I want to run an appliance that uses DC 5V 2.5A at 6 watts consumption using an adapter from the cigarette lighter socket. I have a standard 12v car battery in the small car. Do i need to get a bigger battery/more batteries, special alternator, or something else to run this appliance permanently?Is there an online calculator to help me work out how much battery power i need?Many Thanks to all answerers.
See your APP. Wattage is 6W So Current It will draw6/51.2Amp from the Battery. The Battery is already 12Volts. Check the AHR(Ampere Hour) of your Battery Divide the AHR by 1.2 The max hour you can use that battery when It is fully charged.
First, 5 V times 2.5A equals 12.5 W, not 6 W. I'll assume, therefore that 6 W is the average, but the peak may be 12.5W. Also, assuming no conversion losses by the adapter, 12.5W in 12.5W out. Since the socket delivers 12 V, you're looking at about 1A peak. To a second approximation, divide by the adapter's efficiency (I'd guess 85%) to find out what's drawn - might be just shy of 15W. Most sockets have a current or power rating. My car says 120W, 12V - which translates to 10A. If you can't find the rating, check the fuse rating. It's probably 10 or 15A. If your car socket has the same rating as mine, you could run 8-10 of your appliances with no problem, all at peak, and 20 of them on average.
as was said, 5 volts at 2.5 amps is 12 watts, not 6. But either way, that is a small amount of power for a car battery. Typical batteries have a capacity of about 1000 watt-hours, so the 12 watt load would work for 80 hours, although I'd limit it to well less than 40 for safety. With the engine running, there is no problem, you can run it as long as you want. It's when you have a load of 50 amps or more when you have to worry about a second battery, etc. .
