Do SSR's leak voltage while off?

I seem to remember that being said in another post somewhere. I have a DPDT switch wired (Manual-OFF-Auto). The manual side receives it power right from the dist-block, and the Auto receives a power feed from the SSR. However, if the switch is in Auto mode but I don't have the relay turned on my voltmeter is still showing about 3VAC. I wired a small LED off the middle terminals of the switch so that when power goes to the outlet the light turns on. This works perfectly in Manual mode but the light also comes on during Auto mode even though the SSR is not switched on.

I think you mean leak current. There is no such thing as leaking voltage.

I don't know about your particular SSR, but transistors and related devices pretty much always leak some current when power is applied to them. It's not a mechanical system like an actuated relay.

Yes, I believe they do until a certain load is applied to them. Search you should be able to find it easily.

There is no on and off, there is only Hi/Low.

Okay, so in other words the reason my LED light turns on is because the SSR is supplying a current at all times regardless if the SSR is open or closed?

Anyone know of way to wire an LED to only light up when the SSR is activated/closed?

There was a discussion on the BCS forum about this subject. Do a search, don't remember the outcome.

An SSR is a triac circuit. You cannot put an LED across it (unless you install a load resistor). You should use an incandescent light. The triac can leak just enough current to light an LED (comes on at a lower voltage than a light bulb) but doesn't have enough current to drive a light bulb.

ah ok, makes sense now.

I use line voltage LEDs and run them off the high side. Works like a charm.


MrH

What exactly is the "high side"?

The switched side of the SSR, or the side that feeds your element. I just connected the hot lead to the terminal that goes to the element and ran it back to the LED. For my 240V element, I stuck some parallel resistors in line to the LED (the LEDs are rated for 120V).

MrH

Poobah58 said:

An SSR is a triac circuit. You cannot put an LED across it (unless you install a load resistor). You should use an incandescent light. The triac can leak just enough current to light an LED (comes on at a lower voltage than a light bulb) but doesn't have enough current to drive a light bulb.

Click to expand...

Touching this thread because I just finished wiring my control box last night and wanted to throw in here that even using an incandescent lamp, you can get some confusing results.

After I finished running the last "real" wire for the system, the only thing I had not yet connected was a small panel mount incandescent lamp because it needed to have leads soldered to it and I was waiting for the soldering iron to heat up.

While waiting, I went ahead and plugged the box in and started testing things out; flipping switches and making sure I could power up a 40W lightbulb plugged in where the pump will eventually be, making sure the PID and pulse width modulator were working, etc, etc, etc.

Everything looked great, and I was a happy man.

Now, that little lamp that I was about to solder on i sjust meant to let me know when the element is actually receiving power. My main thinking when I bought it was that it might come in handy trying to diagnose a problem without having to open up the panel and stick the multi-meter in there.

So, IRONICALLY, the lamp is intended to be a debugging device, but what I ended up debugging was the damn lamp itself.

I soldered the leads to it and connected it to the output of the SSR. When I turned the power on for the control panel, the lamp immediately lit up. It should not have been lit up. The control lines to the relay were off.

After some head scratching and multi-meter measurements, I finally figured out that enough current was leaking through the SSR to allow the lamp to light up. The lamp's resistance measured at 1MOhm and it is to be driven by 120V, so it pulls a puny 0.12mA of current when in full/normal operation. This thing is just a 14mW light bulb. I did not measure how much current was really leaking through the SSR, but it was clearly enough to light my little incandescent lamp.

I then connected my 40W lightbulb to the relay output to mimic having a heating element plugged in and the little lamp on the panel turned off. The vast majority of current leaking through the SSR followed the path of least resistance through the 40W lightbulb and only a SUPER tiny amount went to the indicator lamp. Neither device was getting enough current to actually light up.

With an added load on the output of the SSR, the tiny panel mount lamp functions as intended, but if there is no other path for the leakage current to take when coming out of the SSR, it will cause the panel mount lamp to light up.

At first, I considered this a bug, but now I consider it a feature.

(RelayControl=OFF & IndicatorLamp=OFF) means all is well, and no power is going to the heater
(RelayControl=OFF & IndicatorLamp=ON) means that I have no heater plugged in or there is a problem with the circuit through the heater.
(RelayControl=ON & IndicatorLamp=OFF) means that something is causing current to fail to come through the SSR.
(RelayControl=ON & IndicatorLamp=ON) means all is well, and power is going to the heater