Most small to medium electronics use power supplies with a box on the end. I've heard them called "wall warts" or even "bricks." Whatever you call it, it's a power supply and they seem to becoming more common. Everything from cell phones to fax machines use these types of power supplies. What happens when the electronic item powered by these breaks or is lost? I think most peoples reaction is to just throw away the power cord, after all what use is it without the item it's designed to power? Well as it turns out they can be very useful and I would encourage you to save it just in case. Just as you may lose the electronic item and retain the power cord, you may also lose the cord but still have the item. And some of these power cords are interchangeable. The purpose of this post is to tell you how to know if you can reuse an old power cord.
As an example I'll use a real life example that happened to me yesterday. I bought a used wireless router of craigslist for dirt-cheap because it didn't have a power cord. So I went digging through my box of cords to find a suitable replacement cord.
Now let me be clear, do NOT just use the power cord if the connector fits, you're very likely to break the eletronic device! You need to follow these steps to determine if the power cord will work for you.
First, locate the power specs on both the power cord and the electronic device you're hoping to power. The specs should be on a sticker or stamped into the plastic and look something like this.
Step 1: Type
First step is to identify the type of output power, either AC or DC. Most power cords ouput DC, but a small number output AC. If the power cord matches the electronic item then proceed to the next step. If they differ then this power supply will not work. Note, sometimes they don't say "AC" or "DC." A solid and a dashed line means DC and a wavy line (sine curve) means AC.
Step 2: Voltage
Next you need to check the output voltage. The voltage needs to be an exact match. Technically you can go slightly higher on the power cord (10V power cord for a device requiring 9V), but be aware that higher voltage places the device under additional "stress" and may cause it to fail sooner. In this case the power supply is 12 volts which is what I'm looking for.
Step 3: Amps
Next locate the output amps. The amps on the power cord needs to be the same or higher than the device. It's important to note that the amps rating on the power cord is the maximum amp output, it does not mean the power cord forces that many amps on the output. So as long as the amps is the same or higher than your device you can use it. In this case my router needs 1amp and this power cord outputs upto 1.25 amps so it's good.
Step 4: Polarity
Most power cords like this use what's called a barrel-connector. Polarity of the connector is very important, getting it wrong would be like putting the batteries in backwards. For my power cord the inside is positive and the outside is negative. If the polarity does not match your device, all is not lost. You can cut the cord, strip the wires back, rotate one end, and reattach the cord. Bare minimum you need to twist the wires together and then cover with electrical tape, but ideally you solder the wires together and cover with heat-shrink tubing.
Step 5: Physical connector
The last step is determining if the physical connector will work. This information is not printed on the power cord or the device. So just check it, does the power connector fit snugly into the device? If not, you can fix this for cheap. Places like Radio Shack and digikey.com sell replacement barrel connectors. You cut off the old connector and solder on the new one. Just make sure to get the polarity correct. If you need to check polarity use a multimeter (or a LED).
There you go, the steps necessary to reusing old power cords and saving tons of money. Using this technique I found a power cord for my new wireless router and saved at least $20 over other used routers. You will notice we didn't look at the "input" section of the power cord at all. Assuming you don't have any foreign power cords, this should be a safe assumption. If however you have power cords designed to work in foreign countries these steps may not work.
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