Hey solar enthusiasts! I'm putting together the solar array for my camper and have hit a bit of a snag in selecting the right size for my MPPT (Maximum Power Point Tracking) controller. Here's my current setup: I've got an Elios 200W solar panel with characteristics as follows: Voc 48V, Isc 5.68A, Vmp 39V, and Imp 5.13A. I'm using two of these panels in parallel, which gives me a total of 400W at 57.6V with a safety factor on the voltage, bringing the charge current to about 11.36A. My battery bank consists of two 100Ah lithium batteries connected in parallel, charging at 14.6V. Most calculators recommend a MPPT of 100V|30A, which I'll be going for a Victron model. However, my charging current is roughly 27.4A, which is dangerously close to the 30A limit. Do I need to add a safety percentage to the MPPT size? I'd love to save around CAD$75 by going for the 100V|30A instead of the 100V|50A, but I'm also keen on safety. What do you all think?
7 Answers
It's all about the numbers! Victron gives you a maximum charge current and a max Isc, so having extra panels won’t hurt much; most of that excess will just get wasted during peak sun. Just keep your panels well within the safe voltage limits, and you'll be all good.
Thanks for all the insights, everyone! Really appreciate it as I sort through this decision.
There's definitely no harm in having more solar panels than your charger can handle—it's all about the input voltage. As long as your panels are wired in parallel, you won't exceed the voltage limit, and the MPPT will manage whatever current it can. If your panels produce more than the MPPT can handle, that's fine; it just means some of that energy goes to waste, but it won’t damage anything. In normal conditions, you probably won’t push over 350W anyway. Just remember, if you had more panels, you might only see the extra benefit under lower-light situations.
The most important thing to monitor is the Voc rating of your panels. You should choose an MPPT that exceeds that value by about 10%. Some controllers max out at 50V, but I'd suggest looking for one that can handle at least 60V, especially under extreme conditions to avoid any potential fail points.
Don’t forget to use Victron's MPPT calculator! It’s really user-friendly and can help you figure out what you need.
You really don't need to worry about adding a safety margin for current on a Victron MPPT. These units are designed to handle their maximum charge output all day as long as the temperature stays in check. Even if temperatures rise, they will just slightly derate the output.
While having a safety factor is generally a wise move, Victron’s products are quite reliable. Usually, these MPPTs run at peak current often without issues. Just keep in mind that the panels may not consistently deliver full power. If they’re flat, you’re likely losing some efficiency due to angle and shading.