Battery Eliminator for Graco Baby Swing

Introduction

So you’ve got a baby, a baby swing and your considering a direct-buy stock purchase plan with Energizer or Duracell. Or perhaps you’ve talked with some friends and are contemplating an adventure into the world of rechargables. HALT, don’t take that plunge just yet. Why not forget about batteries altogether? In this article, i’ll show you how to stop wasting batteries and pocket some cash rather than investing in rechargables.

Disclaimer

• This article is provided “as is,” without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose


• No warranties of any kind are made with respect to the contents, completeness, or accuracy of the information listed herein


• The Robinson House is not responsible for incidental or consequential damages resulting from use of this information


• This project uses household voltages (~110V) and could result in injury or death


• Improper wiring could electrocute you, your child(ren), your pet(s) or all the above


• Performing any modifications on a consumer product will void all warranties and, if electrocuted, your life


• Modifications to a baby swing are best performed by a licensed contractor and wiring performed by a licensed electrician


• Excess current and voltage with improper wiring could cause the swing to hurl a young child across a room and possibly damage furniture or crush small pets


• Do not submerse the swing in water as this could lead to electrocution if drowning does not occur first


• Operation performed by professional driver on a closed course

Background

This looks a little complicated, why is all this necessary? Short answer: microprocessors. Long answer: microprocessors require DC voltage to operate. Batteries delivery DC voltage. An AC power adapter also delivers DC voltage, but with an inexpensive adapter, its not “clean” (2); it has ripple, which is amplified when placed under load.

If a pin on a microprocessor is expecting a signal of ~5 Vdc for an “on” state, but the voltage fluctuates within some time (frequency, e.g. 60usec.) and value (e.g. below 3.4 Vdc), then the signal on that pin is perceived to drop to an “off” state.

I initially bought only the power adapter, set it to 6 Vdc, hooked it up and expected it to work. The swing has 6 speeds and plays music and with that configuration i could operate the music and speeds 1 thru 3. At speed 4, it would run a little while and stop. At speeds 5 and 6 it would cut off immediately.

Tackling the Problem

I first thought it was an issue of power. <insert Tim “the Tool Man” Taylor grunt here> After all, it was working on the lower speeds. So i went back and grabbed a 6 Vdc adapter that could deliver 1800 mA (versus 300 mA). As you probably guessed, it didn’t work. The only alternative was that it didn’t like the voltage signal. The voltage was correct: four D-size batteries, at 1.5 Vdc each, wired in serial yields 6 Vdc. (This ain’t rocket science ya know.)

Being scopeless (referring to an oscilloscope, not mouthwash), i had to guess what the problem could be and bounced the problem off my co-worker (we’ll call him John, as he wishes to remain anonymous to avoid lawsuits). The only conclusion had to be ripple in the DC output. Searching the web, i found a couple of good resources for designing a ripple filter (1,2). One reference (2) has a great diagram of what is going on.

So, let’s get started.

Parts Required

1. Graco Baby Swing - 6-Speed Reclining, Model 1992CJG or similar - Qty. 1


2. Power Transformer 120Vac to 12.6Vac at 300ma - Qty. 1 (RadioShack part# 273-1385 or equiv.)


3. Capacitor - Electrolytic - 1000uF - rated 15Vdc min. - Qty. 2 (RadioShack part# 272-1032 or equiv.)


4. Universal Power Adapter - rated at 300ma for 7.5V - Qty. 1 (RadioShack part# 273-1662 or equiv.)


5. Alligator clips - small - 1 red, 1 black (RadioShack part# 270-378 or equiv.)


6. 22 Gauge wire - 5in. red, 5in. black (RadioShack part# 278-1224 or equiv.)

Optional Parts

1. Adaptaplug Extension - 6ft - Qty. 1 (RadioShack part# 273-1641)


2. Adaptaplug Hobby Leads - Qty. 1 (RadioShack part# 273-1742)

Tools Required

• Needle nose pliers


• Wire strippers


• Soldering Iron and rosin-core solder


• Heat sink(s)


• High speed drill with 1/2″ bit


• Electrical tape

Schematics

Component List

• C1,C2 - 1000uF Electrolytic Capacitors


• L1 - 120V/12V AC Power Transformer

Assembly

Soldering with the heat-sinks attached.

I used a high-wattage soldering gun. A typical 25-30 Watt soldering iron would lessen the need for the heat-sinks, but they are still a good idea.




The finished goods.

The picture shows the circuit wired according to the schematic diagram above. DCin on the left, wires for DCout on the right.

Though harder to see, i covered the leads for the primary side of the power transformer with black electrical tape to prevent any shorts when placed in the battery housing of the swing.

The completed assembly shows the alligator clips and the Adaptaplug connector.

As above, the assembly is fashioned like the schematic diagram above.

To facillitate the wires entering the battery housing, drill a 0.5 in. diameter hole in the plastic. Drilling from the inside out will keep the bit from walking all over the place.

The modified battery housing cover.




And the finished cover.

Now place the components in the battery housing. Note that the transformer sits nicely on the plastic lip the seperates the two side of the battery compartment.

Close it up and tidy the power cable with some zip-ties to keep it from getting caught in the swing and possibly strangling seat occupant.

The proof is in the pudding; happy baby make for happy family.

(Paid endorsement.)

Appendices

References

1. Electrical Engineering Training Series - LC Choke-Input Filter from Integrated Publishing


2. All About Circuits - Volume 6, Chapter 5 - Discrete Semiconductor Circuits - Rectifier/filter circuit

Addenda

• The RadioShack Digital Camera Power Adapter may provide a ripple free output source.


• Compare with price of quality rechargables at Thomas Distributing.


• If you enjoyed this project, see also Live Cat Audible Voltmeter