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Forum Index : Electronics : Pedal powered generator project?
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hi, I am working on a little trivia project. I am building a pedal generator with a Smarddrive motor. I understand the wattage is approximately the same as the RPM? According to my observations at the gym I can pedal 80 to 100 RPM without problems and produce about the same wattage. Now of course I dont know how accurate those displays on the exercise machines are but at least they are a place to start. So, it appears to me that direct drive to the Smartdrive would be about right? About what voltage could I expect to see on the standard, unmodified, coils at 80rpm with a load of 80 watts? As this is a novelty project with no really serious intent I am considering a complete 'pedal radio' and am considering modifying a WWII transceiver for the job. I would like to use one of the windings to product the HT voltage (about 300volt I think). This would require a transformer which leads me to wonder how the frequency of the Smarddrive produced AC can be calculated? Thanks for any comments on my (silly?) ideas. John
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ozetrade Regular Member  Joined: 15/10/2005 Location: AustraliaPosts: 59 |
Hi John, The Smartdrive motor in it's std form, does not produce any usable power at the RPM's you are talking. In std form Smartdrive, the peak wattage output at approx. 450rpm
The only way to get big wattage from them is to rewire in Star, Delta or Star/Delta configuration. Even rewiring an 80series using the delta method, you would not start to produce wattage until around 480rpm. At 600rpm you would be producing around 6-700W's. The voltage return depends on how you rectify the output from the gennie. eg.
The more voltage you want, the less amperage you get. Your looking for 300volt. Lets say you rig up some gearing and are able to get the gennie to sping at 800rpm - this would produce around 900W.
This is without taking into consideration the "Power Factor" which I dont have a full grasp of yet - but it means less amperage. This site might help you do some calculations. http://www.powerstream.com/Amps-Watts.htm Greg Just North of Brisbane in Redcliffe OZeTrade.net |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Thanks Greg, but I am not looking for watts, with only legs as the primary motive force there will never be many watts out! Lance Armstrong, winner of the Tour de France cycle race, can pedal 500watts all day but I dont think I can. I think the aerodynamic drag of the rotor, not to mention the pole gaps, would be quite considerable and increase by square (may cube?) law with rpm increase. So I want to keep the RPM down if possible.
However, in the light of what you have written I will include one stage of gearing (standard bicycle chain and sprockets) but I dont really think it will be possible for a normal person to spin it at more than a couple of hundred revs even without the electrical load. I will check that link later, thanks. This is a playtime project and I can well accept that it may not prove practical.
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Greg, power factor is term that relates to the amps and volts not being in phase, that is they peak at different times. There is no power factor problems in a DC circuit but with AC once inductance or capacitance is introduced power factor comes into play.
Inductance is what you get with coils. If you apply voltage to a coil the current through the coil does not flow immediately at full strength, instead it rises as the magnetic field builds. When the voltage is cut off the current continues to flow for a little while afterwards while the magnetic field collapses. So, if you put AC onto a coil the peak volts will be before the peak amps so you cant just multiply them together to get watts, you need to apply a correction which is the 'power factor'.
Capacitance is pretty much the same but has the opposite effect in that peak current flows before peak voltage is reached.
These effects of inductance and capacitance are 'reactance' and although they do not produce power they do oppose the current flow. In many circuits it is possible to use one to offset the other.
John |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi John. I would split the stator into two. When we rewire the stators we usually divide the star connection into 7 star connections to lower volts, increase current. I think for your use you could try dividing the stator into two star connections. That should give a usable voltage at the rpm your talking about. As a variable load, how about some light bulbs. 7 watt car lamps and some switches. You could switch bulbs on and off to adjust the workout. Maybe light the Christmass tree Be carefull using a chain drive from the pedal crank to the F&P motor. The cogging of the F&P will play havock with a chain drive. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hi Glenn I got the pedal generator built today, the job was made considerably easier by finding an 'exercycle' at the tip! With the F&P geared about 3.5:1 and connecting the only handy low voltage load I had on hand I find that 6 amps at 10 volts is an easy load without more than very moderate exertion. This is using just one un-altered winding and a bridge rectifier. 50 watt headlamps light readily enough. Yeah, cogging is an issue and it is not very pleasant at low revs, once up to speed though it is not so bad. This is really just a playing-around type project and I doubt that it will ever see any serious work.
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| adelaide Regular Member Joined: 24/03/2006 Location: AustraliaPosts: 46 |
hi. i did it while ago it works direct drive but lower power, when i welded an old 10 speed bike cog to f/p shaft it made alot more power 300w. the direct drive was to slow, think around 50w, think was 100 s delta direct and 80 sp delta bike 12 v ch think efficiencies are around 60% for the 100s delta and 80+for 80sp d 12 v so makes up for it. tip use the bike as platform coz its comfortable help to make progres or radio and vitamin b |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
An old WWII radio huh? Well, the 300V (B+) will have been reasonable during transmit, but receive I'd be very surprised if it was more than 50-100mA. Most of the tubes had a maximum anode current of only a few milliamps, add some bias circuitry, and the output tubes (What were they? 6V6? 5AU6?) and you're still only talking small currents. Some of those radios ran off a low voltage supply anyway (most used 3V or 6V cathode filaments, like the old 5 and 6 series tubes, although some used 12V like 12AU6 etc) - and used a "vibrator" and transformer to produce the high voltage required for the rest of the circuit. Vibrators were electro-mechanical devices that were unbelievably inefficient. Modern electronic devices would replace them with ease, or you could use a small SMPS to do the job, or, all things considered, a small transformer "backwards" would probably do just fine. If you had a (nominal) 12V output from your P&F generator, a 240:12V stepdown transformer wired backwards, with a full-wave rectifier should give you enough for your B+ circuit. It's been a loooong time since I worked on tubes :) |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Ross, the radio under consideration is a ZC1, something made in considerable numbers in NZ just in time to miss WWII! Yep, vibrator supply, I am not sure of the RF output but it was not much. There are about three and a half of these sets in my garage and my friend has a few too! I have put this project aside for a while but I should get back to it!
There is a history of the ZC1 here where you will see it sompared with the Canadian numebr 19 set http://www.nzart.org.nz/nzart/history/zc1 If nothing else the copper plated steel case made a supurb tool box and the long wooden chest for the antenna bits was useful too.
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