the 7812 will work (you are missing some capacitors) but the 7912 will not work. You need a power supply the will have 24v between the +12 and -12.
You cannot connect a negative voltage regulator (7912) to a positive line and get a negative voltage from it.
You would need 2 12v batteries in series to get your +12 and -12 with the center point of the 2 batteries being ground.

Hello. I tried doing something similar with two 9v batteries and 7812. I tried putting the negative voltage of the second 9v into the 7812's ground ( the middle pin ) and it did not work. But after seeing your reply in this thread, I tried the center point of the two batteries, only then did it work.

May I ask how and why this works?


Mod: link to old thread.
https://forum.allaboutcircuits.com/threads/12v-dc-supply-using-9v-battery.42666/post-274807

 

The description of the connections done is not clear to me. Is it possible to post even a pencil drawing of the circuit, but not a wiring diagram?

 

Why do You think that You need a Plus & Minus ~12-Volt-Supply in the first place ?

This is likely to increase the Quiescent-Current-draw of the Circuit way higher than it needs to be,
and shorten your Battery-Life substantially.

A Schematic would certainly help to explain the situation.
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The description of the connections done is not clear to me. Is it possible to post even a pencil drawing of the circuit, but not a wiring diagram?

Hello. So here are the drawing circuits. First circuit is what made sense to me, essentially I pictured two 9v DC batteries in series together to form a bigger 18v battery, thus the negative terminal of the second battery would serve as the "ground"?

Then I tried doing the approach stated from the thread linked here, "use the middle point as the reference". I simply want to know why this works. My understanding from batteries is that the positive terminal should be the one powering the components and the negative is always ground. Please correct me if I'm wrong.

Furthermore the circuit that worked got the second battery hot quickly and the motor stopped working a few seconds after, like 10 seconds. It worked again after resting it for quite a bit of time.

Thank you.

 

Why do You think that You need a Plus & Minus ~12-Volt-Supply in the first place ?

This is likely to increase the Quiescent-Current-draw of the Circuit way higher than it needs to be,
and shorten your Battery-Life substantially.

A Schematic would certainly help to explain the situation.
.
.
.

Hello. I am using a 12v dc pump motor for this project. I hooked up two 9v batteries in series and a 12v regulator to power up the 12v DC motor.

Thank you for your time.

 

A 9-Volt Battery will not run any kind of Motor for very long.

How many minutes do You expect this setup to run ?

9-Volt Batteries are fine for Electronic-Circuits that don't draw very much Current,
but they will fall on their face very quickly with a heavy Load like a Motor.

A small "Sealed-Lead-Acid" ( SLA ), "Gel-Cell", type Battery will be be much more satisfactory,
and doesn't require any kind of Regulator,
and is easily rechargeable.
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Your first diagram shows no connection of the battery to ground. Of couse it dies mot wirk.

The second circuit shows two 9V batteries in series with no connection to the center, as you claimed. Ground is connected to the negative of this combined battery, which is correct. That is why it works.

 

In the second drawing, what is confusing is the connection of the negative of the second battery to "ground" and it looks like the positive is also connected directly to ground, putting a direct short circuit across the second battery. No wonder it got hot!!The connection between the two batteries should not connect to anything else. The circuit works because the regulator is biased with the right connections, so it functions. The motor did not run very long because only one battery was powering it, and the voltage quickly dropped below what it takes to make the motor run.

The TS REALLY needs to study some basic circuitry texts a bit more. That will provide a foundation for getting connections correct.

And the reason that some circuits require both positive and negative supplies, relative to a mid point, is that some electronic devices require both polarities. And I suggest studying from an actual textbook because on line there is a vast sea of incorrect garbage.. Of course some will argue that point.