So, it’s the Christmas season and if you haven’t had a power struggle, you will. No, I’m not talking about a struggle with Aunt Edna over whether you watch her favorite movie. I’m talking about how you power the stuff that you’re given.
Let me start with a disclaimer. I don’t have a degree in electronics. These are just things I’ve noticed from working in tech for years, not what you’d learn in school…necessarily.
Sometimes you need to do things that will void your warranty or that you might not do under ideal circumstances. That’s what this post is about.
Also remember that electricity isn’t something to play with. If a toy requires 9 volts DC, you might be able to safely choose some alternatives. If you’re trying to run a dryer or an electric car from something you hacked together, get your last will & testament in shape first. I know I wouldn’t do that and neither should you. Stay safe.
Now, on to the main event.
The Main Event
A couple of years ago, we got a Wii as a family for Christmas. This past summer, an electrical storm knocked its power supply out. I could have done the right thing and bought another one, but I thought I could hack it. I looked around, and sure enough, I had a power supply that would work. It’s been powering our Wii ever since.
Here are some things to look for if you need to use the “wrong” power supply in a pinch.
AC/DC
I’ve seen the YouTube videos that claim you can run a 42″ plasma television off a 9v battery and they’re just not true. While you can convert AC to DC or DC to AC, most of the time you can’t just swap between the two on a whim. There are electric motors that can run on either, but most of the time you need to use what was specified.
If it’s a two or three prong plug that goes directly into a wall, the device probably runs on AC. If there’s a brick midway along the cord or the plug itself is a box, it’s probably DC. To know for sure, look at the power supply. If it says the output is AC, trust that. If it says it’s DC, trust that. Sometimes, the supply will only have a symbol. The electrical symbol for DC is a solid line next to a dashed line. The symbol for AC is a wavy line.
I generally avoid working with AC. DC is simpler.
How much power?
AC is generally considered more dangerous than DC. It’s not the case that 3 volts AC is more dangerous than 220 volts DC, though. More voltage is more dangerous than less.
If you need 9 volts, look for a power supply or battery combination that will give you something close to that. I wouldn’t worry about 8.5 volts, but 5 volts probably won’t do it and could cause problems.
This goes for amperage, too. When you’re trying to power something, you want at least the number of amps or milliamps that the device needs. If a device says it needs 500 milliamps (aka 1/2 amp) at 9 volts and you have a 9 volt 2 amp power supply, you’ve got enough power. If you have a 200 milliamp power supply, you probably don’t and you could damage your device or the power supply.
Polarity
Look at the power supply or where the batteries go. If you’re dealing with DC, positive goes one place and negative goes another. Depending on how your device is made, applying power backwards might do nothing, might cause a DC motor to run the wrong way, or might “let the smoke out.” Be sure you do this right.
On a power supply, you’ll often see a symbol that looks like a line with a dot on the end surrounded almost completely by a letter “c” with a line coming out of the back of it. This looks kind of like “-c-“. The line that goes into the opening on the “c” is the tip of the connector. If it has a “+” beside it, the tip is positive. If it has a “-” beside it, the tip is negative.
Batteries or Power Supply
Batteries are more convenient, but do run out of power. Power supplies are more reliable, but require you to be where you can plug into an electrical outlet. Here’s something to consider though: 9 volts DC at 500 milliamps is the same coming from either source.
This means you can do some interesting stuff like hack a tv remote to remain plugged into the wall and never need batteries again (it’s harder to lose a wired remote, too). You can also make a battery pack for a device that has a “wall wart” power supply so that it doesn’t stay plugged in if you need to move it.
YouTube and Instructables.com are full of these sorts of hacks, and they’re worth remembering.
Check the connector
Remember the Wii that I hacked? It has a special, non-standard connector. The way I hacked the power supply I had was by lopping off the plug on the broken power supply, seeing which connection was positive (it was marked on the old supply), and hooking it up to the new power supply.
By the way, don’t trust wire colors. Black should mean negative and red should mean positive, but sometimes things get mixed up at the factory and as long as it works, no one notices. Sometimes it’s not as obvious. I suspected a wire I had was negative, but I checked it with a multimeter to make sure the connection the old Wii power supply said was negative was connected to the wire on the other end that I thought was. Better safe than sorry.
Size matters
Other than physical size, what’s the difference between a D, C, AA, or AAA battery? The amount of milliamp-hours they’re rated for. All of these are 1.2-1.5 volt batteries (depending on the chemical composition of the battery and if they’re rechargeable). We can use this to our advantage. If you need to test something that runs on a C battery, but all you have is AAs, you can substitute, just make the physical connections with some wire or a few shiny pennies and you might be able to run certain devices for a short amount of time on the “wrong” batteries.
The opposite is also true. If you have something that calls for AAs, but seems to die quickly you could wire a C cell holder into the place where the AAs are supposed to go for more longevity.
Parallel or Series
I used to have a beard trimmer that ran on three AA batteries. One day, one battery fell out. The trimmer slowed down, but kept running. That’s because batteries in parallel have more amperage. In series, they have more voltage.
A tv remote might run on two AAs. They’re wired so that the positive of one connects to the negative of another. The result is 3 volts instead of 1.5.
In my trimmer, the motor ran off of 1.5 volts, but more batteries in parallel meant that it had more amperage to run off of and the motor ran faster, and for longer.
If you have a device that runs off of a single battery, you might be able to wire multiple batteries in parallel to get it to run longer.
A 9 volt battery is actually six AAAA batteries in series (and placed in a little box) to create 9 volts. In a pinch, if you have an old 9 volt and 6 AAs or AAAs, you could wire your 9 volt device to run off those instead.
Do a little research and you might find you already have the power supply you need to power something that claims you need a special supply from the manufacturer. You might find that batteries can be substituted for a wall wart. Maybe you’ll even want to use different batteries than what the manufacturer specified.
Have you ever powered something with the “wrong” power supply and had it work?
[Image via Tambako the Jaguar]
Raoul Snyman says
Just remember, it’s not the volts that kill you, it’s the amps.