Add an AC adapter to a battery-powered device

With a new baby, we are acquiring an astonishing number of battery-powered devices -- bouncy seats, swings, activity jumpers, mobiles, ... -- and burning through an even more astonishing number of batteries. Now I know why Costco sells those immense packages of AAs.

My wife asked me whether I could attach an AC adapter to our baby's mobile. I'd seen an article in MAKE about modifying noisy toys, so I knew it was possible. It turns out to be surprisingly easy, provided you (okay, I) don't make some dumb choices along the way.

NOTE The project I describe will void the warranty for whatever toy you modify. The manufacturer (rightly) will not support you or provide you with assistance in doing this. If it works, be happy: If You Can't Open It, You Don't Own It. If it doesn't work, take it as a lesson not to meddle in the affairs of Corporations, for they are Subtle and Quick to Anger.

Step 1 This Instructable is Incomplete

You'll notice that two of the Steps don't have useful images. I started writing this up after completing the project on one of our daughter's mobiles, and before starting the second. I definitely don't want to take the first one apart again just for some photos, and we've since decided not to do the AC adapter on the second mobile (the cord wouldn't be adequately secured).

Nevertheless, the descriptions in the Steps are accurate and complete, based on lessons learned the first time. I think this can still be useful to folks.

Comments

[melw365]

I am trying to change 3 sets of branches that have led lights on them from battery powered to direct electric. Each set is powered by 3 AA batteries (total of 6 batteries). I would like to tie all the wires together and I believe attach to a transformer. Any advice .
Thanks

[melw365]

Yes, you are right. A total 9 batteries.
Sorry
Mel

[kelseymh]

I think you mean a total of 9 AA's (3 each on 3 lines). Tie them together in parallel (connect the three + wires together, and connect that to the positive contact on the wall-wart plug, and similarly with the three - wires).

[redtux777]

I have 4 AA batteries in series in golden tee golf game I have. The batteries last 3 to 4 hours.
I am trying to do the math on that. Does that mean I would need 6v .5A power cord?

[kelseymh]

That sounds about right, based on typical AA capacities. Just to give yourself some headroom, you might consider a higher-current supply (say 6V @ .75A or 1A).

My apologies for the delayed response.

[viky_vandna]

Hi I have drum player with 6 1.5v AA batteries thought of converting to AC adapter when opened found that it actually has three wire black and red at each end but found one more green at middle and it seems that it supplies 4.5 to one component and 9 / 4.5 v to speaker. So is there any way to split the power supply to these three wires???.
I checked that when I only place 3 batteries in slot 1,2 and 3 (please see the picture) I get lights on panels but no sound.

[kelseymh]

Blech! If you wanted to do that with a wall-wart, you'd have to build a small circuit to split the voltage. I think you could probably do it with just a pair of big (10 meg or more) resistors: the green wire would attach to the middle between the two resistors.

[viv_virus06]

i'm planning to run my remote controlled helicopter on ac adapter. i know that it use 9.0V but i don't know what mA should i buy. can you help me?

[kelseymh]

Do you mean you want to run the control box from an adapter? You obviously can't connect the helicopter itself to an AC adapter; it won't be able to fly :-) Did you read the manual? Usually toward the back there's a specifications sheet that should tell you the voltage and current usage.

[viv_virus06]

i'm connecting the ac adapter to the remote, or the controls. it requires 6 1.5 volts batteries. the box only specify the voltage requirement and the mAh. i cant find the mA requirement. can i use any 9v adapter without taking note of the current usage requirement?

[kelseymh]

Hmmm....yeah, that's not enough information to solve the problem. In principle, you could measure the current draw with a multimeter and four-lead bridge, but it's not important. Choose an adapter with a high current rating. The remote will only draw as much current as it needs; as long as the adapter can supply at least that much current, it's fine.

[viv_virus06]

thank you very much! you helped me a lot.

[viv_virus06]

anyway, how can i set the polarity of the adapter to its correct setting?

[jayhawk67]

i have a fountain that requires 2 double a batteries what adpater should i use?

[kelseymh]

Each battery is 1.5V.  If they're connected in series, you'd need a 3V adapter.  If they're connected in parallel (unusual), you'd need a 1.5V adapter.

[jayhawk67]

ty very much

[Evil6]

I've done roughly the same thing with ac adapters from a thrift store and dowels cut the length of the batteries used. Using a screw to hold the wire to the dowel and make the connection to the two terminals you don't void the warranty, just route the wires under the battery plate. On my second child and many batteries later you tend to get desperate! Great Ible BTW!

