this is my first post. I'm having a real pain trying to get these little solid state relays to work for me. This is a DC/DC relay.


I have now blown 2 and theyre 75 bucks a pop and I reallllllly dont intend to blow another. I cannot figure out what I'm doing wrong. My circuit seems to follow the data sheet, and in fact, the relay works for an operation or two, but after a while, the things latch shut and go completely kaput as far as I can tell. The indicator light still works normally when I open and close the control switch but regardless, the main line stays latched and I've verified that it remains latched even when completely removed from the circuit.

I'm using appropriate precautions, I even have a 30A fuse in series and the relay itself is rated at 30A! The data suggests a diode but my loads are DC only so I'm not sure it's necessary. Some insight would be greatly appreciated.

Thank you!

Additionally, does anyone have a better solution than expensive SSR's to this problem? I need to switch a 36V power supply at roughly 20A continuous power. This is for an EV so power efficiency is a concern and so is space. Obviously my plan to use SSR's hasnt been working great so far. Here's an image of my circuit side-by-side the data sheet suggested circuit.


Thanks so much for the help! enter image description here

  • 2
    \$\begingroup\$ Isnt Control Voltage 32Vmax? You are putting 36V into it? \$\endgroup\$
    – Wesley Lee
    Nov 17, 2016 at 7:09
  • 1
    \$\begingroup\$ The control turn-n voltage is 3V. Why would someone drive a 3V circuit with 36V? \$\endgroup\$ Nov 17, 2016 at 7:17
  • 1
    \$\begingroup\$ I notice your pin 3 and 4 are swapped in the left drawing. \$\endgroup\$
    – user125002
    Nov 17, 2016 at 7:18
  • 1
    \$\begingroup\$ Maybe you should disclose the power rating of your "load" then? \$\endgroup\$ Nov 17, 2016 at 7:20
  • 3
    \$\begingroup\$ Another consideration is heat. From the data sheet, with no heatsink the SSR is only good for 15 A. This assumes an ambient temperature of 40 C or less, and presumably free airflow. If you have it tucked away in an enclosed area with no cooling (and maybe higher temperature from your controller or converter waste heat) the allowable current will be even less. Once you get it to stop dying in the short term, you need to look to the long term, and not cooking it in its own juices is a good idea. \$\endgroup\$ Nov 17, 2016 at 10:24

1 Answer 1


Your 1st problem is IN current is 15 mA absolute max while 11mA min. The actual input is a 1V IR diode opto coupler

Therefore use 13mA or 36V/13mA= 2.78k or closest value

The second is the surge current on a 30A motor can be 8x or more rated current appears to exceed max load current.

  • \$\begingroup\$ Okay thanks for walking me through the calculation! So as far surge protection is there anything I can really do? Or am I screwed here? \$\endgroup\$
    – Identicon
    Nov 17, 2016 at 7:31
  • 2
    \$\begingroup\$ You are screwed unless you add a softstart PWM control \$\endgroup\$ Nov 17, 2016 at 7:31
  • 1
    \$\begingroup\$ I would suggest you buy a cheap 50A PWM motor controller \$\endgroup\$ Nov 17, 2016 at 7:33
  • 1
    \$\begingroup\$ so that's not enough? what is start time? \$\endgroup\$ Nov 17, 2016 at 7:37
  • 1
    \$\begingroup\$ So when you switch off the SSR if the diode is not rated to take over the motor surge current kick back, the MO.sFEt blows from over voltage by lack of protection \$\endgroup\$ Nov 17, 2016 at 7:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.