Battery Eliminator

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Introduction: 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

Parts:

  1. Selectable DC converting wall adapter
  2. 1" wooden dowel
  3. Wood screws
  4. 1N4001 Diode (optional)
  5. Duct Tape (optional)
  6. Washers (optional)

Tools:

  1. Hand drill
  2. Hand saw
  3. Wire stripper
  4. Voltmeter

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.

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149 Comments

I also replace batteries in a similar way, using a barrel connector in the battery compartment lid, wired to each side of the terminals in the compartment. This way one power adapter powers many of my devices.

Attempting to replace the batteries on my Intex quickfill, will this wall adapter work? Also I'm a bit confused since It uses 6 C batts but the label on the item says "4.5v DC 25W".

Hey cdiaz, cool yeah I have that pump too. Unfortunately you can't use this adaptor, you'll need to find one with either a 25W power rating or a 25/4.5=5.6A current rating.

The reason it uses six C batteries for only 4.5V is that for such a large current draw, the voltage of the batteries is significantly decreased by their internal resistance. I've read 0.1ohms for AA batteries. If it is similar for C, then with six of them and five amps, the batteries provide (1.5-0.1*5)*6=6V, not 9V. The batteries only have 1.5 volts at the very beginning of their lifetime, so this may explain the rest of the difference.

Hey dreens. one last question. Will this adapter work for my pump?

When you say "adapter", if you mean the selectable DC converting wall adapter I used, you definitely cannot use it because as you can see in the picture, it has a 0.5A current limit, and you need more than ten times as much. I don't think you'll find something that mounts in a wall adapter but delivers 25W or 5-6A. Your best bet is something like the power supply I linked you to, which will take care to mount safely but will work well otherwise.

If you mean "adapter" as in the general technique of eliminating batteries by replacing them with a wood dowel with screw contacts, yes that can still work.

Sorry, yeah I meant the technique. Thanks

Thanks for the reply. I'll look into the power supply you suggested.

You might try something like this: https://power.sager.com/rs-25-5-2614691.html

Downside is that you'll have to connect a wall plug yourself and find a safe enclosure to mount it inside of, since you don't want the 120V terminals exposed when you plug it in.

You plugged this into your infant's shaky chair? Really?

Yes, absolutely! And I'm proud to say that it is still working great! In fact, a few days ago we had a power outage, and it was super easy to switch back to battery briefly. He's transitioning away from it now, but for a month or two my son sat in that thing more than half the day.

And no, I'm not worried that 1.5V will somehow set wood on fire, or that the wall wart will magically start passing 120 VAC through, or whatever else the self-proclaimed safety experts around here might cook up hahaha. This thing is safe, trustworthy, reliable, and I built it in ten minutes.