1
\$\begingroup\$

I recently purchased a used IEC Centra centrifuge with a refrigeration feature. Works great, except the refrigeration condenser never cycles off and as a result the chamber gets down to the minimum reading of -10C no matter what I set the target to. I've deduced through testing that the thermocouple works fine and it still manages to get extremely cold (I actually had a sample almost freeze) so I'm assuming the actual refrigerator coil is sufficiently charged and all.

I pulled the temperature controller board tonight and figured that it was probably an issue with the relay to control the condenser. Datasheet for the relay is here. I wired a lightbulb to the AC output and noted that as soon as line voltage was applied the lightbulb came on even though I had not connected anything to the DC side of the SSR. Am I correct in assuming that this means the relay is shorted and I should begin by replacing it? I have never verified if an SSR is working before.

Thanks

\$\endgroup\$

1 Answer 1

Reset to default
2
\$\begingroup\$

Yes, that would seem to be a correct deduction- SSRs will often fail "on".

You can also double-check by seeing if the drive voltage turns on and off with the temperature setting. There's a small chance that the failure is not confined to the SSR.

\$\endgroup\$
2
  • \$\begingroup\$ cycling doesn't seem to do anything. tested my sources with another SSR I had to make sure I wasn't crazy. Applying DC voltage to this relay did nothing. I'll try and check the drive voltage, it's very tight and there's a lot of live voltage so I'm not sure if I can do it safely. The condenser did turn on so I'm thinking it may just be that a ~30 year old SSR finally kicked the bucket \$\endgroup\$
    – quixotic120
    Commented May 22, 2014 at 4:16
  • 1
    \$\begingroup\$ I was able to check the drive voltage. 0VDC when the condenser should be off, 5VDC when the condenser should be on so looks like the relay is the culprit. Going to order another now. Thanks!! \$\endgroup\$
    – quixotic120
    Commented May 22, 2014 at 4:44

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.