Peakfoto Digital Photo Still n Video wrote:
thanks for your help n ideas again.
have a circut daigram for this ?
The circuit is simple. For free, you get one of my bad old ASCII
schematics. :-) View with a fixed width font like Courier:
cell+________|\|______ ___collector
| |/| | |
+__|__ LED _|_ |/ optocoupler
___ _\_/_ | (4N35 etc.)
- | R1 | |\
cell-__|_____/\/\_____| |___emitter
The LED inside the optocoupler has about a 1.1v drop. Pick the other LED
to get the Low Cell Voltage threshold you want. The color of an LED
determines its voltage drop. For example, a red LED has about a 1.6v
drop. 1.7v + 1.1v = 2.8v so you get a Low Cell alarm below 2.8v.
Pick resistor R1 to limit the maximum current the LEDs get at the
highest cell voltage you expect. The LED voltages will rise 0.1v or so
at this higher current. For example, if you expect 4v, and want to limit
the current to 10ma, then 4v-1.8v-1.2v = 1v will be across the resistor.
For 10ma, R = V/I = 1v / 0.01a = 100 ohms.
The isolated collector-emitter outputs are all wired in series. Connect
them all across +12v and ground with an LED in series. This LED will be
*on* cell voltages are good, and *off* if any cell voltage goes low.
If you would rather a light that is normally off, and turns on when a
cell is low, then add a transistor to invert it. Like this:
_________________+12v
|/ c |
| first |
|\ e |
: opto- >
: coupler > 10k
|/ c >
| last |
|\ e _____|
| Q1 | |
|_____|/ c _|_ LED lights
| b | _\_/_ when any
> |\ e | cell is low
> 1k | |
> | gnd
| gnd
gnd
Q1 is any common NPN transistor (2N4401, etc.) The 10k resistor
determines how bright the LED is when it is on. The 1k resistor sets the
sensitivity; 1k needs about 0.6ma from the optocouplers to turn the
light off.
--
Ingenuity gets you through times of no money better than money
will get you through times of no ingenuity. -- Terry Pratchett
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/projects.htm
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