Author Topic: Pancake alternator for pedal power? (Read 10118 times)

jawnn · « **on:** January 16, 2013, 03:35:55 PM »

Is it possible to build a slow speed alternator that will generate more power than any factory made generator?

I want to build a pancake alternator for wind but first use it in pedal power, because we have that set. The wind mill will take quite a while.

How much Horse power do the pancake alternators need???

I saw one factory made that needs about 6 hp. Way too much of pedal power.

Ungrounded Lightning Rod · « **Reply #1 on:** January 16, 2013, 06:52:29 PM »

The power required to drive an alternator depends on the load on it. That factory alternator only requires 6 hp if it's loaded to the tune of 4 kw or so. If it's a permanent magnet alternator it should spin almost freely (mostly bearing friction) if it's completely unloaded. (A non-PM alternator would pull some power for excitation, which could be substantial on a 3-4 kw unit.)

The big problem with pedal power is matching the speed to where the legs are efficient - which amounts to getting the load voltage right for the gearing. (I recall one in the Museum of Science and Industry in Chicago which was underloaded. You had to spin it super-fast to light the light bulb and get any substantial reading on the wattmeter, and this tired you out within seconds. With a substantial load you could have done much better.)

hiker · « **Reply #2 on:** January 17, 2013, 03:23:03 AM »

heres a old web page --might give you some ideas...............
http://www.fieldlines.com/index.php?topic=129080.0

jawnn · « **Reply #3 on:** January 19, 2013, 02:39:31 PM »

I think we will just have to build one to campair it to the DC generaotr we are using on the exercycle we have.

jawnn · « **Reply #4 on:** February 01, 2013, 02:15:22 PM »

I have been visualizing what I need here. I want to build an air gap 3 phase alternator. that will produce at least something with one quarter HP. Make an axle that will hold a bicycle free wheel, then put in the bike in place of a wheel.

Will it generate more power if I make it a larger diameter than for wind power?

Is there a way to calculate the power output at a given speed (to know how big to make it)??

hiker · « **Reply #5 on:** February 01, 2013, 03:15:04 PM »

the larger the rotors the less rpms it takes to make power--you still need the tork
to kick it over--smaller rotors need more rpms to make power -but less tork to spin over....just make a pulley or buy one that will work with whatever size of alt you make..............heres a pic. of one of my old mills with a plywood pulley ..
just make some cutouts and glue togeather......

jawnn · « **Reply #6 on:** February 02, 2013, 01:20:19 PM »

The minimum I would want to pedal is 24/12sprocketsx55 crank=50rpm but the fasted gear is 52/12x60=260rpm

I figure that I would have to use low gears when under a load. Then I thought of using 12 coils instead of 9, but would that work? Would it be a 4 phase alternator?

stratford4528 · « **Reply #7 on:** February 23, 2013, 03:30:51 PM »

If its of any interest I built a low speed alternator which produced 40 watts at 12 RPM That had 36 coils

rustkolector · « **Reply #8 on:** March 01, 2013, 10:58:06 PM »

Statford4528
I would like to hear the specifics on your slow speed alternator. I am looking for similar wattage at about 350 RPM.

jawnn · « **Reply #9 on:** January 24, 2014, 02:49:06 PM »

Ok I have been thinking about this project again. I believe that it is possible to build a 36 inch diameter alternator that will have a much higher out put than anything most people believe is possible.

How ever it may take a small gasoline engine to run it (and maybe we should just use a car's alternator). I saw the plans in the book "home brew wind power" they have one that will produce 3000 watts at 400 rpm., but it will not do anything at less than 150 rpm.

Right now we are using a two stage gear increase to turn a DC motor, only 35 watts can be maintained for a half hour. gear losses are great: Timing belts are around 90% efficient. Chain around 85%. So we intend to give up the gears, and pedal directly, unless it really is impossible to design a pedal power generator that can maintain a higher power, like one hundred watts (with a load of a charger) at some thing like 60 to 80 rpm.

David Butcher has built a 30 inch diameter fly wheel that turns a very small dc motor, and gets more energy than wasting about 30% of human energy into bicycle gears.

So What I need to know is, what speed does it take to generate a given amount of energy? and how wide of a permanent magnet can you get? ( the wider the more electrons?)

