inverter power draw? - : Jeep Wrangler JK Forum
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post #1 of 4 Old 03-28-2010, 04:16 PM Thread Starter
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inverter power draw?

I want to install a power inverter but I dont know how to figure out the power draw. The inverter I have on hand is a 350 watt inverter, but I have plans on getting a more powerful one. I am asking because I dont know what size relay, fuse, and wiring to use so as to not start a fire.

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post #2 of 4 Old 03-28-2010, 05:18 PM
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Watts= volts X amps. So if you have a 350 Watt (max draw) inverter and you plug something in that is 120 volts, then the most that it should draw is 3 amps.
A=W/V----->350W/120V= approx 3 amps at the inverter.

Hope this helps.
edit: Did some research and found that AC watts /12 x 1.1= DC amps

Last edited by Eugene; 03-28-2010 at 05:28 PM.
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post #3 of 4 Old 03-28-2010, 10:55 PM
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Originally Posted by Rednroll View Post
Actually, that's kind of backwards since you calculated the current draw on the output side. If you want to know how much current the inverter is drawing, then you need to calculate the current draw on the input side.

So assuming your battery voltage while the engine is running is at about 14volts and it's a 350W power inverter, then the current calculation is 350/14=25Amps. So the inverter is drawing up to 25 amps from the battery.
It also depends on how the rating of 350W is calculated. Is that the supported output load or gross power draw? If it actually supports a load of 350W, then it must actually draw more than that since it's not 100% efficient. I'd say something like an inverter is at best 85% efficient which would mean that your actual draw is .85 / 350W = 411W /14v = 29A

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post #4 of 4 Old 03-29-2010, 12:35 AM
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The easy way is to look at the fuse the inverter has. For a 350w inverter is should have around a 30amp fuse. That would be your starting point. You need to decide what you will use the inverter for. If it's just a laptop or cell phone charger you don't need anything bigger. If your running an electric chain saw you need to rethink you electrical. For basic stuff a standard relay 30/40 will work.
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