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I have an old lamp which I would like to repurpose to use LEDs. I'm not really sure where to start so I'm looking for some pointers if this isn't the place. I also don't know how much of this is practical or sensible. Here's my ideal.

  1. I'd like to replace the existing incandescent bulb with LEDs.
  2. I'd like (if possible) to have the lamp battery powered.
  3. I was wondering if it would be possible to have a "charging" plug to charge batteries.
  4. For charging or power I was considering using something plug-able, like a micro-usb charger.

I've done basic electrical stuff (replacing ceiling light fittings is about as advanced as I get), I have a very basic knowledge of electronics, but I'm quite a geek so I'm hoping I can make it work.

I realise I may be biting off more than I can chew but I wanted to get some feedback, if possible.

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    \$\begingroup\$ If you google it, you can just buy LED light bulbs. Ex. ccrane.com/lights/led-light-bulbs \$\endgroup\$ – Matt Young Dec 10 '12 at 15:27
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    \$\begingroup\$ You can purchase an LED bulb for about $11 at Wal Mart. If your lamp shade clips onto the bulb, an LED bulb may not be compatible. \$\endgroup\$ – JYelton Dec 10 '12 at 16:59
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    \$\begingroup\$ If you want to just re-purpose your lamp, go buy an LED bulb. Easy, probably cheaper than you'll be able to build by yourself, and guaranteed to work. If you want to make a battery powered, rechargeable LED lamp, then that's going to be an undertaking. Not that it isn't worth it, but it won't be a quick little project if you have little to no electronics experience. \$\endgroup\$ – Nate Dec 11 '12 at 1:09
  • \$\begingroup\$ This question is too broad to be answered. \$\endgroup\$ – Phil Frost Jun 14 '13 at 20:53
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I'd break this down in the opposite direction. This isn't a full solution, but the two parts can be addressed with googling or looking elsewhere on this site.

1) Starting from the USB charger: that delivers 5v.

2) Battery: Lithium polymer batteries have a 3.6V-4.2V range, and ICs and circuits designed to charge them from USB 5V are widely available. This sort of thing (not necessarily the cheapest option). Make sure your design checks the battery's thermistor.

NiCd and NiMH are the other common battery options, but they also require special circuitry. Lead acid is easiest to charge but not very portable.

3) LED and driver: you could have one big one or lots of small ones. If you have lots of small ones you might be able to drive them directly from the battery (their forward voltage is about the same as the battery voltage), but this is non-optimal. Have a read of this paper from Maxim. Again, there's already lots of stuff on electronics.stackexchange.com about "how to drive LEDs".

If you go for one big one it will definitely need a charge pump based controller of suitable current rating. If it's really big then you need to think about cooling it.

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    \$\begingroup\$ Worth noting some USB chargers deliver less power (watts) than others - some will barely manage 500mA (500mA * 5v = 2.5W) whereas others will supply ~1.2A (6W). Depending on the LED's used this could be an issue. I'd look at a 12v wall-wart and GU16 LED bulbs or any number of 12v car bulbs on eBay in all shapes, sizes, and colours. \$\endgroup\$ – John U Jan 3 '13 at 17:11
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    \$\begingroup\$ Connecting LED's to the battery without current limiting mechanism is a very bad idea. Simply don't do this. I don't say you need a series resistor, but you need at least constant current source mechanism. \$\endgroup\$ – Standard Sandun Jan 10 '13 at 13:48
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Making it battery powered and charging from the wall would be too complex to explain, take it one step at a time! (I actually did this last summer!)

Get yourself a LED flashlight that takes 3 AAA batteries. Discard the batteries and use the battery holder to hookup a wire to the positive side that fits in the flashlight, and your negative wire to the metal case (you might to have to scratch off some paint.) And mount your LED flashlight in your lamp, and feed the wires thru it. Now cut the wires on an old cell phone charger, they usually are 5 volts DC and will only light the LEDs one way. Feel free to have it plugged in while you play with it, 5v won't hurt you, just don't let it short out for very long.

DON'T wire the LEDs to the power cord and plug it in; the LEDs won't last long at 120/240v! ...talk about a flash-bang!

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If you're talking about converting a mains powered incandescent lamp to battery powered LEDs, you will either have a considerable drop in lighting, or will need a substantial battery and charger to get a similar light level for any length of time.

Assuming it's a directional light with a 60W bulb, you will want at least 6W and if it's not directional probably 11w which is quite a load for a low voltage battery system.

If battery power is not important then buy a mains powered ready made bulb.

But if you do want to go battery powered, Your best bet is as John U suggests, buying ready made 12V bulbs; either car bulbs or GU10/Mr16 12v spotlight bulbs and using a sealed lead acid battery and charger. If you've got the space A 2.3Ah 12v battery should give around 4.5 hours with a 6V bulb.

Be warned though: the charger will take the battery Voltage to over 14V so you either need a bulb that will take that (car ones should, but not many cheaper ones state the upper voltage limit), or you will need to regulate the voltage going to the bulbs. You will need a low drop out regulator (LM2940 should do the trick) otherwise the voltage drop across the regulator will take the voltage too low for the bulb when not charging.

If you don't have the space for a lead acid, then you will have to use lithium, NiCad or NiMh and decide whether you're making your own LED arrays and drivers, to run at the standard battery pack voltages (so you can use ready made chargers), or making higher voltage battery packs and charging systems to run the 12v bulbs, but you must use a properly designed charger for the specific battery type, to avoid destroying the batteries, or possibly causing a fire/explosion. Again, it may be worth buying a multi-LED or CREE Cycle or Caving head light, and using the parts to make your Lamp.

Whatever you do, I don't think USB power is very useful to you

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