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Thread: Rechargeable lantern

  1. #11
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    They look good. They will restart charge if voltage falls below some preset threshold, and handle deep discharges too. What did they cost?

  2. #12
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    Umm... well, they were free samples from TI. That's a very nice service from them, but I hope people don't start abusing it. I also took the opportunity to get some http://focus.ti.com/docs/prod/folder...t/tlc5940.html and a http://focus.ti.com/docs/prod/folder...ch010512d.html

  3. #13
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    I want to get some log amps from them but those aren't in the free sample program. They cost a bit..

  4. #14
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    You ever thought of doing a HID (High Intensity Discharge) lantern / torch?

    They're just starting to appear commercially and there's nothing brighter that I know of. Could be a good challenge for the next one.

    http://www.hids4u.co.uk/product.php?...&cat=60&page=1

  5. #15
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    Quote Originally Posted by The_Doctor View Post
    I'm going to rephrase this. I'm not implying it might explode. This isn't a careless suggestion, you should always test Li ion systems with full caution if you set up a new one. Saying this doesn't mean I think it will go wrong, you just have to be rigorous.

    So you can't just use a lower current, with a higher resistance. And using 3.6V isn't going to put any significant charge to a 3.7V cell. I suggested 3.8V in my post, because that will. The voltage will closely approach the 3.8V value and never reach the normal 4.2V upper limit used in most fast chargers (note, those switch off the charge at that point). That means you can leave it connected indefinitely. It might be best to use a current limit resistor to limit initial charging current to 400 mA, but with the small difference between cell voltage and 3.8V you might not need one. It won't be a fast charger but it will be a safe one. But that upper voltage is critical. You might improve performance with careful adjustment to 3.9V, but it must be strictly controlled, and never reach the full 4.2V unless your charger has an auto-switchoff if it gets there (either that or strict current limiter). I think using an LM317 regulator is best, because it's far easier to set a safe value than to try to 'economise' with a simple zener circuit. And if you wire it with an adjustable pot, make sure the Adj pin goes LOW, if the pot wiper fails, not high or open circuit, otherwise the regulator output voltage will go high.


    EDIT:
    http://www.batteryuniversity.com/partone-12.htm
    That confirms a strict limit of 4.0V (4.05), stating that trickle charging causes risk to safety by plating metallic lithium if the voltage exceeds this. I suggest 3.8V to leave a margin, as temperature affects this. That page says 3.8V lets you get around 50% charge, but that's good, it's close to the 40% for nominal best storage life. Anyway, this is about the only way I'd consider leaving a Li-ion battery on a constant maintenance charge.

    Small followup to this..
    I've since found the MAX1555 Li-ion/LiPo charger IC. That doesn't stop charging once the charge indicator changes to show full charge. Instead, it limits current with a sharply falling curve as the voltage reaches 3.9V, ending at zero amps at 4.2V. Meaning that if the battery voltage rose while on standby, the current would rise sharply to prevent that, so it wouldn't really happen. So my LM317 idea (bigger, but cheap and easy for people not used to surface mount parts) will work fine so long as you set an upper limit of 4.2V. Or 4.1 if you want to be extra sure. The margin doesn't have to be as wide as I first thought. The only difference in performance between the Maxim IC and the simple LM317 circuit is that the LM317 circuit is regulating voltage not current so the current falls off earlier during charge as it approaches the set voltage, so it takes longer. It's ideal for a cheap standby always-on charger though, if you have one ready and nothing better.

  6. #16
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    Quote Originally Posted by The_Doctor View Post
    I want to get some log amps from them but those aren't in the free sample program. They cost a bit..
    Are you still looking for log amps? I found 5 AD8304ARU and an eval board in the trash. Don't know if they work, but they appear to be unused.

    On another note. I got some SSC P7 LEDs yesterday, damn they are bright! They need a bloody big heatsink as well.

  7. #17
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    Oops.. better late than..
    I got some eventually. Still haven't used them either! I'll get round to it though. Thanks for the offer though. Keep them, I don't think there's such a thing as a cheap log amp so they should come in use whatever they be. AD8304 is different from my needs I think, I chose LOG112AID because they're the closest I found to the kind of thing Bob Moog was doing..

    This thing with LEDs and big heatsinks is curious, not as efficient as they ought to be, perhaps. Maybe there's a tendency to spec them like TECs driven at Qmax. Like TECs, I suspect it really pays to mount more and run them at 700 mA where the Imax is 1A. Makes for long life too.

  8. #18
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    Quote Originally Posted by nehasharma View Post
    India's first eco-friendly rechargeable LED study lamp
    ...is marketed by spamming douchebags like you

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