Wall Transformer for Project Power Supply





Introduction: Wall Transformer for Project Power Supply

Wondering what to do with those old wall transformers? Use them for power supplies to run electronics projects!

You will need some of these:
power supply (go with a junker)
Alligator clips with plastic boots
wire strippers or cutters
needlenose pliers
some tape
about 10 minutes

You will be interested to know what the output values are. This one listed 9 volts DC as the output with 600 miliamps.

The label will also tell what the polarity is. This one has a negative on the outside, positive on the inside.

It also indicated that it came from a telephone. I think it was from the dump. Nobody will cry if this is gone. You should check with any potential owner before you perform this surgery on a wall transformer.

Step 1: Cut Off the Output Plug

Make sure it has been unplugged for a while. They hold some charge.
Cut the wires.
Cut one wire shorter than the other. It is nice if the negative is shorter, but not essential. Mostly, you want to make it so that the two tips cannot easily touch each other. If they contact, you will probably blow the fuse, which you won't want to replace, and will probably cause you to toss the transformer.

Step 2: Strip the Wires

Strip both wires about a half inch.

Step 3: Put the Boots on

Put the boots on the wires. The narrow end is away from the wire end. If you have two colors, that's great. Red, orange or yellow for positive, black or green for negative
If you forget to to put the boots on, you can get them on, but it is a pain.

Step 4: Attach the Wire

Twist the stranded wire to make it stronger and easier to handle. Put the wire through the hole in the gator clip, send it out between the two tabs in the handle.

Bend one of the tabs over the exposed wire. Make sure you have a good mechanical connection. If the wire is loose, it will fall out.

You may want to bend over the other tab, but if you decide to use the clip again, you may be able to salvage the clip and use the other tab. Just make sure you have a good connection.

Step 5: Slip the Boot Over the Clip

Jam the nose of the needlenose pliers into the mouth of the clip. It is a lot easier to do this if you have the mouth open.
Slide the rubber boot over the gator clip.

Do the same to the other clip.

Step 6: Test the Leads

Plug it in
Put the multimeter on the appriate setting for the value you think it is.
Put the clips on the meter.
Check the meter's reading.
If you pay attention to the negative symbol, you can see what the polarity of the wires is.
Label the leads with masking tape, especially if you don't have different colored boots.

Step 7: Glory in Your Completion

This thing is done.
You can use it to power projects. If your project is fussy about what voltage you need, you may need to build a control circuit.

If you are just powering something that needs to go, like a motor or something like that, then you should be able to just hook the gator clips to the project and get going.

Since this is a wall transformer, it will continue to draw power even if it is not being used. Unplug it to when not in use to conserve energy.

Have some fun!



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QUESTION: I was wondering if this would be safe to charge a old ni-cd drill battery. My drill charger went dead. The output on the drill transformer is 12 volts, 500ma. The output on the closest matching ac transformer I have is a 13 volt, 800ma. Would this be safe?

I would also like to know how close your measurements are to the ones printed on the transformer. The actual Output voltage seems to differ a lot from the printed on output value. Does anybody know why these values don't match? I have a 9v (printed on) transformer that is actually outputting 12v.

If you're measuring 12v. dc on a 9v power supply it's generally an unloaded power that you're measuring. If you put a 9v load on it, it should measure 9v. Hope this helps.

The performance for these wall-warts probably isn't linear (i.e. the voltage isn't the same for all current loads). Generally, the voltage goes down as more current is drawn. If you are measuring with a multimeter, multimeters are designed to have an extremely small current flow (ideally it should be zero) to measure voltage. 9v is probably what the transformer provides with a typical current load.

They all have the volts listed on the body of the transformer- may have to get strong glasses to read it but it should be there.

unless the ac adapter is regulated you probably shouldnt use that because those ac adapters are perfectly matched at the device it goes with because the device pulls the exact voltage and current on the ac adapter. using it to power any device or project that doesnt pull the 'exact' current and voltage the ac adapter will put out a much higher current and voltage than it should and that could destroy your project or device or whatever you have hooked to it. it does this because the ac adapter isnt regulated its unregulated and unregulated power supplies are not reliable, maintained, unstable, controlled and they put out very 'unclean dirty power'. use a 'regulated' power supply because the power is controlled, maintained, filtered and is pure, clean lab quality power.

Not true, the adaptor should be rated higher in amperage than your circuit draws. The rating on the adaptor is the MAXINUM it can supply. Your circuit will only draw the current it needs (unless you've done something wrong).The voltage should be the same as that of the circuit. While some things need clean regulated power,for "cheap & dirty", this will work just fine.

Save yourself from a lot of heartache. Use both red an black boots and put the red boot on the wire with the white line (or textured edge). This will alway be the positive clip.

I know this is an old topic, but I wanted to say, for the benefit of beginners, that that is NOT always true. In my 25 years as an electronics technician, I have found that the polarity of the white stripe (or textured edge) various from manufacturer to manufacturer. ALWAYS measure polarity before assuming anything. Better to check and be right, than to not check and be wrong.

One suggestion: you can buy the boots in different colors, so: cut off the original connector, separate and strip the wires, and test the polarity.
Slip a red boot on the positive side and a black one on the negative; the rest of the instructions as posted in the article.