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peternielsen avatar image
peternielsen asked

Choosing the right SmartSolar chargers

Hi,

I have 3x4 and 3x3 constellation of the attached panels. I have tried to use the calculator and i am wondering why it's suggesting 150/60 for my 3x4 side when the datasheet states Nominal PV power, 48V = 3440W and i have Total PV Power : 3720W and then the same on the 3x3 side where i have total PV power 2790W and the datasheet states 2600W, i am sure i am misunderstanding something but what is it ?

Amerisolar-AS-6M30-PERC-Black-Module-1640x992x40mm-Eng.pdf

The next question is about MC4 vs without . As far as i can see all MC4 connectors are rated at 30A. My 3x4 side will be 40A since each series is of 10A and the 3x3 side will be 30A. Does that mean that if i buy a 150/60 MC4 i can't use it with 40A with the MC4 ? If so why then make it at all ?

I should mention that i will run a 48V system (16S of LiFePo4 Batteries)

Best regards,

Peter

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2 Answers
wkirby avatar image
wkirby answered ·

3x4 array. This configuration is good for a 150V controller.
3720W @ 48V = 77.5A battery current at maximum power. So you could use a 150/70. You'd be limited to 3360W when the battery is at 48V and the full power of the array will be available when battery Voltage is higher than 53V. The limits are minimal and a PV array only makes full power in ideal conditions. The 70 limit is automatically imposed by the MPPT and an oversized array will not damage it. If you don't want the array to be limited at all then a 150/85 is the answer.

3x3 array, this configuration is also good for a 150V controller.
2790W @ 48V = 58.2A
A 150/60 would be perfect for this array. Its maximum charge current is just above the capability of this array at 48V battery Voltage. As the battery Voltage increases it will be in its comfort zone.
Only if the array produces over it's rated capacity for those rare cloud edge effects or really cold sunny days then it will limit it's self to the 60A.

I don't know why that solar calculator is acting like it is.

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peternielsen avatar image
peternielsen answered ·

@WKirby Sorry i didn't see your answer, Thank you very much. Not sure i understand all of it but one thing i was wondering. The 3x4 array could be converted to 2x6 array in order to increase the voltage so the voltage drop over 6mm2 cable 15meters is very low compared to how much the voltage is dropped if use 120V. What's your take on that? Am i running to close to the MPPT charger of 250V ? The array would run on 240V 20A. If i use the calculator it states i can't probably because i am close to max ? I don't know if i can trust the calculator. Maybe @Guy Stewart (Victron Community Manager) knows if there are issues with the calculator ?

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klim8skeptic avatar image klim8skeptic ♦ commented ·

I work out a 6 series string to 285.24v @ -40c.

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Alexandra avatar image Alexandra ♦ commented ·

@peternielsen

Panles outputs are rated at certain temperatures. Usually about 25°C. So colder they can produce more than their rating under ideal solar irradiation conditions. Hotter they produce less.

If you scroll a bit further down you will see a graph that you set for your area and it will help you see outputs over the year for the array setup you have chosen.

If your panels are 310w and you are installing 12 then your potential is 3720 watts. If you choose a lower amp output mppt then you will loose so to speak the full peak potential of your array as it will limit to that amps multiplied by battery voltage.

Running at lower string voltages is mostly noticed under lower light conditions. And 15meter runs in my experience don't affect output as much unless you are trying to combine all the strings into one closer to the panels. Then with the higher combined amperage you will need larger cable and possible use the TR rather than the Mc4. If you use the Mc4 then it is best to spread all the strings very all the terminals. Heat is an issue in the cables.

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peternielsen avatar image peternielsen Alexandra ♦ commented ·

@Alexandra So i have two options, combine all the strings from each side of the roof in a combiner box close to the panels then run two sets of cables that will carry 120V 30A and 120V 40A or i can pull all the cables closer to the MPPT charge controller and combine them there. I believe it's best to combine them close to the panels. No ?

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wkirby avatar image wkirby ♦♦ commented ·

240V is getting a bit too close. Remember, this is at 25°C. If you gett good sunshine and the panel temperature drops below ~7°C then the open circuit Voltage will be more than 250V. In hot climates then you'll probably be fine.
Maybe better to go with 4x3 and suffer the power loss in the cable.

Power loss in the cable. 15 metre run of 6mm² = 30 metre round trip.
6mm² cable ~3.3mΩ / metre x 30 = 0.1Ω in total.
So, at 30A, 30²x0.1 = 90W lost to heat in the cable. At 20A you lose 40W in the cable.

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peternielsen avatar image peternielsen wkirby ♦♦ commented ·

@WKirby i was always calculating using 15m but i can see i need round trip according to your calculation so in total i will lose one the 3x3 array 9W and on the 3x4 array i will lose 16W so in total 25W out of 6510W (21 panels of 310W) ? That would be 0,38%, doesn't sound right. What am i doing wrong ?

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