120ac -> 9Vdc, or 12Vdc -> 9Vdc

[Fubble]

Greetings community,
I have an important device that uses 9Vdc, 1.5amp, and that normally uses a transformer to convert from mains to 9Vdc.  I could run this device from the inverter: battery -> 120v-Inverter -> unit's transformer -> unit
Or would it be more efficient to use a step-down resister from 12Vdc?
battery -> step-down-resister -> unit   thereby bypassing conversion DC-AC-DC, but losing 3v in the process?
I'm in the design stage, nothing built or purchased yet.

Thanks

 

[tx2sturgis]

Step down resistor ain't gonna cut it.

You need to be looking for a 12v to 9v DC-DC buck converter...they are cheap, so buy a couple in case one dies.

Here is an example:

https://www.ebay.com/itm/12V-24V-St...854704?hash=item2334647730:g:vpwAAOxyTjNSmjSF

 

[MrAlvinDude]

Using a step-down resistor will cause a lot of power just being converted to heat. 
Likewise with a linear voltage regulator.  A linear voltage regulator can be seen as a smart resistor.


But with a DC-DC switch mode buck/step-down converter  you can minimize the energy loss in the converter
The one linked to by tx2sturgis  is a very good and convenient-to-use example of a switch mode DC-DC converter.

 

[Fubble]

Sweet, that's what I'll do.
Thank you both!