Mismatch Series / Parallel in 5 Panel Configuration

[charlesrg]

I've limited roof space and wanted to use the most out of the panels with less components a possible.
I have a total of 5 Panels LG440QAC-A6 and a Victron MPPT 150-85
Looking to have a series with the first 3 Panels in Parallel connected to 2 panels in parallel, behind the MPPT charge controller.
Just like in this diagram:



Do you guys think this would still be able to generate 2200Watts in perfect conditions ? Or should I just get a second MPPT wired to the 5th panel?

The Victron calculator shows that the MPPT could handle all panels.

 

[MisterSandals]

Looking to have a series with the first 3 Panels in Parallel connected to 2 panels in parallel, behind the MPPT charge controller.

When you combine in parallel, the voltage of both strings is restricted to the lowest voltage string. This will essentially make your array 2S2P, negating the 5th panel.

Or should I just get a second panel wired to a single MPPT ?

Huh? Do you mean get a 6th panel or wire the 5th panel to a 2nd SCC? Or??

 

[sunshine_eggo]

I've limited roof space and wanted to use the most out of the panels with less components a possible.
I have a total of 5 Panels LG440QAC-A6 and a Victron MPPT 150-85
Looking to have a series with the first 3 Panels in Parallel connected to 2 panels in parallel, behind the MPPT charge controller.

3P in series with 2P will cripple the 3P to the lower current of the 2P as all items in a series circuit must experience the same current. Might as well only have 4 panels.

Why not 5P? that will work great on either a 12 or 24V system. Will need a 20A MC4 fuse for each panel.

Do you guys think this would still be able to generate 2200Watts in perfect conditions ? Or should I just get a second panel wired to a single MPPT ?

Almost never. Since they're flat on a roof, there can't be perfect conditions. Furthermore, when the sun is in the other hemisphere, you'll be lucky to get 30-40% of rated power flat on a roof.

 

[charlesrg]

After some research I found that using all the panels in Parallel will be supported and that should lead to best performance.
This also helped:

Solar Panel Series & Parallel Calculator - Footprint Hero

Use our solar panel series and parallel calculator to easily find the wiring configuration that maximizes the power output of your solar panels.

footprinthero.com

 

[MisterSandals]

panels in Parallel will be supported and that should lead to best performance.

Note that with an Isc of 11.2A, the combined amperage will be 56A. So you will need a combiner box and a fuse for each panel. Following 5P combining, your wiring and fusing will need to handle ~75A (so no MC4 connectors).

 

[charlesrg]

Note that with an Isc of 11.2A, the combined amperage will be 56A. So you will need a combiner box and a fuse for each panel. Following 5P combining, your wiring and fusing will need to handle ~75A (so no MC4 connectors).

Will be using 4AWG wire, have about 12 feet for the longest run.

 

[charlesrg]

Note that with an Isc of 11.2A, the combined amperage will be 56A. So you will need a combiner box and a fuse for each panel. Following 5P combining, your wiring and fusing will need to handle ~75A (so no MC4 connectors).

A combiner box in the roof will be hard. I think will just convert the MC4 to heavy 4AWG wire.

 

[charlesrg]

When you combine in parallel, the voltage of both strings is restricted to the lowest voltage string. This will essentially make your array 2S2P, negating the 5th panel.

Huh? Do you mean get a 6th panel or wire the 5th panel to a 2nd SCC? Or??

I meant to say to get another MPPT charger and wire to the 5th panel.

 

[charlesrg]

Why not 5P? that will work great on either a 12 or 24V system. Will need a 20A MC4 fuse for each panel.

It will be lots of current, but why do you feel a fuse will be necessary ? My plan was to use a 60-70Amp fuse for the entire installation.

 

[Jet]

Can you return the charge controller?
You could get the 250 victron 250/70 or 250/85 mppt instead and connect all five in series. Or trade some one your large MPPT for two 150/35 or 45. Do away with the combiner box as you will only have one string per charge controller.

 

[charlesrg]

Can you return the charge controller?
You could get the 250 victron 250/70 or 250/85 mppt instead and connect all five in series. Or trade some one your large MPPT for two 150/35 or 45. Do away with the combiner box as you will only have one string per charge controller.

That is a good idea, however Victron calculator does not recommend using the 250V/85 as all panels series voltage will get very close to it. I would have to get a charge controller from down under I think Outlaw solar has a 300V MPPT.
I'm trying to avoid having two charge controllers to reduce the amount of components since this all go into a truck camper.

 

[Jet]

That is a good idea, however Victron calculator does not recommend using the 250V/85 as all panels series voltage will get very close to it. I would have to get a charge controller from down under I think Outlaw solar has a 300V MPPT.
I'm trying to avoid having two charge controllers to reduce the amount of components since this all go into a truck camper.

