Best power supply for microcontroller circuit with inductive load

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Relay coil and bell load likely causing nRF24L01 heating
#1 21682917 10 Jul 2019 22:39

madhusoodanan er madhusoodanan er

Anonymous

Relay coil and bell load likely causing nRF24L01 heating
Post #1 21682917 10 Jul 2019 22:39

Hello, everyone, I am trying to make a wireless bell system for colleges using atmega328 and nrf24l01+Pa(as a wireless link). The system has 2 unit, one is remote(unit1), contains a trigger switch and another(unit2) contains bell. My problem is when I press the bell switch(unit1) normally bell is on and off but nrf24l01 start heating, then I disconnect ac operated bell from the system it works perfectly. I am using the 12v relay to switch the 230V ac operated bell and i am using pc smps as power source, also all powers are taken from smps (3.3V,5V and 12). How to solve this heating problem. Please help me...
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Clarifying relay drive, SMPS voltages, and isolation
#2 21682918 11 Jul 2019 02:52

David Ashton David Ashton

Anonymous

Clarifying relay drive, SMPS voltages, and isolation
Post #2 21682918 11 Jul 2019 02:52

A bit of a diagram might help - this does not make a lot of sense. What is operating the 12V relay for the bell, a pin on the ATMEGA328 or the receiving NRF24L01? Are you using a transistor or FET to drive the relay? As long as you are using the 3.3V to drive the NRF24L01 it should be within limits. Have you measured the voltages from your SMPS? And is there REALLY good isolation between the 230VAC and the rest of the circuit? is your earth good, are you using that on the low voltage side of the circuit?
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Check relay transistor, flyback diode, and SMPS stability
#3 21682919 11 Jul 2019 03:30

Elizabeth Simon Elizabeth Simon

Anonymous

Check relay transistor, flyback diode, and SMPS stability
Post #3 21682919 11 Jul 2019 03:30

Without a diagram it's hard to picture what is happening here but I suspect that you have something mis-wired.
Since you seem to have normal operation with the bell disconnected, I suspect something in the bell circuit.
Here are a couple things to check.
First, you should be using a transistor to turn on the 12 V relay and NOT try to connect directly to the atmega or nrf24l01. You will also need a reverse biased diode across the relay coil to suppress inductive spikes.
Second, check that the DC voltages on your smps are stable when you turn the relay on.It's possible that turning the bell on could generate noise on the mains which could possibly disrupt the DC voltages.
Either of these could cause your nrf24l01 to heat up.
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#4 21682920 11 Jul 2019 14:21

madhusoodanan er madhusoodanan er

Anonymous

Post #4
21682920 11 Jul 2019 14:21

Thanks for your replay sir. Here I attached my whole schematics both bell side and remote
Clarifying relay current, contact rating, and supply sag
#5 21682921 11 Jul 2019 15:08

David Ashton David Ashton

Anonymous

Clarifying relay current, contact rating, and supply sag
Post #5 21682921 11 Jul 2019 15:08

OK.... more questions than answers here:- How big is your relay? (do you have a type number)- How much current does your relay coil need (the ULN2003 can supply max 500 mA)- did you check that it can handle the bell current?- did you check it can handle 240V on the contacts?- is it just the NRF24L01 module gets hot or anything in the rest of the circuit?- have you checked the supply voltage to the NRF24L01 module while the bell is on?Thanks // David
Hot switching greatly shortens relay contact life
#6 21682922 11 Jul 2019 18:24

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Hot switching greatly shortens relay contact life
Post #6 21682922 11 Jul 2019 18:24

Hi! Also since this is going to be deployed in a school area (which means frequent use), I think he also has to make sure that the type of relay is appropriate.
I've been involved with the automation board design (which deals with a lot of relays) for verification purposes of commercial IC products and there is almost an entire science behind choice of relay regarding its life cycle.
IMPORTANT: Relays that 'hot' switch signals run hotter than relays that don't hot switch (and their contacts will erode much faster)!!
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#7 21682923 11 Jul 2019 18:36

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #7
21682923 11 Jul 2019 18:36

Hello! I'd also just like to add:
If hot switching is really unavoidable in the application, we usually use a BIG heat sink! (but they tend to have quite low life cycles either way). Hehe.. Best regards,Justin
#8 21682924 11 Jul 2019 22:36

Elizabeth Simon Elizabeth Simon

Anonymous

Post #8
21682924 11 Jul 2019 22:36

Contact erosion from hot switching is due to arcing so you really need arc suppression for hot switching if you are getting contact erosion.
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Topic summary

A wireless bell system using an ATmega328 microcontroller and NRF24L01+PA module experiences heating of the NRF24L01 when the 12V relay activates a 230V AC bell. The power supply is a PC SMPS providing 3.3V, 5V, and 12V rails. The heating issue disappears when the AC bell is disconnected. Key troubleshooting points include verifying proper relay driving circuitry—using a transistor or FET rather than direct MCU or NRF24L01 pin drive—and ensuring a reverse-biased diode across the relay coil to suppress inductive spikes. Stable DC voltages from the SMPS under load must be confirmed, as mains noise from the bell activation could disrupt the supply. Isolation between the 230VAC and low-voltage circuits, proper earth grounding, and correct wiring are critical. Relay specifications such as coil current, contact voltage rating, and suitability for frequent switching in a school environment should be checked. Hot switching causes contact erosion and heat; arc suppression or heat sinking may be necessary to improve relay life and prevent interference affecting the NRF24L01 module.
AI summary based on the discussion. May contain errors.

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Best power supply for microcontroller circuit with inductive load

Best power supply for microcontroller circuit with inductive load

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Topic summary