DC Voltage Test (Completed String and Polarity)

The purpose of the following test is to confirm there is continuity between the positive and negative conductors in a string (i.e. positive wire in the positive MPPT, and both positive and negative wires are fully connected). It is also used to confirm that strings designed to be combined on the roof have been installed correctly.

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Warning
This test must be performed when Powerwall 3 is OFF and the system is OFF (stopped) in the device setup interface in Tesla One. Failure to do so could cause irreparable out-of-warranty damage to the Powerwall 3 when swapping strings between MPPTs.

Perform DC Voltage Test on an Individual String

  1. Set the tester to DC test.
  2. Plug the positive and negative meter side leads into the meter.
  3. Connect the positive lead to the positive MPPT input.
  4. Connect the negative lead to the negative MPPT input.
  5. Confirm the voltage reading is between 13V and 30V. This indicates a string is connected between the MPPTs; low voltage is expected as the MCIs are open.
    Informational PurposesAn informational icon, calling your attention
    Note
    This test must be completed on PV strings before they are to be combined (paralleled).
  6. If the voltage reading is 0V there are two possible causes:
    • There is no string closing the loop between the positive and negative terminals of the MPPT.
    • The positive and negative conductors of the string are not landed at the correct MPPTs (i.e. String 1+ is landed at MPPT 1+, but String 1- is landed at MPPT 2-). Confirm by moving the negative tester lead to each subsequent negative MPPT terminal and testing; if the voltage reading is below 30V but above 13V, that string should be paired with the positive string currently being tested. For instance, if the testers at MPPT 1+ and MPPT 2- produce a voltage reading between 13V and 30V, move the negative conductor from MPPT 2- to MPPT 1- as shown below.
      Confirm the issue has been resolved by once again connecting the positive lead to positive MPPT input and negative lead to negative MPPT input and confirming the voltage reading is between 13V and 30V.
  7. If the voltage reading is negative, the string has reverse polarity. Swap positive and negative (i.e. move the conductor in MPPT 1+ to MPPT 1- and vice versa) to correct polarity.

Perform DC Voltage Test on a Combined String

  1. Set the tester to DC test.
  2. Plug the positive and negative meter side leads into the meter.
  3. Connect the positive lead to the positive MPPT input.
  4. Connect the negative lead to the negative MPPT input.
  5. Confirm the voltage reading is between 30V and 60V. This indicates a combined string is connected between the MPPTs; low voltage is expected as the MCIs are open.
  6. If the voltage reading is 0V there are two possible causes:
    • There is no string closing the loop between the positive and negative terminals of the MPPT.
    • The positive and negative conductors of the string are not landed at the correct MPPTs (i.e. String 1+ is landed at MPPT 1+, but String 1- is landed at MPPT 2-). Confirm by moving the negative tester lead to each subsequent negative MPPT terminal and testing; if the voltage reading is between 30V and 60V, that string should be paired with the positive string currently being tested. For instance, if the testers at MPPT 1+ and MPPT 2- produce a voltage reading between 30V and 60V, move the negative conductor from MPPT 2- to MPPT 1- as shown below.
      Confirm the issue has been resolved by once again connecting the positive lead to positive MPPT input and negative lead to negative MPPT input and confirming the voltage reading is between 30V and 60V.
  7. If the voltage reading is negative, the string has reverse polarity. Swap positive and negative (i.e. move the conductor in MPPT 1+ to MPPT 1- and vice versa) to correct polarity.
Informational PurposesAn informational icon, calling your attention
Note
A DC voltage close to 1000V indicates an open circuit (the tester leads are not connected to anything).