hi All, anybody has any idea why some low current solid state relays are design with a Release voltage of 10VDC? In what kind of scenario that the off signal is up to 10V? i thought usually off signal is 0V+/-
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Hi Alvin
Which relays specifically. Most solid state relays operate with a DC control voltage of 3v to 30V. Most are also AC load only and are zero crossing types. As DC never gets to zero it will never switch so it can’t be used as a load with these. I believe you can get “switch at any time” types but I personally have never seen or used one.
Because of a built in snubber circuit it is difficult to turn off a load of only a few mA as there is enough leakage across the snubber to power any light load which you are trying to turn off. This has personally happened to me and the only solution was to increase the load on the load side of the SSR to swallow up the leakage.
By the way a “snubber” circuit is a resistor and capacitor in series across the relay “contacts” so if you draw it out and include this you will see where this" leakage" comes from. Sometimes externally included across mechanical relay contacts to reduce arcing.
Cheers Bob
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Hi Robert,
Thanks for your reply, ive attached the datasheet from Finder. The operating voltage is 16-30VDC but the release voltage is 10V DC. I’m referring to the control input side not the output contacts.
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Hey Alvin,
From my understanding, the release voltage specification is designed for use when you have a variable input or a dimming circuit where the input signal can vary. In some situations, the signal voltage might become unstable or fluctuate due to factors like electrical noise, power supply instability, or something else.
In those situations, if the signal drops for a moment but doesn’t go all the way to 0V, you’d still want the relay to turn off rather than staying stuck in the on state.
For this specific relay, my guess would be whoever designed it decided that 10v was far enough under the 16-30V operating range to assume that whatever the relay is connected to is not getting the correct input anyway so it might as well be powered off.
Other relays will of course have different operating assumptions and vary this depending on the specific intended use case.
Hope this helps!
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Hi Alvin
The operating voltage for this relay is 16 to 30V. That entry indicates that the release voltage is 10V or lower. In other words 10V is the “must release” voltage.
So yes it will release OK at 0V.
This “must operate” and “must release” level is a figure published in the data sheet of nearly all relays of a reputable brand. This data sheet seems to have just worded things a bit differently. The “must operate” figure would be the 16V
By the way, Finder is a very reputable brand indeed and has been around a long time.
Cheers Bob
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Hi Samuel
Not quite correct here. As stated in my reply to Alvin mostly this figure is called “must release” and "must operate. Nearly all relays I have used or come across (including Finder) have used this term. Finder for some reason have changed the wording for this one (maybe Finder have been acquired by someone else).
As this device is quoted to operate 16V to 30V I believe the “must operate” value would be 16V and the “must release” value 10V.
As a blanket statement to allow for multiple relay voltages these 2 criteria are sometimes expressed as a percentage of the nominal rated voltage.
It is not an assumption, it is a SPECIFICATION.
Read some of my replies concerning operating 5V relays at 3.3V when the “must operate” spec says 75% f rated operating voltage. Which in this case is 3.75V. Well outside spec.
Cheers Bob
Edit:
After a bit of thinking it could be that this wording could be appropriate for this device as it is optical as against coil operated. This could be meant to mean it is guaranteed to operate at anywhere between 16V and 30V and guaranteed to release at anything at or below 10V. Means much the same thing really.
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Hi Bob,
Thanks for that, Looks like I should have poked a bit closer into this.
Am I correct in assuming that in this case, this would mean that the relay would normally shut off somewhere in the range of 10-16V but if it hits 10V that’s the hard line when it should absolutely turn off?
Hi Samuel
Pretty much yes. Once operated relays (especially the coil type) will hang in there well below the minimum “must operate” voltage but there must be a point where this is no longer possible. With this device it would appear to be 10V.
Cheers Bob
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