The thing that started me thinking about a 36 inch diameter, is momentum. And increased rim speed. But I also need to know how much foot lbs it will take to turn this concept alternator, what is the magnetic resistance??

Rim speed in inches/minute

Circumference* rev/min

42 inches *pi* 50= 6597 inches/minute.

Mary B · « **Reply #10 on:** January 24, 2014, 04:45:15 PM »

If you are in really really good shape you can maintain 100 watts for 15+ minutes, personally I drop off to about 35-40 watts after about 5 minutes. If it was all I had and I had lots of kids go for it, otherwise it is good for charging my upstairs 12vdc lighting circuit that doesn't get much use.

joestue · « **Reply #11 on:** January 24, 2014, 07:37:53 PM »

stick with chains and sprockets.. provided they are properly lubricated and not filled with rust, 98% efficiency is doable, peak efficiency is in the 99% range, even an old rusty chain should get you 90 easily once its running smoothly. also, they are cheap and easy to configure.

jawnn · « **Reply #12 on:** January 27, 2014, 01:16:36 PM »

I am so tired of hearing how easy it is to produce 100 watts. I need real information. like the info below, but how did he do it? and how much HP does it take to turn it.

I want to hear how every ones generator is made, when you say you can do 100 watts for 15 minutes, how is your machine set up? 90% efficient? I doubt it, how many gears are you using? photo?

Quote from: stratford4528 on February 23, 2013, 03:30:51 PM

If its of any interest I built a low speed alternator which produced 40 watts at 12 RPM That had 36 coils

Mary B · « **Reply #13 on:** January 27, 2014, 04:21:40 PM »

I am using a GE ECM motor as an alt, big flat belt off the 2 foot wheel of my exercise bike to a 3 inch pulley on the motor.

hiker · « **Reply #14 on:** January 28, 2014, 01:55:25 AM »

ive messed around with exersize bike alts for years--tried all kinds of diffrant setups--motors --car alts--homebrew duel rotors alts-ac motors........
with the the ac motor alts i could power up a vcr and a small tv and watch a full length movie with ease.........or power up a hand drill or sabersaw--even a saws all...with the dc alts i could get close to 400watts at 28 volts[aircraft landing light] but only for a really short period of time--just enough to hit the mark !!
like i said lots of time playing around ...i do like the exersize bikes for power--all you need is a flat belt to wrap around the flywheel then down to whatever alt of your chose...getting the right size pully on your alt thou is inportant--i just make mine out of plywood disks glued togeather then installed on your alt...fun stuff.. just go to youtube and in the search window just enter --hiker71453--
have fun............

jawnn · « **Reply #15 on:** January 28, 2014, 02:16:23 PM »

Looks like I will have to engineer this.....ok I calculated that the big wheel generator that stratford4528 built was 48" in diameter and he may have used a water wheel to power it.

I suspect that it may take much more HP than human legs can produce, but at least it wont need to be fast. I can pedal much more torque at 40 rpm a than 80. And 48 inch diameter will produce more momentum......so what HP does a 12" diameter wind alternator need to get up to 50 rpm?

Maybe it's just a matter of how close the magnets are to the coils.

THINK!

Bruce S · « **Reply #16 on:** January 28, 2014, 02:16:55 PM »

jawnn;
do a search on here for a forum member named NORM.
have a look at his posts of building a pedal powered unit for his arms ( he was doing therapy).
Follow them through the designs and the links that should give you more than enough information to decide which way you are going to go.
Some of the bolded questions you asked can only be answered with "depends" on your design.
No two devices, even mass produced are the same, home built gets you "close".
Norm still posts here from time to time and will certainly answer any questions you may have.
You can post those questions here, or use the PM to send directly.
HE is a very helpful when asked.
Bruce S

hiker · « **Reply #17 on:** January 28, 2014, 04:36:21 PM »

THINK simple jawnn.... your still going to have to-- just try it as well--
if its a high speed alt put a small pully on your alt...low speed put a larger pully for tork-levarge....

jawnn · « **Reply #18 on:** January 29, 2014, 02:43:22 PM »

stratford4528 says his slow speed alternator was only 24" and the rest must be just lack of resistance. I think our set up still has too long of a wire, and could be an even higher voltage.

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Author Topic: Pancake alternator for pedal power? (Read 10118 times)