SMA SUNNY BOY 2000HF - Checking the Function of the Varistors

Troubleshooting SMA Solar Technology AG
74 SB20HF-30HF-IA-IEN120431 Installation Manual
11.2 Checking the Function of the Varistors
If the inverter displays event number "74", one of the varistors is probably defective.
Varistors are wear parts. Their functional efficiency diminishes with age or following repeated
responses as a result of overvoltages. It is therefore possible that one of the thermally monitored
varistors has lost its protective function.
You can check the functionality of the varistors in the following manner:
1. Disconnect the inverter from the AC and DC side as described in section 8"Disconnecting the
Inverter from Voltage Sources" (page58).
2. Loosen the screws of the enclosure lid.
3. Remove the enclosure lid.
Position of varistors
You can determine the position of the varistors using the illustration below.
The varistors are bent upon delivery.
Observe the following assignment of the
terminals.
• Terminal A: outer terminal (varistor
connection with loop [crimp]).
• Terminal B: Middle terminal.
• Terminal C: outer terminal (varistor
connection without loop [crimp]).
DANGER!
Danger to life due to high voltages in the inverter.
The capacitors require 5 minutes to discharge.
• Wait 5 minutes before opening the enclosure lid, in order to allow time for the
capacitors to discharge.