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TS4-F/TS4-2F: String Voltage Testing and Troubleshooting

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Contents:

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Overview

Tigo's TS4 family of Fire Safety MLPEs (module level power electronics) includes 2 types that are responsible for providing the RSD (rapid shut down) solution: 

  • TS4-A-F - Single PV Module RSD
  • TS4-A-2F - Dual PV Module RSD

Both the single (F) and dual (2F) models activate upon receiving a PLC Transmitter pulse or signal. However, when the RSS Transmitter signal is not present, their output is reduced to a Safety Voltage of .6 Volt per-unit. This voltage is measurable at the string leads (or home run leads), and will help to identify if all units are functioning as expected, and ready to be activated.

Here's the expected Safety Voltage for a string of 10x PV Modules/Panels: 

  • 10x TS4-A-F (yielding a Safety Total of 6 Volts)
    ...or...
  • 5x TS4-A-2F dual module units (yielding a Safety Total of 3 Volts)

 

🏆 Pro Tips!

Series vs Parallel

Parallel string wiring can sometimes be challenging to troubleshoot. Tigo recommends that the strings be tested in series:

  • For safety voltage testing (one open string at a time)
  • For closed-circuit Vmp testing (only 1 string per MPPT input).

This will simplify the process and reduce the possibility of Reverse Current scenarios during testing (due to unequal string voltages).

Fuses are your friend

If the system is already wired in parallel, removing a string fuse, can allow the strings to be individually isolated from each other, so that they can be tested in series (one at a time). 

String Fusing on Older Inverters

Usually string fuses are found in combiners, or inline fuses on Y-Cables or connectors. However, some older inverters offered string fusing within the MPPT inputs. If you are working on an older system, and do not see any combiner or inline fusing, check the inverter. 

PLC Signal Requirement

The PLC "keep alive" signal requires full DC continuity on the String. If the circuit is not closed, the Transmitter signal cannot reach the Tigo MLPE units, and the system will not activate. 

Individual strings do not activate at start up, or shut down at RSD

In most of these cases, the installer finds that there is a simple wiring or fuse oversight. However, if there are multiple RSS Transmitters on the system, there could be a Crosstalk Issue that is affecting the PLC signal of those strings. If you suspect this is the case, a simple solution is to install the new RSS Transmitter with Pure Signal. 

Entire array does not activate at start up

Check for issues at the RSS Transmitter: RSS Transmitter Troubleshooting Guide

 

Measure Safety Voltage totals (with RSD Enacted)

Since the TS4-F/2F series provides a .6 V (Safety Voltage) per unit, the Safety Voltage can be tested at the string ends, home run leads, or at the combiner's fuse terminals (total voltage should reflect the the expected amount of TS4 units employed on the string).

For example: testing a string of 10 TS4-F units at .6 V per unit, would yield 6 Volts total, on string

To test at combiner: (during sunlight hours)

  1. Disconnect AC power to inverter (that is to be tested)
  2. Disconnect AC power to RSS Transmitter that is providing PLC signal (for Inverter).
    • Check RSS transmitter LEDs to verify the transmitter is OFF
  3. Open all string fuses in Combiner (or Inverter wire box) 
  4. Set your Voltage meter to the expected voltage setting.
  5. Measure the voltage across the positive and negative terminals:
    • Place positive probe on left side positive screw terminal
    • Place negative probe on the negative bus (right side of example below)
       
  1. Measure voltage and compare to the total quantity of TS4s on the string
  2. Document the measurement

If test yields an inaccurate reading (either lower or higher than expected), follow these suggestions:

 

LOW SAFETY VOLTAGE HIGH SAFETY VOLTAGE
  1. Check that the DC loop is continuous. No open circuit (and that DC = ON)

  2. Test PV modules in low safety voltage strings to confirm there are no Panel issues.

  3. If TS4 is identified as a root cause and not the PV module, call support
  1. Review wiring as there may be more PV Modules on a string than expected.

  2. There may be an issue with Crosstalk in the cable trays or conduits.

  3. Revisit design and installation instructions as a violation of the guidelines is likely resulting in interference in some portion of the system.

 

If test yields an accurate reading (all units show a .6 V output), the test is complete. The fuses may be closed and the RSS Transmitter and/or inverter's AC can be reconnected. The tested inverter should start up with the full system Vmp present. 

Move on to the next inverter to be tested, and repeat steps until every inverter in the system has been individually tested.

 

Measure Vmp totals (with system active)

The Voltage at Maximum Power (Vmp) represents the voltage provided by the PV Module(s), when:

  • The Strings are connected to a load source (like an inverter or charge controller).
  • The Fire Safety units receive the PLC signal and are activated (not in RSD).

This value represents the maximum capacity that each PV Module can provide, under standard test conditions. In most cases, the Vmp is 70 - 80% of the Voc (Voltage at Open Circuit).


Test for Vmp: (during sunlight hours)

  1. Confirm that all Combiner fuses are closed
  2. Connect AC for Inverter
  3. Connect AC for RSS Transmitter (confirm transmitter is ON with LEDs)
  4. Allow 2 minutes for inverter startup time
  5. Once started, measure the voltage across the positive and negative terminals:
    • Put positive probes on left side positive screw terminal
    • Put negative probes on the bus to the right
  6. Document the measurement and confirm the total expected Vmp per string, correlates with your results.

Remember: The Vmp testing method (above) will yield accurate per-input-results. The amount of voltage will change, if the system is wired in Series vs Parallel (parallel wirings would yield only one string's worth of voltage, per parallel combination). 

If the results are inaccurate, isolate which string is affected and check for obvious issues (shading, wiring inconsistencies, etc), first. If none found, use the drill-down method (next section, below) to confirm the unit that is not supplying the correct Vmp.

If the results are accurate, the test is complete.

 

Drill Down Method

Since the Fire Safety series does not supply data, the process of finding a PV Module or Tigo MLPE that is not functioning as expected, requires the Drill Down Method. The process is labor-intensive, but it will help you to find the unit (or PV Module) that is not passing the appropriate amount of voltage.

  1. Activate RSD (shut down AC input for RSS Transmitter and Inverter).
  2. When confirmed as safely shut down, shorten the inaccurate string in half by bypassing half of the string with a connected jumper (mid-way)
  3. Connect the half-string to the combiner and reactivate the system
  4. Test for Vmp.

If result is good, repeat steps 1-4 on the second string half. Once you find the portion of the string that shows the inaccuracy, continue to separate that portion in half again, until you narrow the problem down to one unit (or PV Module). Carefully inspect both the PV Module and the Tigo Unit, to confirm which component is experiencing the issue. 

Using this method, an installer can easily drill down to the unit that is experiencing an issue. However, patience is key. Even with a quality testing method, it can still be hard to replicate the issue. The cause could be wire insulation issues, micro-cracked panels, bad diodes or ill-fitted connectors. These can be hard to confirm, as some issues do not exist until the PV Module and Tigo Unit are both under full load.  

 

Warranty Issues

If (after thorough troubleshooting), the cause appears to be Tigo device that is not working as expected, please Contact the Support Team.

Customers will be asked to provide:

  • A full description of system design (including make/model of inverter and PV Modules)
  • A list of the steps taken to troubleshoot, and documentation of measurements at each step
  • Pics of any visible damage to the Tigo component or PV Module

After the system has been reviewed by a Tigo Engineer, an RMA (return merchandise authorization) may be granted if the product meets the basic criteria listed in Tigo's Limited Warranty.

 

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