could using a DVM damage a small solid state relay?

[jumanji]

Long story short - I am using a small solid state relay (Clare CPC1017N - see attached) to mimic pressing a switch on another board. The voltage being switched is only 3V and I am sure it is very low current so I am confident that I am within the specs of the relay. They also spec 1mA to turn the relay on and that is almost exactly what I am using. So I send a friend of mine 15 boards and he tests them and tells me none of them work and send them back. Sure enough, the relay has failed on every board. I am trying to figure out where in our process something went so terribly wrong and I keep coming back to him testing them with his meter. It is a cheap Radio Shack meter and he tested them on the resistance mode while making the relay open and close. I don't have much experience using solid state relays so can't say whether they are overly sensitive or not, but is it possible that this meter caused a voltage/current spike big enough to fry the relay? I have never heard of such a thing but I can't think of anything else that would cause this.

If anyone has any insights or experience I would love to hear it - thanks.


View attachment Clare_CPC1017N_SolidStateRelay.pdf

 

[betwixt]

Yes it is possible but not perhaps in the way you think. It could be the DVM or the circuit driving the LED side of the relay, the likely cause is more than 5V being put across the LED in the reverse (non conducting) direction. Many DVMs use 9V batteries and a resistance check or 'diode test' on these meters often puts the whole battery voltage across the device under test and sees if it conducts by measuring how much the voltage is dropped to. In the case of an LED, in the forward (conducting) direction the voltage will be dropped to about 1.2V but in the reverse direction it will not pass current and not drop the voltage at all, at least until the until the PN junction is destroyed! the maximum reverse direction voltage is 5V.

I would suggest wiring a normal silicon signal diode such as the 1N4148 or it's equivalent across the LED side of the switch with the diode 'pointing' the opposite way to the switches LED. This will clamp the excess voltage to a safe level if the polarity is accidentally reversed.

Brian.

 

[jumanji]

Hi Brian - I greatly appreciate your response. I don't think this is the problem though as the board is laid out with a connector that only provides access to the 2 "load' connections on the SS relay. The connection to the LED on the relay is from the mcu output pin with a 5.1K resistor so should limit any excess current to the LED. I should also note that the same I/O pin from the mcu is also driving another LED for indication, although I don't see why what would matter.