An SMPS should not go over its nominal value on power on. In any case, even if it did it would cause no harm to a relay which would easily stand short term over volts on the coil of considerable magnitude.
If you ramp the voltage up on a relay coil... and lets take your 24 volt coil as an example... then the contacts will close in a very lazy manner at perhaps as low as 12v and certainly above around 15 volts. Once closed the coil voltage can be reduced significantly and our 24 volt coil could well hold the contacts closed down to 5 volts or so.
Ideally a relay should close with force and that means applying a fast rise time voltage of the rated value (so 24 volts here) for a few hundred milliseconds after which we can drop the voltage to save power.
That is what my Triac circuit above does.
> the scariest of all:
I saw that. But considering the simple/sloppy nature of this plan, I didn't think it was "scariest".
My 24VAC sim shows 28V on the relay. Taking a 15% un-sag (he's not going to find a 1VA transformer) we have 32V on a 24V coil. This is 1.34X the rated voltage. This is barely inside the "Recommended". The maker says this is OK.
> Does the 24v rating mean it's the max rating ....Will a 24v relay function with less than 24v?
They vary. A lot.
For small relays like this, I would assume they will give decent life at 1.5X nominal voltage, and will probably pull-in at 2/3rd of rated voltage (very-very variable).
As Mark says, Schrack "recommends" for reasonable ambient temperature working at 0.8 to 1.4 nominal voltage. However the data actually allows over double rated voltage. (I did not look to see if there is a life-derating on this curve.)
Further, in this case *if* the relay burns-up, nobody loses a hand. Or a speaker. The speakers go silent. After some frantic trouble-shooting, a new (and probably low-cost) relay is a complete fix. For a while. When relay replacements get annoying, pick a better plan.
I saw that. But considering the simple/sloppy nature of this plan, I didn't think it was "scariest".
My 24VAC sim shows 28V on the relay. Taking a 15% un-sag (he's not going to find a 1VA transformer) we have 32V on a 24V coil. This is 1.34X the rated voltage. This is barely inside the "Recommended". The maker says this is OK.
> Does the 24v rating mean it's the max rating ....Will a 24v relay function with less than 24v?
They vary. A lot.
For small relays like this, I would assume they will give decent life at 1.5X nominal voltage, and will probably pull-in at 2/3rd of rated voltage (very-very variable).
As Mark says, Schrack "recommends" for reasonable ambient temperature working at 0.8 to 1.4 nominal voltage. However the data actually allows over double rated voltage. (I did not look to see if there is a life-derating on this curve.)
Further, in this case *if* the relay burns-up, nobody loses a hand. Or a speaker. The speakers go silent. After some frantic trouble-shooting, a new (and probably low-cost) relay is a complete fix. For a while. When relay replacements get annoying, pick a better plan.
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