watts, volts, amps......need a bit of help

oh, duh, I didn't think about that. thanks

 

I will try to show this using Ohms law. Lets say you are using a 1500 watt inverter pulling 900 watts. Watts is the measure of work being done. Because of this the 900 watts is both at the battery as well as the outlet. So 900 watts / 12 (volts at battery) = 75 amps. 900 watts / 120 (volts at outlet) = 7.5 amps. It's the current that causes heat not the voltage or wattage. If an inverter is not installed right or you use clip on's at the battery you're asking for trouble. The chances of fire goes up along with the current draw.

 

It's been ages since I took an electronics class, guess I wasn't thinking it all through. Thanks for the explanation!

 

It'll work, I had a big Emerson with a seperate freezer. It peaked at 150 watts on start up and cruised at 70 watts. They don't come on much either unless you load warm stuff or open the door alot. Maybe the digital meter was X10. I forget now. I'll go look at it.

Microwave, coffee pot and other stuff with heating elements it what you have to watch.

 

I looked a the label, it's 1.3 amps, so the 150 watt start up is right.

 

1000 watt or more inverter needs to be properly connected to the Batteries. Resistance causes heat,the less resistance the better.

 

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance,[1] one arrives at the usual mathematical equation that describes this relationship:

I=V/R

where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

 

A 1000w microwave requires nearly 1500w to operate. The 1000w rating is the output, the rated input is on the label on the back and will vary by mfgr 1350=1450w. A battery provides nominal 12v A/C is 120v 1 amp of A/C = 10 amp DC. to provide the same watts

 

The approximate comparison of amps at 12v vs. 120v is a multiplier of 10. A 15 amp 12v circuit is equivalent to a 1.5 amp 120v circuit. The inefficiency of the inverter adds additional draw on the batteries. The best inverters are rated about 80% efficient. If you have a 20 amp 12v input your output will be close to 1.6 amps 120v.

 

What part of my example is the problem? If you look closer I never said in that post anything about the high voltage side. If you are pulling 1500 watts on an inverter you are pulling 125 amps at the battery. In a later post I did bring up the high voltage side. However I ignored the inverter efficiency part so I could show a clean simple example of the math and why it can be dangerous to have that much current at the battery.