# How long does a relay take to "close/switch"

#### cgw94

Joined Jun 11, 2020
42
Hi there,

I have been scouring the internet and can't seem to find an answer to this.

I want to know, either on average or where to find it for a specific model, how long it take for the switch to switch positions on lets say a Double Throw relay.

To preface, I am building a circuit that will use a capacitor to latch a relay. I want to know the minimum time i need to energize it in order for it to latch.

Here's a specific relay we can use for this. It is a general omron relay 12v, 278 ohm coil.

Here is what i have, i calculated that at 278 ohms i can get a charge time constant of about .028s using a 100uF cap at 12V

From what I know, that time constant is for it to reach about 2/3 total charge. This means at that time i would be passing about 8 volts.

According to the relay spec sheet i need at minimum 8.5 volts to energize the coil.

For my circuit to work. I need to have the time between my cap charging that last 30% or so to be long enough to energize the coil and latch the relay.

My unknown is what that time is. (also i know the cap charging is not linear, need to look into that more)

My thinking was if i know the relay time to close is lets say 3ms, I can use that to size my capacitor better.

I unfortuantley dont have any equipment that is fast enough to monitor these state changes.

Any ideas would be lovely! Thank you!

Cheers!

#### dl324

Joined Mar 30, 2015
17,157
I want to know the minimum time i need to energize it in order for it to latch.
15ms. It isn't a latching relay, so the coil needs to be energized for as long as you want the contacts opened/closed.

#### kubeek

Joined Sep 20, 2005
5,796
Hi there,

I have been scouring the internet and can't seem to find an answer to this.

I want to know, either on average or where to find it for a specific model, how long it take for the switch to switch positions on lets say a Double Throw relay.

To preface, I am building a circuit that will use a capacitor to latch a relay. I want to know the minimum time i need to energize it in order for it to latch.

Here's a specific relay we can use for this. It is a general omron relay 12v, 278 ohm coil.

Here is what i have, i calculated that at 278 ohms i can get a charge time constant of about .028s using a 100uF cap at 12V

From what I know, that time constant is for it to reach about 2/3 total charge. This means at that time i would be passing about 8 volts.

According to the relay spec sheet i need at minimum 8.5 volts to energize the coil.

For my circuit to work. I need to have the time between my cap charging that last 30% or so to be long enough to energize the coil and latch the relay.

My unknown is what that time is. (also i know the cap charging is not linear, need to look into that more)

My thinking was if i know the relay time to close is lets say 3ms, I can use that to size my capacitor better.

I unfortuantley dont have any equipment that is fast enough to monitor these state changes.

Any ideas would be lovely! Thank you!

Cheers!
Is this a poem?

#### crutschow

Joined Mar 14, 2008
34,855
Here is what i have, i calculated that at 278 ohms i can get a charge time constant of about .028s using a 100uF cap at 12V
That likely will work for the relay's 15ms operate time, but I would double the cap size just for good margin.

#### sghioto

Joined Dec 31, 2017
5,431
To preface, I am building a circuit that will use a capacitor to latch a relay.
Can you post your schematic? Curious on how the capacitor is getting discharged between operations.

#### LowQCab

Joined Nov 6, 2012
4,314
As per usual in these Forums, no overall goal is stated.
The Capacitor is likely to be so large and expensive, that you would be way ahead of the game to
use an SCR or a FET, or back to back FETs, instead, (in other words, a Solid-State-Relay, SSR).
Why are you using a Relay in the first place ??
How long does the Capacitor have to hold its Charge ??
How are you switching the power from Cap to Relay ??
If you already have Power available, which will be switched by the Relay,
why do you need power stored in a Capacitor to energize the Relay ??
How often will the Relay be cycled ??
What power holds the Relay closed after the Cap discharges ??