I purchased a couple 100W Renogy panels for our travel trailer as dry camping opens up a lot of sites for us and I dont like firing up the generator unless I have to. The panels are deployed on folding stands which is really the only way to get them in the sun in the wooded campgrounds we frequent.
I used them the first weekend with the PWM controller that came with the kit. It blinked nicely at me, but even with a voltmeter added to our control panel inside the camper there wasn’t really a way to see what was going on.
I started looking at adding monitors with shunts, but things start getting rather involved for my particular setup. At home in the off-season the camper is covered and plugged into shore power to keep the batteries up.
I realized a few things. First, Im paying for electricity to charge the batteries when I have two solar panels in a box. Second, the on-board inverter/charger is OK for maintaining batteries, but really lacks the ability to keep them at a full charge as they hover around 13.
4-13. 6 volts regardless of battery condition and with no temperature compensation. Third, to charge the batteries requires the battery kill switch to be on, meaning Im also powering gas and carbon monoxide detectors and who knows what other parasitic loads in the camper.
Not a monetary issue but things without power on them cant cause unforeseen issues. I had originally fallen prey to the argument that youre better off buying another panel vs. paying for an MPPT controller.
That works on paper but I realized that Ill set out 2 panels, but I will never set out 3 or 4. That meant the Victron SmartSolar 75/15 would work nicely and the cost was within my threshold of pain. The need for a separate monitor was also negated.
Installation was easy as I was just replacing the PWM controller. My setup is a couple of group 24 lead acid deep cycle batteries with around 160ah. Power is brought into the storage bay of my travel trailer with 4/0 wiring where it splits off to a 3000/6000 pure sine inverter.
The Victron is wired into the 4/0 cables which are only about 18 away with 10 gauge cabling. The Zamp plug that came with the camper was replaced with a 10 gauge wire unit, and the 20 of Renogy cable going to the panels is 10 gauge.
The storage bay isnt heated so its within a few degrees of the batteries which are on the tongue. After doing an update the unit automatically selected 12v and the default charge setting was for deep cycle gel batteries.
I was initially a little worried that there wasnt a specific setting for lead acid batteries but the parameters of this option are apparently fine from what I can gather. Equalization is off by default.
After installation I zipped the camper cover back up all I have to do now is walk by and log in to see whats going on, no need to unzip/unlock or interrupt my nap when were actually camping to check our state of charge.
The attached screenshots were for the first few days. Im only using one 100W panel as I felt this would be sufficient. The battery bank was at 90% charge the first day (see handy chart) and I was pleased to see that it got fully charged but concerned that my 100W panel was only putting out 35W in full sun.
A 100W panel is going to max out somewhere around 70W in the northern hemisphere on the best day in the summer and this was in January, the lowest amount of available solar energy (insolation) of the year.
The following days were even worse until I understood that Pmax isnt your panels peak wattage, its the peak that the controller will draw from the panel as it manipulates current and voltage to get what it wants.
Youre not going to see a Pmax that resembles the published output of your panels unless you have a big load on them (or drained batteries) and maybe not then. This is a laymans explanation, but if it keeps you from thinking you have a bad panel or connection its worth the keystrokes.
Of the following three January days the first was sunny, the next was cloudy and the next was rain. The Victron doesnt care, it still pulled plenty of voltage out of the panel and quickly went into float.
Its like a honey badger. Perhaps more interesting will be what happens when a live load is applied (such as when were actually camping and using power). Toggling the electric tongue jack gets an immediate response from the controller as it ramps up to offset what youre using, then it goes back to putting the battery back to the state of charge that it wants.
Comparisons between PWM and MPPT controllers are made in somewhat of a vacuum, you can spend hours reading them. In the real world of RV use the MPPT probably offers more advantages than published. On cloudy and rainy days MPPT wins, but though its hard to quantify it also wins when you have partial sun exposure due to your location.
I love wooded/private campsites. Most examples use a sunny day with no loads and the PWM can do what the MPPT does, it just takes longer. Lets say Im fully charged by noon and at.