Stepper Motor Genny - Increasing Amps - How?

[wadlands]

Thanks Madscientist627 & yup it is fun ghurd! 

I think that the 950mA is a reasonable enough figure to start thinking about fabrication of a small wind generator??
What do you think? 
I thought a "simple" Savonius out of 6" pipe would be worth cutting my teeth on with this stepper motor - any comments?

Oh....I couldn't work out how to post the results straight into the forum reply rather than as an attachment - is there a simple way of doing this when the original info starts in an Excel file or Word document?

[ghurd]

Savonius and Simple?
I don't believe they go together in the same sentence.
They always look simple, until you try to make one.
G-

[wooferhound]

It's hard to get a Savonius to go faster than about 60 RPM and they max out at around 120 RPM
You will be much happier if you make a HAWT

[wadlands]

ghurd / wooferhound - thanks for the heads up "warnings" guys.  I was only thinking small scale  a bit like this design which has sometimes been linked to by others in the forum: http://www.macarthurmusic.com/johnkwilson/MakingasimpleSavoniuswindturbine.htm

I'm thinking that I need to test my own fabrication skills first of, cutting a pipe squarely and and getting axles & motors aligned, while I can "still reach it with my hands on the ground".  Also not upto fabricating / using a tower just yet and probably would need to get local authority planning permission!!!

Still a way to go yet - I want to get a couple of cordless drills to hack their motors & gearboxes to see how their generator output compares to my Nema34. 

Meanwhile thinking about what may be the "simplest" approach to creating a frame for the double stacked  pipe savonius in the above link - ie with top & bottom bearings rather than just relying on the assembly to sit as a totem pole on the motor shaft?

Any thoughts - tips - experiences welcome - not withstanding ghurds comment re "Simple & Savonius"....do like your sense of humour!!!

[wadlands]

ok - got hold of unwanted cordless drill - 18v nominal rotation speed is 550rpm.

Connected to my test drill and gave the motor a spin via the chuck and gearing: about 8v @ 100rpm and 6 amps; about 15v @ 500rpm and 10 amps short circuit current.
Cahrging amps into flat 12v car battery - only 0.5 amps at 500rpm - I guess when the generated volts are > 12v for the car battery?

A question to the wise if someone can help me understand?: given that a car batteries internal resistance is very low, I think in the order of 0.016Ohm  what causes this massive loss of amps?  With this DC motor the loss is massive from the short circuit current of 10 amps to a miserly 0.5 amps into a flat battery?

Even with the stepper there was a drop of almost half compared to the short circuit current and actual into a car battery.  I understand there is some loss of voltage in the rectification diodes, but the short circuit current is after rectification.  Would really like to understand this as a piece of learning ??

But otherwise the stepper motor looks like the one I will use in my first wind genny build.  Started work to make a timber frame to mount the motor and at least have the whole genny assembly off the ground for initial trials - ie does the wind and blades actually turn the stepper motor!!!!! Will post a pic when it looks less Frankenstein.

In the meantime would really appreciate if someone can help me understand the missing amps

[Madscientist267]

what causes this massive loss of amps

You're seeing a phenomenon called 'cut-in' at work here.

You spend most of your 'RPMage' just trying to overcome the battery's OTV (open terminal voltage).

Once that happens, the charge current begins to flow.

Usable current is only produced after cut-in, so your charging potential is only 3V at 500 RPM (assuming exactly 15 and 12V). Real world, the battery will usually be higher than this, further lowering the difference, and therefore your current.

You'd be much better off from the sound of things by going with the stepper, even with the diode losses. Main problem I see is that you have significant torque issues to overcome with the transmission in the drill, which steals even more power from the blades.

Hope that helps.

Steve
 

[wadlands]

Steve - thanks - I've read elsewhere on this forum or another forum about voltage doublers or DC to DC "upconverters" wherby the voltage from the wind generator or solar panel is boosted to say 24volts.

