# Relay Board?



## papermaker (Jun 9, 2013)

I've put my electronics in a metal box and I have to 2-3" 12v computer fans installed in each end of the box that are currently being powered of a little plug in DC power supply. I would like to do away with the little power supply and have it be fed from the power supply that is inside the cabinet. The power supply puts out 40v so I will need to step this down to 12v. Is there a relay board or other type board that will step the power down. If so where would someone find one.


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## Mark Lossner (Jun 9, 2013)

papermaker said:


> I've put my electronics in a metal box and I have to 2-3" 12v computer fans installed in each end of the box that are currently being powered of a little plug in DC power supply. I would like to do away with the little power supply and have it be fed from the power supply that is inside the cabinet. The power supply puts out 40v so I will need to step this down to 12v. Is there a relay board or other type board that will step the power down. If so where would someone find one.



You require a DC-to-DC converter or a voltage regulator than can handle 40V input. Try jameco.com, look for DC-to-DC converter. I'll look around as well just as soon as I can.

Mark


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## CluelessNewB (Jun 9, 2013)

*Maybe?*

So if I understand correctly you have 4 fans total?.  Are they all identical?  Is the 40V DC?  If yes you may be able to just hook all 4 fans in series and run directly from the 40V DC.  I have not actually tried this with brushless fans but I suspect they will work just a bit slower.  You will also want to check that the 40V supply can supply enough current to drive the fans.  Note that in series the currents DO NOT add.  If all the fans are the same and rated at 0.10 amps, the series connection of all 4 will also draw 0.10 amps.  Since each fan will actually be getting a bit lower voltage (10V rather than 12V) the current will likely be slightly less than what is marked on the fan.  

Rich


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## Rbeckett (Jun 9, 2013)

Look on Ebay or some of the electronics supply houses for a step down transformer or regulated step down power supply board and youre golden.  They are very cheap if you don't need huge anps or weird specifications.  I think it is an LM2596 and they are about 6 bucks delivered.  I looked and I don't have any in my parts stock, but they are cheap, and really easy to build if you decide to go that way too.  LMK if you have any trouble finding one and I will find you a quick and easy link to an Ebay source I use a ton in China for common boards and circuits.

Bob


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## Hawkeye (Jun 9, 2013)

Keep in mind that a transformer won't work on DC. It needs a fluctuating magnetic field to function. If you're going to make a voltage regulator, you might want to do it in two or more steps. Drop the 40V to 24V, then drop to 12V. This will mean less heat on a regulator doing it all in one step. Make sure to use heat sinks on the regulators.


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## papermaker (Jun 9, 2013)

Just want to say thanks to you guys that replied to me thread. I went directly to e-bay and bid on a LM2596 and got it it for $3.29 including shipping. This web site has been great getting me headed in the right direction and it's guys like you that make it possible Thanks so much!


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