Mitsubishi Electric MELCEC Q Series User Manual page 192

11. TROUBLESHOOTING
Table 11.3 Faults with the output circuit and the corrective actions (continued)
Situation
The load is not
Example
turned off.
3
(Triac output)
When load is
CR type timer,
Example
the time limit
4
fluctuates.
(Triac output)
Cause
• The load current is lower than the minimum load current.
A1SY22
Output module
Phototriac
Control
circuit
• When the load current is lower than the minimum load
current of the output module, the triac does not operate since
the load current flows into a phototriac as shown below.
When an inductive load is connected, the load may not be
turned off since the surge at the time of off is applied to the
phototriac.
A1SY22
Output module
Surge suppressor
Load
Triac
CR
timer
Leakage current
11 - 25
Countermeasure
• Connect a resistor to both ends of a
load so that the load current is higher
than the minimum load current.
Resistor
Load
• Start the relay first, then start the CR-
type timer at the contact.
In some timers, internal circuit may be half
wave rectification type, so the caution as to
the example 1 is necessary here.
Resister
Calculate the
constant of the
resistance based on
CR
the load.
timer