Should I be thinking of doing this sort of thing so that cut-in happens at some lifted voltage.  So that the 15volts at 6amp short circuit current (90 watts) and if the voltage is say doubled to 30volts to get "better" cut-in; then would you not then get three amps into charging a battery? 

Or am I missing something fundamental here - I think I am but I can't get my head round it??

[Madscientist267]

Eh, its kinda a wash to use a boost converter.

Remember that power is power, and so if you increase the voltage, your current will be cut by that amount. For example, if you start out with 10V at 1A, and boost it to 20V, the current at the output will be 0.5A best case, and will actually be less due to conversion losses.

So, would it work? Yes.

Is it practical? Not generally, although it is found to a degree 'in the wild'. There are a few occasions I have seen mention of using a boost converter immediately following a source, but it's rare (and can't even think of one off the top of my head).

Usually, conversions from generation will have a downward (or 'buck') tendency, to reduce the current flow in the transmission wires coming from the source. If it's a long enough run, a buck converter can save you some power loss by converting the higher voltage/lower current 'down to' a lower voltage/higher current, right before going into the batteries.

Steve

[joestue]

Therefore, I'm seeing it from a permeability point of view. It's already given that as the frequency increases, the permeability of the core decreases:
http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29#Complex_permeability
... shows a curve illustrating this.
The effect would also be present in an air core system, but since air already has such a low permeability, the effect is less noticed.
Not saying you're wrong, by any means, because I'm not exactly a physicist, but that's where it points, to me.Steve

It appears that the "complex permiability" is just another way of looking at hysteresis loss.
but i have not read the referance recently M. Getzlaff, "Fundamentals of magnetism" to see how they are applying it.
as far as air is concerned...at Ghz perhaps, or perhaps a few thousand teslas before its sigificant.


as far as iron transformer cores, generators and such, the permiability of the steel is not a significant factor in the operation of the machine.
losses are dominated by eddy current which follows Hz^2 and hysteresis loss, which is linear with Hz and the old books say follows flux to the 1.6 power, but that's for old silicon iron from 1940.
today's iron losses follow the charts provided by the manufacturer.
the most sensitive part of any machine is the teeth, here a decrese in permiability would serve to reduce hysteresis losses, as regions of high flux around the edges and tips would be averaged out, and hysteresis losses would then decrease. 

in a stepper motor there isn't much eddy current from spinning it, at least when compared to the eddy current generated from running it.
I've got a 5 volt 4 amp 6 wire stepper motor (4 inch diameter, about 6 inches long). When you short all the coils and spin it, you'll find the torque and rpm linear to a point,  (perhaps a hundred rpm) at which point it will let go and you can spin it at hundreds of rpm with a drill or even your fingers and there is relativly no torque whatsoever.
I suspect it is due to the hysteresis losses in the teeth, and teeth alone. keep in mind that although the stepper motor acts as a permanent magnet generator, you'll find that down the center of the shaft
(this particular motor had 7 magnets with 8 sets of disks with teeth) is a steel shaft.
when you run the stepper as a stepper motor, you can generate much higher torque than you can shorting the coils, because it stops acting like a stepper motor and more like a switched reluctance motor.

[joestue]

Connected to my test drill and gave the motor a spin via the chuck and gearing: about 8v @ 100rpm and 6 amps; about 15v @ 500rpm and 10 amps short circuit current.
Cahrging amps into flat 12v car battery - only 0.5 amps at 500rpm - I guess when the generated volts are > 12v for the car battery?

A question to the wise if someone can help me understand?: given that a car batteries internal resistance is very low, I think in the order of 0.016Ohm  what causes this massive loss of amps?  With this DC motor the loss is massive from the short circuit current of 10 amps to a miserly 0.5 amps into a flat battery?

there are no missing amps.
a quick calculation would show that the resistance of the entire circuit to include the generator is about 1.3 to 1.5 ohms.
thus supplying 15 volts to a 12 volt battery will in theory provide 2 amps, so i suspect you might have some issues there.
i'd expect more than .5 amps as well.
if you're using a cheap amp meter be sure to include the resistance of the test leads and internal shunt

[wadlands]

joestue - I am using a (very) cheap DVMM / ammeter!!!! - I'll try measuring the voltage drop across a small value sense resistor (0.1 ohm or 1 ohm) instead - in line with the "positive" lead directly from the motor to the thick car battery leads - should give a more "reliable" value? Will post result once I've had a look.

