Electronics Help

[RCP]

I am trying to use a solid state relay to switch a light circuit, unfortunately, the relay passes just enough current to turn the light on even when the relay is not energized. The light circuit has about 3 VDC across it's leads. I am thinking that a resistor in the switch circuit might be enough to prevent the light circuit from being energized. I have attached a picture of the solid state relay. Any suggestions on a solution?

 

[Harry in Ky]

Only one. Use a mechanical relay.

 

[tech4]

What voltage, and current does your light require. That is an optic DC relay (switch) for DC only max 30 volts.

 

[Stan Coryell]

Assuming the voltage is correct and it is DC, I would guess one of the diodes is bad. Can you provide more information?

 

[RCP]

The light is a strobe light and the switch on the strobe is a momentary contact switch that has a 5 VDC supply. I am trying to use a relay to take the place of pushing the momentary contact switch. The problem is the relay I bought "leaks" the 5VDC and activates the light. I did some reading and this is a common problem with solid state relays. I was hoping a resistor would drop the voltage and reduce the "leak". Another option would be a reed switch relay; this would make a mechanical break in the switch circuit.

Any suggestions?

 

[Stan Coryell]

The light is a strobe light and the switch on the strobe is a momentary contact switch that has a 5 VDC supply. I am trying to use a relay to take the place of pushing the momentary contact switch. The problem is the relay I bought "leaks" the 5VDC and activates the light. I did some reading and this is a common problem with solid state relays. I was hoping a resistor would drop the voltage and reduce the "leak". Another option would be a reed switch relay; this would make a mechanical break in the switch circuit.

Any suggestions?

DC circuit theory is way back in my HS years. Do you have the schematic for the strobe light?

Couldn't you just parallel the "start" switch on the strobe light?

Best guess would be to contact the strobe light manufacturer, and try to find a solution,

Someone may have much better direction than me.

 

[MarkB_MI]

Technically, that device is what's known as an optical isolator. Yes, it functions similarly to a relay, but it's not quite the same. These devices are usually used to "float" two circuits that have different reference ("ground") voltages or need to be electrically isolated for safety reasons.

If you add a resistor in series with the relay input side, it's just going to limit the "on" current through the LED. Since the the output side is an optical transistor, reducing the LED "on" current will reduce the "on" current through the transistor, which is not what you want to do. You're not going to reduce any leakage when the device is off. Likewise if you add a resistor in series with the relay output.

What happens when you completely disconnect the input to the device? My guess is you'll see the same leakage on the output. I think your problem is that device is intended to switch devices (such as motors) that draw a lot more current than your light.

What you might try doing is putting a resistor IN PARALLEL with the output load. You'll need to find out how much current the light draws when it's on. Then use ohm's law to figure out its input resistance. I'd then select a resistor that's roughly the same resistance as the light and of similar wattage.

 

[Texasmark]

I'm a big fan of solid state circuit controls having depended heavily on them when in industry. However, there are times when a mechanical device is necessary and in your case, rather than doing a lot of experimenting and fooling around, just get the correct relay (one that meets the circuit constraints) and install it. The limited stress and frequency of use mitigates the need/preference for electronic controlling.

 

[Tony in SD]

I am trying to use a solid state relay to switch a light circuit, unfortunately, the relay passes just enough current to turn the light on even when the relay is not energized. The light circuit has about 3 VDC across it's leads. I am thinking that a resistor in the switch circuit might be enough to prevent the light circuit from being energized. I have attached a picture of the solid state relay. Any suggestions on a solution?

As others have said, the simple solution is to use a mechanical relay. However if you put a grounding resistor on the Vout lead of the electronic relay to 0 V, it should pull the voltage to ground or at least low enough to turn the light off. When the the MOSFET is turned on the voltage should to raise high enough on V out to turn the light on. In other words, place a resistor from the V out to the 0 V.

I would need to know more about your Load on the V out to calculate the resistor value. However if you do not know that information, you could start with a high value resistor and work your way down until the light stays off when it is suspposed to and turns on when it is supposed to. I used a grounding resistor in many of my circuit designs in a former life to accomplish a consistent off condition.
Retired BSEE

 

[Watthour]

Open collector switch using a transistor with a high hFE value. Something along the lines of an MJE15031 should easily handle anything up to 150VDC and 8A. I think most xenon tube strobes are a lot lower current than that.