# Safety of a very basic project

Joined Dec 8, 2015
4
Hello,

I am a student with an interest in physics but sadly little understanding in electricity. I have some concerns about this little project i have in mind.
Given time I will gladly read through the education part of this webside, but i just made an account to get some experienced opinions.

A friend of mine told me she'd like to have a little night light, one of those who project stars onto the ceiling. So I'd love to make one for her.

My idea (of which i will attach an outline) was that i take a piece of wood (got some ash lying around) to make the frame of. In which I will cut an big hole for the top part of a flashlight for the light and another one one on the bottom where i thought i'd store the battery.

For the stars i'd go to a copy shop and let them print me some colorful tranperent foils to lay on top of the flashlight. I have some good ideas for that part.

Now for my question.
My biggest concern is if it is safe to store a battery (i'd use a 9v block or AAs) in a piece of wood. I'd really hate to burn down her house.
Would i need a resistor for this?

Some other thoughts where that i'd like to use a led flashlight (because of the white light and the low power consumption) but i don't know if they have a board in them and whether this would be located in the top part that you can take of when changing the battery, where the leds themselves are. If not then it wouldn't work when i just bring some cables to the parts where the power usualy connects. Am i right?

I have little to none experience dealing with projects like this, so I kept it as easy as I could.

Thanks to all of you in advance,
Alex

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#### GopherT

Joined Nov 23, 2012
8,012
This is a basic electricity project. You just need to open the flashlight and find the answers to your questions. An LED cannot be connected directly to large batteries (9 volt or AAs). You need either a circuit to limit the current or a simple resistor. We can help you with the size when you get there.

Very small button cell batteries do not always need a resistor because they have fairly high internal resistance and current is kind of self limiting when an LED with 2 volts or more of forward voltage is needed to light them.

I doubt you will have so much trouble with a simple LED circuit and a 9 volt battery that you will start a fire. However, I appreciate your concern and, in general, wood is not a preferred material because of your concern. You should buy a "project box" made of fire resistant plastic or sheet metal. Your idea of using an LED flashlight is good.

Another idea you can use is to add a small crystal or "fly's eye" lens to the flashlight to make dozens or hundreds of stars on the ceiling.

#### BR-549

Joined Sep 22, 2013
4,938
Mount your half sphere film frame with a small clock motor. The stars can turn with the minute rate.

Joined Dec 8, 2015
4
Thank you for the fast replies.
I am glad to hear that there arn't some major errors in my idea.
I don't have the flashlight right now and it could be taking me a few days to get to a shop to find one i like. I will update the minute i have it in my hands.

I'd like to stick with the version with the AA batterie(s) or the 9v block if it only takes a resistor to make that work.

I had thought about adding a motor to make it spin, but i didn't know how to do that on my own.

My next step will be to look for a fitting flashlight. In that process i will look for such a tool box as you mentioned. Honestly I have never seen such a thing, but if i don't find one and wood really isn't an option at all i have metal to work with at home.

Thanks again for the replies : D

#### AnalogKid

Joined Aug 1, 2013
8,487
I agree that AA batteries are not a fire hazard. But if you want a wooden external box because of its look, you can put the electronics in a plastic project box inside for protection.

ak

#### Alec_t

Joined Sep 17, 2013
11,388
If you do opt for a metal box, make sure that circuit components are spaced from the box wall, or have insulation, so that short-circuits don't occur.

#### BReeves

Joined Nov 24, 2012
410
A wooden box will be fine, manufactures put a lot more electronics in stuffed toys than you are talking about.

Joined Dec 8, 2015
4
I'm happy to hear that. I guessed that it's possible to do it because of said reason with stuffed toys and so on, but i was worried that i produce a short circuit that could lead to higher temperatures.
But with you on my side i guess everything will work ouf well : )

I just found a led flashlight at home (which i won't use since it's not mine). I examined it and found that it has two C batteries with 1.5V each.
So if i don't want it to shine as bright, because it should not light the room but just project the stars neatly, I could use just one AA with 1.5V
Is that correct?

Also I'll probably have a flashlight by tomorrow.

#### BReeves

Joined Nov 24, 2012
410
Where are you located, just received a flyer from Harbor freight with a coupon for a free 5 LED flash light. Think it runs on one AA or maybe two AAA batteries.

#### Bordodynov

Joined May 20, 2015
2,623
Good AA battery has a capacity of 2000 mAh. 5 diodes consume 5x20ma = 100mA. Boost converter 1.5V -> 3.5V consumes about 3.5 / 1.5 / 0.7 * 100mA = 330mA. Working time 6hours. It is not enough for the night.
Battery Type C is 10 times more capacious than AA.

#### BReeves

Joined Nov 24, 2012
410
Good AA battery has a capacity of 2000 mAh. 5 diodes consume 5x20ma = 100mA. Boost converter 1.5V -> 3.5V consumes about 3.5 / 1.5 / 0.7 * 100mA = 330mA. Working time 6hours. It is not enough for the night.
Battery Type C is 10 times more capacious than AA.
True but he can replace the AA or AAA batteries with D cells as long as he stays with the same number and connections. I think without a coupon that flashlight can be bought for $2.00. Here ya go, a 27 LED light that runs off 3 AAA batteries for$3.99.
Says it will run for 48 hours
http://www.harborfreight.com/27-led-portable-worklightflashlight-62532.html

Joined Dec 8, 2015
4
I just got the flashlight. It has 10 diodes and is meant to be powered by 3 AA batteries. I found out where the points for connection are.

Why i like this one especially is because it doesn´t have a switch but shines when you screw the top all the way onto the handle. I think that´s a cool feature to have on the finished project.
Also it has this thing where you put the 3 batteries in and then has 2 poles. It kind of makes 3 batteries into 1. This will be useful i think.

Is there a way to make the battery live longer by turning down the light?
She won´t have it running all night, she´s older then me and doesn´t need it to not be afraid but because she likes the stars on the ceiling, but still i think it would be a good idea to dim it down so it is not to bright and can shine longer.

If i add a clock motor, would it be a parallel or series curcuit?

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