[joestue]

you have to measure the amps with a separate shunt if you're using the same meter to measure the voltage, or the error from removing the amp meter's internal resistance will change the readings, in some cases significantly.

[wadlands]

Don't know what I was doing wrong before with my test on the drill motor but now getting a more meaningful result :
1.4amps going into the flat battery at 13.7volts and 500rpm.  This cordless drill motor was an 18v version.

Bench test results with another 24v cordless drill gave about 0.7amp @13v and approx 200rpm.....and

3.1amps @14.7v and approx 500rpm into flat battery - so looks like drill motors may also be an option for me to tryout?

But how big (blade size for a HAWT) would the generator have to be to have the torque to turn the gearing? -seen some videos on YouTube etc so it must be doable.

 But I'm starting with Savonius type as a first build - again wonder how big the blades (height & width ) it would have to be to get over the gearing - the volts and amps appear to be there at 200 to 500rpm?

[Madscientist267]

Blades I couldn't begin to tell you about...

But it sounds like you've got a decent starting point, as long as you can get past those transmission losses from gearing up to the motor...

That's gonna be the fun part.

Steve

[Bruce S]

Don't know what I was doing wrong before with my test on the drill motor but now getting a more meaningful result :
1.4amps going into the flat battery at 13.7volts and 500rpm.  This cordless drill motor was an 18v version.

Bench test results with another 24v cordless drill gave about 0.7amp @13v and approx 200rpm.....and

3.1amps @14.7v and approx 500rpm into flat battery - so looks like drill motors may also be an option for me to tryout?

But how big (blade size for a HAWT) would the generator have to be to have the torque to turn the gearing? -seen some videos on YouTube etc so it must be doable.

 But I'm starting with Savonius type as a first build - again wonder how big the blades (height & width ) it would have to be to get over the gearing - the volts and amps appear to be there at 200 to 500rpm?

hate to be the bearer of bad news, but most S types will not get you up to 500RPM probably NOT 200RM either without some sort of gearing.
They can however get past the start up torque.
For speed and torque you may need to go with a tall unit rather than wide.
Hows your building skills? What materials are you looking to work with?

Bruce S

[wadlands]

Hi -  Steve / BruceS

The bench testing with a cordless drill is just to help me understand what different motors are capable of as generators – or more to the point which ones don't even make it into the playground!!!

I am hoping to use Lance's ideas from his project and web pages at: http://www.macarthurmusic.com/johnkwilson/MakingasimpleSavoniuswindturbine.htm

I'll follow the split pipe idea and dimensions (so I can at least start with something that has worked for someone!!) but build it on a timber mount, so that I can readily change motors or substitute a bottom bearing to take the weight of the rotor.  My plan is also to build it with a top bearing so that I can see what rpm's I get at different wind speeds without the drag of any motor attached.  Then to attach different motors to see what happens (probably the whole thing will only rotate when there is a Force10 gale blowing!!!!)

This is probably a slow way into wind power but I am hoping that these small-scale experiments will provide hands on learning.   Building this first prototype with a timber mount will help me better understand how to make a metal frame mount or tall mast

(I also think that from the photos on Lance's pages that his DC motor from a tape drive was probably a legendary Ametek 90v motor – so he had a big head start in terms of what his genny was capable of!!!)

[Madscientist267]

This is probably a slow way

Nothing wrong with slow. At least you're not blowing money hand over fist without doing any research.

They're out there. Dunno why, but they are.

I'm doing the same thing with my solar stuff. Once I have a solid understanding of what to expect, THEN I'll move up to the bigger prizes and sink some money in it.

Till then, it's a learning game (and the cheaper the better!) 

