Re: microcontroller circuit help

mookiewookie@xxxxxxxxxxx wrote:
Thanks for the input guys. Just to clarify a bit, the chip has two
inputs, the wall and the battery, and its supposed to output 12vdc. I
gave this a shot just now:
Output
^
|
------------------------------------
^ ^
Battery Transformer>12vdc
| |
| |
Charger |
|-----------------------------------
^
AC
With this setup, the smart charger outputs 15V instead of the battery
giving out 12 vdc. I dont know if the charger is at fault here. To get
around this, I thought of putting a chip between the output and the
whole block, which in case of AC being connected will just charge the
battery and power it through the transformer. WIth no AC, the battery
will supply the juice until its voltage drops to a a set point after
which the power is shut off completely. Thats why I was thinking of a
microcontroller to do this with.|

lain wrote:

Oops! I just noticed you wanted 12V out of it.. in that case, you could
try doing the same thing without the inverter! Your 12V circuit will
get power from the car battery when the charger isn't getting power,
and it'll power from the charger otherwise.

- Eric A.




From your description, you want to do the following:
1) Charge the battery
2) Provide power to a 12 volt DC load from the AC mains
3) Switch to battery power for the load when AC is unavailable
4) Switch back to powering the load from the AC mains
when AC power is once again available
5) Protect the battery from being discharged too far

Two questions:
Does that cover everything?
How much current does the 12V load draw?

If I have understood what you want properly, you
need a comparator, not a microcontroller.
The comparator will sense the battery voltage, and
when it drops below a specific point, will provide
a signal to switch a relay or a power mosfet or
bipolar transistor. That will open the circuit
between the battery and the load so that the
battery won't discharge any further. A relay
can be connected to the power supply such that the
load will receive +12 V DC from the supply (which
is AC powered) when AC is available, and from the battery
when it is not available. We need to know what the
load draws to provide a design.

Ed
.

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