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cheap and simple AC - DC convertor

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computer

New Member
Hi,

Quick question: I need to run 5v to multiple 20m away locations. I'm using Strand 42 I think speaker cable (thick stuff). I've got a 9v 1.2amp AC (regulated) PSU I will be using and it needs to split into 8 different locations (each from 5m to 20m away). To prevent voltage drop I think I'll keep it at 9v AC until it gets to the remote locations. So I'm after a cheap list of components and circuit diagrams for nice clean reliable 5v power at minimum component cost/heat/space.

Thanks for any help, Googling doesn't seem to help too much :(
comp
 

bonxer

New Member
Here ya go. Make the Bridge Rectifier with four diodes, 1N4007 are the ones I generally use, as I have a tray full of 'em. You could use a lower 1N400x diode, but they're just lower voltage ratings all for the same price. Capacitors are easy enough to find. And since you want 5v, just replace the 7812 regulator in the picture with a 7805 one. You'll also probably need a small heat sink on each regulator if they get hot.
 

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audioguru

Well-Known Member
Most Helpful Member
Hi Comp,
Is your transformer big enough? It is rated to deliver only 10.8W. Therefore divided by your 8 locations allows only 1.35W for each location.
But the rectifier and regulator heat and waste power. The peak voltage of 9VAC is 12.7V. Therefore the max current for each location if they are all the same is only 1.35W divided by 12.7V = 106mA.

Since you have lots of voltage to throw away, with a current of only 106mA thin wires would have been fine.

Where did you get a regulated AC supply? Maybe you have 9V DC.
Hmmmm, do you need 5V AC or DC at your remote locations?
 

Phasor

Member
computer said:
To prevent voltage drop I think I'll keep it at 9v AC until it gets to the remote locations.
You haven't stated the current requirements of your loads - I'm assuming that they are only several hundred mA, in which case, I wouldn't be too concerned about voltage drop, as the drop will be in the order of 100mV or less.

Thus it would be easier/cheaper to make one central PSU, instead of a PSU at each load.
 

computer

New Member
the circuits are small PICAXE chips which are 5v DC. Only drawing about 80ma max with the LEDs and stuff.

if that isn't going to be a problem then will just creating one central 5v (7805 based) supply from say a 7.5v DC regulated adaptor I have that would work just as good?

Cool.
 

bonxer

New Member
The regulators are rediculously inexpensive. You can get them for like 35 cents each online. And you won't need the large 4700uF capacitor since you've already got the 7.5V DC. You could use a much much smaller and cheaper cap, like a 22nF.

Do you have a voltmeter? If so, and you haven't gotten the regulator and such yet, why don't you just go ahead and put on a 80mW load at the end of your 20m wire you are planning to use, and see if the voltage is acceptable. You'll be sending 7.5v DC down the line, so use around a 680-700 ohm resistor (that's not a link why does that always happen :?). If there's very little drop, and it's still close to 7.5v, then we can assume that you will get a similar performance when you regulate it down to 5 volts. When you do use this single central regulator method, and branch out the voltages to all those long wires, you are going to want to put a filtering capacitor at the end of those long wires so the circuits there get clean voltage.
 
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