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Forum Index : Windmills : 24V 48Step Mitsumi Stepper Motor?
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| b.r.b. Newbie  Joined: 03/10/2008 Location: United StatesPosts: 8 |
Hi everyone - I'm going to build the mini mill to get my feet wet so I just found an old laser printer with a 24V 48 Step (7.5 degrees) stepping motor in it. http://www.digchip.com/datasheets/parts/datasheet/304/M42SP- 5.php Because the steps are so low - can I reasonably expect this to charge a 12V battery? I do plan on doubling the volts to 48 by using two full wave bridge rectifiers. I'm very new to this and am excited to try this tiny one out - so if anyone can give me guidance - that would be great! I'd like to have this motor charge a 12V battery that will be used to power a handful of white LED lights - so I can light up my barn. Is that doable with this thing? I live on the coast of Maine - and get a lot of ocean wind - not sure how hard but enough to spin this thing, I think. John |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
There is only one way to be sure John!  Of course we dont know how big your barn is or how much wind your get or how often you would have the light one, or... etc etc!
I suggest you go ahead and build the mini mill as one thing for sure, apart from the fun of it, you will know more at the end of the exercise. You wont get the placard volts, at least not all the time, but there are various ways of arranging things to trade amps for volts. So go ahead, build the mini mill and keep us informed of progress and I am sure there will be plenty of suggestions to help as you go along. John |
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| b.r.b. Newbie Joined: 03/10/2008 Location: United StatesPosts: 8 |
John - thanks for the quick response! You're right of course - and I do plan on doing it anyway! I think the thing that concerns me the most is that the motor seems kind of stiff to turn. The holding torque is: 78.4mN·m I don't really know what that means, though and am wondering if someone here knows enough about that number to tell me if I'm going to need some big blades to turn this thing. |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
As a simple test try turning the motor then short all the leads together and try again. If there is a considerable increase in difficulty with the leads shorted you have a good generator for a low impedance load, just what you need!
Big blades mean starting earlier in low winds but lower top RPM (I think). If you make big PVC blades they are quite easy to make into smaller blades though it is difficult to reverse this process! Hold torque I presume refers to the motor's ability to resist rotation when it is energised. |
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| b.r.b. Newbie Joined: 03/10/2008 Location: United StatesPosts: 8 |
By shorting all the leads together do you mean just connect them to each other? Yes, as far as I know, holding torque just means the amount of torque it takes to turn the motor from a standstill. I made some really sh*tty blades last night - and ran a fan at high speed and couldn't get my motor to turn. My blades were made from a plastic bottle though so I don't think they were a good test - even for prototyping purposes. I'll be sure to post pics when I get some PVC pipe and get the right size figured out! |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Yes, just twist all the ends together, if that makes it very hard to turn you have a potentially effective generator.  |
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| b.r.b. Newbie Joined: 03/10/2008 Location: United StatesPosts: 8 |
Excellent. I tried that and it certainly feels harder to turn. I don't know enough about motors to say if it's "very hard to turn" but there's a definite increase in resistance. I've been busy making the blades for this thing - I'll post some pics after I get them off my camera. The knob on the motor was way too small to drill holes for bolts through - so I had to wing it by using JB Weld and a large washer. I'm going to use that as my blade mount. Hopefully the cold weld epoxy will hold! |
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deaftodd Newbie Joined: 15/04/2009 Location: United StatesPosts: 1 |
Hi, I have the same motor, too. Today was really windy and thought the exactly the same thing as BRB did. I am trying to find the wiring diagram so I can know which places I can add diodes. |
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DaViD Senior Member  Joined: 14/01/2009 Location: United StatesPosts: 120 |
Hi b.r.b., I've used that motor with three blades each at 1 1/2 feet in length and it started in a 6 to 7 mph wind if that helps any If your not living on the edge your taking up to much space! |
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| gb237 Newbie Joined: 31/08/2012 Location: United KingdomPosts: 4 |
Well, I'm a little late (4 years) to this party, but I've just taken apart an old Laserjet 4 and found the same motor. So I'm curious: how did the turbine perform in the end? At the moment I'm more interested in the other motor in there, though. Assuming you had a Laserjet you might have found the same. After A LOT of searching, it turns out the main drive motor is a Nidec RH7-1171, 24v, 1.1 ohm. There's very little about the spec online, and I don't know much about them, but from what I can tell it's a 3-phase hybrid stepper motor. It's a really nice design, which lends itself to turning it into a VAWT with very little trouble. You could literally just stick a set of arms/fins to the top. The question is, how best to wire it for maximum output? I can't open it up (three screws in the top just refuse to budge) but to me it looks like there are four inputs: three coils, which are all joined at one end. I've used an LED against the four inputs in all combinations, and it works in all (which supports that theory - in each case there's at least some coil between them). Like this: http://www.osm-steppermotor.co.uk/img/3-phase-nema-17-steppe r-motor-wiring.jpg So, how to use that to best effect...? |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