Steve

[Bruce S]

I agree with Steve.
 Slow is good and you seem to have a good idea of where you want to go with learning.
There are SOooo many out there that just do not want to take the time. So you're already ahead in the learning curve.
Just to add an extra reading Here's an old article from 1993
 http://www.motherearthnews.com/Renewable-Energy/1993-06-01/A-Wind-Powered-Energy-Charger.aspx
Might help with using what ya got.

IF you drink coffee or buy veggies in large can #10 size, they can be cut in half to be used for Lance's style too.
best of luck!
Bruce S

[wadlands]

Thanks for the endorsements & encouragement - had a look at the motherearth article - interesting use of sails to harness the wind.

Now to find some 8 inch pvc pipe and the biggest challenge of all - where did I put that saw after using it last time???

[Bruce S]

Thanks for the endorsements & encouragement - had a look at the motherearth article - interesting use of sails to harness the wind.

Now to find some 8 inch pvc pipe and the biggest challenge of all - where did I put that saw after using it last time???

IF you're married you didn't get this from me 
Pillow cases work out really well for the sails
Just don't use the "NEW" ones!!

Better pipe is the plastic schedule 40 stuff. or the gray thicker walled. Roller blade bearings seem to hold up nicely too.

[ghurd]

I would not put much money into something designed around the drill assembly.
The brushes do not last very long, and they are not exactly "user serviceable".
G-

[wadlands]

…….well the paddles turned!!! 

Here's some pics of my first prototype:
The removable mounting plate for the Nema32 stepper motor– so that with different face plates I can try out different motors.

The coupling is with a 10mm steel tube and “Jesus-bolts” through the two shafts.
Temporary cross member with bicycle hub as the top bearing needs to have adjustable bolts through it to better centralize over Nema32 shaft and to ensure that it is perpendicular.

My trusted “WorkBench” acting as an off the ground “micro”-tower!!!  Also temporary lash up to get the top bearing at the correct height.

Anemometer clipped to the side for wind speed indication.


Results so far:

Since completing the prototype 8 days of superb British Summer (actually its still Spring!) ie zero wind – what a time to embark on building a wind turbine!!! HaHaHa

Anyway today – the “worm turns” or is it the paddles in this case.  Decoupling the two shafts and the rotor begins to just turn at 5mph.  Definitely steady turns at 6mph and spreads joy at 7mph!! – will then keep turning when wind drops to 5mph – 6mph.

Coupled to the stepper motor – hasn't got sufficient torque? / speed to do anything yet at these very light breeze wind speeds – next week's forecast is for more like 10 to 11mph – so will see then.

But all in all a satisfying first step….more to come….

Reread Lance's notes from his web page and build notes for this 2-stage Savonius -  and note that he says at his site “the wind blast through for at least 24 hours solid”.   Which no doubt is a lot more than my measly  5 – 7mph so far!!!!

....I hear yer ghurd!! ...got to get this stepper going first.
...from what you say Bruce S ...you must have tried it!!!???

[Bruce S]

Ahh so you have met Mr Murphy . AND the old adage that once you get the mill ready and up! NO wind for 3 days maybe more
Welcome. I did try it was fun to do and a bummer when the city came by with a kind request to remove un-approved devices .
I like to make use of various things, just to try commercial sized food can, pillow cases ( found out the hard way not to use the newer better ones : ).

AND May I possibly be the first to say WELCOME TO THE ASYLUM  , no known cure , of course I never went looking for a cure, just a nice cold one.
remember to have fun to.
Cheers;
Bruce S
PS> I like the idea of having the anemometer where the turbine is. Any possibility of being able to store the data from the one you have? I didn't look that closely.
 
 

[wadlands]

..ah I shall wear the Asylum Badge with pride!!!...I am really enjoying myself - I enjoy making (or trying to make) something ...and when it works - it really is very rewarding.  Even these first small steps in this my latest project - re wind power AND late news flash - the wind piicked up and I got the 10,11, 12, 13 mph gusts tonight.

