SMA SB 4200TL HC Multi-String - Manual (Page 48)

Replacing the Varistors SMA Technologie AG
Page 48 SBTLHCMS-IEN080411 Installation Guide
5. If the measured voltages are constant and if their total is roughly the same as the
open-circuit voltage of the string, then there is an ground fault in this string. Its ap-
proximate location can be deduced from the relationships between the voltages.
6. Repeat points 3 and 4 for each string.
If you found a ground fault, it is probably not necessary to replace the varistors.
Instead, make sure the ground fault is fixed. Generally the PV generator's installa-
tion engineer should be hired for this job. In this case continue as described under
point 10, but without reconnecting the faulty string. Instead of reconnecting the
string, protect its DC plug against accidental touch contact (e.g. by fitting the pro-
tective caps or using sufficient high-voltage insulating tape).
If you did not find any ground fault in the PV generators, it is likely that one of the
thermally monitored varistors has lost its protective function. These components are
wearing parts. Their functioning diminishes with age or following repeated re-
sponses as a result of overvoltages. You can now check these varistors in the fol-
lowing way, paying attention to the safety instructions in section :3 "Safety
Instructions" (Page 9)
7. Remove the screws that secure the cover and remove the cover from the Sunny
Boy. Disconnect the PE connection from the cover. Make sure that no voltage is
present.
8. Using a continuity tester, check all the varistors to see if there is a conducting con-
nection between connectors 2 and 3. If there is no connection, then that varistor
is not working. The positions of the varistors in the Sunny Boy can be seen in the
diagram in section 4. 1 "Unit Description" (Page 11).
9. Replace the varistor concerned with a new one
as shown in the drawing to the right. Ensure the
varistor is installed the right way round! If you do
not receive a special tool for operating the termi-
nal clamps with your replacement varistors, con-
tact SMA. As an alternative, the terminal
contacts can be operated using a suitable screw-
driver. Since the failure of one varistor is gener-
ally due to factors that affect all varistors in a
similar way (temperature, age, inductive over-
voltages), it is highly recommended that you re-
place all three varistors, not just the one that is
obviously defective. The varistors are specially
manufactured for use in the of the Sunny Boy SB
4200TL HC Multi-String and SB 5000TL HC
Multi-String and are not commercially available.
They must be ordered directly from SMA Tech-
nologie AG (
SMA order code: „MSWR-TV6“).
Insert the spe-
cial tool to open
the terminal.
Remove
the varistor
The pole with the small loop
(crimp) must be fitted to ter-
minal 1 when replacing the
varistor.