I am using a MPPT 75/10 as a charge controller for a marine application that might be kind of unique.
Essentially I run two 20 watt solar panels to keep either a ten or a fifteen amp hour Lithium ion battery charged. In full sun the two panels will generate between 2.3 and 2.6 amps. I may add a third panel in which case I would guess peak output is somewhere in the mid 3 amp range.
The battery is then used to power a seven inch depth finder which draws roughly 1.2 to 1.4 amps, and I also have a usb charge port that will draw up to 1.2 amps with a phone or other device plugged in and charging.
Generally speaking the battery would be more than enough to get me by on a four to six hour fishing trip and most likely would even be fine over a longer 8 to 12 hour day, but once a year I do an eleven day trip where we do not see electricity once, so the sun is the only way I can keep everything going for the entire 11 days.
Sometimes I have had issues with the system not charging because the margin in voltage between the battery and PV is not greater than 5 volts. Is there anyway around this? Bottom line, if that sun is giving my panels anything, even if its .02 amps, I need that to be going through my system so the depth finder or the usb charger is being offset in usage by the sun as much as possible.
One reason I moved to the MPPT is because the low sun power delivery is so much better than PWM, but, if the system won't turn on, then I am getting no advantage.
So ultimately I wanted to see if there are any other setup options either within the unit itself, or if anyone had any ideas in the physical wiring setup as to how I might maximize the use of this controller for my situation. Bottom line, if that sun is giving anything, I need it, whether to trickle charge the battery, or to hedge reduction on the battery that the depthfinder might be causing.
Here is an example - If I run that depthfinder 8 hours a day, that is 105 amp hours of usage needed over eleven days. Even if that sun is only giving me .4 amps, over eleven days that would reduce my total amp hours of usage needed to 70. So on a trip like this where electricity is non existent, anytime the charger won't start is essentially a lost opportunity to gain more energy for those super grey days where its going to be all battery.
