Alan Star avatar image
Alan Star asked

Is it safe, or possible, to put more pv input to an mppt smartsolar such as 250 /100 than is rated?

So that for example in winter when not getting so much sun there will be more panels there to maximise yield and in summer it will limit to the rated amount. How many watts would a 250/100 be able to cope with beyond rated capacity or is it safe only to make sure it doesn't exceed rated capacity?

MPPT SmartSolar
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3 Answers
Alexandra avatar image
Alexandra answered ·

@Alan Star

You can over panel by 30%.

(Battery voltage x 100A) + 30%

But never over voltage. You can use the page below, it has a good graph showing good and bad month yeilds for your area at the bottom.

Or download the mppt calculator spreadsheet. That is where you can really test several setups and see if you are overpanelled or not. It will come up in red.

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Alan Star avatar image
Alan Star answered ·

Ok thanks, I guess as long as it stays under short circuit rated amps (70amps for the 250/100) then it should be ok ?

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Alexandra avatar image Alexandra ♦ commented ·
@Alan Star

Yes you should be all good.

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matt100 avatar image
matt100 answered ·


So does anyone dare to say that if i use 210v 36 amp = 7560 watts, and try to squese it in to my mppt 250/100 it will be happy and limit output amp to 100 max ?

And if so what happen with the exess power does it burn up from the heatsink?


And yes i have reed a lot and i know what the manual say.That is the reason to this question here i dont know where else to turn.

Does anyone know for sure?

I ask for an answer to be sure!

If someone can back up there answer please!

And please if you dont know for sure dont answer!!!!!

And if you like to but dont understand the question please ask and dont be rude!

Best regards Matt.

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snoobler avatar image snoobler commented ·


FROM 2014:

"Limits to Oversizing a PV array

How to determine by how much you can oversize a PV array? This can be done with help from the spreadsheet tool. Here though is the manual explanation of how it is done.

There are two limits, when determining the maximum array size that can be connected to an MPPT:

  1. The Maximum PV open circuit voltage (Voc at STC)

  2. The Maximum PV short circuit current (Isc at STC)

Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.

Note that these two maximum ratings must not be multiplied to determine the maximum installable peak power. Instead, each of them needs to checked by itself:"

So for a 250/100, if your Voc is under 250V with an acceptable temperature margin AND your array Isc is less than 70A, your array is fine.

By your numbers, you could ALMOST double your array and still be fine.

It really helps to think of the MPPT as a LOAD on the panels. The panels are a source, but the load will only take what it needs.

When you plug a 13W bulb into an electrical outlet, why aren't you worried that the > 1000W outlet isn't going to blow out your 13W bulb? For the same reason you're not worried a 5800W PV charger is going to be blown out by a > 7560W array.

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matt100 avatar image matt100 snoobler commented ·
So lets see if i finally get this:

With the mppt the intake rules are max volt and max current.Thats it.

And the powernumber is what it can produce in power for charging.Not max cellpower.

So the higher volt on intake the more cells i can use.

Do you agree on that?

The reason i get confused about this is as you said,

I think about the cells as the load witch is wrong :)

And 1 say 30& and 1 say 130% and 1 say some more but not too much........

And the massive heatsink on the back i think ooops if this will burn all the exessive wattage.

Ps thank you for a good explanation!!

Regards Matt.

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wkirby avatar image wkirby ♦♦ commented ·
The MPPT will only take as much power from the PV array that can. If it is maxed out at 100A on a nice day, maybe it is making 5.5kW (48V battery), then it will take 5.5kW from the PV array, that's all. When the battery is full and the charge current is small then the MPPT will only take a small amount from the PV.
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