1
\$\begingroup\$

I've built a play kitchen for my kids and would like to make the stove and oven light up.

It's been a long time since I've done electronic tinkering so wanted to check I've done my homework right.

The plan is to take a red 12V LED strip, and divide it into 4x 50cm lengths that I'll coil to make 4 stove burners. The "burners" would be operated by 12V PWM dimmers to connect to a dial.

As this work is definitely in the hobby space, I would prefer to be battery operated than connected to mains.

I've seen various articles about driving 5M 12V LED strips on 8x AA batteries, so I'm thinking that I should be able to use this, but like I say, want to check my math.

The LED strip I've linked above says it's 20 Watts, but I'm reading other things that suggest a 5 meter strip is more like 24 Watts, so conservatively, I'd expect each of the "burners" which is 1/10th of the 5M strip to run at

$$24\text{ W} / 10 = 2.4\text{ W}$$ $$2.4\text{ W at }12\text{ V} = 0.2\text{ A}$$

So in theory, since AA's can do 2 to 3 amps the 8 AA's should be able to support all 4 burners? I was thinking I'd need to hook the "oven" (30cm LED strip + 12V fan from an old PC power supply) off a separate battery pack, but it seems like maybe I could hook everything up to the one?

Although I haven't factored in the dimmers and I assume they'd have some resistance which would increase the current needed but not enough to cross 3amps?

Is this all right? Is there anything I've overlooked or misunderstood?

\$\endgroup\$

1 Answer 1

3
\$\begingroup\$

since AA's can do 2 to 3 amps

No, not usefully. When short circuited, and for seconds, perhaps. Assuming you mean alkaline primary cells of course, as 8 give you nominally 12 V. If you mean 10 x NiMH, see further down.

If you want them to output a useful voltage, and have the toy last 10s of minutes, you're looking at the low 100s of mA.

Run the whole thing from a 12 V output wall-wart power supply. Although it is 'connected to mains', if it's CE marked (or the equivalent), the low voltage output is as safe as batteries for all practical purposes. Safer than batteries in fact, if they're nickel, lead or lithium, all of which can deliver fire-starting currents if short-circuited.

You'll also get a stable 12 V from a power supply, whereas batteries deliver a variable output voltage as they discharge. 8 AAs alkalines will give you from 12.8 V when new down to about 8 V, depending on what you want to call end of life.

NiMH output is much more stable, 10 will give you more or less 12 V over their discharge life, and AAs will deliver amps. The pack needs to be fused, to protect the wiring against short-circuits. NiMH are fairly tolerate of over-discharge at the cell level, and don't suffer damage even down to 0 V per cell. A battery OTOH could reverse charge the first cell to give out, which does cause irreversible damage. With a few cells in a battery, setting a 1 V per cell limit on the whole battery pack generally works. With 10 cells, this is not tight enough, and you may need to monitor each cell voltage individually, or do coulomb counting for end of life.

Given that they will have to be charged, and fused, and protected from over-discharge, I think I'd still be inclined to simply use a 12 V plug-in power supply than a 12 V NiMH pack plus charger.

You are quite right not to contemplate making your own DIY connection to mains.

\$\endgroup\$
4
  • \$\begingroup\$ Thanks. Yeah, i was thinking NiMH \$\endgroup\$
    – ChrisJ
    Sep 1, 2021 at 10:52
  • \$\begingroup\$ Thanks for the extra details on NiMH. Yeah, after what you've said I'm leaning towards a 12V wall converter. Would I be fine to run the 5 parallel circuits off that, or should I be looking at a 12V LED river with multiple outputs? \$\endgroup\$
    – ChrisJ
    Sep 1, 2021 at 11:13
  • \$\begingroup\$ The LED strips you've linked to contain their own current limiting, so need a 12 V supply of power, not 'LED drivers'. If the wall brick has sufficient output current, run them all from one. \$\endgroup\$
    – Neil_UK
    Sep 1, 2021 at 12:27
  • \$\begingroup\$ In the spirit of this answer I can also recommend a 12V USB power bank/battery brick that comes with a barrel connector for 12V output. You'll get reasonable battery life and it'll come in handy for other uses as well. If you google for "Rechargeable 12V DC Output Lithium Ion Battery Pack for LED Strip" you'll get some pretty specific results \$\endgroup\$
    – nvuono
    Sep 1, 2021 at 15:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.