My 12 volt dc tv uses more amps by DC than AC?

Question

Im trying to use 12 volt solar system to power around the house. I have a 12 volt battery and inverter. works well with CF lights. Now i found a AC/DC TV. But the math says it uses more power under dc than ac. DC specs are 12 volts and 16 watts. works out to 1.3 amps. AC is 120 volts and 35 watts. works out to .3 amps. watts divided by volts equals amps. So its better to just use AC power? I was going to run direct by battery but it looks like going thru the inverter would be better. Is this right? Is their that much difference? 1 amp. I guess internally it has to make ac and that is consuming more power? Man, i thought i was getting somewhere with a dc tv but really i'm losing by going DC. Is this right?

Answer 1

12 volts and 16 watts or 120 volts and 35 watts?
P=IE I=P/E
12 volts 1.3 amps
120 volts 0.3 amps

I don't think this is correct labeling. It really doesn't make sense that at 120 volts AC, the unit would use more wattage than at 12 volts DC. The 120 volt AC has to be converted internally in the set to 12 volts DC because the set is engineered for a 12 volt supply. I think I would be inclined to put an amp meter on this unit and see what the actual draw is at the different voltages.

Answer 2

I don't understand what you're saying. If the DC specs state that it uses 16 Watts of power, how is that more than the 35 Watts of power that it uses from the AC source?

Power = Voltage * Current

The AC source uses much higher voltage and a little less current, but over twice the power. It seems to me that you are confusing power (measured in watts) with current (measured in amps).

The AC uses more power because it must be converted to a DC source when used by appliances (Why do we use AC then? Many benefits over DC in power transfer, from plants to homes). This is usually done internally using an RLC circuit which basically keeps the voltage (and consequently current) at a constant positive rate (through the charging and discharging of the capacitor).

Hope this helps and good luck with your project.

Answer 3

Keep in mind that the same number of watts will require more amps at 12V than at 120V.

I'm taking a stab at guessing why it needs more watts under AC power.

It all depends. It depends on the circuit "strategy". I'm assuming this TV has a CRT screen.

When its powered by DC there has to be a step up inverter. When AC powered there has be a step down power supply and also a step up inverter. The extra wattage loss under AC power could be inefficiency in the power supply.

When DC powered, the efficiency of the power supply may be higher resulting in less losses.

Answer 4

Your TV needs more current under less voltage than it would under high voltage, because you must have the same power to run the TV. Power equals voltage times current(P = VI). You AC outlet will typically be in the 110~120VAC range. To get the same power with a 12V source, you need roughly ten times the current.
You definitely won't get more power by using the inverter, because the inverter will exhibit losses, so the power output of the inverter will be equal to the input power, minus losses.

Answer 5

If the output of the adapter is a fixed 12 to 14 volts DC only, you should be able to run it from a direct 12V battery source with an appropriated fused cable. You might not want to power it from vehicle power with the engine running, as engine noise can affect TV operation.