backup battery

edlikestoboogie

I haven't seen any schematics for a backup battery for microcontrollers. Say if you are keeping time with your propeller, you wouldn't want that data being erased, when a blackout occured. How do you implement a backup battery like that?

AHMET AKSU

I trying same thing.there are same supervisor ic from maxim max 807 and some other ic.this ic measure the voltage of
circuit and charge the battery when it lows from the charge voltage .but in turkey these ic hard to find.I m thinking abaut that
propeller can measure voltage with adc and can decide abaout charge

Basil

Hi [noparse]:)[/noparse]

How long would you need to hold power to the prop?

It was suggest for a project I am working on to use a super cap. You could use a 4.7F cap which should keep the power up for a while.
I dont believe you'd need any additional circuitry for this either.

Of course, this wouldn't hold power up for hours, rather a number of minutes.

deSilva

I found a 3,3 F cap for 3 Euro and a quite astonishing 22 F cap for 6 Euro...
But attention, not all are rated for 5 V some are only for 2,5 V !

Post Edited (deSilva) : 6/26/2007 10:11:21 PM GMT

edlikestoboogie

no, sorry that won't do, a power failure might last for a few hours, I need a circuit involving one of those mini disk- shaped like cell batteries, that could keep the propeller running. Similar to how a PC's motherboard keeps system time even while the computer is off by using one of those type of batteries. Only, I need to not only keep time, but maybe run some instructions to handle events, thus I need the prop fully running while the main power supply is out.

AHMET AKSU

I think batteries better when long time needed .But interfacin hard .are there any way to do that
one cog of propeller check voltage of battery and when its below the charge voltage statrt the charge

codemonkey

Wouldn't the cap give you enough time to do something to switch the battery? What about a relay that's held on by mains power and when that goes off it automatically (because there's no more power) switches to battery backup and the cap holds you running during the switchover. Maybe?

AHMET AKSU

I think when power goes out by diodes sytem start to eat from battery and when the user press the shutdown buton the hero relay must cut the power which comes from battery

sharpie

Or if your goal is to have a backup source for a realtime clock only(may be useful to some).... Use a clock chip(ds1307 and the object exists for the prop) that has provisions for a battery... Sparkfun has a breakout for one...

http://www.sparkfun.com/commerce/product_info.php?products_id=99

Basil

Ahh ok.

Im using something which I think is similar in my rocket controller.
I have 2 batterys and a big cap.

The prop can draw from both batteries while running(or 1 if only 1 is installed). When the high current pyro's fire, they can only draw from the main battery and the prop still runs off the 2nd battery. This prevent brownout's.

Only problem is, both the main and secondary battery need to be the same voltage as they are in parallel.

I will post the schematic when I get home if your interested?