Which Victron SCC ?

[getalab]

I’m planning 4 x 305w panels, specs
VOC 39.9
VMP 32.3
ISC. 9.76
In series, that’s 159.6v/9.76A
Series/parallel gives 79.8V/19.52A
I assume the 100/50 would work as minimum, and the 150/45 would work and offer a little expansion.
My confusion is the 79.8V X 19.52A = 1557 watts, which is over the allowed watts for each unit.
I assume you use VOC for one calculation, and VMP for another. Will either unit work as I’ve described?

 

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As I learned, the max power for a Victron MPPT depends on the voltage of your battery bank. See

What is the Max Power capacity of Rich (Renogy,etc) MPPT?

So, I know that the Rich Solar 20 MPPT can handle a maximum of 20 Amps. So, in theory, since it has a max input voltage of 100 volts, it should handle 2000 Watts of solar power. Right? But, the Victron brand of MPPT's - which, arguably are much more robust products - are not rated for I x V =...

diysolarforum.com

 

[getalab]

This is a 24v system, as at 12v these units only support 650/700 watts respectively.
When I take the 79.8 VOC and multiply it by the 1.22 for some headroom, I get 97.3v. This seems to cut it close for the 100/50, suggesting the 150/45 is better choice. Correct?

 

[mrdavvv]

I’m planning 4 x 305w panels, specs
VOC 39.9
VMP 32.3
ISC. 9.76
In series, that’s 159.6v/9.76A
Series/parallel gives 79.8V/19.52A
I assume the 100/50 would work as minimum, and the 150/45 would work and offer a little expansion.
My confusion is the 79.8V X 19.52A = 1557 watts, which is over the allowed watts for each unit.
I assume you use VOC for one calculation, and VMP for another. Will either unit work as I’ve described?

Doesnt matter if you overpanel / overwattage a little bit. Just dont pass the voltaje limit Your assumption of using the 150/45 for a greater margin its correct (I think).

You should use the VOC in this situation, as its the maximum voltage that the panels can produce, and the one that can end up damaging the SCC.

 

[unsubscribed]

I bough the 150/35 and am now wishing that I had bought the 100/50, since it can handle 1400 watts (in a 24 system. (Whereas mine is limited to 1000W.)

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

 

[getalab]

Doesnt matter if you overpanel / overwattage a little bit. Just dont pass the voltaje limit Your assumption of using the 150/45 for a greater margin its correct (I think).

You should use the VOC in this situation, as its the maximum voltage that the panels can produce, and the one that can end up damaging the SCC.

Thank you. Max voltage should be 97.3, and at 1220 watts I’m under the 1300w max of the 150/45 at 24v.
Thx again.

 

[MisterSandals]

When I take the 79.8 VOC and multiply it by the 1.22 for some headroom, I get 97.3v. This seems to cut it close for the 100/50, suggesting the 150/45 is better choice. Correct?

What is your coldest temperature in your area? That will let you calculate the max Voc accurately rather than using a rule-of-thumb.

 

[getalab]

What is your coldest temperature in your area? That will let you calculate the max Voc accurately rather than using a rule-of-thumb.

In the mid south, so temps of 20 F on occasion. Having 50v left over on the 150/45 should more than cover that. I assume.

 

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I expect that you'll end up using a 2s/2p configuration. Seems like the best.

 

[MisterSandals]

In the mid south, so temps of 20 F on occasion. Having 50v left over on the 150/45 should more than cover that. I assume.

Yes 150/45 is a big hefty SCC.

For the sake of doing the math, let me see if i can muddle thru this.
Using a temp coefficient of .4 (if your number is significantly different as listed on the panel let me know, its almost always between .3% and .5%):

That changes the voltage .4% for every degree the temperature is below 25C where the panel Voc is rated.
20F = -6.7C which is a change of 25+6.7= 31.7

At YOUR lowest temp the panel Voc will be: (39.9v x (1 + (31.7 x .004))) = 44.96Voc

Gosh its been a while, did i do that right?

 

[getalab]

Yes 150/45 is a big hefty SCC.

For the sake of doing the math, let me see if i can muddle thru this.
Using a temp coefficient of .4 (if your number is significantly different as listed on the panel let me know, its almost always between .3% and .5%):

That changes the voltage .4% for every degree the temperature is below 25C where the panel Voc is rated.
20F = -6.7C which is a change of 25+6.7= 31.7

At YOUR lowest temp the panel Voc will be: (39.9v x (1 + (31.7 x .004))) = 44.96Voc

Gosh its been a while, did i do that right?

Looks good to me? The Seraphim 305w spec sheet didn’t mention temp. I don’t have panels yet to check there. Thanks for info.

 

[MisterSandals]

The Seraphim 305w spec sheet didn’t mention temp.

https://www.renvu.com/Solar/Solar-Clearance/Seraphim-305W-Mono-60-Cell-All-Black-SEG-6MB-305WW

• Temperature Coefficients of V (Uoc)-.32