Battery performance & heat

Ideas and questions about MintyBoost kits

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RichieD
 
Posts: 1
Joined: Mon Jan 22, 2007 4:07 pm

Battery performance & heat

Post by RichieD »

Thanks for a great project, takes me back to being 13 years old when I last played with this stuff ( a long time ago ) when I built a transistor radio into a soap box. I think it emitted a squeak then nothing.

My Minty tested out fine and I have used it with my Samsung YP-U1 Mp3 player and Motorola V3 ( with modded cable). I have, however had strange experience with batteries. I first tried NIMH batteries charged up a few weeks earlier. After a while it stopped charging the Samsung player, though output voltage still showed 5+ volts. and input voltage ( without load ) 2.5 + volts; each battery showed 1.23v tested individually. When it was connected the input voltage showed 1.23v and if I tested across each battery in turn, one read 1.23v and the other -.05 t0 -.10.

I then tried new Lithiums, nice and light and a full 3v input. But when it stopped charging one battery read .47v the other 1.15 and combined input 1.5. output still 5.02. Is it normal for the batteries to discharge at different rates and when will the Minty stop charging?

I re-checked all the solder joints and redid 2 or 3 to be safe. I inserted new Lithiums, have charged the MP3 player fully but on charging the phone it gets to 4 bars out of 6 and at that point Minty, batteries especially, gets very,very warm so I unplugged it. Still shows a healthy 3v ( 1.5v each )input and steady 5.05 v output, so maybe there was a bad joint, but the heat now worries me. I also disconnected R5 at the outset as I thought that maybe the problem I had originally with charging, maybe I should put that back.

Ideally I would like to use re-chargeables but will have to test again to see how they perform.

Richard

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Post by adafruit »

when charging a devices thats drained, the batteries will get -quite- toasty (drawing half an amp from each!)
the input voltage can be as low as 1.8V i think, maybe 1.2? but there have been reports that some devices dont like to be charged past 50% or 80%
one thing you can try is the resistor hack documented on the page (for v1.1) maybe that will make a diff?

Illuminum3415
 
Posts: 21
Joined: Fri Jun 22, 2007 12:11 pm

Post by Illuminum3415 »

according to the spec sheet for the Max756 the Vin limit is 0.7V

its incredible it can still achieve the 5V Vout :shock:

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