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# Relay's operate and release voltages.

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#### alphacat

##### New Member
Hey,

I read a datasheet of an 1W single coil latching relay, which its coil's nominal voltage is 6Vdc.
It is said in the datasheet that its operate voltage is <80%, and that its release voltage is <80%.

Does it mean that the relay can be switched when a power of (80%)² * 1W is applied on it?
Meaning when only 0.64W is applied on the coil?

I reached that number since P = V²/R, and since R stays the same, than when decreasing the voltage to 80%, the power is decreased to 64%.

Thanks.

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In theory, this is correct.

In practice, the designer applies voltage. The "must operate" voltage is specified so the designer knows how much latitude there is between nominal and worst case.

How would you go about regulating the energy to a relay coil without regulating the voltage? And why would you care?

In theory, this is correct.

In practice, the designer applies voltage. The "must operate" voltage is specified so the designer knows how much latitude there is between nominal and worst case.

How would you go about regulating the energy to a relay coil without regulating the voltage? And why would you care?

Here is my problem.
I only have a 5V VCC to drive the relay's coil.
5V are 83% of 6V, therefore does it mean that i could operate and release the relay with this 5V?

What did you mean please when saying regulating the energy to the coil without regulating the voltage?

They do make 5V relays, plus you have to take into account any voltage drop through the driving transistor.

They do make 5V relays, plus you have to take into account any voltage drop through the driving transistor.

I'm currently interested in this specific 6V relay (due to reasons which I didnt specify here).

Therefore i'd like to know if i'd manage to operate the mentioned 6V relay with 5V VCC.

Also, I didnt understand what does it mean regulating the power to the coil and not the voltage.

Thanks.

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Toy operate a relay from an output from an MCU it needs to operate down to 4V.

Post the relays datasheet.

Therefore i'd like to know if i'd manage to operate the mentioned 6V relay with 5V VCC.

Also, I didnt understand what does it mean regulating the power to the coil and not the voltage.
The relay will be marginal at 5V. It may not always reliably pull in at that voltage, especially at higher temperatures where the coil resistance increases. Once the relay is actuated you can reduce the voltage but it's poor design practice to actuate a relay at below its rated voltage.

In theory you could use some time of capacitive voltage boost (doubler) circuit to momentarily apply a higher voltage to actuate the relay and then use 5V to hold the relay closed. But the circuit to do that would be somewhat complex and likely not practical for most applications.

The comment about power was that you can't change the power without changing the voltage and, since most relay coils are specified for operating voltage not power, the voltage is the main parameter of concern.

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