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UPS to RV Battery conversion

This is just notes for now, Updated last 6-4-2014

The goal of this project is to replace the "Power Converter" I found in my Tent trailer with a UPS. Effectively they are similar, except that the UPS also has a built in inverter.

Right now, when attached to shore power (Utility power) the "Power converter" is powered on, the battery is being charged, and the 110vAC outlets work. When disconnected, you have 12vDC power in the trailer.

In the end, when attached to shore power (Utility power) the batteries will charge, 110vAC will work, then when disconnected from shore power you have 12vDC power and the 110vAC outlets can still be turned on.

I will be adding the added benefit of solar panel, this will allow the batteries to be charged by shore power OR solar OR both.

First challenge is to find the right UPS. I have looked at many APC ups. Problems:
-12vDC vs 24vDC
    It seems like most UPS are 24vDC, this sucks because my solar panel and controller are 12vDC. If I use a 24vDC system, then I need a 24vDC panel. You cant mix 24vDC controllers and 12vDC solar panels.

-full sign wave vs half sign
    Measuring the sign wave of 110vAC is a pain in the ass if you don't have the probes to do it with, so what you can do is grab a 9vAC (or there abouts) and measure that. The reason this works is because what happens to the 110vAC power also happens to the 9vAC. Alternatively you can build a voltage divider... Or use a wall wort like I said... 

    Too big means power consumption goes up even just turning on the inverter. 

-larger battery
    The dinky little batteries inside the UPS wont cut it, so I am using a 35amp hour battery (about the size of a car battery)