Thursday, 16 October 2014

AC Adaptor Power Supply – Recycle – Part 2

CAUTION: Modification of AC Power Adaptors is potentially dangerous. Read the specifications on the adaptor and observe output and polarity. Mistakes with AC Power can kill you. If you are unsure of the specifications of the adaptor that you are tinkering with … throw it away and get one that you know. Do not do ANY soldering on the adaptor or it’s cable when the adaptor is plugged in. I take NO responsibility for your safety, that’s your job.

Okay, so I’ve repeated the safety warning … I’ve completed the breadboard edition of the circuit and, honestly, this is enough. I don’t need to make a PCB for this at all.

Power Supply - 01_thumb[1]

This is the top view of the supply. The power comes in from the left (at the moment it is connected to a 9V NiMH battery, but I intend to connect it to a 9V AC Adaptor). You can see the layout, it’s pretty straight forward.

Power Supply - 02

This view shows the arrangement more clearly. I have spaced everything to fit on a 50 mm x 70 mm prototype board. It could be smaller, but it really doesn’t need to be.

Power Supply - 03

I’ve pad soldered the components and used the component legs to bridge. It’s a pretty tidy solder job and I’m pleased with that aspect of the build.

Power Supply - 04

When the SPDT switch is thrown, the LED lights up to indicate that there is power running through the circuit.

When I built this on the solderless breadboard, I had the unattached SPDT pin connected to GND and another indicator LED connected to the wiper (Leg 2) of the potentiometer. There was also a connection from Leg 1 to GND in t he solderless breadboard version. When it was running, the 9V battery was getting very hot, so I decided to cut these elements from the circuit rather than try to work it out (I know, sometimes I’m lazy) … I figured that there was re-routed power going back to the terminal block (and on to the 9V battery). I was going to look at putting in an IN4001 diode to protect the power source … not sure if that would have any benefit, but I’ll re-breadboard it at some later date and report back and improve the circuit.

I probably should connect Leg 1 on the potentiometer to ground via a resistor, but what the hay … this configuration works out just fine. There isn’t much variation in the power output when you spin the dial though. With a charged 9V battery I get 8.9V through to 8.1V when turning the pot.

I plan to make an enclosure out of acrylic sheet and using the circuit to supply power to a resistive wire for a heating element.

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