Arduino fried while measuring current

Hello Everyone,

I was trying to measure the current drawn by a motor(12V DC motor) using the ACS712(5A model). After about may be 15-20 times of turning the motor in both directions(with a short wait of about may be 30 secs between each direction) for a duration of about 15 secs in each direction, my Arduino(nano) fried :relaxed:

My question is....why?? As far as I know, the ACS712 regulates the output current with max current on the 5A model being about 3.3V. This is well under what the Arduino can handle...right? it can handle input of about 5V on the analog pins(or on most pins for that matter)?

Why did the Arduino even get that hot and then eventually fry? is it because I had it measure the current a little too frequently? how can I measure how often I can measure the motors current drawn without frying the Arduino it in the future?

Best regards,
Uber

Measuring current with ACS sensors should be safe.

However, if you disconnect a motor, or jiggle a loose motor connection with the power on, you get voltage spikes of possibly thousands of volts -> fried electronics.

jremington:
Measuring current with ACS sensors should be safe.

However, if you disconnect a motor, or jiggle a loose motor connection with the power on, you get voltage spikes of possibly thousands of volts -> fried electronics.

To change directions, I had to disconnect the the cable from the power source to change polarities(connections to Arduino were intact during this process and the arduino was powered on). And I am almost certain there was some jiggle involved at some point(accidental of course). Really though?? I am glad I asked. Not only did I not find a straight answer to this when I googled, but I could also have never guessed this was the reason!

Is this really it? Wire disconnection and jiggle? So if I turn off the arduino and do my polarity change and keep the motor relatively secure so it doesnt jiggle anything, I can potentially measure the current with the intervals I mentioned without a problem?

jremington:
However, if you disconnect a motor, or jiggle a loose motor connection with the power on, you get voltage spikes of possibly thousands of volts -> fried electronics.

That's true - but ... the motor would not normally be directly connected to the Arduino. How could motor spikes get to the Arduino?

I suspect there was an accidental short circuit somewhere, and maybe the motor was not the culprit at all.

...R

Robin2:
That’s true - but … the motor would not normally be directly connected to the Arduino. How could motor spikes get to the Arduino?

I suspect there was an accidental short circuit somewhere, and maybe the motor was not the culprit at all.

…R

Exactly…Actually I am manually controlling the motor with its positive wire literally in my hand (the current sensor is connected in series with the motor and power supply of course). Motor only turns on when I connect the positive end to the power supply. The only thing that’s connected to the nano is the “out” pin of the current sensor on analog pin A0. So even if there is a spike, I can understand the current sensor itself burning out, but not the arduino since the max voltage outed by the sensor is 3.3V

So what I am really asking is, if everything is setup correctly, can I have the arduino continuously measure an incoming current indefinitely? Or is there a run time after which I need to stop so it cools down or something before I have it measure it again?

uberJoker754:
Exactly....Actually I am manually controlling the motor with its positive wire literally in my hand

If that was me I would be having a serious Q an A session with my hand to find out exactly what it did with that wire :slight_smile:

...R

Robin2:
If that was me I would be having a serious Q an A session with my hand to find out exactly what it did with that wire :slight_smile:

…R

Hahaha

According to the datasheet, the ACS712 provides 2.1 kV isolation between the current carrying part of the circuit and the output part. That may not be enough.

2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8

So if I turn off the arduino and do my polarity change

The ONLY safe way to change any wiring is with ALL POWER OFF.

uberJoker754:
Hahaha

I did not post that entirely as a joke.

...R

Robin2:
I did not post that entirely as a joke.

…R

That seriously cracked me up xD. But on a serious note, from all this convo, it seems like jitteryness is the culprit and not the frequency of reading the current.

But something to note however is that the Arduino did get noticeably hot before it fried. I was like ok…its hot, but my wiring and code and everything seem ok, so it should fry. After all, all I am doing is having it measure the incoming signal on A0. And that too in intervals.

Hello Folks,
I have a similar problem and, I am not to knowledgeable about electronics.

With an Arduino Uno, and an H-Bridge, I am successfully driving a 12 volt DC motor in both directions (CW, CCW).

I want to have the motors change direction once some resistance (amperage) is detected. To do this I am using an ACS712.

I have the H-Bridge powered by a 12 volt source which is connected to the H-Bridge +12V lug.

I connected the ACS712 "Load" line to the same H-Bridge +12V lug. The H-Bridge smoked.

With a new H-Bridge, I tried just touching the ACS712 "Load" line to the H-Bridge "OUTx" lug. This seemed to work, that is my motor changed directions as desired (Serial Monitor review showed increase in values as expected/hoped for).

If I hold the wire to the H-Bridge "OUTx" lug (the same lug I just touch to cause a motor direction change), the motor will not run. I suspect I am causing some kind of short and because I am a little gunshy at this point, I am afraid to go any further without a bit more understanding of whats going on.

I have said all of this to ask "where is the proper location for the ACS712 Load wire?"

Appreciate the guidance,
Dan

'blah blah blah.... the output current with max current on the 5A model being about 3.3V blah blah'

raises some serious concerns about your understanding of the difference between voltage and current

Why not invest in a $5 DPDT, center OFF toggle switch?
https://www.amazon.com/Toggle-Switch-TOOGOO-Position-Silver/dp/B01EYDAS00/ref=sr_1_25?ie=UTF8&qid=1526878544&sr=8-25&keywords=dpdt+toggle+switch
mot-sw(1).png
Poking and scratching around with a loose wire in a live circuit is a sure way to destroy things, especially an H-Bridge motor controller.

The ACS712 is isolated, but has stray capacitance between the current path and the low voltage
side, so that inductive spikes could easily induce damaging currents across this capacitance if not suppressed,
thousands of volt spikes from disconnecting a motor are savage, and its even worse if just playing with the wires
as you get arcing which can cause RF oscillations at very high voltages due to resonances in the circuit.

If you haven't paid attention to how the grounds are wired you might directly get interference from
the motor ground which will carry destructive spikes too.

Always use free-wheel diode(s) to switch any inductive load, whether semiconductor or mechanical switching.

How long is the spark when you disconnect the motor? 1000V will jump about 1cm in air at sea level. That makes a neat voltmeter calibrated in kV.

I don't believe that a hobby motor can generate thousands of volts. Not even hundreds. That also cannot explain the Arduino getting warm.

I suspect a different kind of wiring error. One popular error is using the ground pins on the Arduino to pass the motor current. If the power supply is connected on one side of the Arduino and the motor is connected to a ground pin on the other side, the Arduino will get hot and fail.

Or it could be a different error. Photos may help.

INTP - Sorry I offended you, you are correct in that I do not have a good understanding of electronics.

outsider - great idea! at least I could switch on and off to get results! Thank You!

MarkT and MorganS - most of that is way beyond me, but I get the drift, Thank You!

I did find an tutorial that may be the answer, (http://www.instructables.com/id/Sensor-tutorial/) I will have to study a bit more but i think I should not have both leads of the motor connected to the OUTx lugs of the H-Bridge. One of the motor leads should have the ACS712 in the loop. I am now rambling, got to go study and think about this a bit as its very confusing to me (LOL).

Kind Regards to all