Converting an excersize bike to a generator test bed

[willib]

Converting an excersize bike to a generator test bed :

Parts required :

2 bicycle drive sprocket assemblys

Dremmel w/abrasive wheel attachment

Mororcycle brake rotor

an excersize bike

An excersize bicycle makes an excellent way to test coils and/or generate power to charge a battery , all while getting excersise !! lol

On the test coil i was able to get 600 RPM with one coil loaded with 1ohm reststance(not pedeling , but crouching next to bike and turning by hand)

I imagine that once i get all 18 coils wound that it wont be so easy to turn, and may have to resort to actually pedeling..i'm hopeing that the new magnets (7/8" dia.)and coils (1.75" dia.) will give me more  resistance(physical resistance) to my pedaling than the 1/2" magnets i was using before.

If you like , click on my name to view the pics that i uploaded .

*sigh* unfortunatly the rotors that i have are BOTH bent slightly so i cant get them as close to the coil as i would like !! ( can i sue the people that threw them out for junk abuse ??) lol

coming up are the pics with explainations:

[willib]

this is it!! a finished testbed!!



>


more to come..

[dinges]

Hi Willi,

You too working on a generator bike?

Have just made some pictures of my exercise bike (work in process...). Will upload them ASAP.

I am using a double rotor design, 320mm (1ft) diameter, with 2*16 magnets and 12 coils, of 70 turns each. Magnets are 20*20*10mm N40; normal RPM will be about 240 (80RPM with the pedals, very sustainable). BTW, I measured the resistance of the coils, they are .134 ohm each (so about .5 ohm per phase).

At the moment, the mechanical assembly is finished, apart from the sprocket; it is back-ordered, should arrive next week. Then mechanically it will be finished. My aim is about 100-150W without too much effort, with short bursts of up to 350W possible (at least the generator should be capable of it; whether the cyclist is up to it...)

I had the same thoughts as you: an exercise bike that was gathering dust in a corner of the garage.

Only major hurdle is the stator: coils are finished, but I need a plate of epoxy printed circuit board to make the statorplate (300mm diameter).

For me, it's not really a testbed, but a finished product to be used; will connect it to a small tv and radio too. Battery charger will be on it too (13.8V). Maybe this thing will even help me lose a few kg...

Looking forward to updates from you & to compare outputs.

Peter

The Netherlands.

[dinges]

You stole my idea!

Actually, your bike looks VERY similar to mine. Only difference is that I'm using a double rotor design.

Do you intend to mount only one coil on the stator plate (for testing purposes?) or to build complete stators to test on the bike?

This bike looks much better than your previous one, if I may say so (the one with the wooden stator plate; pictures were in another thread).

Peter,

The Netherlands.

[willib]

Yes Peter ,i intend to put a whole stator/coil  arangement on there , but for now i am just going to test a few different coils . the next step is to wind a double strand of #20 gage , and see how that compares to the # 17 gage coil and the #20 single strand coil..

As you can see from the pics i built the whole thing without using a lathe or a welder , just a dremmel , and two drive sprockets from two different bicycles !!

On the outside of each end i have a bicycle sprocket with associated bearing housing and bearing .thats why you need two bicycle drive sprocket assemblys.

They are connected in the middle with the part of the brake that fits over the spiral ( dont know what its called )

Now if you try to use the connector without grinding each spiral gear you will find that they are too long to fit , so i ground one end concave  and the other convex with the dremmel. then i added some wire between the central shaft and both spiral gears , so that they run true. I was surprised how true i was able to get it.!!

if you look closely you can see the spiral gear from the right sprocket just to the right of that sleve thingy..

This is how it looked before i put the magnets and the test coil on.

[Jerry]

Hey guys, take a look at these stories. They might be of intrrest.

http://www.fieldlines.com/story/2003/11/27/21353/553  and http://www.fieldlines.com/story/2003/12/7/23158/6010  and

http://www.fieldlines.com/story/2003/11/24/225711/78

Hope these work?

                   JK TAS Jerry

[willib]

Very cool , Jerry .

When i had the board on the excersize bike i was getting 4:1 , but now it is just 2:1 ,but the motorcycle brake rotor acts like a flywheel, which is good..

You must be in really good shape now!!

[dinges]

Very nice, especially considering you don't have acces to a lathe.

Fortunately I do have one, I wouldn't know how to do it otherwise...

Here's a picture of my semi-finished bike; I need to attach the sprocket, and the entire stator-plate needs to be made and mounted, but for the rest it's mechanically finished.

