Let's Make Robots!

Relay control with arduino

Hey everyone 

I am making a circut to power my APRS from 2 batterypacks. one batterypack is backup incase the other batterypack runs out. my APRS takes 12V and it works with the battery pack with a transistor to give it exact 12v or else it will be damaged. anyway I am tryna setup a relay with the arduino that can switch the power from one battery pack to another one. what relay should i use and anyother components i need with it, but i have to keep it 12v to the aprs cant go above it, and can you give me the link that is available in radioshack cause thats were i will go to get it. i need to finish this project and in a hurry. :S

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Why not hook the batteries up in parallel, watch the voltage level, and recharge them when need be?

because the project I am doing these is no way for me to recharge them. I am doing the weather balloon project. so need backup battery pack for the tracking system.

that paralleling the batteries should work and be easier than constructing a circuit to switch between the packs.

I hope someone that is more knowledgeable will chime in on this topic.

I have read (not I'm 100% sure) that when paralleling the batteries, if just one battery is slightly less charged, high currents will be flowing from the other batteries to that cell because they try to charge that battery up.

In general paralleling battery packs is not a good idea, at least without some sort of monitoring mechanism.