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150w inverter, 60w draw, car battery life?

  1. Mar 9, 2007 #1
    Using a 150w inverter to power the mac mini & LCD monitor in my truck camper. My Kill A Watt meter shows that the draw (on regular home power) is about 55-60 watts, or .05 KWH per hour. Can I assume that I could use this set-up for several hours, if need be, without danger of depleting my normal/average car battery?
  2. jcsd
  3. Mar 13, 2007 #2
    Say you were to draw the full 150watts. This means that the battery will be sourcing about 13amps @ 12vcd to the inverter. Most car batteries these days have around a 60amp/hour rating before they die. This means that with a 60Ah battery, you should be able to run the inverter for about 4 hours safely without the battery going dead. At 60 watts I would say about 10 hours if the battery is good, and hopefully you have enough current to start the truck afterwards. If you are ever worried, you could always start the truck for 15 minutes every once in a while to charge the battery. If you have a bigger battery in your truck, you can probably extend the time a little bit.

    The equations are: P (in watts) = VI so 150watts/12vdc = 12.5amps
    For a 60Ah battery: 60Ah/12.5amps = 4.8hours at 150watts. I would always extend that time buffer a fair bit..maybe to say 3~4 hours instead of 4.8
    Last edited: Mar 13, 2007
  4. Mar 13, 2007 #3
    I have since read that anytime a regular battery (as opposed to deep cycle) is discharged more than 20%, its life is considerably reduced. I haven't verified this.
  5. Mar 13, 2007 #4

    Indeed, regular batteries tend to sulphate if they are discharged too far. Although having sulphated plates ruins the performance, you can usually revive them using a high-voltage charger (20 volts or so) for short periods of time. This higher voltage blows the sulphated crystals off the plates so that it can be used again. This is how most automotive shops revive bad batteries. For an inverter application, I would use a deep cycle battery - marine or otherwise - to power the equipment. You should monitor the voltage of the battery even on a deep cycle to make sure that it isn't totally discharged, as deep cycle batteries still can be damaged. Anything below 12.0vdc means that the battery is completely dead. Around 12.6 - 12.7 vdc is where the battery will be fully charged. If the voltage gets too low you can hook it up to your truck with jumper cables to recharge it.
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