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Low AC to DC conversion Answered

Hi, I'm looking for simple way to convert a low AC into a usable DC, of say 4 - 5 volts for charging batteries. I recently saw one discussed online, specced at costing about a quarter, but couldn't find a way to do it, or a way to purchase something like that. Thanks!

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FC77 (author)2011-08-15

Hi , just say you had 20 volts , 55amp ac , and wanted to convert it to dc , what type of bridge diode rectifier would you use ? Would you use one close to the stated power or would you use one that is say 150amp and 1000volts for instance , does it make a difference ? Also Does the phase of the rectifier matter ? Thanks !

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guyfrom7up (author)2007-10-29

are you talking about the windbelt project? What I'm working on is using a low voltage drop shottky full wave bridge rectifier hooked up to a filtering capacitor hooked up to a max1709 chip (my favorite boost chip ever!)

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fafnir665 (author)guyfrom7up2007-10-29

Yes! Do you have a diagram for this?

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guyfrom7up (author)fafnir6652007-10-29

well, I'm to lazy to draw up a diagram, but I'll walk you through it.

a full-wave bridge rectifier is 4 diodes that when correctly connected together convertes AC into DC (google it). The out put of this is basically if you were to take the AC wave and flip it all onto one side. Diodes have a volotage drop across it, which means you lose voltage. For this project you want as many volts as possiable, so you use low voltage-drop schottky diodes for the bridge rectifier. The output of the bridge rectifier is really ripply, so all you need is a capacitor (maybe around 100-1000uF) at the output so that it smooths out the ripples. That filtered voltage then will pass through a DC to DC converter.

Here's the one that I'm going to be using: http://datasheets.maxim-ic.com/en/ds/MAX1709.pdf

If you most of it then it will be easy to pick out the parts. A nice schematic is on page 8 where you just have to fill out some values.

I might post a diagram later

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fafnir665 (author)guyfrom7up2007-10-29

Ah, and the boost chip is has a pinout too sweet. Thanks!

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guyfrom7up (author)fafnir6652007-10-29

make sure you read the datasheet first! Remember, reading for about 10 minutes could save you 50% or more on electronics parts I have never seen the geico commercial ever

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ketan.isro (author)guyfrom7up2008-07-09

The thing is that i want to use for space aplication not any normal application so want to avoid boosters . So is there any technioque to convert low voltage high frequency AC to propotionate DC. ketan.isro@gmail.com

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Goodhart (author)2007-10-29

Define "low AC". If you are a few volts above your target, a bridge rectifier and power regulator (and a few capacitors) would fit the bill.

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ketan.isro (author)Goodhart2008-07-08

hey i need a help about conversion of a low voltage (<1V) Ac at frequency of 1 MHz to linear DC level can u help!!!!!!!!

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Goodhart (author)ketan.isro2008-07-09

As suggested, a bridge mde with Schottky diodes instead of silicon or germanium diodes might work. Schottky diodes are useful in switch-mode power converters; the high speed of the diode means that the circuit can operate at frequencies in the range 200 kHz to 2 MHz, allowing the use of small inductors and capacitors with greater efficiency than would be possible with other diode types. Small-area Schottky diodes are the heart of RF detectors and mixers, which often operate up to 5 GHz.

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guyfrom7up (author)2007-10-29

here's a basic way of converting ac to dc remember to use the boost chip, because this is not likly to put out a huge amount of voltage.

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guyfrom7up (author)guyfrom7up2007-10-29

huh, thought you could edit comments but you can't. Make sure to use schottky diodes!

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Goodhart (author)guyfrom7up2007-10-29

Or he could use a ready made bridge :-)

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guyfrom7up (author)Goodhart2007-10-29

yeah, but I don't think that they make bridges that have an extremeley voltage drop, the lowest drop diodes I could find were single diodes on mouser.

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Goodhart (author)guyfrom7up2007-10-29

I'm sorry, I am not sure I understand. I thought he meant a low voltage ac input, but he didn't specifiy how low (I was assuming 60 v or so. But if he meant 4-5 v AC in, maybe a half wave bridge would work well enough ?

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guyfrom7up (author)Goodhart2007-10-29

Windbelt video:
http://www.popularmechanics.com/technology/industry/4224763.html

trying to work on an instructable version.

I'm assuming it's around a couple volts AC

This thing has to be extremeley efficient, so I'm going with the full-wave

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russ_hensel (author)guyfrom7up2007-11-01

A full wave bridge is not more efficient. Since it has two voltage drops across the diode it is less efficient. If your AC source is a center tapped transformer you can get full wave with just one voltage drop. Half wave has more ripple and needs a bigger filter cap. Shocttky diode are much better in low voltage applications because they have about half the voltage drop of a silicon diode.

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guyfrom7up (author)guyfrom7up2007-10-29

IIIIIIIII can't wait tillllll my mouser stuff commmeesss in the maiilllllll!!!! I also requested a catalog and that's gunna be HUGE!!!

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Goodhart (author)guyfrom7up2007-10-29

Wow, I haven't seen a Mouser catalog in like ages....

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