I have 2 x100W Renogy solar panels on the roof of my 5th wheel. Hooked up to a Victron 100/15 Smart solar controller. They are in Series, so my voltage is around 42V and the amps around 5, well within my 100/15 max. It works very, very well. My question: I have a 3rd identical panel on a stand and with 30ft of quality flex wire, I would like to use or add to my existing setup to catch more sun on occasion. Like when in a wooded area.
How would I wire it to my existing setup? Can I simply plug it into the existing wire going to the controller ? I'd love to use the UI on my Victron to see it's performance... I really do not want to buy another controller...
You can use the same controller no problem since you are in series - your amps are the same, but voltage goes up. So you simply add the third panel in series with the other two, see this diagram from renogy
If you are asking can you use this third panel only on occasion and not as part of your permanent set up, then you'd need connect reconnect in series every time you swapped in and out- something that I would not recommend as the likelihood of connecting them wrong at least once over time would be high. If there's a simpler way, I dont know it though.
Solar charge controllers are rated in 2 ways. Voltage which is the maximum voltage the controller can accept from the solar panels and amperage which is the max charging amperage the controller will supply to the battery. The panel amperage doesn't matter for output amperage.
To determine what size charge controller for a specific array the formula is panel wattage divided by battery voltage. In your example that would be 300/13=23 amps. Most 15 amp controllers would be fine with the added panels (check the manufacturer to make sure their charger can be over paneled) but your output amperage will be limited to 15 amps or roughly 200 watts for a 12v nominal battery.
Since panels rarely achieve full rated power the third panel would help keep the charging amperage at or near that 15 amps in lower light conditions.
It doesn't matter if you run the panels in series or parallel other than series should perform marginally better in low light conditions and parallel will perform much better if there is any shade on any panel(s)
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