Hi,
I'm making a display with 10 x 7 segment LED (4 inch height).
I've been using a table top DC power supply while developing but it will be battery powered in the real situation.
It's been working good with the DC power supply (set to 12V, 600mA) but when I replaced the power supply to a battery pack (8 x AA batteries = 12V), it stopped working (no display shown) and voltage regulators (L7809, L78L33 & L78L05) got very hot.
While running with DC power supply, these regulators won't get so hot.
I have no idea what could be the problem. The power was replaced via a DC jack connector, nothing else is different between the DC power supply and the battery pack.
If anyone can suggest what could be the problem, it'd be appreciated.

I also found that the DC power supply's voltage output shows 9.5V instead of 12V. So I tried the battery pack by removing 2 x AA batteries to make it 9V but it didn't work neither but regulators didn't become as hot as the case of 12V.
That seems suggesting over current from the battery pack but nothing could be powered (LED, arduino, microbit) with the battery pack.

Thanks in advance for your help.

 

Are you sure you're not giving reverse polarity with the battery pack?

 

Are you sure you're not giving reverse polarity with the battery pack?

It was. How stupid I am.
Actually the power line from the DC power supply was reversed. I didn't doubt it.
I think I picked up a wrong extension lead which reversed the polarity.
That means the power connector on the display side is also reversed... (that was lucky, tho).
Thanks a lot.

 

I've been there and done that, except in reverse. Batteries worked, PS made it get hot. Install a series diode for protection.

 

PS made it get hot. Install a series diode for protection.

Thanks, peterdeco, I'll do that.

I found another reversing extension lead at the display side. I think I have done it like that when I first setup and forgot about it. Stupid thing is I should do it centre positive on dc jack connector at the first stage or never forget what I did... (or never trust what I did...)

Thanks a lot again.