Ok, I was going to keep my mouth shut but... Yeah right.
Your inverter is designed to output 750W AC but it is not very efficient. In order to get your 750W, it's going to draw >60A DC. You might think your loads are small but using your figures as an example: Your XBox? Over 300W. Your TV? over 600W. Your laptop charger? Over 200W. In case you didn't know, Power (W) = Volts (E) x Current (I) therefore, in your XBox's case, 3A x 115VAC = 345W. Now look again at your made in China inverter label. Notice what they did? They give you DC input ratings and then the AC output ratings but they changed the rated items. 12.5VDC, 67.5A? Just over 840W. 750W, 120VAC? A whopping 6.25A! So it's going to draw 67.5A, but in the process of converting the DC to AC, it's going to consume over 60A to output 6.25A!!! This relates back to my first sentence in this paragraph.
A 750W inverter is not very large BTW. The rating is very deceiving.
So your postulated 20A draw is quite underrated, and at 10AWG, your wire capacity under best conditions is about 30A. The issue with your wire is that wire has resistance and larger wire (lower AWG number) has lower resistance than smaller wire (higher AWG number). Your 10AWG wire has about 0.001 ohms of resistance per foot, so 20 feet = 0.020 ohms. The power equation for this would be I^2(R). So at 30A, that would be 30(30)(0.020) = 18W. At 67.5A, that would be 67.5(67.5)(0.020) = 91.13W. This 18W or 91.13W of power is lost as heat which can melt your insulation and cause a very bad day (aka fire). Change to 8AWG wire and the resistance drops to 0.0006/ft, 0.012 for 20ft, and 10.8W/54.7W respectively. Quite an improvement.
Back to the fire, I say fire because if the insulation breakdown occurs between your protective device (fuse) and the battery, there is no means to protect you from the large electrical transient, therefore it could cause a fire or damage equipment. This is where the 18 inches comes in. (That's what she said.) 18 inches is the industry standard for just this reason. The protective device should always be as close as possible to the power source, i.e. 6 inches is better than 18 inches. (She didn't say that.)
I won't tell you my background because Antonm is a big meany and will make fun of me.
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Last edited by RUFFSTUFF; 07-14-2012 at 09:55 AM.