bruceb
Diamond Member
- Aug 20, 2004
- 8,874
- 111
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From the FAQ section of the datasheet for the SSR relay:
Q : I have an SSR driving a load. The load turns on
okay, but never seems to turn off, unless I remove
power from the relay entirely. What might be happening?
A: This is normally a problem when using an SSR with a hig himpedance
load, such as a neon lamp or a small solenoid.
Loads like these often have relatively large initial currents, but
relatively small “hold in” currents. The result is that the off-state
leakage current through the relay (see previous section) is
insufficient to cause the load to turn on to start with, but
sufficient to keep it on, once started. The solution is to place a
power resistor, sized for 8–10 times the rated maximum
leakage current for the SSR in parallel with the load. Make sure
that this resistor has a high enough power rating for the
application. For example, for a 5 mA leakage current at 120
VAC, a resistor drawing 50 mA would be desirable. Using
Ohm’s Law, the resistor value becomes 2,400 ohms. This
resistor will dissipate 6 watts, so a 7.5 or 10-watt size power
resistor should be used.
Q : I have an SSR driving a load. The load turns on
okay, but never seems to turn off, unless I remove
power from the relay entirely. What might be happening?
A: This is normally a problem when using an SSR with a hig himpedance
load, such as a neon lamp or a small solenoid.
Loads like these often have relatively large initial currents, but
relatively small “hold in” currents. The result is that the off-state
leakage current through the relay (see previous section) is
insufficient to cause the load to turn on to start with, but
sufficient to keep it on, once started. The solution is to place a
power resistor, sized for 8–10 times the rated maximum
leakage current for the SSR in parallel with the load. Make sure
that this resistor has a high enough power rating for the
application. For example, for a 5 mA leakage current at 120
VAC, a resistor drawing 50 mA would be desirable. Using
Ohm’s Law, the resistor value becomes 2,400 ohms. This
resistor will dissipate 6 watts, so a 7.5 or 10-watt size power
resistor should be used.