The stepper motor has earned its place in this project's history - coupled to the rotors it just turned at 10mph and turns steadily at 11 to 13 mph.  So now I have my reference bench mark of what wind speed is needed, with this blade area to actually turn my stepper motor - I have a line in the sand!!

But before the stepper motor gets too smug with itself - it has to produce some volts and amps to stay in the project!!
I guess that will need at least 15mph winds - I'll have to wait and see.

Meanwhile I'm going to salvage my converted pedometer RPM counter (used in a former life for counting turns when making coils) - save me having to count past 10 when the rpm's pickup!!

[wadlands]

Bruce S - oh forgot - the anemometer is just a simple press button and records average and max wind speed.  I use the time proven technique of real time recording with alert observer and paper and pencil...never failed yet...but you do have to reboot the observer sometimes!!

[Bruce S]

Now that you have a "gold standard" there's few things you can do to assist with getting even this unit over the high-torque start-up.
You could possibly build a larger unit by having a larger swept area. Leave this one as is and if you can squeeze in larger paddles.
What are your current dimensions?
you may find that by slightly adjusting the size you could get a lower cut-in, 13mph is going to be a lot harder to come by than possibly a nice breezy 10.
Since your are at the point where it begins to turn at 10mph and is "going" at 13... then slightly larger swept area will increase this units ability to grab the wind and get the stepper over that start-up speed.
Have fun
Bruce S

[wadlands]

Hi Bruce – This Mark1 prototype has each stage at 300mm high and the two rotors have an overall diameter of 278mm.  Giving an overall aspect ratio of about 2.2:1 (height to diam).  I was going to leave this as is as I don't think the thin pizza pan cover aluminium can take the load on the bottom one where it couples to the output shaft (a 10mm bolt through the bottom plate).  But I could strengthen it and spread the load with a plywood disk.  I was then going to use this Mark1 at a different height (cause I can still lift it!!) and see what I get for a different height.

In the meantime I've cut up the rest of the pvc pipe so that I can build a Mark2 - another two stage Savonius with the same diameter but each stage will now be 820mm.  Giving an overall aspect ration of 5.9:1 and also more swept area.  Made some plywood disks this time as I think this will make it more studier – but then weight and balancing problems beckon …..



A question to yourself or anyone else who can chip in: -

My understanding is that in a Savonius (with simple pvc pipe halves) the swept area in a single stage = height x half the diameter, because only one rotor at a time is facing the wind.

My question is for a two stage it must be some factor greater than this as for each revolution the second stage catches the wind half way around – is there a “simple” factor / multiplier? 

So that for a three stage with each stages rotors offset at 120 degrees there is another factor and perhaps for a four stage with rotors offset at 90 degrees there is another factor. 

I guess four stage would also be the practical / sensible limit anyway?

[RP]

The swept area for a Savonius is simply height X width. 

Yes, half the rotor is moving upwind.  That's why they're not terribly efficient but still the swept area for any turbine is the area of the "shadow" cast by the spinning parts.

[wadlands]

Had some “better winds” today – 6 to 10mph – still light breezes I suppose but got the top bearing support sorted out so that I can align better in x – y – z axis rather than using the clamps I had before.  Good learning for assembling the next slightly larger prototype.

Also got my anemometer onto a removable mount (Velcro) instead of risking the clamp anymore.  Sited a kitchen timer next to it for the minutes part of the rpm!!


Here's my modified pedometer – reed switch – and small Neo magnet for the revolutions part of rpm.

     

The only thing lacking now is the 4 independently swiveling eyeballs so that I can record the wind speed and revolutions along with the time!!

Getting about 100 to 150rpm in 6 to 10mph.  But that's with the rotor decoupled from the stepper motor.  Since I know from previous “test” that it can't turn the stepper until the wind gets upto 12 – 15mph.

Going to start assembling the Mark 2 prototype with twice the swept area and better aspect ratio – hopefully that can make better use of the available wind.

[Madscientist267]

Looking good man.

Not bad at all for a month's work.

I think someone already mentioned it, but just in case... "You've got the disease now!" LOL

Keep it coming, following this one pretty close.