[xrobevansx]

CONGRATS ON THE BABY!! By the way look at my instructable or kill your friends. Your choice.

http://www.instructables.com/id/A-More-%22Baby-Friendly%22-Doorbell/

PS- great instructable! I am going to give it a go on a few things.

[kelseymh]

Thanks :-) Ironically, we haven't had your doorbell problems -- ours is already "broken" and we just get a dull "dong-k" rather than a proper chime. Perhaps the previous tenants already implemented your hack ... :-/. As for my Instructable, note that the components cost about $35 bucks. I tried finding cheaper sources than RS, but the single-voltage adapter was a dead end :-(

[Goodhart]

Ah, a doorbell like the one at the Huckstables' house LOL

[Goodhart]

VERY well put together.

This is a very good ible for any toy that is not actually touched or played with by the baby. I personally get a bit skiddish when having AC main current anywhere near a baby if there is any possibility of contact through fault or ground fault.

Of course, a simple ground fault circuit in the wall plate might be overkill, but I would probably do it if I were doing this....but that is just my paranoia showing, maybe :-)

[kelseymh]

Not paranoia at all! As I wrote in my very first I'ble, "babies have a terrific knack to find whatever cliff is around them to fall off!"

For that reason, I haven't installed an adapter on the other mobile (the one on the side of my TV chair, featured in [Silence of The Toys]). This one is on her crib, and I've tied off the adapter cord at four different places in such a way that the plug cannot actually be pulled out of the jack.

[Goodhart]

It is amazing how fast they learn to climb, sometimes to rather scary heights too :-) I know how much I got into when I became just a little older and could hold a screwdriver and almost remove a plug from the socket. The experience had me fearful of electricity even today (funny that I picked electronics as a hobby though LOL ) . I'd love to be as skilled with hardware as I am with a p/c board and solder :-)
Oh, and sorry for cluttering up you comment section with my ramblings.

[mman1506]

when i was little i tried to stick a fork in a socket to see if it was working (before i knew that it has more volt tthan a 9v batterry

[Goodhart]

THAT could have ended up worse then it did. Thankfully you did not cross between both contacts. The shorting out of 110 vAC can melt through screwdriver handles (blush). Don't try this at home....

[mman1506]

when i was about 6 i was playing with an old outlet timer in the garage and touched a contact (no i didnt take it apart) and blzzzz my arm got a shock,it kinda feels like an overly strong massager when it goes through the musle,my arm was sore for a few days later and i think possibly it may contrubuit to my right arm not being able to write very well

[Goodhart]

Well, I do hope that improves as you practice, and yes, I don't mess with 60 hz AC much without an isolation transformer in between me and that mess.

[Noodle93]

I did that heaps. And those flappy-safety switches? They're are no match for my cognitive skills!

[kelseymh]

Sorry? For what? I think "ramblings" are just what comments are supposed to be. Thanks very much for your feedback and for your ramblings :-)

[Goodhart]

Ah well, if I don't do a self-check now and then, my ramblings can be very much like Edith Bunker's ;-) Starting the subject with Toy modification, and ending out talking about the local VFW meeting :-)

[gwyche]

If it works, be happy: If You Can't Open It, You Don't Own It. If it doesn't work, take it as a lesson not to meddle in the affairs of Corporations, for they are Subtle and Quick to Anger.

Hehe you gave me a chuckle there. Very nice instructable - I KNOW I'll be using this.

[kelseymh]

:-) Thank you! I hope that you find it useful. A fellow I'bler recently published a similar project, using an external switch to select AC vs. batteries.

[dodo91]

do you live in las vegas? i do. i have a costco that sells them near the entrance. they are a good price for that. amount of AAs.

[samfiller]

Great post, I was thinking of doing just that! Just wanted to ask why you chose 750ma is there a chart or something on how to figure out what is required? Sam

[kelseymh]

I cheated -- I measured the current draw at the two battery terminals with the back off. It was about 400 mA in the "lights and motion" switch position.

[atombomb1945]

Congrats as well. A quick and dirty way would be to take the adapter and strip the ends, wrapping one end on the Positive and one end on the Negative of the battery case. In addition I have seen dummy batteries made with wood dowels and thumb tacks. THIS however is definitely a cleaner and probably safer option, especially around a newborn.

[kelseymh]

You are correct. In fact, someone else posted such an I'ble a while ago (which I didn't find until after I published mine. Mine is intended as a permanent conversion, rather than a temporary hack.

I had thought about the idea of just attaching to the battery terminals, but on my particular device, it was not easy to tell which ones were the endpoints without opening the case. And once you've done that, well, you might as well do the job right :-/

P.S. I see you're using the ATLAS toroids (the same picture used on the CERN jigsaw puzzle) as your icon. Just because it's cool, or are you a collaborator?