Do SSRs leak voltage on the high side with no input on low side?

[bcrawfo2]

I'm almost done with my electric build and have been doing some troubleshooting with a multimeter. I'm confused when I'm not signaling for the SSR to send power...that I'm still reading 120v on it's output side. What's odd is that if I hook up a load to that side, the load doesn't work (a light, pump, tool, etc).
Also...on my element SSRs, I read 40v across the load to ground and 80v across the load and the other hot leg. This is enough voltage to light up the LED that I have running in parallel with the element load. In this case...if I hook up an element (I'm not there yet)....will that draw enough to cause it to not light the LED?

THanks

 

[augiedoggy]

mine does the same...I have been told that is a limitation of how the ssr works... I wonder if going to a dual lead ssr for both hots would help?

 

[bcrawfo2]

I found this after I posted.
I wasted hours on this. Glad I can move forward

 

[pvtschultz]

SSR's are current blocking and not voltage blocking. You will be able to measure a potential on the switched side due to the high resistance of the meter without the element. The element has a low resistance and therefore a higher current flow so you will not measure voltage with the element connected.


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[theonetrueruss]

yes this is correct... the SSR clamps down on current not so much voltage. VERY little current should be able to flow. In fact your LED shouldn't be at it's full brightness. Once the element is hooked up you will be find and the LED will not light. The current isn't enough for the element to even notice.

 

[augiedoggy]

yes this is correct... the SSR clamps down on current not so much voltage. VERY little current should be able to flow. In fact your LED shouldn't be at it's full brightness. Once the element is hooked up you will be find and the LED will not light. The current isn't enough for the element to even notice.

mine still lights ever so faintly with the element hooked up.

 

[pizza_man]

mine still lights ever so faintly with the element hooked up.

They never turn all the way off or all the way on.

 

[Minbari]

SSR's are current blocking and not voltage blocking. You will be able to measure a potential on the switched side due to the high resistance of the meter without the element. The element has a low resistance and therefore a higher current flow so you will not measure voltage with the element connected.


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x2

open load, you will read a voltage, with a less than ~20ohm load of a heating element or motor coils, it will read nothing.

 

[jgalati]

With no load connected to your relay, you are in a high impedance state. Because of this, your output voltage is now "floating". Depending on your home grounding and your brewery system grounding you can have variances in an "off" state relay. You'll notice that if you connect a 2k resistor to the output of the relay to GND, you'll hit roughly 0V. This is called a pulldown resistor, and is used in any and all switching in electrical engineering.

 

[ajdelange]

An SSR in series with a load is a voltage divider. If Rl is the load resistance and Rs is the SSR resistance the voltage across the load is 220*Rl/(Rl + Rs). When the SSR is switched on Rs is small - smaller than Rl anyway so that Rl + Rs ~ Rl - and the voltage across the load is ~ 220*Rl/Rl i.e. close to 220. As Rl is low the current drawn is large. If the load is replaced by something which has a much higher resistance like you or a voltmeter then the voltage is 220*Rl/(Rl+Rs). If your meter has Rl = 9 meg input impedance and the leakage impedance of the SSR is Rs = 1 meg (?) then the voltage across the meter terminals is 220*9/(9+1) = 198 V. If you touch the output and your impedance is 4 MΩ (about what I am running today) the voltage across you is 220*4/(1+4) = 176 V. In a mechanical relay, by contrast, the open impedance is much higher (it's not 0 because of the capacitance of the contact pair) and the voltage across a voltmeter or unwary brewer is much lower when the contacts are open.