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I'm building a simple circuit to control a 100W that takes 30-34V using a 30V LED power supply with constant current of 3.2A. I am controlling the switching of the LED with a Crydom DC60S5 connected to an Arduino Yun and the LED power supply with the following wiring:

Circuit Configuration

Here is a photo of the actual wiring:

Actual Wiring

The problem is that when I plug in the power without even connecting the Arduino (nothing connected to terminals 3 and 4 on the relay, just as seen in the picture) the LED switches on. I've double checked that I have the DC60S5 relay, not the DC60S5-B which defaults to closed. If the circuit is unplugged and I do a continuity check with my multimeter across terminals 1 and 2 I don't get any beeping, and measured resistance is too high to register. If I put a 9V battery across the inputs the resistance drops to 60kOhm. This is confusing since 60kOhm is the AC impedance as stated in the data sheet, but I have the Crydom DC60S5 not the Crydom DC60SA5 which is the AC controlled model of this relay so I would have expected to get 1.5kOhm resistance as stated in the data sheet for DC control.

The relay doesn't seem broken, since I can still control it with a battery and measure it turning on/off. However without anything connected to the inputs it defaults to on which is not the expected behavior. Can anyone point me in the right direction as to what I might be doing wrong here?

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  • \$\begingroup\$ Link to data sheet is here would not let me post it in the article as I don't have a high enough score on this particular Stack Exchange site. \$\endgroup\$ – Jamie Quint May 2 '16 at 17:48
  • \$\begingroup\$ You did not state whether you could control the relay properly from your Arduino. Note that behavior with no control voltage connected is typically UNDEFINED. \$\endgroup\$ – Richard Crowley May 2 '16 at 18:16
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That's simple: you have swaped the polarity on the SSR output, so the current goes trough freewheling diode to the load. The correct wiring is this

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Hrm, I am following the wiring diagram from the datasheet. The one that is on the right hand side here. Is that one wrong also? dropbox.com/s/esxifvbduovh16g/… \$\endgroup\$ – Jamie Quint May 2 '16 at 19:27
  • \$\begingroup\$ In the data sheet it shows 2+, however on the relay itself it shows 1+. In fact in the wiring diagrams it shows it one way, and in the Equivalent Circuit Block Diagrams it shows it the opposite way. Super confusing. dropbox.com/s/di2m7000t16qiov/… \$\endgroup\$ – Jamie Quint May 2 '16 at 19:32
  • \$\begingroup\$ I got this to work by simply swapping the connections of terminals 1 and 2. It seems the data sheet wiring diagrams as shown here are actually incorrect. \$\endgroup\$ – Jamie Quint May 2 '16 at 21:07
  • \$\begingroup\$ @JamieQuint Yes, the first connection in the manual is wrong, perhaps it could work with inverted source polarity, but then also the freewheeling diode on the load should be inverted. I guess, your connection is like this, now. \$\endgroup\$ – Marko Buršič May 3 '16 at 7:37
  • \$\begingroup\$ @JamieQuint And the second connection in the manual is wrong, too. \$\endgroup\$ – Marko Buršič May 3 '16 at 7:56
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The input to the SSR will not behave like a resistor so the readings you got are not alarming. It should follow the graph -- 9VDC should draw about 5mA.

When you open the circuit to a constant-current LED driver circuit (with the SSR) you may be getting unexpected behavior, such as the voltage increasing to the point where the SSR switches on to protect itself.

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