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Topic: Issue with 12V 2A power supply into Arduino Uno (Read 108 times) previous topic - next topic

jmvar

I am putting together a fan controller for my smoker that takes temps from a thermistor and controls a fan using the PID library.

I am having an issue with my prototype when I use the 12V 2A power supply plugged into the arduino.  This makes the temperature jump around randomly.  When I use the 12V supply from an ATX power supply there is no issue and temps read perfectly.  When I power the arduino with the USB port there is no issue, only with the 12V power supply.  Here is a link to the power supply I am using:

http://www.amazon.com/gp/product/B000VRIK54/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Here is my BOM:

16x2 LCD
Maverick ET 732 Thermistor
22k resisor for thermistor circuit
1k resistor for fan circuit
TIP120 transistor
diode for fan circuit
12v brushless fan


Here is my wiring diagram:



Is this an issue with the power supply or do I have to filter out noise in my circuit somehow?

I apologize for the simple questions, I am a mechanical guy having fun learning this electronics stuff.

Thanks

MarkT

Have you considered that 12V brushless fans aren't designed to be PWM'd?  You
will be shorting the 12V supply to the decoupling caps in the fan on every cycle of PWM,
causing the 12V rail to dip...

Brushless fans consist of a brushless motor and a driver circuit to commutate the
motor.  They are not motors.

You can get speed-controllable fans which take a logic signal as PWM input specially
to allow speed control.
[ I won't respond to messages, use the forum please ]

jmvar

Hi MarkT, thank you for the response.

I did not consider that brushless fans are not designed for PWM control, thanks for the heads up.  I have a brushed fan I can use.

As far as the circuit, I stripped down the prototype looking for culprits of interference and basically was left with just the 12v power supply and the thermistor circuit.  The motor and LCD circuits were removed one by one to diagnose.  That is when I found that with the ATX power supply I didn't have the temperature fluctuation issue but with the 12v power supply from Amazon I did.

I guess what I could try is moving the probe circuit to different pins on the arduino to see if that has an effect.  The issue with this is that eventually I would like to use all of the analog inputs for temp probes so I will eventually have to resolve the issue.

Do you think my issue is with the power supply or interference within the circuit that I need to filter out?

Thanks

MarkT

The ATX supply will ride out the glitches much better due to its higher current rating
I suspect.  Try putting 10 ohms in series with the fan and see if that cures the problem,
if so then the switching glitches definitely crow-baring the 12V supply as I suspect.

If not its something else (noisy supply?)
[ I won't respond to messages, use the forum please ]

jmvar

The ATX supply will ride out the glitches much better due to its higher current rating
I suspect.  Try putting 10 ohms in series with the fan and see if that cures the problem,
if so then the switching glitches definitely crow-baring the 12V supply as I suspect.

If not its something else (noisy supply?)
I am currently just running the temp sensor circuit without the fan or LCD circuit to diagnose the issue.  Should I introduce the fan circuit with the 10 ohm resistor to see if that gets rid of my issue?

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