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240v to power 2 12v computer fans what trany I need

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April 23, 2012 12:32:37 PM

Hello, 240v to power 2 12v computer fans with 4 led's what trany I need ?
a c 139 ) Power supply
April 23, 2012 12:44:37 PM

Hello dogb8t;

You can't directly use 240V alternating current (AC) to power 12V direct current (DC) PC LED case fans. You need some type of converter or transformer.

That's what a computer's power supply does. It converts AC input to DC output for your computer parts.

What you need is a computer power supply -> probably the one you already have?
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a b ) Power supply
April 23, 2012 12:56:47 PM

if you have to ask the question you should not be playing with mains electricity like that. do you know what a bridge rectifier is, learn this and then come back to us.
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April 23, 2012 1:16:50 PM

for conversion of an alternating current (AC) input into direct current a (DC) output
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a c 139 ) Power supply
April 23, 2012 1:21:51 PM

Using PC case fans outside a PC case?
So you're not using a PC power supply?
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a b ) Power supply
April 23, 2012 1:40:33 PM

OK, so its about sizing the transformer, what voltage do you want the fans to run at?

I'm asking the questions and leading you along so that I have some vain hope that you know what you are doing, and aren't going to electrocute yourself.
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April 23, 2012 1:48:26 PM

The full story ! I have a TV cabinet with my new amp in an enclosed area which generates a lot off heat the shelf cavity is H130mm / W500mm / D600mm, my amp is H110mm / W480mm / D500mm and made from solid jarrah.
I want to install 2 computer fans with 4 led's 1 to push air in and 1 to suck air in.

I tried to use a trany from a 12v halogen light while it turned on the led's but didn't make the fan rotate.

I would like to know what transformer to use that will operate the 2 computer fans with 8 led's in total I have 2 120mm computer fans with 4 led's on each with no spec's written any were on the fan's.

I have worked as a TA for a Electrician for 9 years doing rewiring house's and making wiring loom's from plan's for shopfitting. This in more Electronics and not my area of experience.

Any help would much appreciated cause were there's a will there's a way, so just call me WILL !!!!!
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a c 139 ) Power supply
April 23, 2012 1:57:51 PM

You should be able to rig any cheap PC power supply as the transformer and someone with your background shouldn't have too much trouble doing it safely.

You'll probably need +5VDC for the LEDs and +12VDC for the fan motor.

Pin # Color Function
1 Yellow +12 V
2 Black Ground
3 Black Ground
4 Red +5 V
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a b ) Power supply
April 23, 2012 2:03:53 PM

OK, happier now.

well you need a 20:1 steo down transformer, if you are talking about 'transformers' as opposed to transformers.

http://www.maplin.co.uk/chassis-mounting-transformers-4... N64JB would do you, 2 Amps max at 12V and then build a rectifier on some breadboard.

I've just brought a noctua which claims to be 0.6W at 12V = 0.05A and it claims that it really low power, so lets say that normal is 2W, = 0.16A. so for your 4 fans you need about 0.64A total.

what I don't understand is why the halogen transformer couldn't rotate them, you were connecting the right pins weren't you, or are we talking about big molex connectors and not little 3pins? the 3 pins one of them is for a sensing circuit.

I don't see why this wouldn't work http://www.maplin.co.uk/low-cost-6w-multi-voltage-power... not sure if it is rated for 24x7. Unless the 'chopper' type systems being used in cheaper lighter power supplies don't allow fan to function, probably the electro magnetics.
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a b ) Power supply
April 23, 2012 2:05:24 PM

Or as WR2 suggested, buy a cheap power supply and learn how to trick the 24pin connector into thinking its connected to a mobo. I think its shorting green and black? but thats very googleable.
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a c 139 ) Power supply
April 23, 2012 2:07:37 PM

13thmonkey said:
I think its shorting green and black?
That's the right combo. A simple switch should work OK.
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a c 139 ) Power supply
April 23, 2012 2:15:06 PM

Looks like it would work. DC12V 6A - certainly enough to run the two fans.
You'll be able to use an in-line resistor to get 5VDC if that's what the LEDs need.
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a b ) Power supply
April 23, 2012 2:15:25 PM

Probably, BUT until we understand why your halogen tranny didn't work its difficult to tell. Also note that that is passively cooled itself and is probably simple compared to a PC PSU, i.e. it might have the majority of it working at full power regardles of what you are drawing.

You could try looking for a flex TFX or a SFF power supply.
http://en.wikipedia.org/wiki/ATX#ATX_power_supply_deriv...
They are smaller and will definately provide rectified and not chopped DC power
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April 23, 2012 2:30:22 PM

Thanks for all the help, I let you's know how it go's when I receive the trany.
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May 27, 2012 3:47:34 PM

I've since found out that the halogen tranny didn't work cause of the amp's output was not high enough.

The AC100~240V To DC 12V 6A 72W Power Supply Adapter Transformer work fantastic with 2 CoolerMaster 120mm LONG LIFE Fan Blue LED.

I have installed the 2 fan's into the back of the TV cabinet, I've added some fine stainless steel mesh so no wires get court in the fan's and also a hood over the fan's to get better reflection from the Led's. All wiring joint's are soldered and re-insulated with heat shrink insulation. And every thing is recessed so the TV unit is sits almost flat against the wall.
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a b ) Power supply
May 27, 2012 4:21:55 PM

Electronic 12V halogen ballasts/transformers are often designed as resonant circuits with narrow operating ranges, they will fail to operate properly when under-loaded or when connected to anything other than a purely resistive load. Fans are highly non-linear loads and as such, would have very poor compatibility with such transformers.
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