I would take a pic of the label on the solar panel. Should tell you VOC (Voltage Open Current) and Watts and all that. Post here if you can.
Mixing panels can be done. Just try to get the VOC as close as possible so the loses are at min. There are so many different panels out there. You can find another 400 watt panel with the same or close to VOC.
if you add panels are you planning running in a 2 S config? meaning in series to each other. That what I would do.
As long as you charge controller can handle the VOC (Volts open current) Also for each panel when figuring this up add about 5% for them perfect days and cooler weather. The VOC will go higher than what's on that label. You will fry the change controller if you go over the volts.
You can over panel all day and have a million watts. LOL it will only bring in what the amp rating of the charge controller is rated at.
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If you are going to go full off grid with your camper.
More good info if you don't know. People that go with lets say a 48V AIO (All in one) I have several. But in a camper environment. This would be way more efficient than a 12V system. 12 VDC system are terrible.
So most AIO can do about 500VDC of solar. BUT require about 100 to 150VDC to even start charging the batteries, Issue here is camper only have so much roof to add panels and run in series.
Solution fine commercial solar panels. I got some for free they usually will give them away after an upgrade.
Anyway you will notice that commercial solar panels will have a lot higher VOC ratings. This helps because you can get that min voltage requirement with less panels.
Also with a 48VDC system. for 12VDC loads such as fridge. I would run 48VDC to the fridge area and then convert to 12VDC there. Much more efficient to run 48V long distance than 12V. Again 12VDC systems are Cr#@%$#%$#
Good luck.
I also have the 400 watt panel and asked dealer what it is and nobody knows Alliance probably don't even know. LOL
I plan on getting a pic of the label soon.
