low power 12vdc lcd monitor

Re: low power 12vdc lcd monitor

Just remember "wall wart" type 12 volt systems is that they many times do not like the ~10.5-15.5 volt range of a solar PV system (they may work better with a car where the voltage is around 13.6-14.2 volts).

And, 7805, plus other "analog" regulators are not energy efficient... They "burn off" the excess voltage as heat--so they do not save any energy. For example, converting from 14.2 volts (charged battery) to 5 volts (with a 5 watt load) would require the regulator to dissipate:

(14.2v-5v)

---

* 5 Watts = 9.2 Watts of "lost" power
5 volts

Switch mode power supplies (buck, boost, etc.) are much more efficient when converting voltages (and currents) from one level to another. But can be more expensive and difficult to implement--the above example would have wasted less than ~0.5 Watts of power as a properly designed and sized switch mode power supply (as with anything electronic--it all depends on the application, needs, and volume).

-Bill

Re: low power 12vdc lcd monitor

Yes and no...

Yes, your math and basic assumptions are correct.

No, in the sense that many devices do not use their name plate ratings...

For example, many ratings have maximum current and maximum voltage listed... However, for many devices, they are "constant power" devices (many electronics and motors)--So, at minimum voltage (of say 10.5 volts) it will use maximum current (example: 10.5v*4amps=42 watts). At the other end, of the limits, high voltage--the current may be less (example: 42w/15v=2.8amps, but nameplate may look like; 4a*15v=60w vs 42 watts actual).

Other examples are devices that use power in cycles (like a refrigerator), or use at different levels (fridge in hot weather vs fridge in cold weather, monitor back-light on high vs low, washer mostly empty vs mostly full).

In the end, you usually will have to measure the actual current/voltage/time profile for your needs and plug those into the equations.

And, the amount of sun you gather can easily vary by 10%-20% over time (weather patterns, pollution, etc.). So, getting "too accurate" does not help much either.

-Bill