Electronics question

wsmahan · 12-02-2007, 01:58 PM

Any one know how I would go about applying power to a battery pack? What I have is a small hand gun safe that seems like when I want to get in it the batteries are dead and I have to use the key. What I would like to do is tie in a plug in power supply to it. My question is how would I do that? Do I just need to add a diode inline to prevent the batteries from back powering the battery charger? Any help would be greatly appreciated.
Thanks
Wes

fish_on · 12-02-2007, 02:07 PM

how many, what type, and how are the batteries wired (series or parallel)? You could take a 3V 5amp power supply cut the end off and wire it to the battery terminals in the safe.

wsmahan · 12-02-2007, 02:41 PM

There are 8, 1.5V batteries in series for a 12V system. I would still like to leave the batteries in there. I would convert over to rechargeable batteries. Thanks

fish_on · 12-02-2007, 02:46 PM

Probably isn't a solution for using rechargeable batteries and continuously supplying power to the system and charging the batteries.

wsmahan · 12-02-2007, 03:00 PM

Thanks, maybe I will just put a plug in system so that when it is plugged it it removes the power from the batteries to the safe and restores it when the plug is removed.

StickFish · 12-02-2007, 05:42 PM

Diode would do what you want, unless you wanted to set it up to trickle charge. Either that or get real religious about changing the batteries

wsmahan · 12-03-2007, 08:41 AM

Trickle charge would work for me. Why would it not work with a diode in it that is fwd biased when power is applied and would be reversed biased when the power is removed?
Thanks
Wes

Gus Orviston · 12-03-2007, 02:55 PM

If you just use a diode, how it will operate assuming your external voltage is set correctly (Less than max battery, more than minimum system requirements). Then the batteries will eventually die and then the external power kicks in.. and they will cook the batteries that don't want to be charged - assuming alkaline.

If you use LION , or Nicad, same thing will happen XOR ;-) , you need to know the charging current of the batteries and have a constant voltage with a resistor to set the correct trickle current or you cook them too, or create a constant current source. none of these is as simple as using a diode.

What is the factory spec for battery life and the current draw, battery type etc.. . I would check the circuit to see what leakage is going on. Try some industrial quality batteries with low internal resistance.

gus

DAB · 12-03-2007, 08:24 PM

Just get a good power supply ( not a charger ) of the correct voltage and amps. cut the battery pack off , hook up power supply ***. to *** . and neg to neg and you wont need any batteries at all.
DAB

jvp · 12-04-2007, 05:35 AM

i would be more concerned with why the batteries are always dead. i have never changed the batteries in a year and a half and mine is still fine.

wsmahan · 12-04-2007, 02:36 PM

Thanks for all the replies.
Wes