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October 8, 2025 10:42 pm
Hi all - hoping you guys can help me figure out how concerned I should be about this config that my installer is hooking up for the Canadian Solar panels in parallel strings going into 2 flexboss21's.
Panel Specs
Watts (STC):450.0
Watts (PTC):426.4
Voc:38.900
Vmp:33.0
Imp:13.660
Isc:14.550
Voc Temp (%/ºC):-0.2500
Pmax Temp (%/ºC):-0.2900
Isc Temp (%/ºC):0.0500
I see 2 issues...
1- string counts are not the same... my understanding is that in a parallel string config where the panel count is different (10 vs 9), the MPPT will use the lesser of the 2 strings and it would be the same as if there were 9 panels in each string, wasting the 10th panel. I think that I can have them move a panel from stringA to stringD to make the paralleled strings equal.
2- Imp in parallel string config is over the 26A for the MPPT
My installer has the following parallel string setup for each flexboss21:
Inverter1
StringA 10 panels --> String1/MTTP1
StringB 9 panels --> String2/MTTP1
StringC 8 panels --> String1/MTTP2
StringD 7 panels --> String2/MTTP2
StringB 9 panels --> String2/MTTP1
StringC 8 panels --> String1/MTTP2
StringD 7 panels --> String2/MTTP2
Inverter2
StringE 10 panels --> String1/MTTP1
StringF 10 panels --> String2/MTTP1
StringG 6 panels --> String1/MTTP2
StringF 10 panels --> String2/MTTP1
StringG 6 panels --> String1/MTTP2
With the panel's Imp of 13.66 doubled when in parallel strings that would exceed 26A for MPPT1 & MPPT2 of the flexboss21. In fact, the EG4 string sizer calls that out with "Imp Warning - Imp too High". While the manual states that "MPPT 1 and MPPT 2 can each utilize up to 26A of solar input, with a maximum input of 31A. Exceeding 31A can damage the equipment.
o When both strings of the same MPPT are used, the inverter will parallel the two stings together. Each of the single strings cannot exceed 13A. This is to ensure the total amperage of the paralleled strings does not exceed 26A (Imp)."
o When both strings of the same MPPT are used, the inverter will parallel the two stings together. Each of the single strings cannot exceed 13A. This is to ensure the total amperage of the paralleled strings does not exceed 26A (Imp)."
So on 1 hand it says don't exceed 26A(Imp), but also says can utilize up to 26A of solar input, with a maximum of 31A.
My installer is telling me not to worry, and that since Imp of 27.32A is less than Isc of 31A, I'm fine. But am I? It seems to me that the config would be putting stress on the inputs. Would EG4 honor the warranty on the inverters if the input is over 26A?
Appreciate any feedback on this... thanks
October 9, 2025 8:17 pm
You should be fine regarding the amperage. You’re correct, as long as you don’t exceed 31A on MPPT 1 and 2, it will not cause issues. The amperage can increase slightly in hot conditions, but that depends on how high the temperatures get in your area.
As for the warranty, it does not cover issues caused by poor workmanship by an individual, installer, or company. In other words, if you knowingly install the system in a way that could cause damage to the inverter, the warranty will not apply.
