Thevenin resistance of a car battery?

Question

If I have a 1.3 ohm load on a car battery and measure 12.46 volts at the battery terminal and then I also turn on the radio and measure a total of 20 amps of current flowing and now have 12.3 volts at the battery terminals; What is the Thevenin resistance and Thevenin voltage associated with the battery

Answer 1

With the 1.3 ohm resistance you have 9.5846 A flowing.
With a 20 A load, the terminal drop is
12.46-12.3 = .16 V. The current increase is
20 - 9.5846 = 10.4154 A so the Themenin resistance of the battery is
.16 / 10.4154 = .01536 ohms.

The Thevenin voltage would be
12.46 + .01536*9.5846 = 12.60 V


Doug

Answer 2

12 volt 12 amp-hour gel batteries stay above 12 volts for various months = 1200 hours, so theoretically they could grant 10 milliamps for 1200 hours. that's one hundred twenty milliwatts = one million/8 watt, so which you will placed 3 tiny 1200 ohm resistors in each gadget you want to stay above 0C, and capability each resistor with a separate battery. 360 milliwatts heavily isn't adequate warmth, except bigger units have very reliable thermal insulation. Odds are between the three batteries will drop to eight volts or much less meaning it can not be recharged. 12 volt a hundred and ten amp-hour deep cycle batteries fee approximately two times as lots, can capability a a hundred and fifty ohm, one watt resistor for extra or less 1200 hours, yet one in 3 batteries will probable be broken after 1200 hours. it incredibly is by means of fact batteries self discharge. a achievable answer is 5 watt, or there abouts image voltaic panels, which will keep the two battery above 12 volts for years at this small a load, assuming some hours of sunlight fall on the panel each month. The image voltaic panel and robust thermal insulation additionally will insure that the battery heavily isn't broken by using freezing, whether it gets chillier than -20C. 15 watt image voltaic panels won't over fee the two battery, yet they fee two times as lots and are lots extra probable to be stolen, considering they is extra seen. With the 15 watt image voltaic panel and a hundred and ten amp-hour battery approximately seventy 5 ohms, 2 watt resistor is sensible, in case you will hit upon room for it on your gadget. in all hazard your units would be overheated in case you depart the batteries linked contained in the summertime time. Neil