DC Relay Heat when it's closed bypass suggestions

[Zedestrian]

Hello everyone,

I'm working on a projects that countains a stm32l152re to communicate with temperature/Humidity sensor amongst other sensors and a DC relay to control some light bulps. However, when the relay is closed, it overheat and corrupt the measured data from the sensors. I know this problem can be looked at from different perspectives (electronics, Mechanics and firmware).

I'm a junior embedded system developer. I contributed to this project by developing firmware for some of the sensors and I've been asked recently to give a suggestion for the heating problem. I searched on the net but couldn't find some valuable info that I could use. Any suggestions will be very welcome especially a firmware one.

I'm open into any questions or more detailed informations. Thanks !

[TDK]

Relays have a maximum current capacity. If you exceed that, it will overheat.

All relays will heat up to some degree in normal use. Latching relays, where the current is applied only briefly to transition between states, do not require constant power and may be preferable.

[Zedestrian]

Thanks for the reply. I appreciate the informations you presented. However, my question is there any firmware solution or a coding method that can reduce that ?

[TDK]

You generally cannot solve a hardware problem with a firmware solution. However, you've given little insight into the details and the precise answer will depend on what exactly you mean by "overheat" and if the problem is caused by incorrect hardware selection or an incorrectly driven relay (edit: or a misunderstanding of how relays work).

[Tesla DeLorean]

This falls into the How many SW Engineers does it take to change a light bulb..

If you're not qualified to give suggestions, say so, the electro/mechanical issues are surely someone elses responsibility in the design.

Coils in relays will warm as current flows. Larger relays tend to need a bigger magnetic field to hold switching contactors in place.

Perhaps look for solid-state alternatives?

What voltages/currents are you looking to switch?

[Nikita91]

Does the overheat come from the coil or the switched current ?

Does it overheat when the relay is closed without switching current?

What is the coil rated voltage?

What is the voltage you supply to the coil ?

Can you give the reference of the relay?

[Zedestrian]

I appreciate the answer and to answer your question :

What voltages/currents are you looking to switch?

>> 230V/10A

[Zedestrian]

First, I appreciate the time you took to answer my questions and to be more precise. I doubt there is a an electronic issue. I suppose it's a mechanical issue regarding the electronic board packaging which provides one output from the sensor positions. To answer some of your questions :

What is the coil rated voltage?

>> 12V

What is the voltage you supply to the coil ?

>> 12V

Can you give the reference of the relay?

>> T77V1D10-12

[Peter BENSCH · Accepted solution]

Well, the relay you are using has a rated coil power of 450mW, which is felt as heat generation after a while.

As everyone here has already written, the relay naturally needs energy to pick up. However, the holding current is usually smaller than the pickup current.

It is possible to control the relay with an additional circuit that only allows a higher current pulse when it is switched on and then switches back to the holding current. Theoretically, this should also be possible with PWM (first switch on fully and then generate the holding current using PWM).

However, I don't know of any ready-made proposals for either the hardware or the software variant, but it should be easy to realise with a little development work. At least the hardware variant has been discussed many times on the internet in the last decades.

Regards

/Peter