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pshekelle avatar image
pshekelle asked

smart solar MC4 to Tr connection

I bought a SmartSolar MPPT 150/60 charge controller as part of an upgrade of a small off grid cabin PV system. This upgrade also included going to larger solar panels, 3 200W 12V panels (to power a 12V DC refrigerator). But I did not realize the difference between the MC4 model and the Tr model in terms of the connections when I bought the charge controller. So now I have 3 200W panels in parallel that are capable of producing 36A of current (12A from each panel) but the MC4 model I have will max out at 30 A for each input. I have only 1 run of wire coming from the panels to the charge controller. If I had a single screw terminal version I would be OK, but I have the two separate MC4 connectors. Is it possible to convert these 2 MC4 connectors back to a straight wire configuration?

MPPT SmartSolar
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Mike Dorsett avatar image
Mike Dorsett answered ·

The modules will have bypass diodes built in, and thus can be wired in series even with partial shading. The MPPT function will sort out the loading on the panels to obtain maximum power. In parallel, any partially shaded module will not produce any significant power if any other module is in full sun. so you may end up with more power this way too.

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JohnC avatar image
JohnC answered ·

Hi @Pshekelle

If your panels really are '12V' (ie. a Vmp of ~18V) then you'd be better off anyway mounting them in series. Don't exceed the 150V of your mppt, but that's unlikely for any 200W panels. That will reduce the Amps to that of just one panel.

The 30A is just an official rating of the MC4 connectors, the mppt itself won't restrict each pair to 30A. Read into that what you will, but it's nice to follow the rulez.

The only good reason to wire 12V panels in parallel would be if you have selective shading. Or a pwm cc.

You could also arrange a T-in outside the mppt.

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pshekelle avatar image
pshekelle answered ·

Hi John,

selective shading is the problem and why the panels are wired in parallel. Can you tell me more about the “t-in” option? I am not familiar with it.

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seb71 avatar image
seb71 answered ·

You should have fuses and a PV disconnect between the PV panels and the solar charger anyway.

So for the last segment for this wire run you can combine two pairs with MC4 connectors.


Normally when you put panels or strings of panels in parallel, each string should also be protected by a fuse.

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steffen-graap avatar image
steffen-graap answered ·

I think the only reason for panels connected in parallel is the limitation by the max.input voltage of the MPPT.

But since there is enough reserve (150V) I would connect the pannels in series. Due to the built-in diodes in the panels (all newer panels have these), the shading is negligible, since the MPPT takes care of it as long as the input voltage is 5V higher than the battery voltage.

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Fra avatar image Fra commented ·
But series panels have a higher PV voltage. These is possibly more dangerous and have ever a lower conversion efficiency of the controller.

If parallel is possible, it ever perform equal or better than series.

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