There looks to be 2 types of wiring types for the motor you have, do your motor have 3 wires or more (how many wires) 
The basic wiring for a generator will require 6 diodes to make a 3 phase rectifier. Honestly i feel you will be fighting a loosing battle with that motor for a generator, due to the fact of its strong cogging effect, and is likely to not spin until there is a cyclone approaching. Over all the power output might charge a couple of Nicad cells but will be next to useless. That said and understood its still worth making a wind generator from it just to learn how hard it is to extract energy from the wind and make power with it, dont expect to disconnect from the grid anytime soon. Sometimes it just works |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
One thing to be aware of. It is normal practice to always connect three phase alternator windings in star connection. The reason for this is that if the voltages generated are not three perfect sine waves, connecting the three windings in closed delta will result in circulating currents around the three windings. That could well waste power and heat up the windings all for no useful purpose. You can test this for yourself by breaking into the closed delta connection at one point, and measuring the circulating current (if any) with a low impedance amp meter. It may not matter, or it could be a significant problem, depending on what you have. Cheers, Tony. |
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| gb237 Newbie Joined: 31/08/2012 Location: United KingdomPosts: 4 |
Thanks for the feedback and ideas. Pretty sure that what I've got/want is one of these: 
Downwind: are you talking about the Mitsumi or the Nidec? Because whilst the Mitsumi seems pretty tough to turn, the Nidec seems like it's made for the job. Nevertheless I'm interested to hear how others have got on with the Mitsumi since I've got one kicking around. The purpose isn't to power my house, it's to give it a go, learn a few things and see what I get out of it. Turning a few LEDs on is an ok start. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Put it this way if you can tape a pop stick (icecream stick) onto the shaft and blow on it and make it move, then there is little cogging and should work ok. Some of us have used steppers and other motors before and learnt the pit falls of what we think to what actually happens, this is why i comment it might not work as well as you would like. Yes that is a 3 phase rectifier (6 diodes) and you will find plenty on Ebay cheap, or simply make one with 6 diodes, which should be cheaper for the low current the stepper will make. Have you seen the Mini Mill Gizmo made long ago, it might give you a few answers although his motor was much smaller than yours. http://www.thebackshed.com/windmill/assemblyMini1.asp Sometimes it just works |
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| gb237 Newbie Joined: 31/08/2012 Location: United KingdomPosts: 4 |
Yeah, should be ok I think - the Nidec turns when you stroke it with a finger, whereas the Mitsumi is pretty stiff (would need a serious amount of wind). I'm not sure how it compares to the ones in the Mini Mill, but I reckon it's about 10x as powerful as a typical computer fan, and you can get one of those to light a few LEDs. If it works and there's enough wind in my garden to get anything out of it, I'll think about multiplying it up. If not then I'll start looking into solar more. Out of interest, how have you fared with vawts vs hawts? |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
[quote]Out of interest, how have you fared with vawts vs hawts? [/quote] That can be a can of worms subject here??? My personal view is a Hawt is the only way to go, i would not waste the time to even think about building a Vawt, its just too inefficient. (i duck for cover about now) Most alternators require reasonable speed to operate effectively, and a hawt with 1:1 ratio can give that, a vawt will always be slower but often greater torque, all good but dont suit most alternators that need speed, and if you add gearing in anyway you loose efficiency. 1:1 ratio on smaller mills is the only way to go. All wind generators need to get up to some speed before the load draws power, or they do what we call STALL, they dont get to reach a high enough speed to break out of stall then accelerate or decelerate with wind speed, the load just keeps them stalled, similar to driving with the brakes on. Most times our battery voltage determins the cutin speed, when power flows to the battery. A vawt might only get to cutin at full speed so wont make a lot of power, they really need an alternator designed to work at the lower speeds and higher torque. Sometimes it just works |
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| gb237 Newbie Joined: 31/08/2012 Location: United KingdomPosts: 4 |
Haha, understood. I was considering vawt due to low/unpredictable wind in my back garden. I figured the stepper would help as it's designed for low rpm. But you'll be glad to know that I've changed my mind! |
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