The stator plate, with some hardware on it to show size:

The white label is on it so I can measure RPMs with a handheld RPM-counter.

The bike, in the state it is now. My gearing-ratio is 45:15, so generator RPM will be 3* pedal-RPM.

For more pictures, look in my photo-list; the 5 photos at the bottom are from the bike-genny project. The stator-mount hardware has been crimped on the axle (alu, heated to 300deg.C, while cooling the axle in the deepfreezer).

Peter,

The Netherlands.

[willib]

Let me clarify the 600 RPM posted in my first post .

While its true that i have achieved 600 RPM with an excersize bicycle , that was  in its other configuration ( ie 4:1 drive) , in its present config. i was only able to get 555 RPM and that was no load .

sorry for any confusion

william

[motorhead2]

These would work great in fitness centers.They could power the lights and fans.As long as whe dont tell them what the cord is for.Ill see what my wife can put out.Good thinkin.

[motorhead2]

You could even adjust the airgap for resistance.

[willib]

Yeah you could put power gages on there and label them MPH ..

i'm having a bit of trouble getting the other rotor on , but it should be on by tomorrow

This is a video of my generator as it was working earlier today ..http://media.putfile.com/Rotor20/320  

Putfile.com is a free video/picture webhosting site , you can upload your videos at www.putfile.com   ..

I used my webcam to make the video..

This is the back side of the rotor where it connects to the other sprocket .I was lucky thst the bolt pattern on thr rotor just fit the sprocket..

this is the drive sprocket side  

now that i think of it , the bent rotors are what is giving me the problem, maybe i'll just go down to the junk yard and get two that arent bent..

[willib]

this is a great site for somone who wants to build a lot of little blades , and i dont see why a DIY alternator couldnt be used in the center of this setup..i've lit an auto tail light # 1156 powered with copies of his blade design ,and the only wind was my  fan!! Till the load slowed it down ,and the fan couldent keep up, it was going 500RPM..

What he does is use seven or eight small propellers attached to a central shaft, check it out , very cool stuf..

scroll down the left side till you reach his  400W mini gen , also very cool stuff

http://www.selsam.com

[willib]

Last night i finished the double rotor

and did some testing .

First let me describe the setup : The test Coil is  (round of course)measuring 1 3/4" dia x .390 wide with a 7/8 " hole wound with # 20 gage enamel coated  wire.

Magnets are 7/8" dia N40 neos, incredably strong for their size.

Since  i dont have 48 ,  7/8" neos  i put 12 on one side of the rotor and the other 12 on the other side. six pole on each side, its kinda hard to explain , but looking at it face on, i had six poles on the top and six on the bottom .equally spaced as if i had the full 24 poles around the 10" dia rotor..

ok when i tested the same coil i had been using it reached 20V p-p (1 ohm load)at 333 RPM , Thats 20A AC ! Double the previous current !! at the same RPM as before!

That poor 1 ohm resistor was so hot i think it melted the carpet a little..

[willib]

So i guess its not that unusual to get 20 A from one coil ?

on some of the big machines , when youve done the single coil test , what kind of cuttent were you getting?

[willib]

sorry i ment , what kind of current did yall get from a single coil test?

i usually read these before i post , but that one slipped by..

[dinges]

Hi Willib,

Sorry to burst your bubble, but you haven't got 20A current;

You have 20Vpeak-peak; this is 10Vpeak; this is 7Vrms

in a 1ohm load--> 7Arms

I understand where your error comes from; with a scope you can easily see Vpp. Vpp is NOT Vrms...

Still a very nice amount of energy, but quite a bit less than your 20A;

The power to your resistor is thus 49W; no wonder it started complaining...

Can't help you with your question on single coil vs. complete rotor current, but when you have wired your coils in delta, you get 1.7 times the single-coil current.

But I assume you already know this. If what you mean is 'how much more power would I get with a completely filled rotor, as opposed to your now half filled one', I think you may simply extrapolate linearly; i.e., when you use only 6 magnets on a rotor that should have 12, you get 1/2 the power. I think.

Have just installed the sprocket on my own exercise bike and did a few testruns; it runs a bit rough, but I think the sprocket needs a bit of running in. No elecricity yet though, I'll have to finish the stator first.

Good luck,

Peter,

The Netherlands.

[willib]

Your right of course . i was just so excited that the peak to peak was twice what it was at the same RPM ( 333) than it was before i put the double rotor on there..

i guess i just wasnt thinking clearly.

all i have to do now is get some more magnets and construct a better coil  holder than the one i have on there now..

lots more testing to do before i commit to a stator design..

