Energy Bike - Pedal Powered Generator

Discussion in 'The Projects Forum' started by kfrazie1, Jan 4, 2010.

  1. kfrazie1

    Thread Starter New Member

    Jan 4, 2010
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    SEE BLOCK DIAGRAM & WIRING DIAGRAM

    I'm working on building a pedal powered generator for a school project. Utilizes a 0 - 24 V DC Permanent Magnet Motor, however, im designing the system to work off 12 V appliances. The voltage from the motor can be directed to a bank of 12V CFL DC lightbulbs or Incandescent OR it can go to an inverter to convert to 110 AC. To ensure the user can not introduce more than 12 V into the system, a DC-DC converter(input 10 - 30 V, output 12V 10 A) is used. I need to ensure the user can not pedal over 24 V so motor is not damaged. Essentially I'm looking for a voltage activated switch that activates at 24 V and redirects voltage to another circuit to introduce a load to create mechanical resistance preventing user from pedaling more than 24 Volts. Also, is it possible to replace voltage regulator with just relays? BTW there is a capacitor with an on/off switch in the system. Any input would help, but I'm a Mechanical Engineer so simple is good. No programming stuff. Not sure if my wiring diagram is correct, so feel free to make corrections. Don't know how to ground this system either.​
    Thanks
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    Last edited: Jan 4, 2010
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    Looks good. I like the idea of the DC - DC converter with the 10 - 30V input range. Don't know why you want to switch the capacitor, just leave it connected permanently. Motor won't be damaged if the user pedals so fast that the motor produces over 24V. The DC-DC converter might be damaged if the motor produces more than 30V. Probably won't happen though!

    If you are worried about this, you could use a shunt regulator made from a large power transistor on the output of the motor that regulates at about 28V. Most of the time the transistor would not be conducting. At voltages over 28V it would conduct and sink some current. This power will be dissipated in the transistor so a heatsink is required. A simple circuit is attached. A better circuit would use an op-amp and voltage reference.

    A large MOV varistor of about 24V rating would also be useful for removing voltage spikes.

    No, the voltage regulator cannot be replaced with relays.

    I have heard somewhere that a fit cyclist can produce an output of about 250W - but not for long!
     
  3. kfrazie1

    Thread Starter New Member

    Jan 4, 2010
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    Thanks for your help JDT,

    The capacitor has a switch because this is being made for a teaching aid. I wanted to show you can charge the capacitor, stop pedaling, and let the capicitor run the appliances. Any idea as if the wiring for that is right? Had to put a SPST switch to the + side of the Capac so voltage didnt bypass the SPDT switch and flow into the Capac even when the SPDT capac switch is off. Also, any idea how to ground this circuit? I kinda based this off wiring a home, where you have hot, ground, and neutral, but since its a motor I don't have that 3rd ground wire.

    Keith
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    You have as potential drains, 120W of light bulbs, a TV, fan, and laptop computer.

    Have you considered what that adds up to and what a human can produce in peak and continuous terms? What size capacitor are you considering?

    John
     
  5. kfrazie1

    Thread Starter New Member

    Jan 4, 2010
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    I've considered that. CFL and Incandescent cant run at the same time in this circuit. For CFL you have 45 watts, for Incandescent you have 75 watts. Monitor at the AC Inverter runs at about 65 watts, the laptop on the left is for measuing purposes (LABVIEW) and is externally powered. With a regulator output of 12 V DC and 10 Amp, and 85% efficiency, i'll be getting around 102 watts for the DC stuff, and with the inverter inefficiency, I'll be getting around 91 watts for the AC appliances. Im trying to find a regulator with an output of 13.8 VDC and 12 Amps to get slightly better results. Only problem with the higher ratings, is if the voltage from the motor is under 8 volts, the current draw on the motor is as high as 120 amps (1 V motor output), the limit is 14 amps; however, the regulator's input is only 8 - 30 V so not sure if the regulator only turns on when there's 8 V, which would really help me out and save the motor.

    I'm looking at a 2 Farad capacitor to show power can be stored.

    Any ideas on how much startup current on appliances can screw up this design?

    Thanks for the input John
     
  6. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    2 Farads! that's 2,000,000 uF

    At 12V that's a room full of capacitors!

    Let's see:-
    1000uF at 16V is 10mm dia. x 21mm long and costs 0.37 GBP each. You need 2000 of these. 740 GBP. OK, you can get a quantity discount!

    Then solder them all in parallel...

    Actually I exaggerated. 2000 of these capacitors is only 40 x 50. So a block 400 x 500 mm. Not bad!
     
    Last edited: Jan 4, 2010
  7. iulian28ti

    Member

    Dec 4, 2009
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  8. kfrazie1

    Thread Starter New Member

    Jan 4, 2010
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    I'm really not sure how big a capacitor I should use. Ive seen people use 54 Farad ultra capacitors for this and I've also seen some 2 Farad capacitors. I found a good deal on a 2 Farad digital capacitor (35 bucks) about the size of 2 soda cans stacked. Any input on the size would help. Only looking to be able to light these appliances for 30 seconds or so with the capacitor.
     
  9. iulian28ti

    Member

    Dec 4, 2009
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    The bigger the better ?

    54Farad.....? I bet it's expensive as hell

    Or not.... Heh :D
    http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=18_20_67&products_id=1206

    U mean with charge level digital display, right ?
    35 bucks is a bit too large. You can easily hook up an analog voltmeter to a bank of those i pointed you to.

    Well, that 2F soda sized cap is most likely not an EDLC (ultracap)

    You need to know one thing then. Not many caps have high current capability. So before you go to KW range by using TVs and stuff, CHECK THE DATASHEETS.

    Oh, and one more thing, you are going to need extreme regulation if you do use capacitors. Their voltage drops like a skydiver without a parachute.
     
  10. kfrazie1

    Thread Starter New Member

    Jan 4, 2010
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    hmm good input. Idk if it was a charge digital display, it displayed Voltage is all I know. Now that I think about it I may have to buy a capacitor that can charge up to 24 volts and place it before my voltage regulator. Hopefully it can spit out 10 amps......

    I considered using a battery but it didnt seem practical. Im not looking to store energy for 5 or 10 minutes and also I didn't want to have to worry about damaing the battery from a 100% discharge.

    I suppose I will have to look into some capacitor data sheets.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    10A for 30 seconds is a very large capacitor. You can calculate that size. Now, consider you need at least 24V and a capacitor's voltage starts dropping instantly. So >24V at 10A for 30 sec will need to charge the capacitor...

    NiCd batteries have thousands of charge/discharge cycle lives and can provide what you need. If you don't want to go to "zero" capacity, pick some other number and size the battery accordingly.

    John
     
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