Victron 250/100 that has 3 MC4 connections

[cyberfed]

I'm tagging @sunshine_eggo as I saw a previous post that you seem to well versed in this area. I need some help understanding exactly how the 3 sets of MC4 connectors work with say series/parallel arrays and what happens at the end when it hits the Victron. Let me say I read the entire manual (not the little card but the 80 page PDF on the SCC). It seems that the 270/100 acts as a busbar or better put parallels the connections from each input of the 3 sets of MC4 connectors.

I have the 270/100 in my Amazon cart, waiting to buy it until I understand more. The version with the 3 MC4 connectors is attractive to me because I figure I can spec out each set on the Victron to come in just under 30A per set for a total of 90A.

But I'm a bit confused, again I read on a post that it basically acts as a parallel connection. So I'm a bit confused with what at the end end of the day I get into the Victron.


I have 12 panels that have shipped, they are 245watt panels (second hand). The plan of course it to build an array to help maximize getting all the wattage possible to the MPTT. I know I'm going to need to go into a series parallel type configuration to ensure I stay under the 250V limit of the Victron as well as 30 A per MC4 coonnection.

Voc = 38.7
ISC = 8.63

Now assuming these were new panels and got their ratings (which I'm sure they will not) 5 in series is the max before I go over the limit on the voltage for the Victron at 284V.

Since I have (or will have if I order it) 3 MC4 connection "sets" on the SCC 2S2P would yield ~34A at 95V. I know this is over the 30A limit. But given these panels are used it's probably safe to assume I will not get over 30A in a 2S2P. Yes I'm "assumming" but for the sake of discusion lets say it doesn't go over the limit because we'll pretend for discussion that 2S2P yields 25A. Ok cool so if that were true I would do three sets 2S2P for each of the MC4 connectors, giving me in a perfect "assumption world" 95V and 25A per MC4 connection.
Would the Victron treat this as a parallel connection inside the unit and see each MC4 as 95v/25a, 95v/25a, 95v/25a and give me 95v/75a?
Just trying to understand how the Victron finishes the math.

I want to obviously stay within the limits of the unit as well as spread the panels in different positions to capture more of the afternoon sun. Now also I have to step into the real world of 30A MC4 limits. I suppose its possible the panels will yield more than that in a 2S2P configuration. I was playing around with the victron calculator and it seems the optimal configuration is 4 panels in series and 3 "strings".

My brain says that means that as I need to put 4 panels in series to make 1 string (189V 17A). Repeat this 3 times --using up all the panels and plug each MC4 connector and inside the Victron it'll be treated basically as a 4S3P connection. So 189V 17A in parallel 3 times giving me 189V 51A. Yes? No?

The Victron calculator of course takes into account all the other factors and gives me the following numbers when I put in the solar panel specs and do 4 series 3 strings in the calculator...

System calculations​

PV input voltage
PV max. voltage @ min. temperature	168.7 V
PV min. voltage @ max. temperature	101.9 V

PV input voltage
MPPT max. input voltage	250 V
MPPT min. input voltage @ mpp	59 V
Output current
MPPT max. output current	100 A
PV max. current @ MPP min. temp.	68.3 A
PV max. current @ MPP max. temp.	52.6 A
PV power ratio	51% (undersized)

Am I complete off base here on how the MC4 connectors work on the unit. Yes before someone says it I fully understand I do not need the 250/100.

My problem is I will need to reconfigure panels to charge my self made 24/48V packs. So that's the draw to the MC4 connectors vs cable connections (which would ultimately lead me to a combiner box). Sometimes I will likely end up disconnecting some panels and re-arranging them especially for 24V charging. Or I may end up having the 12 panels split up to charge 2 packs or maybe 3 packs at once mix of 24/48. So its not a stationary setup by any means in terms of wiring. Now if I'm charging a 48V pack and dont need to charge anything else of course I'm going to use all 12 panels to charge it with as many amps as I can throw at it, the BMS and batteries can can handle 100A (BMS) 180A (batteries).

I have the 250/70 with wires right now. But seems like unlike most people I am drawn to the MC4 connections for ease of use. I'm sure this could also be done in the combiner box - the rearranging I assume?

