Charge controller sizing

Need help in sizing panels and charge controller.

Victron energy 150/80 charge controller
355 watt panels, see attachment for specs
12 volt system.
coldest outside temp around -25 cels.

What would the absolute maximum number of panels in any configuration for the charge controller that I have? I currently have 3 but want to add more to the maximu.

Voc of 40.6 makes three series max. May want to check the temp coifficient to see if a low temperature takes that over the 150v limit. 122 probably is enough headroom. The three is just under the max wattage but the controller could be over driven some. Maybe add one more panel and go 2S2P.

Newfiejeff said:

Victron energy 150/80 charge controller

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Do you mean 150/85?

Lets do some math

The controller has a hard limit of 150V. If you have three in series that gives you 40.6 x 3 =121.8V. That is 150/121.8 = 1.23 or a 23% margin. Since we don't know the Voc temp coefficient we can't calculate the rise at -25C, But a 23% margin is probably enough for almost any panel.

However, 4 in series would be 162V. Consequently, to add a panel you would need to go to a 2S2P configuration. That would have an even lower array voltage so there is no concern about cold temp rise.

However. You currently have three 355W panels for a total wattage of 1065W. at 12.8V, that is 1065W/12.8=83A. Therefore, if the panels produce at their full rating, the controller is about maxed out. In reality, most panels only produce at 75% - 80% of their rating so your panels are probably producing around 1065W x .8 = 852W. This translates to 852W/12.8 = 67.6A. Consequently, there is a little unused capacity.

If you add a 4th panel, it would be a nominal 1420W, but probably closer to 1420 x .8 = 1136W. This translates into 88.75A. This means the controller would probably clip a little at mid-day. Any more panels than 4 would have significant diminishing returns.

I vote for 2s2p.

What is the distance between the solar charge controller and the pv array?
The voltage drop may be the deciding factor between 3s1p and 2s2p.
@Newfiejeff do you know the temp coefficient for the panels?

Thanks guys, I am home right now and this is at the cabin which I will be there in the next couple of weeks. I can find out then what the temp cof is then.
There is exactly 100 feet of cable between the charge controller and the panels.

So does clipping the controller each day do any damage?
I am getting the fourth panel this spring. So if I wanted to add extra panels( extra 2 or 3 beyond the 4th panel) after that then I would need another charge controller and another run of wire for them? The wire that was supplied to me was PV wire but don’t know the size, it bought it from a local solar dealer.

distance is 200' round trip

single panel
VOC = 40.6
ISC = 11.25

3s1p
VOC = 121.8
ISC = 11.25
1.92% voltage drop with 10 awg wire

2s2p
VOC = 81.2
ISC = 22.5
9.14% voltage drop with 10 awg
2.25% voltage drop with 6 awg, requires a combiner box

At maximum power point the numbers are a little closer but not much.
single panel
vmpp = 34.6
impp = 10.27

3s1p
vmpp = 103.8
impp = 10.27
vdrop with 10awg = 2.06%

2s2p
vmpp = 69.2
impp = 20.54

vdrop with 10awg = 6.17%
vdrop with 6awg = 2.41%

Maximum voltage (VOC) will be when there is no charging. Wire voltage drop will be 0.
Maybe use some heating pads to keep a load on SCC.
12v heating pads

John Frum said:

At maximum power point the numbers are a little closer but not much.
single panel
vmpp = 34.6
impp = 10.27

3s1p
vmpp = 103.8
impp = 10.27
vdrop with 10awg = 2.06%

2s2p
vmpp = 69.2
impp = 20.54

vdrop with 10awg = 6.17%
vdrop with 6awg = 2.41%

Click to expand...

Yes. To go to 2S2P means the voltage will drop and the current will go up.... this in turn will make the line loss (Voltage drop) much higher if the same size wire is used.

IMHO: Voltage drop from panels is just too messy. It's more relevant to calculate Power Loss in Watts.
You need to find your wiring ohms. Wire resistance calculator
A 25ft run is a 50ft round trip. For 10 gauge it's 0.05 ohms.
Current * Current * Ohms = Watts lost
10A * 10A * 0.05ohms = 5W
Double the current and it quadruples the loss.
20A * 20A * 0.05ohms = 20W
Of course you may never hit that peak.
My panels don't have the same facing, one is better for morning-noon sun, the other for noon-evening sun. Works well for partly cloudy days.

Thanks guys, I have a 10 gauge wire.
will go with 3S1P.
i should have bought a 24 volt inverter/charger

So is this possible? This was on explorist life website.
so I am below the amps and volts of the controller but I would have to toggle down the max output to 85 amps as that is the max charge of the battery.

Newfiejeff said:

So is this possible?

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Well, yes and no.



Nothing directly wrong with that, but a panel almost never outputs it's full wattage. In fact, a good estimate is that a panel will produce 75-80% of it's STC rating. Consequently 2130W x .8 = 1704W is probably more realistic.



The statement is correct, but there is an important point that is missing. If the battery is nearly empty the voltage will be closer to 12V so the current would calculate out to 2130W/12V = 177.5A if you use the STC rating of the panel and but it is more likely that you will see
1704W/12V = 142A.

Newfiejeff said:

So does clipping the controller each day do any damage?

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No, it is meant to be over paneled.

Newfiejeff said:

So is this possible? This was on explorist life website.
so I am below the amps and volts of the controller but I would have to toggle down the max output to 85 amps as that is the max charge of the battery.

Click to expand...

My Victron100/50 Smart Solar max amps can be set below 50A.
The amp rating is for the output. That's where the limitations are. Torroid size, FET current. The controller can monitor current and back off.

i am trying to have loads of power for the fall to spring, so I am fine with just the max of 85 amps. So the question now is as long as I keep the voltage done with configuring the panels I am fine but what about the increased amperage and much can I max on that?