going from 12v to 5v

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computerwiz1101

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i saw a cable > http://www.evercool.com.tw/categories/global/cables/fancablesadapters/ec-df004/ec_df004.php < here that says "goes from 12v to 4.5v" well based on everything i've read case fans go and start at 12v then get ramped down to 7v then down to 5v and that the lowest they get, is this some kind of cheap scam or a amazing deal..it's 3.99 for just one from another site, although there supply prollly comes from the site posted in the link. thank you.
 
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Maxx_Power

Maxx_Power

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These things are quite common. You can do it yourself with the right equipment (soldering iron, etc) and parts (diodes and/or resistors for a given fan). If you have a non-3pinned fan header (a 4 pin PSU molex header), it is even simpler to just swap the red wire with the yellow one to power the fan with 5V instead of 12 (just DON'T use the other side of the header, because voltages are swapped).

I don't think it is worth 4 bucks, though. Most motherboards offer speed control and monitoring, so it is just a matter of using the BIOS settings to control the fan speed to what you want/need.

BUT FYI, 5V is now-a-days more than you'll need to start up most fans. The only ones (for computer use) that typically requires a higher voltage to start are some of those ball-bearing varieties.
 
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Kursun

Kursun

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It doesn't reduce voltage from 12V to 4.5V.
It reduces 12V BY 4.5V. That makes 12-4.5=7.5V

An amazing deal? Hardly... I have many such voltage droppers either in the form of a potentiometer or a fixed resistor on all of the fans on my case. This seems to be a fixed resistor in series with the 12V line. It shouldn't cost much.

BTW I don't think voltage drop by 4.5V is an exact specification. Series resistor drop voltage by the amout of current drawn. Not all fans draw same amount of current. It should have said "by about 4.5V", but that wouldn't look good on paper.
 
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Maxx_Power

Maxx_Power

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They MIGHT be using diodes in series to guarantee a 4.5V drop. 7 silicon diodes with an average forward voltage of 0.65V each is nearly exactly 4.5V drop. Unless it is one Zener diode. I can't tell with their heat-shrink wrapping.
 
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Maxx_Power

Maxx_Power

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I used these resistor/diode series devices for a lot of my equipment, mainly where I don't need to adjust the fan speed, or when the adjustment isn't useful (like in a case with 7 fans) or where it isn't possible (like a stow-away NAS).
 
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Kursun

Kursun

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You're right Maxx. It could even have a 78xx voltage regulator IC... But I have several of these things and all seem to have only a voltage dropping resistor, no fancy semiconductors.
 
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Maxx_Power

Maxx_Power

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I have only seen the diode approach once, on a 3 speed controller that used a rocker switch. All the inline, wrapped in heatshrink stuff I have seen have just been a single resistor, but those were bundled with particular fans, to ensure that the voltage drop is what they calculated. I think a 7805 might be a bit expensive to accomplish this.
 
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