Below is a pic of the double rotor





These are the 1 ohm resistors i use for testing .They are rated for 10W ..





ps looking foward to hearing more about your excercise bike generator..

[willib]

got some new data for the 17gage coil

i could have gone faster than 400RPM but the rotor assembly needs some more work.

loaded single coil (dual rotor )10"dia

         RPM    Peak V

Point 1: 200    4.0

Point 2: 250    5.0

Point 3: 285    6.0

Point 4: 333    7.0

Point 5: 400    8.0

I just  need a support in the center for the other rotor

This one here isnt supported in the center, it is actually bolted to the other rotor  which is bolted to the the other sprocket.

[willib]

Note: the Graph should read peak voltage (not peak to peak),i forgot to change it.(insert blushing smilely here)

[willib]

this is my first try at a double wind, and also my first attempt at winding the pigtail from the center  of the coil , so it comes out flat.i think it came out nice

 

[willib]

all voltage readings are peak voltages

          no load        load( 1 ohm)

          RPM  Volts   RPM  Volts  

Point 1: 182   4V      200   4V      

Point 2: 270   6v      294   6V

Point 3: 333   7V      357   7V      

I got two used motorcycle rotors off of ebay for $22 including shipping.

They are not bent like the ones i had, so i was able to decrease the air gap to 0.450 ( coils are 0.390 wide).

also ordered 24 more magnets .

the double wind worked out real nice, for the same size coil the double wind reduced the resistance by a factor of four.it went from roughly  .494 to .124 ohms/coil.

[willib]

this graph has a 0.25 ohm resistance load included with the no load and the one ohm load.Thats 4 1 ohm resistors in parallel.

at 333 RPM with .25 ohm load at 5Vpeak thats 20A peak or (14.14A RMS times 3.5V RMS) is 50W ??correct??

When i add 18 coils can i add the power from each coil?? to give a total power?

if so thats 300W per phase and 900 W total output .

Is this right ??

as soon as i can prevent the coil from vibrating as much , i know i can get it to go at least 6V peak .

[willib]

i was able to get 6Vpeak @ 400 RPM. Yay !!

and i've been running some numbers these are my revised calculations for 4V peak ..

Vrms = 2.83V

R(int)= .124 ohms  coil resistance

R(load)= .25 ohms

R(total) = .374 Ohms

the power = V(rms)^2/R(total)= 21.41Watts

so I(coil) = Vrms/R(total)= 2.83/.374 = 7.5668 A(rms)

so the voltage drop in the coil I(coil)* R(int)= 7.5668 * .124 = .938 V

and the voltage drop in the load is I(coil) * R(load) = 1.892 V

If you draw a little series circuit with Vrms in series with R(int) and R(load) you should get the same results..

and the power dissipated in the coil is V(int)^2/R(int)= 7.10 W

the power dissipated in the load is V(load)^2/R(load)= 14.31 W

the total power is the addition of the power in the coil plus the power in the load is 21.41 Watts

similarly for 6v peak the power is V(rms)^2/R(total) = (4.243)^2/ .374 = 48.128 Watts.

i'm still not sure how to apply this to the total power of the generator .

http://www.otherpower.com/images/scimages/2965/graph_single2.bmp

[willib]

I would need 4 more 1 ohm resistors to match the resistance of the double wind 20 gage coil .

it would be interesting though..

whoever said that you cant get a perfect sinewave from round coils,check this out..

it's hard to take a picture while cranking the pedals.. but this is the kind of waveform you can expect with this setup ..

http://www.otherpower.com/images/scimages/2965/wave.bmp

that was the last time i'll see 6Vp from this machine because under the .25 ohm load its just too hard to pedal  the speed needed by hand, since i got all the magnets, and the fastest i can pedal while sitting is somewhere around 365 rpm , as i add more coils it should be really interesting .

I'm beginning to wonder whether or not i will be able to pedal it once i get all 18 coils done.

this is a recent pic of the generator with all 48 neos and the new rotors..

http://www.otherpower.com/images/scimages/2965/my_setup.bmp

[willib]

yes three strands of 20 gage ,thats 0.0499 ohms calculated (15 feet, three strands ), more graphs comming soon.

preliminary results are 4V open circuit at 263 RPM & 5V OC  at 358 RPM with a projected 6V at 450RPM , wow thats considerably higher RPM than the two strand version..no load.

thats my coil holder in the pic.

large picture warning for slower connections

http://www.otherpower.com/images/scimages/2965/Picture_193.jpg

[willib]

This is a comparison of all three 20 gage coils that i've made so far.

