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Old 5th May 2008, 05:04 AM   #11
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Join Date: Nov 2004
Location: Florida
My LEDs get warm on the flashlight. Their spec says 3.3V nom, 3.6V max. I'm drving them with at most 3.4-3.55V. As long as they are not really hot, is it Ok to have warm LEDs? I have them on a 10ohm resistor each from the 3.7V cell, and they run nice and bright.

Will they last long still if they are warm?
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Old 13th May 2008, 05:46 AM   #12
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I just got my Maxim 1551/1555 Samples! Oh my these are tiny! I'm so glad you told me about these IC's!

The LM317 regulator is working great as a charger so far, but I'm very delighted to get these chips.

But now that I have these, it could be a lot easier to make a smaller (and more precise) charger.

For a typical charger, the Maxim chips need 5V, I'd just use a 7805 or a 5V AC adaptor to get that. I was also thinking of using a PNP CCS Transistor as a current booster for the Maxim chip to make it capable of charging much more than 100 or 280mA.
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Old 29th May 2008, 03:38 AM   #13
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Default This is getting fun!

The Mini Maxim chargers are really good, they charge to a good voltage (4.16 avg, 4.19 open V) and charge the cell quickly.

I also found other ways to use these chargers. I designed and made 2 so far using the 1555. I made them 12V since more it's easily found than 5V sources, and you can use them from a car battery or cig lighter.

The first charger uses a heatsinked-7805 from 12V to feed the Maxim 1555 the 5V power into the DC pin for about 250-280mA. It runs a bit warm. I have a LED on the CHG pin and it comes on when a battery is connected. It shuts off when fully charged! I've used it to charge my extra Li-Ion cells and it works good. However, I wanted more charge current for bigger 18650 cells.

The second charger has a 650mA output and also runs from 12V, and uses the 100mA USB lead of the Maxim 1555 +7805 to drive a PNP 650mA CCS. The Power PNP adds extra charging current for the battery, disspates the majority of the power, instead of the IC, and it follows the voltage of the IC chip, maxes out @ 4.18V. The Maxim chip runs much cooler using the 100mA input, so the chip doesn't run as hard and hot as normal use. The CCS only comes on if the Chip uses over 65mA, so when the battery is nearing full charge, the CCS shuts off, and it's being charged by only the Maxim IC at lower currents. I also used a LED for this charger, and it works as well. However, the 80W Power PNP gets HOT and I need to mount a suitable heatsink. If I get a good enough heatsink, I may mod it for more current 1-2A.

I love how these chips can run other circuits. It saves complexity, parts count, and is reliable to charge at the right voltage.

I used a IC-chip Circuit board for ease of use and mounting for both chargers.

I haven't yet used a chip for another flashlight yet, but I plan on making a small board for them.

Thanks Anonymous1 for the helpful tip on the Maxim chargers. Hopefully many DiyAudio members can benefit from this, esp since Li-Ion cells are hard to charge properly.
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Old 29th May 2008, 03:46 PM   #14
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Default Li-Ion Charger Schematic

Here's a schematic for the 650mA Maxim-Based charger

Enjoy
Attached Images
File Type: jpg 650maliion.jpg (25.8 KB, 61 views)
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Old 29th May 2008, 04:59 PM   #15
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Fixed a few minor errors

updated schematic
Attached Images
File Type: jpg 650malich.jpg (27.3 KB, 57 views)
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