possible power problem

Projects General Guidance
1

Hi
My Arduino project isn't working consistently and I need a little help.
The project controls a heating pad for a plant propagator.
I use a
AC-DC Power Supply Buck Converter Step Down Module 12v 450mA to power the Arduino
The Arduino runs
A 5v 2 Channel Relay, switchers an externally powered a heat mat
A 20x4 Character LCD
A temp sensor
A clock

The thing does not always successfully switch the heat mat off/on
The LCD dims or brightens when the relay activates

I'm wondering if the relay needs an external power supply or the power supply is inadequate or I should be looking elsewhere

Any thoughts/help appreciated

2

Post a link to the data sheet or product page for the relay. However, the symptoms do suggest that a beefier power supply is in order.

3

relay like this one on ebay

4

The relay coils require 71 mA each. How are you powering the relay module?

5

AC-DC Power Supply Buck Converter Step Down Module 12v 450mA to power the Arduino and the Arduino powers the relay

6

What sort of Arduino?
How does the Arduino power the relay? Hopefully, not an I/O pin.

The voltage regulator on most Arduinos is not capable of supplying much additional current, but one relay at 70 mA should be OK. On the other hand, 12V is at the upper limit of the allowed Arduino input voltage on the barrel jack, and the voltage regulator may be overheating and shutting down. Try a 7 or 9 V power supply.

7

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thankyou ... Tom... :slight_smile:

8

arrrg just realised that during a OS reinstall i've lost the ExpressSCH (finally crafted) circuit, it'll take ages to redo

9

An unexpected result
Turns out jremington was right the Arduino doesn't like 12v, plugged a 9v supply into the barrel jack and it works ok. I did research before going for the 12v supply and didn't find any mention of possible problem. It probably answers a question about another project i have that hasn't worked quite as expected.
jremington thanks - even though i at first dismissed your suggestion.
And thanks to everyone else who helped