On Aug 18, 2008, at 3:53 PM, Charlie Wallace wrote:
>> I'm using the TS-7300 with the TS-BAT3 and an industrial touch
>> monitor
>> with a serial output together with a custom quadrature input board
>> and
>> DeviceNet communications module.
>>
>> Of the whole system the TS-BAT3 has given me the most trouble - to
>> the
>> point where I might remove it from the design. All I wanted it to do
>> was give my system a little time to shutdown safely in the event of
>> power being removed while the system was running, but my
>> confidence in
>> the TS-BAT3 doing this long term (3-5 Years) is not high. I may
>> end up
>> using an external DC UPS which would be a shame.
>
> Yes I did get the TSBAT3 working sort of, it'd gracefully shutdown,
> but the charging software drops out now and
> again as i said, so i made a looping script, so no big issue there.
> the problem is that my system may have long
> periods of offline, and its already being fed by a battery, so i'm
> better off using a smart power controller that
> just allows a grace period, sustains cranking voltage drops etc.. i
> don't need the complexity of the extra
> batteries, plus heat is a bit of a concern, as well as the usable
> battery life.
I solved the graceful-shutdown problem a different way.
I used a TS7260 because it has an on-board power supply that allows a
wide input voltage range. Its on-board ADC is conveniently connected
to Vin with a voltage divider, which lets me monitor Vin in software.
I then put 3x 2.5F/5.4V super-caps (in series) across Vin, which gave
me a UPS from 12 V (nominal, lead-acid battery+charging system) down
to 4.5 V or so when the power-supply would give out. You need low-
ESR supercaps for this to handle the board's entire load.
This gave me several seconds of running time depending on what was
plugged into the board (just a USB flash drive in my case).
This cost around $15. I used EMHSR-0002C5–005R4 from Nesscap, but I
see digikey doesn't sell them anymore, so I'll have to find something
equivalent next time.
I wrote a polling-program (userland, not kernel) to poll the ADC
every 100mS, and do a shutdown if Vin dipped below a configured
voltage. Since there was no convenient way to halt the CPU and bring
it back up if the voltage never got low enough to actually shut it
down, I just shutdown my application (separate program), dismounted
all the filesystems and left the polling program running. This let
me re-mount everything from within this program (and restart my
application) if the voltage climbed back up to a preset "turn-on" level.
The TSBAT3 scared me away because it just seemed way too complicated
(and expensive).
Supercaps don't last forever either, but they last a good long time
if they don't get too hot.
No charging programs or circuits, just dump the upstream power supply
straight into the supercaps (which is a very big load if they're
fully discharged).
Works great.
-Ilya
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