# Building a 24v AC to 24v DC rectifier circuit



## sortafast (Aug 15, 2014)

I need to build a rectifier to run a cooling fan I wish to install on my mill to help keep things happy in the cabinet. I have a 24V power supply but it is AC. I need to get this over to DC to run the fan. This is the fan in question. Just wondering if someone could help me out with a schematic or something so that I can build a rectifier or some such. I know i need some diodes and maybe some sort of Voltage regulator, but aside from that I have no clue. I do know that the fan will take 10-27v and is rated for 1800mA or 0.18A. This is the last piece to the puzzle, other than figuring out what the 3rd wire is for on the fan. Any help would be appreciated. I have a friend helping me with this, but I am not sure how long it will take them to get it done for me so I may have to DIY by myself.


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## DrunkenDonut (Aug 15, 2014)

It sounds like you can simply hook up the fan directly to a suitable rectifier. Full bridge will be nicer and you can choose to have a DC filter cap but that's optional. A voltage rectifier is also nicer but optional as it appears your fan can take the extra voltage. 

When you rectify, the DC voltage will typically be higher than the 24V input due to the diode bridge. It looks as if the fan can handle it so you don't absolutely need a voltage regulator.

The rectifier will have 4 terminals. Two are AC input. It's indicated by a sine wave or "tilde" and the output will be positive and negative which you apply to the fan leads.

The third wire may be a speed output (is it blue?) which you can ignore.

Oh, you if you want to build a rectifier, look up "full wave bridge rectifier". There are lots of those schematics around, and it's a simple circuit using 4 diodes. If you have to buy parts, it may be nicer to buy a rectifier instead of diodes. Everything will be packaged cleaner in the end.

Good luck.


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## gadget_lover (Aug 16, 2014)

$3 gets you a bridge rectifier from Radio shack. http://www.radioshack.com/product/index.jsp?productId=2062583

You should not need any other components except hookup wire.

The fan will run a little fast if the rectified voltage is a little bit high. That should not be a problem.

Dan


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## sortafast (Aug 16, 2014)

Ok, I just started on my destructive path to becoming a hack EE. Thanks to the intertubes I think I have enough knowledge to be dangerous.:devil: Going to head to the local Surplus electronics store to get some things. From my under standing, I basically get one of those full wave bridge rectifiers listed above, a smoothing cap which I think I have some left overs from my VFD repair mess that will work and and a board of some sort and I am gtg there. Then I think I want to get an LM317 for regulating the voltage and I should have a pretty sound little set up for the fan. I think it should work pretty well. I just don't want to burn up the fan with too much voltage. With how its located and how the VFD is situated it will be a royal pain if it blows up. Not to mention I would loose a fair amount of cooling for the VFD which would be no bueno.


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## precisionworks (Aug 17, 2014)

> the fan will take 10-27v and is rated for *1800mA* or 0.18A.




1800mA = 1.800A (3 decimal place move as milli means one thousandth) 
180mA = 0.180A (same 3 decimal place move) 
 
From the fan description you'll need a rectifier that's rated for about 30v & 1/4A. IMHO the easiest way to get there is to purchase an AC adapter used to power electronic devices. Here's one on eBay that's 24v & 1000mA so it has 400% more capacity than you need ... but for $6.69 with free shipping it's hard to beat. Cut off the plug tip that's supplied & connect the leads to the motor. If the motor runs backwards reverse the leads.

http://www.ebay.com/itm/High-Qualit...=US_Server_Power_Supplies&hash=item51b3751301


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## gadget_lover (Aug 17, 2014)

The PDF on the web site listed in the first post shows it as 0.10 to 0.14, depending on which model. A 4 inch fan that uses .1/8 amp creates a good breeze. A 4 inch fan that pulls 2 amps will move a LOT of air. 

I would think that the voltage regulator will not be required. The insulation of the fan is listed as able to handle 750 volts, if I read the PDF correctly. The fan is a simple DC motor and there is no specific RPM requirement. 

Most electrical devices (not electronic, but simple electric devices like motors and lights) are designed to be able to use a wide input voltage. 10% variance is normal with the voltage supplied from your electric utility. Depending on where you live, 15% is not that unusual. 

Dan


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## sortafast (Aug 17, 2014)

WEll I went to the surplus electronics depot here in town and picked up all the parts, made the board but then shorted something out when I was testing it. I think it hit something metal and killed the cap or one of the resistors as I now only get 3v. Was getting 20ish before it sparked up after hitting something. Oh well, I was only a couple buck worth of parts into it. Will probably go grab more parts next week and then try again. Need to also get some more cheap wire for some other stuff in the cabinet anyway. Right now my big issue is figuring out some of the communication parameters for my VFD. Its becoming a bit of a headache. Hopefully I can sort all of this crap out this week.


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