Am I sizing my SCC incorrectly

[tony95]

I have 8 panels with the specs shown above. I thought I needed a 100amp SCC to charge my batteries. I have 2x 100ah in series for 24V. I used an amp calculator with 335w, 46V, 8 Panels and it say it is 60 amp. Not sure if that is correct. The DC output side is 24v so does that means I need 100 amp output? The SCC seems to be describing input voltage not output voltage, see link. Is the 60A rating for both or just input?

Amazon.com

This calculator is giving me 71 amp to SCC

Solar Charge Controller Calculator

www.explorist.life

 

[rmaddy]

8 335W panels is 2680W. 2680W at 24V requires up to 111A of charge current. Since you likely won't get 100% from the panels and most of the time your battery will be more than 24V, 100A is plenty big enough.

60A charge current x 27.5V battery = 1650W. If you had a 60A charge controller then any time your panels could produce more than 1650W the extra power potential would go unused. The 60A of the linked controller is referring to the charge current out to the battery. It's too small.

Go with a 100A controller or go with 2 50A controllers in parallel.

Another option, given how much solar you have, is to create a 48V system instead of 24V. Then you only need one 50A controller.

But why so much solar for so little battery? You only have 2 12V 100Ah. That's only 2560Wh. 2680W of solar will be able to recharge that from 0% to 100% in an hour. Make sure those batteries support a 100A charge current. Some don't support that much charge current.

Input voltage is another important, more important actually, factor. The Voc of your solar array, adjusted for the coldest temperatures you will encounter, must be less than the SCC's max input voltage. Given a Voc of 46.81V, if you put your 8 panels in 2S4P, you will need a 150V controller since 2 x 46.81V = 93.62V. That will go over 100V at a temperature below 36ºF/3ºC. If you will NEVER see such temperatures then a 100V controller could work.

 

[tony95]

I am running them all in parallel, so I will not go over 100V.

 

[tony95]

I was originally going to run two 40a SCC, Now I am looking at

Amazon.com

 

[tony95]

If I go with the 100a SCC what size break would I need in front of it? Just in case it gets super cold. But when it is super cold there isn't much sun and what sun there is is so low in the sky wit will be obstructed by the tree line

 

[tony95]

Solar Charge Controller Calculator

www.explorist.life

 

[schmism]

Go with a 100A controller or go with 2 50A controllers in parallel.

You can not have the same pannels wired to 2 SCC. The SCC's "fight" each other. You can still do 2 50A controlers, you just have to split the array in half. (4 home run wires, not 2)

 

[rmaddy]

The breaker between the SCC and the battery should be 125% of the rated charge current output. So a 100A SCC should have a 125A breaker using at least 4AWG. 2AWG might be better.

 

[rmaddy]

You can not have the same pannels wired to 2 SCC. The SCC's "fight" each other. You can still do 2 50A controlers, you just have to split the array in half. (4 home run wires, not 2)

I definitely meant 4 panels to one and 4 panels to the other, if two SCCs are used.

 

[tony95]

I definitely meant 4 panels to one and 4 panels to the other, if two SCCs are used.

Yes, I asked about this early. I am wanting to go with a single SCC and 8 gauge wire but maybe I am better off sticking with the split.

 

[MisterSandals]

You should strongly consider getting SCCs with a higher input voltage than 100V because of your panels. That is a terrible match.

You can make your life and installation half as complicated by just getting an SCC (two actually) that accepts at least 125V input.
Then you can run 2S2P for your 2 arrays. Easy easy.

 

[rmaddy]

Yes, I asked about this early. I am wanting to go with a single SCC and 8 gauge wire but maybe I am better off sticking with the split.

If you used one SCC and put your 8 panels in parallel then you can't use 8AWG wire. The panels in 8P would put out 72A of current. You would need at least 4AWG. Depending on the length from the panels to the SCC you would might need 2AWG.

Getting a 150V 100A SCC allows you put the panels in 2S4P which means only 36A. Then you might be able to use 8AWG if the distance is short enough. Likely 6AWG.

Or using 2 150V 50A SCC each with 4 panels as 2S2P would likely allow for 10AWG between the panels and SCCs. This setup would also preclude the need for any combiner boxes since you won't have 3 or more panels in parallel. The other setups require combiner boxes and lots of extra fuses/breakers.

 

[timselectric]

All in parallel, is not the best option. The wiring is going to cost way more than buying a better SCC.

 

[tony95]

All in parallel, is not the best option. The wiring is going to cost way more than buying a better SCC.

I am not doing any panels in series because of the shading I am dealing with. I will have to do 4 panels in parallel and 2 SCC. I think the charge controller can't accept anything bigger 8 AWG. Maybe I need 4 SCC? My run is at least 50feet.

 

[rmaddy]

4 of those panels in 4P will be 36A. For a 50' run (100' round trip) you will need at least 6AWG. You may still be able to do 2S2P even with shading. It depends on the nature of the shading and how you arrange the 4 panels.

 

[tony95]

4 of those panels in 4P will be 36A. For a 50' run (100' round trip) you will need at least 6AWG. You may still be able to do 2S2P even with shading. It depends on the nature of the shading and how you arrange the 4 panels.

What determines the gauge, is it only the amps or does voltage play any part in the calculation. Do you have a link to a calculator online?

 

[rmaddy]

What determines the gauge, is it only the amps or does voltage play any part in the calculation. Do you have a link to a calculator online?

The ampacity is the primary followed by voltage drop. You could use lower gauge wire but then you would lose a lot of the panel voltage on the way to the SCC. Kind of defeats the purpose.

I really like the Blue Sea wire and fuse chart. They also have an app for your phone.

See the following:

Their online calculator: http://circuitwizard.bluesea.com which also has links to the phone apps.

Their wire/fuse chart: https://d2pyqm2yd3fw2i.cloudfront.net/files/resources/reference/20010.pdf

When dealing with PV wire runs you need to account for the higher voltage. In your case I would choose a 24V system and then enter just half of the actual roundtrip distance. If you go with 2S then use 1/4 the roundtrip distance. You want the PV voltage drop to be as low as possible (under 3%).

 

[MisterSandals]

am not doing any panels in series because of the shading I am dealing with.

Putting pairs in like-shaded areas is all it takes to make this 5x easier.
So 4 pairs is fairly good for shading issues.

That’s the last I will say on this. Sorry if too many already. It’s good advice.

 

[tony95]

Putting pairs in like-shaded areas is all it takes to make this 5x easier.
So 4 pairs is fairly good for shading issues.

That’s the last I will say on this. Sorry if too many already. It’s good advice.

I understand, thanks

 

[tony95]

The ampacity is the primary followed by voltage drop. You could use lower gauge wire but then you would lose a lot of the panel voltage on the way to the SCC. Kind of defeats the purpose.

I really like the Blue Sea wire and fuse chart. They also have an app for your phone.

See the following:

Their online calculator: http://circuitwizard.bluesea.com which also has links to the phone apps.

Their wire/fuse chart: https://d2pyqm2yd3fw2i.cloudfront.net/files/resources/reference/20010.pdf

When dealing with PV wire runs you need to account for the higher voltage. In your case I would choose a 24V system and then enter just half of the actual roundtrip distance. If you go with 2S then use 1/4 the roundtrip distance. You want the PV voltage drop to be as low as possible (under 3%).

Cool, thanks. One more question. If an MC4 Y connector is rated 30a 1000VDC does that mean you can't exceed 30a or you can exceed it at lower voltages?