will have positive and negative leads...what are the two extra wires? Sorry I am not very familiar with this. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
The stepper motor you have has two coils in it, and each coil can be treated as a seperate AC generator. The coils are out of phase with eachother, meaning the peaks in voltage wont be the same at the same time. Out of phase also means you cant really connect them together without some more electronics. To connect them together, you would need to first convert the AC to DC ( with a rectifier ) and then add filter capacitors. But for your purpose, its not needed. This circuit explains how you would connect the wires together to light 4 leds, two on each side are conneced back to back as Ross said.
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Also note, with AC there is no Positive or Negative lead. AC ( alternating Current ) is like a battery that swaps its positive and negative poles around, many times a second. The 240 volt AC power point on the wall swaps its polarity 50 times a second. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Yup, exactly what Glenn said/showed - except I would add two more components to what he's shown there. A resistor in series with one side of each of those coils, between the coil and the LEDs. The value will depend on the voltage present and the LEDs you use. For "rule of thumb", most LEDs can handle currents up to 50mA without any drama. If your "generator" can't break that, then no problems - skip the resistor if you like. If it's possible it could, then try to find/measure/estimate the voltage (RMS if you can) with some nominal load. Don't do it open circuit as that's almost meaningless. Lets say you get 15V AC out of it. Allow 2V drop across the LED. Since it's only half-wave rectified, multiply by 0.7 and we're back to about 9V. Pick a "safe" current for the LED, lets say 20mA, R=E/I = 9/0.02 = 450 ohms. It's not critical, and since there's a standard 470 ohm resistor, I'd use that. They're available in lots of power ratings, and P=E*I, you're looking at about .2 watts, so a 1/4W resistor should be adequate. (The purists will pick up here that I'm wrong, that the peak LED current is much higher than this at about 21V, and instentaneous current would then be 40mA, but that's why I chose a relatively low "safe" current limit and rounded the resistance UP to 470, not down to 390R) |
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| drew Newbie Joined: 16/04/2006 Location: United StatesPosts: 3 |
ok, thanks again for all the replies. switched the multimeter to AC, i get get about 3 volts turning the motor by hand (so very slowly). doesnt seem to make a difference which two wires i hook up, can always get about 3 volts max, how can i tell which wires are for which coil? just trying to get this all planned so when i finally have time to attached the blades next week i can wires everything else up the same day. |
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