Victron MPPT Series String MC4 Riddle

[InTheHills]

I was playing with the Victron MPPT Calc trying to figure out which MPPT to purchase to use as many of these 330W 40V 10A panels as possible. The calc spit out this 250V 85A MC4 MPPT using 20 of these panels with 4 in series and 5 strings. How on earth would one go about wiring that all into 3 SETS of MC4 connectors which are limited to 30A each?

 

[ricardocello]

I've got a Victron SmartSolar MPPT 250|100 and a 250|70 VE.Can.
I recommend the terminal version (Tr) over the MC4 versions, those are just dorky, and limited to 30A (as you point out).
Unless you like them.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf

Also, if Victron recommends the 85A, I'd buy the 100A.
I made that mistake buying the 70A thinking it was good enough.

If all of those panels are pointing in the same direction and have no shading issues,
you can put all of them on one big controller by buying/building a combiner box.
It will need 5 breakers/fuses, because more than two strings in parallel require it.

I urge you to consider multiple smaller MPPTs if shading or different directionality's are involved.

 

[InTheHills]

If all of those panels are pointing in the same direction and have no shading issues,
you can put all of them on one big controller by buying/building a combiner box.
It will need 5 breakers/fuses, because more than two strings in parallel require it.

I think the MC4 is the confusing part for me. So if I were to get all that to the combiner box... how does it get to the MPPT given the 30A limitation?

 

[ricardocello]

I think the MC4 is the confusing part for me. So if I were to get all that to the combiner box... how does it get to the MPPT given the 30A limitation?

The 30A limitation should be avoided by getting the Tr version. It's an unnecessary limitation.
If your Isc * 5 strings is above 30A, it could melt the MC4s.
EDIT: unless you split up using all 3 sets of MC4s available per Eggo, see below.

 

[ricardocello]

So if I were to get all that to the combiner box

I don't recommend any of these, I did my own

But here are examples:

https://www.midnitesolar.com/pdfs/pvCombiner_frontBack.pdf

5 Strings Solar Combiner Box

Renogy Solar roof top combiner box is the ideal solution to combine inputs from up to 5 strings of solar panels into a single output. It accepts up to five 1P miniature circuit breakers and one 2P surge protective device for improved safety of the solar system.

www.renogy.com

 

[ricardocello]

OK, I ran it myself with your panels and setup, but selected Terminals.
They shouldn't recommend the MC4 versions, maybe @sunshine_eggo or @Brucey knows why they would do that, I sure don't.

 

[InTheHills]

So jsut for discussion... how would Victron solve this riddle with the MC4 connectors in the equation?

 

[sunshine_eggo]

There are three SETS of MC4 connectors on the 250/100. Each is rated for 30A with a 70A Isc limit on the controller.

Not sure on the specific panel, but I'm guessing Isc is <10A.

4S2P on the first MC4
4S2P on the second MC4
4S on the third MC4

All MC4 are seeing < 20A Isc.

What problem am I missing?

 

[ricardocello]

There are three SETS of MC4 connectors on the 250/100. Each is rated for 30A with a 70A Isc limit on the controller.

Not sure on the specific panel, but I'm guessing Isc is <10A.

4S2P on the first MC4
4S2P on the second MC4
4S on the third MC4

All MC4 are seeing < 20A Isc.

What problem am I missing?

Doesn't sound like there is one! Thanks.

The OP was asking how to go from 5 strings in parallel to 3 MC4s at the MPPT.
I thought you need a combiner box with 5 strings going in, and 3 MC4s in parallel after the combining going out to the MPPT.
Do people really do that? I guess not.

Your approach is better because it avoids the combiner box altogether.

 

[Brucey]

I was playing with the Victron MPPT Calc trying to figure out which MPPT to purchase to use as many of these 330W 40V 10A panels as possible. The calc spit out this 250V 85A MC4 MPPT using 20 of these panels with 4 in series and 5 strings. How on earth would one go about wiring that all into 3 pairs of MC4 connectors which are limited to 30A each?

6600W of panels on an 85A controller is fairly overpanelled I'd go with the 250/100

 

[InTheHills]

There are three SETS of MC4 connectors on the 250/100. Each is rated for 30A with a 70A Isc limit on the controller.

Not sure on the specific panel, but I'm guessing Isc is <10A.

4S2P on the first MC4
4S2P on the second MC4
4S on the third MC4

All MC4 are seeing < 20A Isc.

What problem am I missing?

Your explainination makes it very clear. My problem is that Im ignorant and was reading 4 Series and 5 Strings as 4s5p and didnt understand. Your explanation or conversion helped me translate the 5p in my mind to the reality of 5 STRINGS setup in 2p + 2p + 1 makes it much more clear.

Thank you!

(I changed 'pairs' to 'SETS' in my original post in case that upset you for some reason)

 

[sunshine_eggo]

Your explainination makes it very clear. My problem is that Im ignorant and was reading 4 Series and 5 Strings as 4s5p and didnt understand. Your explanation or conversion helped me translate the 5p in my mind to the reality of 5 STRINGS setup in 2p + 2p + 1 makes it much more clear.

Thank you!

(I changed 'pairs' to 'SETS' in my original post in case that upset you for some reason)

No worries. Not upset at all. I came into it when @ricardocello tagged me, so I think I missed some detail. When someone thinks there's a problem, and I fail to see it, I assume I'm missing something because that's more often true than it's not...

FWIW, MC4 units aren't my first choice. I use a MNPV6 combiner box. It was more expensive, but it's cooler.

Worth noting that since the three MC4 are connected internally in the MPPT, it still counts as a 5P array, and you need an MC4 fuse inline with each string (1 fuse on the (+) line per string, 5 total fuses). When we used parallel MC4 on my neighbor's 3P array to get it down to one 8awg wire on his FM80 controller, we put them right at the controller to make them easy to access.

If that bit has already been discussed... see... I missed some detail.