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harrib0 avatar image

SmartSolar MPPT 75/10 and max solar panel output

Hi,

Have a SmartSolar MPPT 75/10 and an 80W solar panel.

I wish to upgrade the panel and I am confused at to how much solar I should stick on the roof. I am limited to 10amps. Am I correct in saying that if I put something like a 175w panel (or larger?), depending on conditions, the charge controller would limit it to 10amp? (It is currently set to that)

Any thoughts and/or recommendations on a suitable panel


MPPT - Solar Charge Controllersolar
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2 Answers
harrib0 avatar image

Thanks for the quick reply.

I understand your reply and was hoping that the controller could shed the excess amperage and this seems like the case.

I am limited to 10amp due to factory wiring (and other items) so my thinking was, as you say I'll never see the full output from a 150-175W panel, but hopefully, in the right conditions, I'll get better than the mediocre output from my 80W?

All within limits by the looks of it.

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I have the same controller and have 4 x 100W (kinda cheap) panels. My battery is Li-ion so I charge to 16V and hence can get 160W out of the controller (10A*16V).

This was fine in UK November through to Jan but it's starting to hit over-current warning later in Feb as we're getting stronger sun. Based on testing the same panels connected to grid-tie inverter instead, the MPPT is working fine up to about 230W in. At which point it disconnects itself from the panels.

I'm going to rewire my battery soon so it's 32V. I'll be able to get 320W out of the controller then. Victron quote 28.8V as max charge voltage on the datasheet but you can actually set it as high as 34.8V via VictronConnect.

Justin Cook - Bay Marine Supply USA avatar image

@harrib0, is your battery nominal voltage 12v or 24v? If 12v, the controller can handle 145w from the PV side - of course, that's not to say that you can't connect a 175w panel (so long as you stay well under the 75v input limit of the controller), but the controller will simply clip any excess power when it needs to. The controller will self-limit input current -within reason- so it's okay to connect a panel that will generate 12A of current because the controller will simply shed the extra ~2A as heat. The controller cannot self-limit input voltage, however, thus the criticality of making sure you stay under the input voltage limit.

The reality is that unless you're standing on top of a mountain on the equator at high noon on a perfectly clear day, you will never actually see 175 watts from a "175 watt" panel - more likely 150w under ideal conditions, and if less-than-ideal conditions, anywhere from 120 to 140 is fairly common.

Bottom line: unless it's egregious (ie, maybe don't connect a 300w panel to this controller) it's not a bad practice to "over-panel" by a little bit, so if you wanted to connect a 150w or even 175w panel to this controller, you'd realistically be fine... you could even just get a second 80w panel like you already have and connect the two in either parallel or series. The absolutely critical consideration here is make sure you stay well clear of the input voltage limit. The 75v input limit is a hard limit, you must not exceed this under any conditions. So long as your max panel VOC (or combined VOC if you're connecting panels in series) doesn't go above ~60v, maybe ~65v, you'll be fine and the controller will simply clip any excess input current.

...of course, the maximum charge current this controller will deliver to your batteries under any conditions will be 10A, no matter what panels you connect it to, so if you're looking at upgrading your system, I'd strongly consider upgrading your controller at the same time so that you can deliver more charge current to the batteries. A 75/15 doesn't cost much more than the 75/10, but will deliver up to 50% more charge current; even a 100/20 is relatively inexpensive, and obviously doubles the charge current potential (20A) and also increases your input voltage limit (100v).

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