working out 12 volt draw through inverter

Yes, power-out divided by power-in. (Times 100 if expressed as a percentage.) [It's the same as any efficiency formula - ie, output/input.]

oldspark wrote: Yes, power-out divided by power-in. (Times 100 if expressed as a percentage.) [It's the same as any efficiency formula - ie, output/input.]

:)Kevin Pierson

KPierson wrote: oldspark wrote: Yes, power-out divided by power-in. (Times 100 if expressed as a percentage.) [It's the same as any efficiency formula - ie, output/input.] :)

I don't understand a lot of what you are saying, and I feel that my question isn't being heard let alone answered. It must be that I simply don't understand enough to be able to grasp what you are saying. Thanks for trying to help anyway.

KP - your inbox is full. (Minor technical issue/trivia.) Sorry boristhemoggy, it is your latter. Read through the thread again. Many things have been repeated - eg, forget nameplate ratings as they have NOTHING to do with what your PCs & laptops are actually consuming, & power P = VI [hence Pout/Pin = (Vout x Iout)/(Vin x Iin) etc]. But if you want my short conclusion - forget it - you will not be able to design a PC that consumes less or equal to that of a laptop unless you use laptop components or wait for the next generation of chips if you want a PC that is more powerful than your laptop. But hence why I asked you WHY you had your limited power (or current?) specification. I assume it isn't a battery reserve issue because then you probably would not be using a inverter. Nor would you use an inverter if you needed cranking ride-thru etc (not needed for a laptop, but essential for a car PC). You should be able to google your laptop consumption... Then add ~30% to get an inverter's power input (and I = P/V from P-VI) or ~10% if using a dc-dc converter. But read thru again and then feel free to ask for clarification or more detail. And please use only relevant measurements and specs - not plugpack etc ratings. PS - "efficiency" is a basic definition. See f.ex wikipedia Electrical efficiency. So too formulas like P=VI. PPS - wiki has IMO made many pages more complex - too mathematical etc. EG, only the first part of the above link is relevant. Maybe their Electric power page is better for you (again, first section only).