Relay coil set and reset with momentary switch

Question

I am having trouble with the activation of a set-and-reset coil of a relay which is dual coil-latching.

The datasheet mentions that to set or reset the coil I need to apply the rated voltage for max. 20ms (in the coil data specifications section) and also mentions a min. 100ms pulse length to set and reset in the Notes section.

I am not sure which one to consider. I would like to know the minimum and maximum time length I can apply to the relay coil to set or reset.

I am thinking of doing it with a momentary SPDT toggle switch (I am not sure if can go with it). Do I absolutely need a control circuit to set or reset the coil? Or will an other method which is not necessarily cheap do the job? If anyone has any experience with dual coil latching please help me with this.

PS: Supply for the coil is coming from a DC supply

Answer 1

Set and reset times are the time needed by the relay to physically move, and stabilize the latch. (It might be bouncing around a bit before settling)

A rule of thumb is to energize the coil for 5x this time, to be sure that even an aged/hot/cold relay is able to switch states. Note 2 states this: Use a minimum pulse of 100ms.

That being said, unless you are continuously switching, or operating the relay very frequently, there should be no issues energizing the coil for several seconds without damage.

Answer 2

I would like to know the minimum and maximum time length I can apply to the relay coil to set or reset.

There is no maximum time length you can apply to the relay coil to set or reset as long as the maximum current rating is not exceeded. It is confusing, but the Max value given in the datasheet is the maximum minimum time you need to apply your pulse. You see, the minimum time you need to apply your pulse may vary from device to device and from environmental condition to environmental condition. So the manufacturer says that the maximum value of this minimum length of time you need to apply your pulse is 20ms.

The datasheet mentions that to set or reset the coil I need to apply the rated voltage for max. 20ms (in the coil data specifications section) and also mentions a min. 100ms pulse length to set and reset in the Notes section.

I think the manufacturer is being a little "sneaky" or "wafflely" here. On the one hand they are claiming the latch will work within 20ms, but recommending that you pulse for 100ms. I would go with the recommended 100ms pulse, because it is more conservative.

If you are using a mechanical switch, it is likely that your pulse will be at least 100ms anyway. (Although keyboard switches are likely to be pressed for short durations, people tend to press "control" switches for longer).

Contact bounce may be an issue with a mechanical switch. If it is, it can most likely be corrected with a capacitor, and not require any more complex circuitry.

Answer 3

It’s just a different perspective.

This is the guaranteed max time needed to activate at room temp. It may switch sooner in this benign environment and longer under repetitive stress use.

Core strength may reduce with thermal and saturating effects or max ambient temp. depending on duty cycle of changes, so time can increase.

Therefore they recommend >= 100 ms for reliable long-term repetitive use but be mindful of average power dissipation and heat rise.