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.

 

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.

 

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.

 

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.

 

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.

View attachment 206534

Yes it's correct, i would use a Shottky diode as they have a drop of of approx 400mV.

 

Thanks. Much appreciated.