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firealarmfreak
10-03-2008, 02:02 PM
hey can someone tell me if I would be able to connect a 9 volt power supply for continuous power to my board of education, but also have a 9 volt battery connected to my board of education at the same time?

The reason is so when the power goes out, my stamp will remain usable on battery backup.

However I was concerned that this may cause the stamp to be powered by 18 volts due to the 9 volt power supply and 9 volt battery connected at the same time.

I need to know if the stamp will only use one power source at a time or if the voltages will double and if my idea above will work.

Chris.

Sutton Murray
10-03-2008, 06:48 PM
The Board of education was specifically designed in the way so that only one can be pluged in. Both are not a good thing. I would also like to hear what other have to say about this. Never tried this myself, but in my theory/believe: the battery will quickly get destroy. You will basically be charging the battery with the power supply. Are the battery chargeable? Secondary the power supply does not have the correct charging characteristic.

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For in much wisdom is much grief, and he who increases knowledge increases sorrow." ~Ecclesiastes 1:18

MSDTech
10-03-2008, 07:05 PM
The easiest way would be to use a small UPS unit to power the 9v power supply. This way you have the battery back up without any problems with the voltage fed to the stamp. The ups also has a rechargable battery and the proper circutry to charge it and switch to battery power if the AC goes out. An inexpensive unit is:
http://www.walmart.com/catalog/product.do?product_id=3910294
With the low power drain of the single 9v power supply, you should be able to get a fairly good run time when its on battery.

Geekgirl
10-03-2008, 07:54 PM
ˇYou're makingˇthis more complicated than it has to be. While a UPS is the best way to go, there's a much less costly approach.

ˇIf you put a diode in the + line from the 9V power supply and and one in the + line from the battery (this means you'd need to use a battery connector with leads that you can cut inhalf, not plug it right onto the board clips),ˇˇˇˇ Then whichever is more positive would power the board, but not be able to backfeed the other source.

If your 9v power supply is a quality one andˇregulated at 9v (as opposed to a wall wort that runs higher but drops under load), you should add a second diode (possibly 2) in series in the battery lead to be sure that the power supply voltageˇis slightly higher than the battery when measured at the board.