Lunar System PV Installation and Troubleshooting Guide
Application Note | lunarenergy.com
This guide outlines PV stringing requirements and troubleshooting recommendations for the Lunar System, including the Lunar Maximizers (module-level DC converters) and Lunar Maximizer Hub (PV junction box).
Quick PV Install Checklist
Confirm continuity from each Maximizer mounting flange to the Hub's ground terminal.
Measure 20–30 Vdc at each location: each string home run (isolated), Hub DIN rail terminals (all parallel strings terminated), and Inverter PV terminals.
If <20 Vdc: verify stringing between Maximizer outputs, and verify a single solar panel is plugged into each Maximizer input.
If >30 Vdc: verify grounding of Maximizers, starting at both ends of the string.
Voltage Reference Values
Measurement Location | Expected DC Voltage |
5–20 Maximizers (individual string) | 20–30 Vdc |
Maximizer Hub DIN rail terminals | 20–30 Vdc |
Inverter PV terminals | 20–30 Vdc |
1 Maximizer (with PV connected) | 4.5–5.5 Vdc |
2 Maximizers in series | 9–11 Vdc |
Line to Ground (at inverter or Hub) | Positive/Negative to Ground: 9–18 Vdc |
Note: Measure only when Rotary switch is OFF (Rapid Shutdown) or inverter is disconnected.
Design Requirements
PV Module Requirements | 650W Maximizer | 420W Maximizer |
Maximum Rated Power Output | 650 W | 420 W |
Maximum Short Circuit Current (Isc) | 20 A | 20 A |
Maximum Open Circuit Voltage (Voc) | 75 V | 60 V |
Series String Requirements | 650W Maximizer | 420W Maximizer |
Maximum Modules per String | 24 | 20 |
Minimum Modules per String | 9 | 9 |
Maximum Usable Power per String | 6.5 kW | 6.5 kW |
Maximum DC Current per String | 16 A | 16 A |
Parallel String Requirements | Value |
Number of Parallel Strings Allowed | 3 strings |
Uneven String Length Allowed | Yes |
Maximum Total DC Current from PV to Inverter | 37.5 A |
Maximum Total Usable Power | 15 kW |
PV Troubleshooting
Safety: When working on DC PV circuits, ensure the inverter rotary switch is turned OFF first.
When in Rapid Shutdown:
String voltage <20 Vdc → One or more Maximizers are unplugged on inputs/outputs, or a subset have reverse polarity.
String voltage >30 Vdc → One or more Maximizers are not properly bonded together or to the Maximizer Hub.
Negative string voltage → Check multimeter probe polarity; if correct, the string has reverse polarity.
Roof Doctor
Roof Doctor is an optional PV commissioning tool for verifying solar panels and Maximizers are correctly wired early in the install, before the ESS is operational. The Roof Doctor Hub is a palm-sized, USB-powered device enabling phone-to-Maximizer communication wirelessly (100+ feet range).
Features in the Lunar Installer App: Update Maximizer firmware | Verify Maximizer power, communication, and state | Send a 1V signal to verify string wiring.
Getting Started: (1) Disconnect the Maximizer Hub. (2) Power the Roof Doctor Hub via USB-C. (3) Log in to Installer App and click "Roof Doctor." (4) Join the Roof Doctor Wi-Fi network. (5) Scan Maximizer QR codes. (6) Confirm all communicating via Health Check. (7) Push Firmware update. (8) Confirm all have a healthy state.
FAQs
1 string of 20 panels vs 2 strings of 10? 1 string of 20 panels is recommended.
Is the Lunar Inverter grounded or ungrounded? The Lunar Inverter is ungrounded (functionally grounded). The PV ground wire must remain isolated from both positive and negative DC circuits.
Must each individual string voltage be verified? Yes — strongly recommended. One string may read 20–30 Vdc at the Hub even if a second string is wired incorrectly.
Lunar Support
Email: [email protected] | Hotline: (650) 535-1969 | Support Hours: 8:00 AM – 7:00 PM PST, Mon–Fri