I have purchased a 12v 130ah lead carbon gel deep cycle battery for my VW Crafter camper-van. Apparently the max charging current on the battery is 25 amps.
I have 5x 385w mono panels and 1 x 325 watt mono panels.
If I use a 325 watt panel to charge a 12v battery the charge current would be 27.08 amps which exceeds the max charging current for the battery.
So there are two options:
1 - Go and buy a 250 watt panel that will produce 20.83 amps in optimal circumstances, then buy a 20 mppt controller.
2 - Use the 325 watt panel with a 20 amp mppt controller knowing that the controller will limit the max output current to 20 amps. We know that a 325 watt mono panel will only make the full 27.08 amps or thereabouts when the sun is directly overhead in the middle of summer on a fine day when the panel is relatively clean. It will also only produce max current for several hours either side of noon (I stand to be corrected :).
A rule of thumb I made up :) is that on a rainy overcast day, panels will only generate around one third or 33 percent of their max current. So instead of generating 325 watts, they may only produce 110 watts sometime around noon :).
So by putting a larger panel on the camper, you will increase the overall generation on either side of the noon day sun because the mppt controller will continue producing the max 20 amps longer with the 325 watt panel than with the 250 watt panel. With a 325 watt panel connected to a 20amp mppt controller, you loose 7a of "potential" generation at the peak of a sunny day around noon but you gain on either side of that.
I already have the 325 watt panel sitting here and would rather not go and buy a 250 watt panel. But I can. I don't normally like apply excess current to the system but I know a 20a controller will limit charge current to the battery to 20 amps.
WHAT ARE YOUR THOUGHTS.
Under different circumstances, you could buy a 200AH battery that would accept a higher charging current. I buy my batteries off auction sites and they don't usually mention max charging current.
What is the appropriate charge setting for a lead carbon gel battery? The seller said to set the controller to GEL battery.
