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ernesto avatar image
ernesto asked

Smart Solar MPPT 150/100 MC4 - 3 PV panels each connected individually to each of the 3 MC4 ports

Hi, is there a disadvantage in connecting three 200 watt PV panels; each of them individually to each of the three MC4 ports on the Smart Solar MPPT 150/100? Rather than connecting the panels in series and running only one connection into the MPPT?

The reason for my question: I have a portable 250 watt solar panel I’d like to connect directly to one of the MC4 ports when our vehicle is parked. I would disconnect one of the 200 panels and connect the 250. This would allow me to physically position the 250 panel for more efficiency - which begs the question. Is it even possible to connect panels of different wattage into the same MPPT using the multiple input ports on the unit?


Thanks in advance and sorry for the rookie question.

-E

MPPT ControllersMPPT SmartSolar
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Ernesto

It's possible to do this, but how well it works depends on how well matched the panels are.

Ideally you'd hook up all 4, hey..

What is your battery V?, and the Vmp of each panel?

Are the existing 3x 200W series wired?

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ernesto avatar image ernesto commented ·

Thanks @JohnC. 12v battery and 27.3 Vmp per panel. All three connect in series. Thank you!

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JohnC avatar image
JohnC answered ·

@Ernesto

27.3Vmp is enough to run 12V batts, so you could parallel those panels into the mppt. But they don't have to be spread between the 3x MC4 sets, they can be all fed to a single MC4 pair, or spread between 2x sets. The Amps on each panel will be added together now, but won't exceed the 30A rating of a single MC4. Use decent wire though, and 6mm^2 will fit a standard MC4.

The 250W portable can then have it's own MC4 pair. But it has a Vmp too, and if it's far off 27.3V then you'll lose efficiency, as the mpp's can't be tracked individually. MC4's are a bit of a pain to unplug, and shouldn't be unplugged under load, so maybe rig a switch and an Anderson plug on the portable so you can stow it as needed.

Note the 3x MC4 pairs really only exist because of current limits, and they combine together inside the casing.

The key to satisfaction will be how close those Vmp's are.. but at least you'll have 4x panels, and you should get more than the 3x alone.

Good luck.


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ernesto avatar image ernesto commented ·

Hi @JohnC

Thank you! I’ll need to check what the vmp on the 250 panel is. Hopefully it’s close to 27.3. — While doing a little more reading on whether different panels can be connected to the same MPPT; I read on a FAQ an explicit ‘NO’ as an answer. However there was no mention as to why. I understand the likelihood of running into inefficiencies but as you mentioned, if it is close to the same VMP it should work, yeah?

Another reason for wanting to connect each panel directly to the MC4 connectors is that I could get around potential losses related to arrays connected in series when cells/panels are partially under shade or if for some reason a cell/panel goes bad which will affect the efficiency of the entire array, correct? Of course, I worry that the panels connected directly to the MPPT could also drop below the +5v above the battery voltage that is required for the MPPT to kick in. Especially under poor sunlight conditions. I’d like to avoid a parallel array to simplify the connections and to not have to run thicker cables/wires. Is my reasoning valid or am I over complicating myself. Thanks again for your help. Much appreciated it.

Have a good weekend!

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JohnC avatar image JohnC ♦ ernesto commented ·

@Ernesto

That "explicit NO" you quote is probably a fair call. There may be a few other factors involved too (like orientation and shade), but you're mostly there if you can match up the Vmp of the panels. You wouldn't design yours this way from scratch, then go buy the panels. But you have spare mppt (and solar) capacity, and could make use of it if you target the important 'rules'.

That +5V difference applies to Voc, and becomes +1V at Vmp after it starts tracking. Voc can get quite high in poor light (like at first-light, before sunup), but there's no current. Vmp, once it starts producing, can actually get far lower than spec in poor light, and if that's an issue you can take consolation that the current flow at that time would be minimal anyway.

Have a go..

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