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[DPRG] Lithium Ion Batteries from BGMicro

Subject: [DPRG] Lithium Ion Batteries from BGMicro
From: Ed Paradis legomaniac at gmail.com
Date: Mon Mar 29 13:56:34 CDT 2010

On Mon, Mar 29, 2010 at 11:57 AM, David M Wilson <davidmw at tx.rr.com> wrote:
> It is unlikely that a cheap single cell battery pack with a protection circuit will control the charging process like you are hoping.

Ah well, bummer.  I am glad I've been cautious.

I asked recently about outboard chargers, and I've gotten a lot of
great responses.  But now I'm tending towards "on board" charging, to
simplify using my robots.  This year's booth demos have been hampered
by constantly having to babysit my batteries.

So the design goal is the sort of 'fire and forget' charging of Li-Ion
batteries such as we do with cellphones, mp3 players, and laptops.
Charge it whenever you want, however long, and have it be smart enough
to not let you over-discharge or over-charge.

These batteries will handle the over discharge case by popping the
reset-able fuse when the battery voltage gets too low. (Which seems to
be reliable enough for hobby grade detection of over-discharge.)

The over charge case is somewhat handled by the over-voltage, but that
is really a different thing.

Sparkfun uses this chip, the MAX1555, on their product.
http://datasheets.maxim-ic.com/en/ds/MAX1551-MAX1555.pdf

It is relatively easy to solder, being in a pin 5 SOT23-like package.

You cannot buy this chip in Qty 1 from Mouser or Digikey.  You can buy
them from Sparkfun for $4 a piece (seems steep, but see below).

So does anyone have experience with a 'single chip charger' that is
conducive to hobbyists in quantity and package?

Mouser's search says:
TI BQ24090DGQT and BQ24091DGQT  ( 0.5mm pin spacing which is a bummer,
$2.50 qty 1 )
Maxim MAX1811ESA+ ( 8 pin SOIC - not terrible to solder at home, but
these are $4.67 Qty 1 )
Maxim MAX745EAP+ ( switch mode and will do multiple cells, but these
are nearly $12 each and require external circuitry )
Microchip MCP73837-NVI/UN ( 0.5mm pin spacing but gives you status
LEDs and only $1.22 qty 1 )
and it seems like you could probably use ON Semi's MC33341PG if you
wanted to 'roll your own' timing and logic.

Ed

PS: I checked Pololu and they seem to be all NiMH stuff.

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