Intro: Battery Eliminator
Do you have an appliance that eats through batteries? Follow this instructable for a simple, quick and dirty trick to power it directly from an outlet! If you want to do something more intense, check out doncrush's Battery Eliminator from a recycled wall wart.
I will focus on replacing a single D battery, used in my baby's bouncy seat, but the basic technique could be applied for multiple battery appliances as well.
Step 1: Materials
- Selectable DC converting wall adapter
- 1" wooden dowel
- Wood screws
- 1N4001 Diode (optional)
- Duct Tape (optional)
- Washers (optional)
- Hand drill
- Hand saw
- Wire stripper
I chose a selectable adapter because it was the cheapest with a 1.5V option. If you can find an adapter that provides exactly the voltage you need, don't bother with the selectable one.
The diode is useful if you end up needing to reduce the voltage of your adapter, like I did. If you suspect your appliance may be pretty sensitive to precise voltage, (most battery powered devices are not, since batteries fluctuate in voltage during their lifetime) check out DIY Hacks and How-to's very well done instructable that uses an actual voltage regulator.
Step 2: Prepare Dowel
Cut your dowel about the length of the battery to be replaced. Pre-drill holes in the ends for screws which will mimic the terminals of your battery. It's important to pre-drill with such a short dowel to avoid splitting. Drill a hole or two through the center perpendicular to the dowel which you'll thread the wires through for strain relief.
Step 3: Prepare Adaptor
Chop off the funny barrel style connector at the end of the cord.
At this point it may be a good idea to drill a hole in the battery cover of your appliance and feed the wire through it. You may also just be able to force the cover closed even with the cord sticking out.
Now push the cord through the perpendicular holes on your dowel and strip the two wires generously.
NOTE: You may wish to purchase a switch to go between your adapter and the wall, because these adapters are notorious for eating energy even when the electronics they serve are turned off. A cheap switch like this would do the trick.
Step 4: Connect Leads
Screw two screws in the ends of the dowel, but not all the way. Wrap the stripped wires around the screws, and then tighten the rest of the way. Make sure the wires are tight and can't be pulled off.
If the wires can pull off, you might try using a washer to better trap them.
Step 5: Install and Test
Your dowel can now replace a battery! Install it in the battery slot just as you would a normal battery. If your dowel is too thin you can wrap it in duct tape for a better fit.
You may wish to check the voltage while you turn on your appliance. The power adapter I chose says it can deliver 1.5 V, but it actually was delivering 2.3 V. This isn't too surprising, since crappy adapters have a lot of internal resistance which means their voltage will vary with the current load. In fact, if you try to check the voltage without any load, you may see something crazy high. My adapter delivers 4V with no load on the 1.5V setting. This doesn't necessarily mean you will fry your appliance. As soon as you turn it on the voltage will drop to a reasonable level.
If the voltage is still too high when your appliance is running, you can follow the optional additional step.
Step 6: Reduce Voltage
In this step we add a diode in series with the battery eliminator. In addition to forcing current to travel in only one direction, diodes have a relatively current independent 0.6-1.0 V drop, which is just right for reducing that extra voltage on the power adaptor. If you need a bigger drop, you can put two diodes in series (they're $0.40 each), and if you draw more than one amp, you should put two in parallel to prevent overheating.
Just add another screw on the side of your dowel, connect the diode from the end screw to this new screw, and move the adaptor wire to the new screw.
Don't worry about direction if your adapter has a polarity knob, but otherwise diode should point from the extra screw, where positive voltage must connect, to the plus side of the battery.