Sunny Boy 700
Technical Description
SB700-11:EE
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39
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SMA Regelsysteme GmbH
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Failure of the thermally monitored varistors
On its DC input side the Sunny Boy is equipped with thermally monitored varis-
tors (plus and minus pole to protective earth each). They are installed in order
to prevent the inverter from being destroyed by atmospheric surge voltages
(electric fields from thunderstorms etc.). A thermally monitored varistor is the
serial circuit of a varistor and a thermal fuse. If the thermally monitored varistors
have triggered for several times they can lose their effect by not letting any cur-
rent pass anymore and therefore not provide the intended safety anymore. This
condition is indicated with the “Erdschluß / Earth Fault“ LED.
The replacement of a thermally monitored varistor should be
conducted by qualified personnel.
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Determining the Failure
The red LED indicates one of the above mentioned failures. A short description
on how qualified personnel can distinguish between these and conduct the ap-
propriate countermeasures is given in the following.
Please take note of all relevant information in chapter 3.3, “Electric Connection”
and 5.1, “Opening and closing of the Sunny Boy”.
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Open the Sunny Boy according to the description in chapter 5.1.
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Remove the two internal thermally monitored varistors (see Fig. 5.3
“Interior of the Sunny Boy 700”) with a screwdriver.
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Connect the connectors 2 and 3 of the terminal strip on the main board.
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Connect the PV-panel by the MC plug connector
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Connect the grid voltage
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If the red LED is off see “A“ - if the LED is on see “B“.