I added up the VOC of the panels before my original comment and thought they were a bit close with 3 of them for the 150. The panel voltage for three solar panels on 150 should be the same as 5 on 250. The 300 volt would definitely be better. Less wires and no combiner box doing a small build where every inch counts can be advantageous. Two mppt adds redundancy. If one fails you can still charge the battery without a generator or vehicle alternator while waiting for a replacement.

 

[Jet]

Out of curiosity, I'm wondering does anyone know if it's dangerous to have three panels on one string and two on the other going to a combiner box as OP said or is it just bad practice? I realize the fifth panel wouldn't be useless in that configuration. However, a six panel could be carried in the vehicle and ground mounted and added to the system at the campsite.

 

[Rocketman]

When you connect three or more (I.e. 5) panels together in parallel you need to fuse each panel - a 20a fuse as recommended above.

They make MC4 fuses that just go in inline on the positive wire.

If you want to carry the 6th panel, I think it would be best to wire them up as 2s3p (with 3p you will still need 3 fuses). The four panels-2s2p will be permanent wired - then for the third parallel string, use 45a Anderson Connectors (or something like that) to connect the third string - and close the circuit (Quick and simple).

That way when you are traveling or don’t setup the 6th panel the four work just fine with 2s2p. Also this will drop the current. The 2s2p could use MC4 10awg wire. Same with the 5th and sixth panels- then from the combination point to the mppt- 8 or 6 awg would be needed (that could be done inside - although that would mean you would have 2 penetration sets instead of one.

<edited out incorrect info>

To get to full power with flat panels it takes Noon in June with Perfect sky’s and batteries that are still in Bulk.

Good Luck

 

[sunshine_eggo]

It will be lots of current, but why do you feel a fuse will be necessary ? My plan was to use a 60-70Amp fuse for the entire installation.

The wiring for each panel is insufficient to withstand the current from the four other panels should a short develop in one panel, e.g., if panel one goes dead short, panels 2-5 will pass their Isc - upwards of 44A through the single panel's wire... likely no thicker than 10awg.

Fuses/breakers protect wires. In the above scenario, the single shorted panels fuse would blow, and it would be taken out of the circuit, thus protecting that panel's wiring and restoring the function of the 4 remaining panels.

Out of curiosity, I'm wondering does anyone know if it's dangerous to have three panels on one string and two on the other going to a combiner box as OP said or is it just bad practice?

I presume you mean 3S in parallel with 2S? How well do you expect putting a 24V battery in parallel with a 12V battery would go?

If you can find the room inside - return the 150/85 and get a 100/50 - hook the 2s2p to that one then add a 100/30 and connect the one or two (or three?) panels in parallel.

The 100/50 with 2s2p - 200w panels will be slightly overpaneled. That’s 800w of panels into a 700w mppt. I have that setup on my MotorHome- I have only very occasionally seen it hit the 700w. To get to 700w with flat panels it takes Noon in June with Perfect sky’s and batteries that are still in Bulk.

Absolutely not. These panels have a Voc of 48.2V. You absolutely, positively do not put 96V on a 100Voc limit controller unless you want to buy a new controller, or it NEVER gets below 59°F.

 

[MisterSandals]

A combiner box in the roof will be hard. I think will just convert the MC4 to heavy 4AWG wire.

MC4 is a connector that typically is rated only to 30A. I am not sure if your statement means you intend to put MC4 connectors on 4AWG wire or ??? Replacing a connector with wire does not make sense to me.

 

[charlesrg]

MC4 is a connector that typically is rated only to 30A. I am not sure if your statement means you intend to put MC4 connectors on 4AWG wire or ??? Replacing a connector with wire does not make sense to me.

I'm planning to get the MC4 20Amp fuses connected to the panels, then connect that to a 8AWG MC4 cable and combine it all to a 4AWG cable, might need to use a busbar or weld it all together.

 

[MisterSandals]

connect that to a 8AWG MC4 cable and combine it all to a 4AWG cable,

MC4 is a connector type not a cable (and does not accept anything bigger than 10AWG).

Amazon.com : mc4 connector

The problem remains as to how you connect 5 10AWG wires in a manner that supports 75A.

 

[Rocketman]

Absolutely not. These panels have a Voc of 48.2V. You absolutely, positively do not put 96V on a 100Voc limit controller unless you want to buy a new controller, or it NEVER gets below 59°F.

@sunshine_eggo thanks for fixing my mistake. I confused a couple of posts that thought he was putting in much smaller panels.

 

[sunshine_eggo]

@sunshine_eggo thanks for fixing my mistake. I confused a couple of posts that thought he was putting in much smaller panels.

I can't count the number of times I've confused something... or myself on this site. ?