Wiring for Battery and/or Transformer Power

Thread Starter

George Langley

Joined Mar 7, 2011
7
Hi all. Want to power a 12-volt motor, with the option to use batteries (eight AA) or a transformer.
I'm assuming the schematic attached will work for one or the other. My concern is if I have batteries in the box, and then plug in a transformer, will that create an issue? Would that put 24 volts on the line? Or risk overheating or blowing up the batteries? Do I need some diodes, a relay or extra wiring to make this work?
Have searched the internet and this forum, but no luck.
Thanks.
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dl324

Joined Mar 30, 2015
10,998
How much current does the motor require.

If the batteries aren't rechargeable, you need to use a power jack that disconnects them when using an adapter.
 

Thread Starter

George Langley

Joined Mar 7, 2011
7
Thanks Dennis. (My first time building something not just battery powered or tapping into a pre-existing power source.)
Current is 60mA no load, 150mA load, according to the spec sheet for the motor I'm looking at (https://www.digikey.ca/products/en?keywords=108990017).
So to confirm, using a "switched" jack, batteries would connect to pins 2 and 3, normally closed. Then inserting the plug of the power adapter physically disconnects that circuit and connects 1 and 3 to the adapter, correct?
I read it's also a good idea to add a diode as a backup should the mechanical switch fail.
 

Thread Starter

George Langley

Joined Mar 7, 2011
7
Think this will work.
Question: is the diode required, and in the correct location/orientation, to protect the battery pack from accidental charging should the 2-3 contact fail to open when the adapter is plugged in?
Thanks.

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