Need to make a lamp.

[Rodville]

Ok so to a few poor life choices on my part I will not have power till my next pay check (about two weeks) so I need to make a lamp so I am not in total darkness. I want it to run on this Belkin battery backup I got from AT&T that puts out 12v at 3amp max. I have about 90 white LED's and about 100 470ohm  resistors. I want it to be as bright as I can make it to fit into this lamp I got from target a few years ago. I will post pics of it below. The lamp measures 5 1/2 by 3 1/2 by 8 1/4 I was thinking of using a piece of cardboard with LED's sticking out both sides, I have till Monday to make it so any help and insight you have would be awesome. Thanks

[danadak]

Data sheet on the LED, its spec ?

What is amp hour rating on battery ?

Goal for light continuous hours of operation ?


Regards, Dana.

[sokoloff]

You probably want some light as long as possible rather than as bright as possible in such a situation.

Typical Vf on a white LED is just a hair over 3 V. 4 of them in a series string with no resistor is bad engineering practice in general, but should work fine for a temporary knock-up situation like this.

Maybe wire up one string of 4 on a switch and then a few other parallel strings of 4 series LEDs each, so you have a low setting (1 string) and a high setting (all).


Other non-EEVBlog things that I'd consider in such a situation:
1. Borrow money from a friend/relative and turn the power on sooner.
2. Get an extension cord and bum power from a neighbor.
3. Go crash at a friend/relative's place.
4. Find a temp job for that two weeks to try to kill two birds with one stone.

[Ian.M]

How are you going to charge the Belkin Battery Backup unit?   If its the common Belkin RG one, the internal SLA battery is only 7.2AH,  and if you try to use more than about 70% of its nominal capacity, you'll probably kill it. 

Without charging it, starting from fully charged with a good battery, 90mA for four hours a day for a fortnight would be possible - that's about 12 LEDs in four series strings running at 22.5mA.  If the battery is old and tired, you wont get more than 2/3 of that

 How to wire it up with the parts you have on hand depends on the LED characteristics.   At the very least we'd need to know their rated current and their Vf and what current its specified at.   The basic idea is multiple series strings of three LEDs to get a total Vf drop of around 9V then add a resistor to limit the current to each individual string.  The resistor will probably be several of your 470R ones in parallel to get a suitable value.  If you try to use series strings of 4 LEDs without resistors, they'll be bright to start with, but the light output will drop off very quickly as the battery discharges.

Frankly you'd be daft to put it in that light housing - the diffuser just wastes light.   You'd do better to tape three or six LEDs together to the end of a piece of solid copper wire you can bend to aim it where you need it, or bounce the light off the shiny side of a crumpled piece of aluminum foil to diffuse it with less loss.

[soubitos]

and that is why JOULE THIEVES come in handy!
i live in a remote area where power is not something to take for granted!

[Karlo_Moharic]

Use candles

[Nusa]

Last time we had an extended power outage (it's been a few years), we brought some of the solar yard lights for background illumination. Then rotated in others the next day.

For specific tasks needing more light, LED flashlights last quite a long time on basic batteries. We hung one with a flood beam from a ceiling light and it was enough light for us to do a jigsaw puzzle.

And as suggested above, old-school candles in fireproof bases work great, so long as small children and/or pets aren't going to disturb them. Or kerosene lamps, should you actually have any.

If you have a gas stovetop, they can usually still be used if you light them with a match. The electronic ignition is the only thing electric about them.

Clean out your refrigerator and freezer. You may even want to clean it, so it won't smell so bad after two weeks. Either find friends to store your perishable food, or cook up anything that you can consume over the next few days, or toss it.

[cdev]

You might be able to generate electricity from heat if you have gas. Ive heard of people doing that with peltier devices..

On second thought, don't do that. It might be dangerous.

Also, please don't freeze to death? Are your pipes going to be okay?

I have a feeling we're going to see a lot more people in this situation here in the US soon.  (Price of electricity maps to the price of natural gas)

http://www.crai.com/sites/default/files/publications/CRA_LNG_Study.pdf