Solid state relay

[garytom]

The issue i am experiencing is intermitent humming noise on contactor which a solid state relay activates, not sure if relay is getting required voltage
I am a using J7 I/0 2 as output to turn on 3v solid state relay, but only getting 2.7v output when relay is turned,
i have tested voltage when relay is off and voltage reads 3.3 volt.
Could anyone help with problem.

[TomKerekes]

Hi garytom,

You might try connecting the SSR to +5V and have the KFLOP output sink to GND. That should provide over 4V to turn it on. When off (not sinking to GND) the relay would see ~1.2V or ~1.7V depending on whether it is driving to 3.3V or floating as an input. You would have to determine if that is low enough to turn it off.

HTH

[garytom]

Hi Tom

Thanks for reply.
got explanation slightly wrong, got 3.3v on kflop pins when setting I/O bit 2 high with relay not connected.
Is this normal to have a voltage drop when connected to hardware?

Regards Gary

[TomKerekes]

Hi Gary,

Yes that is normal. LVTTL Outputs are only guaranteed to go to at least 2.4V when high and less than 0.4V when low under a load of 16ma or less. The 5V tolerant IO on KFLOP also have 47ohm series resistors (to avoid damage if driven to 5V) which will cause an additional voltage drop depending on load.