Re: How to charge a 9V Ni-MH

On Tue, 01 Jan 2008 17:08:20 -0500, Fred Bloggs <nospam@xxxxxxxxxx>
wrote:



Fred Bloggs wrote:

He can add a 9.1V zener reference diode and automatically taper it off
to float charge at full charge of 1.4V/cell, like so, the series diode
prevents battery discharge on loss of line power. At 15mA, the 1.7V will
be enough headroom for the '317:
View in a fixed-width font such as Courier.
.
.
.
.
. -----
. +12 -+----|LM317|-----.
. | ----- |
. | | [82R]
. | | | 1N4148
. | '--------+---|>|----> To NiMh +
. | |
. | |
. +|10u |
. === | 1N5239B
. |16WVDC -/ 9.1V
. | ^
. | |
. | |
. | |
. | |
. Gnd -+----------------+----------> To NiMh -
.

The characteristic is sharper with the bigger diodes, and it is more
likely to withstand a momentary reverse battery connection with a wimpy
150mAH NiMH...all available from Radio Shack.

View in a fixed-width font such as Courier.

.
.
.
.
.
. -----
. +12 -+----|LM317|-----.
. | ----- |
. | | [82R]
. | | | 1N4001
. | '--------+------|>|-------> To NiMh +
. | |
. | |
. +|10u |
. === |
. |16WVDC | 1N4739
. | -/ 9.1V, 1W
. | ^
. | |
. | |
. | |
. Gnd -+----------------+----------------> To NiMh -
.
.

I doubt that any off-the-shelf zener is accurate enough for long
battery life.

I'd use a TL431 (or CMOS equivalent) and a pot.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave
.

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