Troubleshooting For Output Circuit - Mitsubishi Electric MELSEC-L Series User Manual

8.2

Troubleshooting for Output Circuit

(1) When the output is off, excessive voltage is applied to the load (triac output).
• The load is half-wave rectified internally. (In some cases this is true of solenoids.)
Cause
• When the polarity of the power supply is as shown in [1], C is charged. When the polarity is as shown in [2], the voltage charged in C plus
the line voltage are applied across D1. Maximum voltage is approx. 2.2E. (If a resistor is used in this way, it does not pose a problem to
the output element. But it may cause the diode, which is built into the load, to deteriorate, resulting in a fire, etc.)
• Connect a resistor (several tens to hundreds of k) across the load.
Action
(2) The load does not turn off (triac output).
(a) Case 1
• A leakage current occurred due to a built-in surge suppressor.
Cause
• Connect a resistor across the load. (Note that a leakage current may occur due to the line capacity when the wiring distance from the
output module to the load is long.)
Action
Case
TRIAC
output module
D1
Load
Resistor
Load
Case
TRIAC
output module
Load
Leakage current
Resistor
Load
CHAPTER 8 TROUBLESHOOTING
[1]
[2]
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