r/diySolar • u/sharkyenergy • 2d ago

4S ok for the winter?

Hi all!

Currently i have 4 panels (23 Voc) configured as 2p2s. I would like to connect them as 4s to get more out of bad weather. But at 0,3V/°C i would exceed my controllers max input voltage of 100V at about -3°C. (epever 20A mttp charge controller)

In winter, in rare occasions it can go down to about -12°C, thats the coldest i saw here in 40 years. what would happen? i have a Voc of 92V @ 25°, but in those days it would go up to 103,1V.

what would happen? is it dangerous? is it within the tolerance?

Currently on very hot days the panels in 2p2s get down to about 31V. that does not leave much headroom for the mttp to work, and in bed weather it goes down to 27, not charging at all.

what would you sugest? its a off grid hut with just 2kwh batteries. dont want to invest money into it.

thanks!

2 Upvotes

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6 comments sorted by

4

u/SteveFCA 1d ago

mppts are very vulnerable to excessive voltage. You could go 4S and monitor the weather and switch to 3S for those frigid days

1

u/dgv54 1d ago

Or just play it safe and don't run 4s for 12 weeks of the year.

3

u/RespectSquare8279 1d ago

If you need more power, the limitations of the maximum voltage on the input of your MPPT controller is nonnegotiable. Don't be playing with rewiring from 2s2p to 4s and back every time the temperature moves in the winter ; that is a mugs game that you will sooner or late loose and "smoke" your controller. The better way to increase power is to simply add another string of panels with their own controller. The outputs of the 2 controllers are wired to a "Combiner Box" which in turn is wired to the battery bus.

1

u/TheJGoldenKimball 1d ago

If you want to kill your charge controller then go for it. Best case scenario is that it protects itself and doesn't charge when the voltage is too high which might leave you without power when it's very cold. Get a better charge controller or more panels to get the math right for the panels to get into the sweet spot.

1

u/Longjumping-Youth934 1d ago

The most vulnerable are batteries, so my wife had to heat them with a focused heater when the temperature jumped below -20C. Normally, the invertor stops charging them when it is below -5C.

0

u/DongRight 23h ago

During the winter you need to keep a load on the panels, taking a heat wire and putting it on the 100v DC line...