How to lower voltage

[Jane]

I use this digital multimeter
http://www.range.com.hk/products/RE890G.html
works great but it needs battery  9V to function. I have a power supply adaptor but it provides 12V, 3A.
What ways would you suggest so that I can use that adaptor with the multimeter? I was thinking about a resistor connected between multimeter and the power supply.
From my calculation it seems 0.25M Ohm could lower those 12V to 9V.

Is it possible?

Thank you for your hints

[Vovk_Z]

1. It is bad (wrong) and inconvenient to use handheld multimeter with a mains-powered power supply.
2. It is wrong to use a single series resistor to lower the voltage because current consumption vary much.
3. Just buy a 9V battery (I buy at least two usually).

[tszaboo]

Please dont. You will either electrocute yourself or blow up the electrical network.

[comfortcube]

The reason it is not good to power your multimeter from mains power is because now (I believe) the negative terminal on your meter becomes Earth ground, or at least Earth ground referenced, and depending on where you place it in your circuit, you can easily cause something to blow up or get damaged or hurt yourself. Such meters need to remain "floating" in terms of their power supply, which is why they are battery powered.

Also, the resistance you calculated would lower the voltage to the 9V you want only at the current you used to calculate; the current draw will certainly vary and cause that voltage to fluctuate. Also in general, this is not how voltage regulation is done at all.

[Zero999]

If it's only to be used for measuring extra low voltage, i.e. <60VDC, then it's safe to use your power adaptor with the LM7808 to reduce the voltage to power the meter, but it shouldn't be connected to any other circuits, powered from the same power adaptor, otherwise it might not work properly, or be damaged.

As many others have stated: this is a bad idea. If you want a mains powered mulitimeter, use a bench top unit.
https://www.rigol-uk.co.uk/product/rigol-dm3058e-5a%C2%BD-digit-digital-multimeter/