Having trouble with MAX31850 and external power

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phischmi
 
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Having trouble with MAX31850 and external power

Post by phischmi »

Hi all,

i'm trying to build up a wiring, which on the one hand measures temperature using two type-k thermocouples and on the other controls a 12V DC fan with PWM.

For the first part, i followed your great tutorial on the MAX31850 breakoutboards and it works as proposed.

For the second part, i took the above mentioned 12V 4-Pin DC fan and first connected it to an external 12V mains adapter.
The fan runs at full speed.
Then i connected the PWM-lead of the fan with a pin on the Arduino and the GND of the mains adapter with the GND of the Arduino.
Using the PWM.h library i now can control the fan using PWM at 25KHz. Works.

My problem now is, as soon as i connect the fan to mains, the temperature readings of both MAX31850 go haywire and jump e.g. between 0°C and room temperature. If the mains adapter is switched off, everything looks good again.

It makes no difference, if i either connect the PWM or the GND of the fan with the Arduino - or both. The irritating behaviour is the same.

Do you guys have any idea, what's the problem and how i can solve this?

The wiring is exactly the same as in the tutorial with the only difference, that there are few terminal blocks for the fan and the 12V mains adapter. Those are in no way connected to the other circuit except for GND and PWM-lead of the fan to Pin 9 on the Arduino.
If i cut those connections everything works, but i'm certainly not able to PWM-control the fan...

Thanks for your help!


Best regards

Philipp

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adafruit_support_mike
 
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Re: Having trouble with MAX31850 and external power

Post by adafruit_support_mike »

Post a photo showing your hardware and connections and we'll take a look. 800x600 images usually work best.

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phischmi
 
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Re: Having trouble with MAX31850 and external power

Post by phischmi »

Hi Mike,
Thanks for your reply!
Here're some pics of my setup.

First the working wiring (without connections between GND and PWM):
Image

Second the one WITH connections between GND and PWM and irritating Temp-Values:
Image

Last a video of the whole (working) setup:
https://youtu.be/kVI6fAjAa_I

The connections between A1 of the level shifter and Data on the MAX31850 breakout cannot be seen, as it'as covered by the breakout-board.


Merry Christmas!

Philipp

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phischmi
 
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Re: Having trouble with MAX31850 and external power

Post by phischmi »

You guys have no idea either, what causes the problem? :/

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ImaginaryAxis
 
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Re: Having trouble with MAX31850 and external power

Post by ImaginaryAxis »

Thermocouples are easily susceptible to electromagnetic fields and/or poor grounding practices.

Mains ground is noisy; "dirty". Then you have this noisy return path connected to a bread board (inherently parasitic) with lots of long jumper wires.

You can add more bulk capacitance at the mains adapter in hopes of providing a short return path and shielding for the thermocouples.

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adafruit_support_mike
 
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Re: Having trouble with MAX31850 and external power

Post by adafruit_support_mike »

Sorry for the delay following up.

Your assembly looks excellent, so we can probably rule out any problems there. All electromechanical sytems are noisy though, and motors are especially bad. Try putting a large capacitor (at least 100uF, 1000uF will be better) between the 5v and GND rails for the breadboard that holds the MAX31850s and see if that helps.

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phischmi
 
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Re: Having trouble with MAX31850 and external power

Post by phischmi »

Hi Mike,

i recently had the time to make some modifications to my setup - but the problem ist still the same :(

What i did:
  • connected both the fan AND the Arduino to the same 12V/2A PSU via Y-wire
  • put an 100nf ceramic capacitor before the MAXs
  • put an 470μf electrolytic capacitor before the ceramic capacitor
Any other ideas?

Image

Image

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