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Hi Friends,
Here are the requirements:
In a critical setting where equipment are backed by UPS already, we need to monitor all/any batteries that has deterioted/missing and send Signal identifying the bad/missing battery.
Any idea/suggestion will be appreciated.
Regards,
Jyoti Pakrashi
Kolkata, India

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Hello
Considering 12Vcc bateries, make a voltage divider with high value
resitor (to reduce current) in such a way that you will have a maximum
of 5V in the middle of the resitors.
Then use getADC to measure this value and then make a direct-proportion
calculation to find out what you have in the battery
Additionally, add a transitor whith the base connected to a GPIO port
and put the voltage divider on the colector side. This way, you will
have current on the voltage divider only when the transistor is
saturated, ie, when your GPIO is on a high state

Regards

David M.

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> ... add a transitor whith the base connected to a GPIO port and put
the voltage divider on the colector side...

As it happens, I am just finishing a battery state-of-charge monitoring
and switching device. I've found that a voltage divider of 100k over
220k provides a good range for 12v applications, yielding 5v at the tap
for a 16v sense. Unless your device needs to be low-power, perhaps
operated from its own primary battery and using processor power-down
mode, switching the voltage divider current is not necessary - and it
probably reduces the voltage at the top of the divider, adding some
inaccuracy to be corrected.

Also, for _under-load_ battery voltage measurements to be accurate and
revelent, it might be necessary to measure differentially - at both
battery posts, not just the positive post, subtracting the measurements
- to avoid false indications due to voltage drop in the battery ground
lead. And, if you are trying to judge the battery state when _not_
under load, charging voltage might conceal the battery condition. Since
UPSs often do periodic self-testing (but usually without switching the
AC load), it might be possible to sense battery droop during that brief
test period and make your battery-condition judgment then.

If the processor is remoted from the battery location, the loss in the
cabling between them can become important, particularly if the processor
is powered by the battery, due to voltage drop, again, in the ground
line due to current drawn by the processor itself. It might be
necessary to also measure a stable voltage reference - perhaps a 78L05,
placed at the battery end - to use to correct the apparent voltages at
the processor end of the cable; this can be a significant error if not
corrected. If the processor is at the battery end, it is not an issue.

I'm using an LCD-X for this project - a perfect fit in my situation.
http://rightime.com/images/DSCN0133.JPG As long as it is active, you can
see it in live testing here: http://www.ustream.tv/channel/hydralight
Tom

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Stellaris® MCU Family: New Parts, New Package, New Price.


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