Coil 1 is a single strand with a resistance of .45 ohms . about 45 feet

Coil 2 is a double strand with a resistance of .12 ohms . 24 feet each

Coil 3 is a triple strand with a resistance of .05 ohms . 15 feet each

All three coils have the same dimentions 1.75" outer dia x .390" wide with a .83" hole.and all three are loaded with 1 ohm , and Volts are AC peak voltage..

There are  48 total magnets  , of  .875 dia. on  dual rotors ,evenly spaced on a 10" dia circle.. http://www.otherpower.com/images/scimages/2965/svdvt_rpm_per_volt.jpg

The RPM per volt calculations are interesting , because all the other variables being equal this graph can be used to  estimate the cut in speed for different numbers of strands per coil .

Because there are indeed a lot of variables when making a gen ,hope this helps .

[willib]

i've extended/extrapolated the single strand coil graph to 500 rpm in this graph , to make it easier to read hopefully..

http://www.otherpower.com/images/scimages/2965/rpm_per_volt.jpg

if you have a test coil , of say 17 gage and are getting 5V AC from the coil .

And you are wondering " at what RPM will i need to get the same voltage  out of this machine with two strands of 17 gage " ??

The graph says that you'll need 1.5 times the RPM to get the same voltage.

similary you will need 2.15 times more RPM if you triple wind the same coil.

Please correct me if i'm wrong on these points , otherwise i will assume that i'm right, that the graph can be used for any gage coil.

[willib]

Although i'm not expecting a reply , maybe i'll get at least ONE !!

Would you wind a triple coil # 20ga. @ 0.05 Ohms/coil and 0.3 ohms per phase OR go with the easier to make double wind @ 0.125 Ohms/coil and 0.75 ohms per phase??

[ghurd]

I always go for the lowest ohms that will fit.  

Even for the little tiny stuff I play with like stepper motors, I no longer bother with anything past about 5 ohms for 12V.

If the coil gets too thick, thats not good either.

Thinking outloud,

The cut in RPMs look kind of low for a bike with gearing, I don't know? Looks like charging voltage at 180RPM.  My wife pedals at 90~120 per minute constantly for 14 or 17 miles on the road.  I don't pedal anything any more.

Maybe wind them 3 in hand, with a few less turns (10%?), to get the ohms a little lower even.

Or maybe use a smaller sprocket on the alt to get the RPMs higher to make up for less turns (25%?) than that?

G-

[willib]

Thanks for the reply . i thought i was typing all this for myself .!!

are you saying that .3 ohms per phase is too high ??

as for the pedeling speed ,150 rpm (gen speed) is an easy pace .

at 150 rpm is 2Vp = 1.414Vrms *6 * sqrt(3) =14.7 V ok so probably closer to 180 rpm into a lead acid battery .

What is the internal resistance of a typical lead acid battery anyway?

has anyone ever used ulta capacitors in their charging systems , they've been making 12-14 volt ones for a while now..

[dinges]

Ghurd,

The RPMs you mention are PEDAL RPMs?

90-120 RPM seems like VERY VERY MUCH to me (90-100 would be doable & sustainable; 120 definately not, for me, a 30 year old young god :-) )

Yesterday I provisorily mounted the statorplate (not yet cast) in the bike, and installed only one rotorplate (two of them are really scary; I only want to handle them ONCE, for final installation). Whilst cycling, I noticed that above 90 RPM I would get tired very quickly, within a minute. Cycling at 60 RPM was easily sustainable.

When the genny is finished (statorcast is hardening now) I'll post the story; expect this weekend.

Peter,

The Netherlands

(Willib: I got up to 10A out of my genny (one rotor, but cycling like crazy); however, I had much wiring losses (about 2ohm, yes). Each of the three phases has a resistance of .55ohm)

[ghurd]

Yes 90~120! I timed her last spring because it looked so fast, a few passes, at the end of her ride even. She knew I was timing her so it is possible she gave it her all and that was faster than normal.

She's getting toward the end of her 30's, but in very good condition.  Maybe she uses a higher gear sometimes, but not much higher.  She has the gear set so low I can hardly make it around the house. Feels about like no resistance to me, like the chain fell off.

I always prefered a much lower RPM, maybe 40 in a high gear? Much higher gear than my friends used.

Wind gets some extra respect after math about bicycle chargers. 100AH is a lot of sweat!