Pecron F5000LFP We own this
This calculator’s worked example is the unit we own. Manufacturer published limits on each of two inputs: 180V, 25A, 3,200W (2x XT60/XT60i at 3200W each, 30-180V).
MPPT wiring
Solar string sizing calculator
Check a series and parallel arrangement against cold-weather voltage, current and power limits. Start with our setup or enter your own equipment.
Check your panel arrangement
Enter values from the exact panel and controller manuals. All limits and results apply to one MPPT input. The preset is our SunPower E20-330-COM / Pecron F5000LFP example.
YOUR ESTIMATE
Example per input: 2 in series × 3 parallel strings = 6 panels, 152.8V cold Voc, 19.56A short-circuit current and 1,980W nameplate power. Fuse protection needs review.
Use V/°C, not %/°C: multiply a percentage coefficient by panel Voc and divide by 100. These checks cover cold open-circuit voltage, summed Isc and nameplate power only. They do not verify operating voltage, separate short-circuit ratings, controller-specific oversizing allowances, wiring, connectors or installation compliance. A result within these limits is not installation approval.
Worked example: our twelve-panel array
Three limits decide a wiring plan. Series count is capped by panel open-circuit voltage in the cold — Voc rises as temperature falls, so an array sized from the 25°C datasheet number can overvolt the controller in winter. Parallel count is capped by the input's current limit. And once you run three or more parallel strings, the others can backfeed a faulted string, which requires in-line fuses if(strings − 1) × Isc × 1.25 exceeds the module's maximum series fuse rating.
Worked example: a SunPower SPR-E20-330-COM (330W,64.9V Voc, 6.52A Isc) into aPecron F5000LFP (180V / 25A /3,200W per input).
Why cold matters more than heat
Open-circuit voltage climbs as panels get colder. For this panel the coefficient is -0.1766 V/°C (SunPower E-Series E20-330-COM datasheet), so a string that measures safe on a warm afternoon can exceed the controller's ceiling on a clear winter morning — the worst case is a cold, bright, no-load moment right at sunrise.
| Cell temp | 1 panel | 2 in series | 3 in series |
|---|---|---|---|
| 40°C | 62.3V | 124.5V | 186.8V ✗ |
| 25°C | 64.9V | 129.8V | 194.7V ✗ |
| 0°C | 69.3V | 138.6V | 207.9V ✗ |
| -20°C | 72.8V | 145.7V | 218.5V ✗ |
| -40°C | 76.4V | 152.8V | 229.1V ✗ |
Three in series fails at every temperature in this table, including a hot 40°C day. It is not a cold-weather edge case — it simply does not fit. Two in series stays below the voltage ceiling across these temperatures; that alone does not establish complete system compatibility.
Every wiring option, checked
| Wiring | Panels | Cold Voc | Current | Watts | Verdict |
|---|---|---|---|---|---|
| 1S × 1P | 1 | 76V | 6.5A | 330W | OK |
| 1S × 2P | 2 | 76V | 13.0A | 660W | OK |
| 1S × 3P | 3 | 76V | 19.6A | 990W | Fuses required |
| 1S × 4P | 4 | 76V | 26.1A | 1,320W | Over current limit |
| 2S × 1P | 2 | 153V | 6.5A | 660W | OK |
| 2S × 2P | 4 | 153V | 13.0A | 1,320W | OK |
| 2S × 3P | 6 | 153V | 19.6A | 1,980W | Fuses required |
| 2S × 4P | 8 | 153V | 26.1A | 2,640W | Over current limit |
| 3S × 1P | 3 | 229V | 6.5A | 990W | Over voltage limit |
| 3S × 2P | 6 | 229V | 13.0A | 1,980W | Over voltage limit |
| 3S × 3P | 9 | 229V | 19.6A | 2,970W | Over voltage limit |
| 3S × 4P | 12 | 229V | 26.1A | 3,960W | Over voltage limit |
| 4S × 1P | 4 | 306V | 6.5A | 1,320W | Over voltage limit |
| 4S × 2P | 8 | 306V | 13.0A | 2,640W | Over voltage limit |
| 4S × 3P | 12 | 306V | 19.6A | 3,960W | Over voltage limit |
| 4S × 4P | 16 | 306V | 26.1A | 5,280W | Over voltage limit |
Choosing modules for this station? Read the F5000LFP solar panel and array-sizing guide.