Hi,

I am very new to electronics and wiring and I am working with a DAQ system that was made by someone else which has a short circuit at an unknown location. There is a 12V power supply that connects to an Arduino board and from there to a relay (goes to a valve), and also 12V to a 24V converter and to a couple 24V barriers and devices in parallel. Lastly there is a 5V side from the arduino to a bunch of sensor chips. When I connect the battery to the converter everything seems to operate normally (lights are on and no visual failures) but when I connect the 12V to arduino, it fries it at the voltage regulator. I have no indication if the 5V side works since the arduino does only send current to the 5V devices for a split second before they die. My plan is the following:

• [ ] do continuity test on 12V side and 5V side (not sure how to preform continuity test on devices, only wires)
• [ ] check each connection if loose and verify soldering and insulation
• [ ] test 5V side (I have access to an independent 5v power source but would like to avoid connecting it until I have inspected it more)
• [ ] test how to measure V and current flowing through Arduino without Arduino (not sure yet how to do this)

Does anyone have suggestions of steps to add or methods on bullets 1,3 and 4?

Thank you!

 

it fries it

Can’t tell which it is which. What is getting fried, the power supply or the Arduino?

 

Can’t tell which it is which. What is getting fried, the power supply or the Arduino?

The Arduino's voltage regulator fries

 

• do continuity test on 12V side and 5V side (not sure how to preform continuity test on devices, only wires)

  The simple continuity test will not be very conclusive unless there is a dead short on the circuit. You can test the continuity between the voltage regulator's output and GND pins with an ohmeter to check the resistance of the entire circuit. If you see something similar to 0Ω or whereabouts, then you might have a dead short wire on the circuit or on the output of the voltage regulator. You can remove it and test the continuity between its input (or output) and GND pins to see if there is something close to 0Ω.

• test 5V side (I have access to an independent 5v power source but would like to avoid connecting it until I have inspected it more)

  That is your best bet to get to the bottom of this mystery, especially if your power supply has a current limiter. Set the current limiter to something relatively small (50 or 60mA) and see if the voltage stays at 5V when connected to the Arduino after the fried voltage regulator. If the voltage drops, try to increase the limiter to some 100 to 150mA and check the other parts of the Arduino for temperature (your finger is a good test probe). If you only have a simple 5V voltage supply, you will have to insert a series resistor between the power supply and the Arduino to limit the current. Start with a larger value (82 or 68Ω, which should limit any short circuit current) and follow the sequence above, reducing the resistance on the second step to 47 or 33Ω.

• test how to measure V and current flowing through Arduino without Arduino (not sure yet how to do this)

  The procedure above should cover this.

 

The Arduino's voltage regulator fries

Your Arduino voltage regulator looks about like this:


Applying 12 VDC to X1 should not be a problem. However, this also depends on how many 5.0 volt loads your Arduino is driving. The available current is limited. This is why if you have a heavy 5.0 V load you really do not want to use your Arduino board to support a heavy load. The regulators will normally shut down if they have an excessive load due to heat. Figure the board uses a linear shunt type regulator so you apply 12.0 VDC to get 5.0 VDC leaving 7.0 volts at whatever current you draw. The regulator has no heat sink either. Less any loads on my 5.0 volts out powering my UNO with 12 VDC my regulator runs warm. I assume Arduino UNO.

Ron