Baby swing power mod

Torben · Mar 13, 2007

Hi all,

OK, the title probably sounds more impressive than what I actually plan to do. I mostly want people to post why what I propose might be a Really Bad Idea (TM), if it is in fact a bad idea.

Gonna have a baby this month, if the docs are to be believed. So we've got one of those little automatic baby swing chairs, powered by 4 C cells. Now I don't want to spend the money on the batteries, and I'm not a big fan of the new "battery economy" which seems to be getting crazier and crazier. And the darned thing doesn't have a simple jack for a 6 VDC wall wart or anything.

I've got a box of discarded wall warts. What might be some dangers/downfalls of putting in a DC input jack and just using a 6VDC wall wart (assuming I've got one with sufficient amp capability) to power the thing? Could it short internally and somehow wind up delivering the 120VAC to the device's motor? If so, would a fuse be enough to protect against it? Any other dangers?

Thanks for any ideas/warnings!

Torben

audioguru · Mar 13, 2007

An ordinary 6V wall-wart has its voltage unregulated. It is 6V only at its rated current. It could be 10V or 14V with less current than its rating. Then the swing will fly.

Wall-wart adapters are made very cheaply. Sure something could go wrong and make the swing fly. The adapter or the motor in the swing might catch on fire.

The swing manufacturer didn't include an adapter to avoid liability if something goes wrong with it.

Batteries are safe and are fairly inexpensive. Use them.

Torben · Mar 13, 2007

audioguru said:
An ordinary 6V wall-wart has its voltage unregulated. It is 6V only at its rated current. It could be 10V or 14V with less current than its rating. Then the swing will fly.

Wall-wart adapters are made very cheaply. Sure something could go wrong and make the swing fly. The adapter or the motor in the swing might catch on fire.

The swing manufacturer didn't include an adapter to avoid liability if something goes wrong with it.

Batteries are safe and are fairly inexpensive. Use them.

Hehe. OK, that's pretty much what I was looking for. The lack of regulation I was aware of and I was planning on matching the power ratings, but that wouldn't solve the problem of the wall wart possibly failing in a way which could burn up/overpower the chair.

I have images of Mythbusters strapping rockets to a swing chair in my head now, except with a baby sitting in the chair. Not what a first-time father needs to worry about.

Thanks for the reply!

Torben

philba · Mar 13, 2007

Congrats - your life is over!

I seriously doubt that a wall wart will turn the swing into a baby catapult. The motor in those things is pretty weak. All it really does it keep it swinging. It won't start the swing from a dead stop. It will swing at the resonant frequency of the pendulum (baby+chair), regardless of the motor drive.

Lack of regulation isn't that big a deal - it's driving a motor which probably could take 2 to 3X the voltage before burning out.

But on a different tack, I think you will discover that you will use it for only a few months. I don't ever recall changing the batteries on ours and we had 2 kids. Once they were crawling, they couldn't stand being in the swing - too much to explore even in a play pen. Also, you (or your wife) will move the swing around so plugging/unplugging is kind of a pain. Not worth the effort, imho.

AllVol · Mar 13, 2007

Torben said:
Hi all,

Gonna have a baby this month, if the docs are to be believed.
Thanks for any ideas/warnings!

Torben

Idea/warning: If there is a doubt, and you can't trust the doctors to be truthful, perhaps you should hold up on the batteries. >)

To be sure, have your wife check with some present or former mothers who can advise her with some certainty.

Seriously, congratulations!

Sceadwian · Mar 13, 2007

I've seen automatic baby swingers before, they don't use electricity, they use coil springs, like a giant wind up toy. Built with a thick enough casing they're intrinsically safe, don't mix electronics experiments with baby's. Electronics experiments barley mix well with adults

mneary · Mar 13, 2007

Rechargeables?

mroberts · Mar 13, 2007

+ AA to C adapter

Hero999 · Mar 14, 2007

I agree with philba, the poor regulation shouln't be a aproblem and there's no chance of the primary side shorting to the secondary as the trasnsformer is wound on a double section safety bobbin.

The only thing that can be a problem is if it's used in a thunderstorm but I hope you're not that stupid.

Oznog · Mar 14, 2007

How much voltage do you think it'll take to send that baby all the way over the top and back down the other side?

