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I was inspired for this project by the new, brighter solar-charged landscaping lights that are available these days. They actually put out enough light to illuminate a pathway after dark, so I wondered why I couldn't do the same thing for indoor use?
Most evenings I'm either watching TV or a movie, working/playing on the computer or chatting with friends; none of these activities require a huge amount of room light. Generally I put a light on low just to provide enough illumination to avoid tripping over the cat when I go to the bathroom. I have a pocket LED flashlight with a single 3W Cree LED in it, and it seemed to me that it put out plenty of light for low-level illumination of my living room for those sort of activities. So I created an LED room light with a rechargeable battery in it, and installed solar cells to recharge the battery. I prop the unit outside in the sun when I go to work in the morning, and in the evening it's charged up and ready to light up my living room.
Update: I've been poking around and I see that I'm far from the first person to have this idea -- there are a lot of very nice "sun jar" designs which I was unaware of. I think my room light is different primarily by having a larger battery and solar collecting area, which allow it to drive the LEDs much harder and put out a lot more light. My unit is very esthetically challenged compared to most of the sun jars, but it's much brighter.
Most evenings I'm either watching TV or a movie, working/playing on the computer or chatting with friends; none of these activities require a huge amount of room light. Generally I put a light on low just to provide enough illumination to avoid tripping over the cat when I go to the bathroom. I have a pocket LED flashlight with a single 3W Cree LED in it, and it seemed to me that it put out plenty of light for low-level illumination of my living room for those sort of activities. So I created an LED room light with a rechargeable battery in it, and installed solar cells to recharge the battery. I prop the unit outside in the sun when I go to work in the morning, and in the evening it's charged up and ready to light up my living room.
Update: I've been poking around and I see that I'm far from the first person to have this idea -- there are a lot of very nice "sun jar" designs which I was unaware of. I think my room light is different primarily by having a larger battery and solar collecting area, which allow it to drive the LEDs much harder and put out a lot more light. My unit is very esthetically challenged compared to most of the sun jars, but it's much brighter.
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This is the battery I chose to use; it's available at http://www.all-battery.com/li-ion1865037v2600mahrechargeablebatterieswithpcb-1.aspx. It's a single-cell lithium-ion battery with a nominal voltage of 3.7V and a rated capacity of 2600mAh. What makes this battery fairly unique is that (as can be seen in the picture) there's a small round PCB underneath the plastic sleeve of the battery, which contains an IC that protects the battery against severe overcharge or over-discharge. If the battery voltage drops below 2.5V, the IC disconnects the battery from the load and will only reset when a charging current is detected; if the cell voltage reaches 4.25V the charge current will be shut off until a load current discharges the battery somewhat. Unfortunately these thresholds only protect against severe mistreatment -- they allow moderate abuse to the battery which can pretty quickly shorten the life of the battery. I'd like to find a self-protected battery that keeps itself better protected, say with thresholds of 3.0V and 4.0V, but it doesn't seem like there's anything available.
Because of the embedded PCB, it's not a wise idea to solder directly to the battery (and anyhow that's a lot of heat for a Li-ion battery), so I sprang for a battery holder, and soldered to the leads of the holder instead of directly to the battery.
Because of the embedded PCB, it's not a wise idea to solder directly to the battery (and anyhow that's a lot of heat for a Li-ion battery), so I sprang for a battery holder, and soldered to the leads of the holder instead of directly to the battery.
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I also originally planned to build another one, and show it going together, but contract work is overwhelming me right now and this has slipped down the priority chart. I may not build another one at all, and if I do it will be a while.