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locke987 asked

MPPT Sizing

I have a Smart Solar 150/85 in use where I connected 12x 400W Pannels in a 3S4P configuration.

I used the Victron MPPT Sizing Calculator and everything works fine at the moment.


Every 3S String is connected to a 15A Breaker before it's connected parallel with the other 3S Strings. In between the parallel connected Strings and the Smart Solar Charger there is also a DC 63A Breaker.


In Wintertime with all the cloudy and foggy weather condionions we only a few days where the solar really peaks, so mostly I just have below 1000W output from the charger.

Lets say I would add 2 additional 3S Strings to the Charger so I get a 3S6P configuration. The smart solar charger provides max. 85A Output and it's Input short circuit current is 70A. The panels I use have a short circuit current of 13.52A, means 6x13.52 = would bee 81,12A which is more than the allowed 70A of the charge controller. Though I still have the 63A Breaker in between.


So here's my question: Is it possible to "overprovision" the solar charger on the input side without any risk? It's clear that the output will be never more that 85A/4900W, I'm fine with that, in summer I have more than enough power, but it would be helpfull for classic winter condtions.

What would happen on a sunny day where the output of the panels could theoretically peak to their maximum of 400W? Would the MPPT Tracker of the charge controller take care of that the Input current never exceeds the supported 70A Input Power and cut off the power.

Is this a common/supported configuration?

Thanks Stefan

MPPT ControllersMPPT SmartSolarcharger
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kevgermany avatar image kevgermany ♦♦ commented ·
You say current configuration is 18 panels in 3s4p, but this is only 12 panels. Did you mix current and proposed configurations?
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locke987 avatar image locke987 kevgermany ♦♦ commented ·

you are right, I mixed it up, I have now 12 panels connected to the charge controller, the goal is to connect 18 panels, I changed the original post, thanks

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kevgermany avatar image kevgermany ♦♦ locke987 commented ·
I do it myself, all the time, especially with people's names.
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locke987 avatar image locke987 kevgermany ♦♦ commented ·

Thanks for helping! Your answer confirms of what I expected. 48V Bat is correct. The Note regarding the Quality of the DC breaker: I assume This hint is not really only related to overprovisioning, it is also correct if I would stay in my current setup, Right? To safeguard the charger if ohne Panel freaks out for example I additionaly have a 15A Fuse in Between Every string and the DC breaker so i would assume i‘m safe. But i have to Say the DC breaker is a relatively cheap Chinese one.

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kevgermany avatar image kevgermany ♦♦ locke987 commented ·
This based on web reports.


The cheap Chinese breakers have a reputation for inaccuracy. Also a short life if used to switch on/off frequently. I've had no problem with mine, but I also never tested it for accuracy and do not use it very often.
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1 Answer
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kevgermany answered ·

In principle, the obstacle is Isc. If the DC breaker is good quality and will properly protect the MPPT from excess current, should work fine.

Assuming a 48V battery bank. Your panels are already well over the controller max output. Adding more panels like this will not increase the input voltage, so that killer isn't an issue. All that will happen is the controller will track up to max output current and stay there. If you have MC4 connectors, be aware that they're rated up to 30 Amps only.


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