Steve

[Norm]

You really need to upscale ......3 stage .....trashcan halves for the blades
funny how you can accumulate trashcans when you find a worthwhile project
like this....how many times have you seen trashcans blown out in the street
and smashed by passing cars all because some concerned citizen wasn't
around to .....eh...rescue them?  (tongue in cheek)
Norm.
Just kidding...

[wadlands]

Hi Steve – sure have ….but it's a pleasant condition!!!….with hopefully a pleasant outcome of free juice going into a battery….eventually

Norm  - I need to thank you for one of your posts where you suggested using pizza pan disks as the separators – it got me started with this Mark1 prototype.  I like your idea of scouring the neighbourhood for trashcans!! ……but I've already cut the balance of my pvc pipe (see my previous post above).  At the moment this will still be two stage but give me a swept area for the Mark2 of 4.9 sq ft compared to this current Mark1 at 1.8sq ft. 

Do you think this will be sufficient?….or should I start planning my Mark3 now!!

The Mark2 will also have a better aspect ration at almost 6:1 compared to the current 2.2:1 and stronger plywood disks.


Need some help from those who understand the theory better than I do at the moment – beginning to get a grasp of it though from reading the various posts on the forum.

 I've “built” my crude Torq-O-Meter so that I can get a feel of how much torque is actually required to get my stepper motor to turn.



The shaft will begin to rotate at around 8Lbs (~4Kg) pull on the spring balance.  The radius of the shaft is 4.5cm ie 0.15ft.  Using this link

http://hyperphysics.phy-astr.gsu.edu/hbase/torq2.html

Putting in 36Newtons (for 8Lbs force) I get an answer for the torque as:
1.6Nm = 1.2 Lb Ft – have I got it correct?

and my additional questions are:

I know that with my current Mark1, with a swept area of 1.8sq ft, a wind gust of  11 to13mph, say 12mph will just start turning the stepper.  So the rotor must be providing (after conversion losses / efficiency etc) a torque of 1.2 Lb Ft.

My Mark2 will have 2.7 times larger swept area so at what wind speed should I expect the rotor to be able to turn the stepper motor?  I know I will find out when I get the Mark2 up and running.  But I am hoping to be able to distil some rules of thumb guidelines to help “design” my Mark3.

From my reading so far, I am aware that the power in the wind is related to the cube of its speed – but that's as far as I've got.

[wadlands]

Got some nice gusty winds to do some “proper” wind trials on the Mark1 now that its fully equipped with the laboratory standardised measurement equipment.  Stepper measured rpm's:

·   12 to 15mph gusts = 130rpm
·   15 to 17mph gusts = 225 rpm

and a very satisfying whine sound from the stepper motor as it spins in unison with the rotors!….time to see if  there's any volts and amps??

Max open circuit voltage seen was 57 volts and max amps into my “standard” flat car battery were 0.48 amps (well its nearly half an amp!!).  Both at wind gusts of 15 to 18mph and the rotor doing about 150rpm. 

Here are some pics of the max reading I was able to capture (by the time my old camera phone has focussed -  of course its digitising an image that happened a few seconds earlier!!)

53.6 volts open circuit voltage



0.15 amp short circuit current



0.33 amp going into flat car battery



0.44 amp going into flat car battery



I feel really satisfied now that I have some benchmarks to compare my Mark2 with…still not really a wind generator…but one small step(per) ….

Of course the whole assembly is also developing the shakes at 15 to 18mph – nothing alarming yet
– but it's the genny's way of saying “don't forget to balance!!!”…hmmmmm

Norm – meant to ask you in my last post regarding 3-stages versus 2-stages:

If I stick with my PVC pipe assembly for the time being and stay at the same diameter.  My Mark2 will be 2-stages of 820mm to make a complete rotor height of 1.64m.

If this Mk2 were to be 3-stages BUT still with the same overall height of 1.64m and each stage rotated through 30degrees - I guess it will start a tad more easily (in lower winds?) with each stage offset by 30 degrees – but apart from that what additional benefits are there?