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Problem in making a voltage regulator

Hi everyone! I have a dynamo on my bicycle which can generate AC 12v-30v during normal to fast cycling. I want to power electronics and charge batteries with the dynamo but do not know how to limit the voltage to around 12v DC. Any help would be greatly appreciated.

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1
tech-king says: Feb 6, 2008. 8:46 AM
1) you will need to rectifie the voltage using a full wave diode bridge. 2) you will need to smoothe out ripple using a capacitor of at least 2200 uf. 3.1) you can use a 7812, but it will need a good heatsink 3.2) a better solution is a zener diode rated to 13 volts turnover voltage. it will bleed off exess voltage 4) i recommend a second zener with a 12 volt turnover voltage to cut power to electronics when it falls below 12 volts. otherwise, the resulting brown out could damge electronics.
sirajmunir (author) in reply to tech-kingFeb 7, 2008. 8:04 AM
How will i connect the zener diodes? Can you illustrate it using a simple diagram?
gito in reply to sirajmunirFeb 7, 2008. 8:26 AM
Connect Zener Diode parallel with your output ( your electronics & batteries ). Connect Diodes which have line sign with plus side (+) of the output & the other side of Diodes with Ground or the center pin of 7812. But I think, 7812 is enough, because I'm afraid the voltage will be drop if your output needs high current. If you want to charge the batteries, i think you shouldn't use the power electronics. Try to use PWM (Pulse Width Modulation). If you still use the power electronics, I'm afraid you will damage the batteries, because the batteries will be very hot.
1
tech-king in reply to gitoFeb 7, 2008. 1:56 PM
the 2 zener diodes are a must! one limits and regulats voltage, the other cuts power below 12 volts to protect electronics. a 7812 is a BAD choice for this probleme.
codestroy7 in reply to tech-kingAug 31, 2011. 2:01 AM
how will cut power when it is below 12 using zener?
sirajmunir (author) in reply to tech-kingFeb 8, 2008. 2:18 AM
Do you think this is a good way? http://www.vwlowen.co.uk/java/zener.htm
Is the diode in the website limiting the voltage or regulating it?
This is one zener diode, where to put the second?
1
tech-king says: Feb 8, 2008. 8:35 AM
yes. that works. here is another drawing the second zener goes between the regulated output from ZD1 and the load. it goes in reverse (cathod towards power supply) to cut off voltage below 12 volts.
instructables 001.jpg
sirajmunir (author) in reply to tech-kingFeb 9, 2008. 2:04 AM
Thank you. BTW neat handwriting ;)
1
tech-king in reply to sirajmunirFeb 9, 2008. 3:31 AM
1) your welcome. if you need more help, just ask 2) thats not my handwriting. its from a book. i wish it was that good. here a sample of what mine really is:
img_0061.jpg
sirajmunir (author) in reply to tech-kingFeb 11, 2008. 9:06 AM
Just one more thing! I bought a 25v 2200uf capacitor but then i realized that the dynamo could produce up to 30-35v if i cycle fast. Will i have to replace that one because i have already soldered it :(?
1
tech-king in reply to sirajmunirFeb 11, 2008. 2:02 PM
probably. when overvolted, electrolytic capacitors can expload violently.
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