[SOLVED] Relay operate voltage variation with respect to temperature

[Brother]

Hello,

Can somebody tell me about variation of relay operate voltage with respect to temperature? Has anybody experienced the failure of relay to operate due to operate voltage variation caused by temperature ? What care is to be taken while deciding operate voltage of relay ?

I hope this is correct section for this post. Any suggestions?

Thanks,

 

[usmanyousaf]

Relays has their rating like e.g. 220V/10A. untill you keep your load current limited to the rated current (10A) there wont be any issue of voltage drop due to temperature. while the coil voltage needs to be maintained otherwise the relay will switch back to normally closed contact.

usman

 

[andre_luis]

I already noticed a minimalist histeresys circuit wich operates using basically 2 relays as either comutation element, and comparator.
At cases like this, we can expect deviation on voltage setpoints, due magnectic coil core have properties changed by temperature.


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[Brother]

Relays has their rating like e.g. 220V/10A. untill you keep your load current limited to the rated current (10A) there wont be any issue of voltage drop due to temperature. while the coil voltage needs to be maintained otherwise the relay will switch back to normally closed contact.

usman

Thanks for the information!
I would like to know what would be the impact of temperature. As you said, coil voltage needs to be maintained. Does it mean - relay would not be able to operate at the coil voltage at higher temperature; which used to operate at the same voltage at nominal temperature. Please correct if I am wrong.

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I already noticed a minimalist histeresys circuit wich operates using basically 2 relays as either comutation element, and comparator.
At cases like this, we can expect deviation on voltage setpoints, due magnectic coil core have properties changed by temperature.


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Does it mean - coil operate voltage change if magnetic coil properties changed by temperature ?

 

[FvM]

You didn't tell about AC or DC coil. For DC coils, the expectable main effect is caused by copper TCR, R is about proportional to absolute temperature, as with most pure metals. Thus you'll notice a slight increase (10% per 30 degree C) of operate and release voltage with temperature for DC coil relays. It's sometimes specified in datasheet, see below a diagram for Omron G6K series.

 

[Brother]

You didn't tell about AC or DC coil. For DC coils, the expectable main effect is caused by copper TCR, R is about proportional to absolute temperature, as with most pure metals. Thus you'll notice a slight increase (10% per 30 degree C) of operate and release voltage with temperature for DC coil relays. It's sometimes specified in datasheet, see below a diagram for Omron G6K series.

Thanks for appropriate information! Sorry, I forget to mention the DC coils. I interprete from the graph - Over entire temperature range Operate voltage varies approximately +/- 15% of the its nominal operate voltage at 20 degree Celsius. Over entire temperature range Release voltage varies approximately +/- 5% of the its nominal release voltage at 20 degree Celsius.
Please correct me if my interpretation is incorrect.
Two more queries -
1. Does the operate voltage varies also with the previous state of the relay ( cold state or pre-energized) ? If yes, please share details.
2. Will it affect the reliability of the relay if it is overdriven at higher voltage ? As overdrive may be required to cover the operating range of relay over entire temperature range and at nominal/low temperature it may be facing the higher voltage.

Thanks,

 

[FvM]

I think that your questions are anwered in relay datasheets and application notes.

Permitted "overdrive" is a matter of thermal rating, not covered by the posted diagram. With common relays you won't have problems to drive the coil with fixed (rated) voltage over the full specified temperature range. In so far I don't see a particular problem.

 

[andre_luis]

If you are using relay as a standard driven comutation device, pehaps this question will not be an issue, considering it is operating under nominal specifications, above threshold limit.
It simplifies design development, due you will deal just with saturating region.


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[Brother]

I think that your questions are anwered in relay datasheets and application notes.

Permitted "overdrive" is a matter of thermal rating, not covered by the posted diagram. With common relays you won't have problems to drive the coil with fixed (rated) voltage over the full specified temperature range. In so far I don't see a particular problem.

Thanks again for appropriate information!
I have one datasheet as a reference which states that in cold state relay, over entire temperature range Operate voltage varies approximately +/- 20% of the its nominal operate voltage at 20 degree Celsius. However in pre-enegised state, operate voltage itself is ~2.5 times the nominal operate voltage at 20 degree Celsius. Does the operate voltage increase by so much factor ? Any past experience ?

Thanks,

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If you are using relay as a standard driven comutation device, pehaps this question will not be an issue, considering it is operating under nominal specifications, above threshold limit.
It simplifies design development, due you will deal just with saturating region.


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Thanks for information! That means Little overdrive is ok .. but with reference to one datasheet, Preenerigzed relay Operate voltage is ~2.5 times the relay operate voltage at COLD state .. What should we do in such cases about deciding the operate voltage ?

Thanks..

 

[FvM]

However in pre-enegised state, operate voltage itself is ~2.5 times the nominal operate voltage at 20 degree Celsius. Does the operate voltage increase by so much factor ? Any past experience ?

I don't understand what you mean exactly. There's a factor of e.g. 2 or 2.5 between engage and release voltage by nature of the magnetical circuit. In some application, it's utilized for an energy-saving circuit, that reduces the operate voltage after engage. Relays with AC coil have a built-in current reduction feature, by the way.

 

[Brother]

I don't understand what you mean exactly. There's a factor of e.g. 2 or 2.5 between engage and release voltage by nature of the magnetical circuit. In some application, it's utilized for an energy-saving circuit, that reduces the operate voltage after engage. Relays with AC coil have a built-in current reduction feature, by the way.

Thanks! I understand "There's a factor of e.g. 2 or 2.5 between engage and release voltage by nature of the magnetical circuit.".
I would like to clarify about my question by giving example - If a relay is not energised for a long time (i.e. it is in COLD state). Suppose, now we energise it successfully by giving voltage V1 and keep it energised for a long time ( i.e. now it is in pre-energised state). Later, if we de-energise the relay for 1-2 seconds and energise again, shall we need to give voltage V2 (which is ~2.5 times V1) for successful energising it as it was in pre-energised state ?

 

[FvM]

I think you are somehow misunderstand the meaning of the diagram shown in post #5.

It does not imply, that the relay should be operated at lower voltage "V1". The diagram primarly says, that if you reduce the coil voltage down to to the dropout voltage, it must release. The diagram does not specify a minmal reliable hold voltage.

You can in fact reduce the steady state coil voltage to save power, but a save value will somewhere between pick-up and drop-out voltage, means it might release at a higher voltage.

As a simple point, to "re-energize" a relay, you always apply a voltage above the maximum pick-up voltage, ususally the rated coil voltage, independend of how long it has been de-energized.

 

[Brother]

I think you are somehow misunderstand the meaning of the diagram shown in post #5.

It does not imply, that the relay should be operated at lower voltage "V1". The diagram primarly says, that if you reduce the coil voltage down to to the dropout voltage, it must release. The diagram does not specify a minmal reliable hold voltage.

You can in fact reduce the steady state coil voltage to save power, but a save value will somewhere between pick-up and drop-out voltage, means it might release at a higher voltage.

As a simple point, to "re-energize" a relay, you always apply a voltage above the maximum pick-up voltage, ususally the rated coil voltage, independend of how long it has been de-energized.

Thanks again for appropriate and useful information! Now, I understand, for reliable energizing the relay, we shall give minimum rated voltage independent of COLD or pre-energised state over it's operating temperature range.
Thanks!