Relay taking longer time time to switch OFF?

Relay Coil
PArt of circuit i would to share

a. When Relay 27V SW1 is ON we get signal as shown marked 1

b. When Sw2 is ON we get waveform marked 2

c. When Sw2 is OFF we get waveform marked 3.

My analysis is it is taking longer time to switch OFF

What can be the reason is relay is not working properly

Its a 27V 5A relay Part NO HFW5A1201K00

Unclear schematic, what are you measuring at all? What's the load?

Why do you think the relays isn't working correctly?

FvM said:

Unclear schematic, what are you measuring at all? What's the load?

Why do you think the relays isn't working correctly?

Click to expand...

Total load current is 1Amp.

There is LED connected at the output the moment I switch OFF SW2 the LED does not switch off immediately. it switches off with some delay .

There's no LED shown at "output", neither any connection of the relays contacts or both terminal of the relays coil. Please come back with a complete schematic, clarifying where the oscilloscope probe is connected.

angy said:

My analysis is it is taking longer time to switch OFF]

Click to expand...

Put a reverse diode across the relay coil. You will see significant improvement.

c_mitra said:

Put a reverse diode across the relay coil. You will see significant improvement.

Click to expand...

That will make it longer to turn off, not shorter.

crutschow said:

That will make it longer to turn off, not shorter.

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I beg your pardon?

If you look at current, the switching is probably instantaneous.
If you look at voltage, you see the difference between
(Rclosed||Rload)*Cload and (Ropen||Rload)*Cload

c_mitra said:

I beg your pardon?

Click to expand...

Without a diode, the coil current stops immediately when the voltage is removed, with a rapid collapse of the magnetic field, and the relay opens as fast as it can.

If you add a diode across the coil, the coil current continues to flow through the diode after the voltage is removed, due to the coil inductance, delaying the collapse of the field, and causing the relay to take significantly longer to open.

Why did you think it would speed up the relay?

dick_freebird said:

If you look at current, the switching is probably instantaneous.

Click to expand...

The question is badly cast.

The output (contact end) side of the relay is not shown; we know that the contact rating is 5A and it can switch max 28V. But that is of no concern in the present case.

Because of two switches, there are four states. The original post is very confusing.

SW1 SW2 Stat
on on 1
off off don't know
on off 2
off on 3

(strictly speaking we should discuss the switch transition: on --> off OR off --> on)

Like in a grey code, we should consider only one transition at a time (e.g., SW1 on--> off while SW2 is on AND also SW1 on --> off while SW2 is off ETC ETC)

The relay is taking longer time to turn off BECAUSE the current has no path to decay and the relay has a large hysteresis.
The circuit has two switches in series (I do not know why) in series with the coil and a diode. From the specs (Digikey), the max turn on voltage is 13.5V and the min turn off voltage is 1.5V. This is a good relay.

As per the official data, the operate time and the release times are equal (4 ms).

c_mitra said:

........
The relay is taking longer time to turn off BECAUSE the current has no path to decay and the relay has a large hysteresis.

Click to expand...

That's not correct.
The relay switches fastest when there is no current path and the inductive current stops rapidly (which generates a large inductive spike) along with a rapid collapse of the magnetic field.
If there is a path for the current (such as from a suppression diode), then the magnetic field collapse is slowed until the current stops, delaying the relay turn off.

If you need spike suppression and a faster turn-off time, then you can put a resistor in series with the diode, or alternately a zener diode.