FM100 and String Sizing Tool

Discussion about the FM100, FM80, and FM60 Charge Controllers

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My RE system: Two systems:
- Dual Radian 8048's, two FM100's, 10.3kw pv, 12 Simpliphi 3.5's, 1 Kohler 14Resa, 1 Honda EU7000IS
- SystemEdge FP1 3648, FM80, 1 Simpliphi 3.4

FM100 and String Sizing Tool

Post by Jpro556 » Sat Mar 30, 2019 12:19 am

Hi All,

According to the latest string sizing tool, I can have 3 strings of 5 panels connected to an FM100.
Using Solarworld SW350's, at minimum temp of -25F, bumping the voltage up to around 281Vdc of Min Temp VOC for each string.

This is a little confusing to me because the FM100 is supposed to only have input wattage of 6000W. The array STC wattage is 5250W, but at Min Temp VOC, and Isc of 9.8A, I get about 8260W.

The String Sizing Tool puts this configuration in the green zone as ok. Is it really? Will my FM100 be ok if Array Wattage spikes over 8kw from time to time in the winter?

I want to make sure I don't blow a $1000 Chrg cntrlr.

Thanks for any insight

Mike Curran
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My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 repl'd MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied, no longer AC- coupled

Outback Skybox - Barn roof: (2019)
- 14 (2x7) Talesun 275W (DC array input to SB charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 modules

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: FM100 and String Sizing Tool

Post by Mike Curran » Sat Mar 30, 2019 4:51 am

STC rating is at perfect solar irradiance conditions - 1000W/m^2, 25┬░C. Your 8,260W calculation is based on minimum ambient temperature and Isc, which you'll probably never see in real life. You'd be better off considering the PTC rating of your panels, which reflects more of a "real life" condition. I'd say you're probably okay. ... -solar-ptc

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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: FM100 and String Sizing Tool

Post by raysun » Sun Mar 31, 2019 9:47 am

Calculating maximum PV power by using VOC and ISC leads to erroneous results. No system can be simultaneously in an Open Circuit and Short Circuit state.

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