Thunderchild · Mar 14, 2007

if you want to be real safe just get a dry led acid battery 6 volts 4 amps you can recharge it quiker than NiMH or NiCd and won't have regulation problems just tape it to the swingers legs, 6 volts won't harm anyone perhaps box it just to make sure, a fuse won't hurt

Hero999 · Mar 14, 2007

It's not about the voltage, it's more about power; between 1W to 5W of power output from the motor should be enough.

audioguru · Mar 14, 2007

Oznog said:
How much voltage do you think it'll take to send that baby all the way over the top and back down the other side?

A tiny amount of power added to each push will add up and make the baby go around and around. The thing should be bolted to the floor!

Torben · Mar 15, 2007

Hero999 said:
I agree with philba, the poor regulation shouln't be a aproblem and there's no chance of the primary side shorting to the secondary as the trasnsformer is wound on a double section safety bobbin.

The only thing that can be a problem is if it's used in a thunderstorm but I hope you're not that stupid.

Oh, I have my moments. But I'm very, very careful about anything to do with electricity, fire, or firearms. All can be useful but everything's always loaded and should be treated that way.

Torben

Torben · Mar 15, 2007

mneary said:
Rechargeables?

Thought about that, but then realized that the thing is meant to be used only until the child can grasp with its hands (it says "if the child grabs the supports, discontinue use"). So given that this is the only item I've owned in over a decade which uses C cells, I just went with alkalines since I'm unlikely to need them again.

Torben

Torben · Mar 15, 2007

philba said:
Congrats - your life is over!

I seriously doubt that a wall wart will turn the swing into a baby catapult. The motor in those things is pretty weak. All it really does it keep it swinging. It won't start the swing from a dead stop. It will swing at the resonant frequency of the pendulum (baby+chair), regardless of the motor drive.

Lack of regulation isn't that big a deal - it's driving a motor which probably could take 2 to 3X the voltage before burning out.

But on a different tack, I think you will discover that you will use it for only a few months. I don't ever recall changing the batteries on ours and we had 2 kids. Once they were crawling, they couldn't stand being in the swing - too much to explore even in a play pen. Also, you (or your wife) will move the swing around so plugging/unplugging is kind of a pain. Not worth the effort, imho.

That's a good point. For the moment I've just gone with alkaline C cells; we'll see how long they last. The regulation I'm not worried about; I just wonder about the inherent safety of your everyday wall wart.

Torben

Torben · Mar 15, 2007

AllVol said:
Idea/warning: If there is a doubt, and you can't trust the doctors to be truthful, perhaps you should hold up on the batteries. >)

To be sure, have your wife check with some present or former mothers who can advise her with some certainty.

Seriously, congratulations!

Hehe. Thanks! Naw, our moms are both nurses (mine in the delivery room for the first 10 years of my life) and I grew up on a farm, so we're pretty certain about what's up here.

Torben

Torben · Mar 15, 2007

audioguru said:
A tiny amount of power added to each push will add up and make the baby go around and around. The thing should be bolted to the floor!

I would normally agree: frequencies can do crazy things (check out the sinking of the Estonia a few years back--6 inches of water flowing at the right freq sank a superferry).

But in this case, there's something else: I got some C cells and powered the thing up. Listening to the drive mechanism, it does not sound like it's direct drive. It sounds more like a cam bumping either the arm inside the plastic fairing, or bumping another cam. i.e. the device should be incapable of going all the way 'round, regardless of how hard it's driven. There are also positive stops at each end of the swing arc; it would have to develop enough torque to break the stops to catapult the child. I suspect the motor would stall long before that point.

It seems like ridiculously overpowering the motor might at worst make the whole thing just vibrate across the floor, until the motor burnt out or it lost the fuse.

Maybe I'll hook it up to my bench supply (<=33 VDC @ <=1A) and see what the darn thing really does. Of course, this might mean getting a new one.

Torben

Torben · Mar 15, 2007

Oznog said:
How much voltage do you think it'll take to send that baby all the way over the top and back down the other side?

Rather a lot; it's not geared to do that. It'd probably just vibrate and maybe then burn the motor out. The swing doesn't have the range to go all the way over.

Torben

Sceadwian · Mar 15, 2007

I still don't understand why you don't just caniblize local church sales or garage sales and find one of the wind up ones... Your child is going to be much happier with you right there in their face gooing and gaga'ing and makeing a fool out of yourself and just generally interacting. A child that has been kept active while awake will not need a rocker to go to sleep, or to keep them occupied =)

Baby swing power mod

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