Maintenance and cleaning
SMA America, LLC
80
SB20_25_30HFUS-eng-IUS113711
Installation Guide
9.4 Inspecting and changing the varistors
Varistors are used to protect circuits against excessive transient voltages by incorporating them into
the circuit in such a way that, when triggered, they will shunt the current created by the high voltage
away from the sensitive components. Varistors are designed according to the expected product use.
Their functionality may diminish with following repeated responses as a result of overvoltages. It is
therefore possible that one of the varistors has lost its protective function.
Inspect and change the varistors in the following manner:
1. Disconnect the Sunny Boy from voltage sources (see section 8.1 ”Disconnect the Sunny Boy
from Voltage Sources” (page 65)).
2. Open the SMA DC Disconnect (see section 8.2 ”Open SMA DC Disconnect” (page 66)).
3. The position of the varistors are shown in the figure
(A).
Inspect the varistors for discoloration or other signs
of visual damage. Furthermore test the varistors
with an ohmmeter: when the resistance of the
varistor is nearly or equal 0, the varistor is
damaged.
If varistors are discolored or damaged, you must
replace them. Always replace the entire set of
varistors.
manual)
One and Two String Wiring
(for more strings and further information see manual)
g
Negative Grounding
Positive Grounding
GROUNDED
UNGROUNDED
UNGROUNDED
GROUNDED
Terminal
=
~
L1
N
L2
+
L1 L2
N
N
L1 L2
+
+
A