Last question I know that Windynation sells 8AWG wire w/MC4 connections. Does that change the amperage limit, I know cable-wise it does but is the 30A limit due to the physical MC4 connector itself? I was planning on ussing 8AWG MC4 cables everywhere (minus what's going to my battery pack, that'll be thicker). I'm hoping someone can understand my confusion and what I'm struggling with. Its hard to explain..I think I'm going to invest in a Solar Panel meter to measure each panel on a sunny day to see what they will actually produce. I guess if nothing else can someone explain with an example how the 3 MC4 connectors finish the math in a series/parallel situation.

Thanks in advance to anyone who can help with this hot mess of questions. Sorry

 

[cyberfed]

FYI the 8AWG MC4 Cables.. does this change things?

 

[sunshine_eggo]

The 3 sets of MC4 are in parallel.

Each MC4 has a 30A limit. The 250/100 has a 70A input limit, so the sum of the three should not exceed 70A.

4S3P array with each string into a pair of MC4 connectors would have a nominal 154.8Voc. Each MC4 would have 8.63A Isc (under 30A), and the total into the MPPT would be about 27A (under 70).

You would need an inline MC4 fuse on each string.

 

[robbob2112]

SOooo

I was thinking about the 250/70 and ended up with the 250/100 TR model - Why you ask - The 250/100 with the terminal screws works with larger wire as a combined feed from a combiner box. This means you don't need to run your stuff all the way from the arrays to the MPPT as 3 separate lines.

The combiner box gives a place to fuse each string, add a SPD either per string or more commonly just to the combined set.... I can't figure why someone would do SPD per string verse SPD per box...

And I like the idea of a breaker to cut off the solar panels per string.

And - do yourself a favor and make sure to buy from a vendor that will support it in the future - Current connected comes to mind

When I was MPPT in box on amazon I happened to read a thread where someone bought a MPPT and it failed but they couldn't get the vendor to respond.... so I ordered from CC.

 

[cyberfed]

Awesome thank you guys. So on the Victrons w/the MC4 inputs just think of them as paralleling with its neighbors (2 other MC4 connectors) got it. Thank you, I thought that was the case but wasn't sure! That being said I'm giving more thought to the combiner box and just sticking with the 250/70 I already have. I guess I will need to read up on those more, I have the basic understanding of them, I saw the price of one from Midnight solar "pre wired" woah boy basically $1K but I get it, they quality components..

Is it possible to charge 2 or 3 banks of batteries some 24V and some 48V with multiple SCC's coming from a single combiner box?

I do agree on the other points you made as well, it will be fused in line and a PV disconnect for each string is already planned as well. I always look at the output part of the combiner box and wonder how it manages to keep a water tight seal for 2 larger cables (4 AWG 2 AWG..) or do you need to punch out another hole and wire it up that way one for pos one for neg to keep the box weatherproof?

I bought my Victron's through Amazon, but through Inverters-r-us which is an authorized reseller of Victron. I've had no issues with support, while troubleshooting an annoyance more than anything else they sent me a new bluetooth adapter to try out, that was cool (didn't solve the annoyance though lol).

Thanks guys! Any good links to get good info on a combiner box and more importantly how all the wires go? I think I understood it from watching the video from Midnight solar. All pos to pos, all neg to neg busbars ground of the PVs themselves to ground busbar and then one pos/neg out of the proper gauge to the battery bank. I think..

Cheers

 

[sunshine_eggo]

Is it possible to charge 2 or 3 banks of batteries some 24V and some 48V with multiple SCC's coming from a single combiner box?

Yes, if each MPPT has its own array.

If you try to connect one array to multiple MPPT, they will constantly fight over it trying to find the maximum power point as their efforts will influence each other.

MPPT 1 pulls a load
MPPT 2 pulls a load
:LOOP
MPPT 1 sees the power decrease, MPPT 1 reduces the load
MPPT 2 sees more power available, MPPT 2 increases the load
MPPT 1 restarts algorithm and pulls a load
MPPT 2 sees the power decrease, MPPT 2 reduces the load
MPPT 1 sees more power available, MPPT 1 increases the load
MPPT 2 restarts algorithm and pulls a load
Goto LOOP