Author Topic: Solid State Relay flashing when it should be off  (Read 2887 times)

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Offline bitshift

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Solid State Relay flashing when it should be off
« on: February 06, 2016, 11:49:32 am »
Hey guys,

I'm trying to use a solid state relay to switch a light bulb through the 230VAC mains. The relay is controlled with a 10VDC signal. I've connected everything as follows:



The lightbulb turns on great when 10V is applied to pin 3 of the relay. When the control signal is turned off, the light bulb flashes on or off at around 1-2Hz. I've tried a 10k as well as a 1k pull down resistor.

Any ideas as to what could be causing this? Here is a link to the datasheet. The model I am using is on page 6.
« Last Edit: February 06, 2016, 11:51:25 am by bitshift »
"It’s all fun and games until an innocent opamp gets hurt!" - Dave Jones
 

Offline Ian.M

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Re: Solid State Relay flashing when it should be off
« Reply #1 on: February 06, 2016, 01:00:14 pm »
Use a real incandescent lightbulb not a LED or CF bulb!

It only takes a minuscule leakage current to slowly charge up the LED or CF bulb's reservoir cap, and when the voltage gets high enough for the control chip to come out of UVLO (undervoltage lockout), it will switch on till the charge on the cap is used up.   The result is a bulb that 'blinks' on briefly at intervals varying from a fraction of a second to several minutes depending on the leakage and the UVLO mode current consumption of the control chip.  I've seen it happen just due to wiring capacitance on stair lighting with mechanical switches top and bottom.  You could try adding a snubber network (Class X cap and low value series resistor) across the bulb to shunt the leakage current and keep the reservoir cap under the UVLO threshold.
 

Offline bitshift

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Re: Solid State Relay flashing when it should be off
« Reply #2 on: February 06, 2016, 02:05:31 pm »
Ah those pesky parasitic parameters :palm: Tried a incandescent bulb and it works as expected. Thank you Ian  :-+
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Offline Zero999

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Re: Solid State Relay flashing when it should be off
« Reply #3 on: February 06, 2016, 02:32:56 pm »
But aren't incandescents inefficient, especially if you're living in a hot country such as South Africa?

Try connecting a 100K resistor in parallel with the CFL/LED lamp. Also note the minimum load current so it may not work with very low power lamps.

Another thing you could try is a solid state relay with a MOSFET output stage.
 

Offline bitshift

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Re: Solid State Relay flashing when it should be off
« Reply #4 on: February 06, 2016, 02:35:24 pm »
What I'm actually doing is testing the temperature of the SSRs heatsink. I'm using the SSR to control the elements in my reflow oven. I built up the circuit and tested it with my desk lamp and was surprised when it was flashing on and off.
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Offline Seekonk

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Re: Solid State Relay flashing when it should be off
« Reply #5 on: February 06, 2016, 03:54:18 pm »
Place a .47uF in series with a 220 ohm 1/2W resistor in series.  May work with a .1uF.  Caps should be X2 type rated for line voltage.    That RC network should be placed in parallel with the lamp.  That will shunt any leakage of the SSR without wasting energy.
 


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