Sorry if this is a dumb question….
I have a 250/85 MPPT, two strings of panels that come into a combiner box (output then to MPPT). The strings are 200V each and 14 Amps (in series). I’m assuming because the combiner box puts the strings in parallel that the output to the MPPT would be 200V @ 28 Amps and therefore within the 250V limit?
Since you dont provide all technical details, or at least the exact model names, on the combiner box or the panels we also can only assume.
If the combiner puts the string in parallel, which i would guess all do (havent seen one that does a series connection, but you never know), then you add the currents together, that is correct.
If in doubt, use the MPPT calculator
Thank you. I’m not sure what good the specs of the devices/panels would do as the question is about (2) 200V arrays at 14 Amps each (that’s a given) would result in 200V and 28 Amps to the Victron 250/85 MPPT from the combiner box when the combiner box connects those two strings in parallel before sending the total power to the MPPT. It’s likely a rhetorical question but it felt odd to have (2) 200V arrays not exceeding the 250V limit of the MPPT even though the standard calculations would say that it’s ok. Looking for a sanity check so I don’t blow up my MPPT!
The specs would tell us if you used Vmp or Voc and what the temperature coefficients are of the panels. Your setup might overshoot 245V in the cold, which is the limit for the 250 MPPTs. Without the full specs its not a sanity check but only another guesstimate.
Touche. You’re absolutely right. Voc of 37.4 per panel and 5 panels per string in series – those two strings are connected in parallel. I used the 200 V number simply as a high end possibility (in Florida so temp never goes lower than -5 C). However, the real question I was asking (which again was likely rhetorical and not super clear) is that the resulting paralleled output of the combiner box would not exceed the 250V limit of the MPPT.
Let me break this math question down to its simplest form. I am not looking for validation of my system design. I’m asking what I hope is a simple math question. It’s not dependent on Voc, wire gauge, model number or ambient temperature in Zambia. Just a math question.
2 arrays.
Each bringing in 200V at 14amps.
Arrays are tied together in parallel.
Is resulting output 200V at 28amps?
Yes
Very much appreciated.