# I have a 12v wall power supply, but need a 9v power supply - how to change 12v to 9v ?

#### Lumenosity

Joined Mar 1, 2017
634
I have a 12v wall power supply, but need a 9v power supply

Is there an easy way to change the output from 12v to 9v by simply adding a resistor?

#### GopherT

Joined Nov 23, 2012
8,012
I have a 12v wall power supply, but need a 9v power supply

Is there an easy way to change the output from 12v to 9v by simply adding a resistor?
What kind of power supply is it?

#### Audioguru

Joined Dec 20, 2007
11,249
You did not say if the 12V output is AC or DC and did not say if you want 9VDC.
If you use a resistor then the output from the resistor will be 12V if its current is low and the output will be near 0v if its current is high.
You did not say how much current you need at 9V. If you need 9VDC at up to 1A then use a 7809 voltage regulator IC with the input and output capacitors shown on its datasheet.

#### Lumenosity

Joined Mar 1, 2017
634
Sorry.

I need 9V DC output.....1Amp

The power supply I have is 12v 2amp output. The 2Amps is ok. I just need to lower the voltage.

It's just your basic Wall Wart common 12v Power supply that you might get with a modem or other device.

#### GopherT

Joined Nov 23, 2012
8,012
Sorry.

I need 9V DC output.....1Amp

The power supply I have is 12v 2amp output. The 2Amps is ok. I just need to lower the voltage.

It's just your basic Wall Wart common 12v Power supply that you might get with a modem or other device.
How accurate does the 9v have to be? How accurate is the 12V?

If 9v is approximate, you can just put 4 diodes in series on the 12v output.

#### #12

Joined Nov 30, 2010
18,223

If you only need 9 VDC at 1.0 Amp you can also buy a LM7809 regulator for about $1.00 USD. With 12 VDC available you don't even need a low dropout regulator. Ron Thread Starter #### Lumenosity Joined Mar 1, 2017 634 Or you could go to a second hand store and buy a 9V wall wart for$1
I have about 10 pounds of wall warts which accumulated over the years, but I don't suppose you want to wait a few decades for your junk box to get full.
I know. I have probably 100 of them in boxes here and there but after going through ALL of them, I can't believe that I don't have a single 9V Wall wart....tons of 12v ones tho. But I can ASSURE you....when I was looking for a 12v wall wart a few months back....I couldn't find a single 12v Wall wart either among those 100. I have no freaking CLUE how that happens. I could have 1000 and not have THE ONE I'm looking for.....lol

I'm just being impatient. haha. Got an Arduino R3 CH340 board today and wanted to test it out.

#### Lumenosity

Joined Mar 1, 2017
634
Thanks for all the replies.

You guys are the electronic BOMB !!!

lol

#### Audioguru

Joined Dec 20, 2007
11,249
I have a very cheap Chinese wall wart that came with a product. It is labelled 9VDC at 100mA which measures correctly. But its output is a little higher than 18V with a low load current and it gets hot even without a load. It is not certified to be safe so I don't dare use it.

#### Lumenosity

Joined Mar 1, 2017
634
I solved the problem until the 9v Wall wart I ordered arrives.

If I'm like you, I have a LOT of misc electrical hardware that I collect over time. I just happened to have some male and female DIN connectors AND 9V battery connectors.

I think you know what I did

#### bertus

Joined Apr 5, 2008
21,588

#### Ramussons

Joined May 3, 2013
1,084
Whether you use a 3 pin Regulator or 4 Diodes to drop the 12 volts to 9 volts, you'll be dissipating 3 watts as heat. Just make sure that the "heat dissipators" are in the open and not inside the enclosed adapter (wall wart).

#### Holes Flow

Joined Oct 26, 2017
11
Oh, just thought of this... Don't rule out your local Goodwill store (or equivalent)... They always have a pile of wall warts of every voltage... And they usually have a powerstrip, so if you bring a tiny VOM...

Just sayin'

#### Audioguru

Joined Dec 20, 2007
11,249
Don't trust a cheap wall wart to produce its rated voltage without a load. A 9V wall wart will produce 12V to 16V with no load but it will probably produce 9V at its rated load.