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Voltage from 4 wire bipolar stepper motor!

I've stripped a 1.8 deg stepper motor out of an old fax to make a bike generator but I can't get any juice from it. I'm spinning it using a multi tool so I should get something, right?! I did do some research and found out that 4-wire bipolar stepper motors are controlled differently from 5+ wire ones. I guessing then that generating power is different also. I'm reading 2.1 - 2.3 ohms off each coil. Tried wiring the coils in series but still nothing. I need a long serving instructablator to help me!! The label reads: STP-42D1020 1.8deg/STEP 2.1 ohms 33.5 V D.C. 0.7 A 17845G SHINANO KENSHI CO LTD. CHINA

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kretzlord5 years ago
I just used an old stepper motor from a laser printer to power some LED's. It had the 4 pin output as well. An easy way to find a single circuit out of the four pins is to start shorting them while spinning it. When the motor becomes harder to spin, you've found the pair! Also, and easy rectifier can be found in any wall-wort a/c to d/c power adapter, just remove the transformer (unless you want to play with voltage/current) and solder your leads in. I've had these things for a year and a half and didn't do a thing till I saw this. Thanks for the Inspiration! might get some pics up tonight if i feel motivated.
110100101108 years ago
the stepper can work ok. i think it'd be better than any motor with brushes there are steppers without magnet inside though. with them you cant generate electricity easily. (you need to do hacks like suply electricity to one coil and spin to get more electricity from the other etc. the power company uses such hcks in their generators cause they cant use huge static magnets) there are 2 types of steppers with 4 wires 4 phase - there are 2 coils at 90 deg angle to each other. each makes ac voltage when the motor spins but if you connect in series you get at most 1.4 X the voltage and not 2 X. i recommend rectyfying the current from each coil to dc (4 diodes / coil) and then connecting the dc and dc in parallel 3 phase (star setup) - there are 3 coils at 120 deg to each other. one wire is common to all 3 and called neutral. the voltage betwen it and each of the other wires is A volts. the voltage between 2 of the not neutral wires is about 1.7X A volts. i again recommend rectifying each alone to dc and then connecting the dc outputs in parallel when spinning the motor at its rated speed it should output voltage close to its rated voltage. if there are no magnets inside it won't output anything without external power
ZdEEvO (author)  110100101108 years ago
I'm sort of getting it. I just popped it open to see and it's got 8 coils (2 x 4 alternating) i.e following the coils in sequence it goes 'coil 1, coil2, coil 1, coil2 etc..) then the 2 wires from each coil forms the 4 wires on the ribbon. Should I rectify the output of each coil ('set' of coils) then connect in parallel? Thanks for the help.
thats what i'd do if you need higher voltage rectify and connect in series if you have enough voltage try to maximize current. to do it connect in parallel you allready found out how to get any volts from it ? if you connect a led (with or without resistor) across a coil and spin you get light ?
ZdEEvO (author)  110100101108 years ago
I've checked it with a meter and nothing. There's a millivolt blip at first then nothing which seems like it might be AC. I'll try to rectify it first then see what happens. It's been years since I've done any proper electronics so it's taking a little while to creep back into my brain! I'll let you know what happens.
if you get nothing at all then its cause there really is nothing at all if in the motor there are no magnets (open it again and see if there are) thn you wont get any electricity from it without additional hacks
ZdEEvO (author)  110100101108 years ago
I feel like an eejit. I was testing for DC, completely forgot it was AC! Did the LED thing and it worked at hand crank speeds. Now I can start my 'ible. Thanks for the help.
lemonie8 years ago
I don't think stepper motors are the best for generators. Generally you want a motor which is designed for speed. L
Kiteman lemonie8 years ago
Agreed - steppers are for precise, controlled motion. Any ordinary DC motor will be suitable for a bike generator.
ZdEEvO (author)  Kiteman8 years ago
Thanks guys, I was checking out some stuff on generating setups and they recommended steppers:

Electricity-with-Stepper-Motors

and

Generating Electricity with Stepper Motors

I do have spare cordless multitool (no charger) with a 9.6v motor. This should be speedy enough to cope with bike wheel revs, yeah? I also have a 30v from an old fax. I'll have to try a few things out. Any more advice would be great, then maybe I can publish my first Instructable!