Have I blown something?

Other Hardware General Electronics
1

Hi All,
Looks like I might have blown something up in a project I'm working on and wanted to get some opinion from those with more experience on what might have happened.

In short, it is a battery monitor for 12v lead acid batteries built on an Arduino. The main thing is an INA219 voltage/current sensor connected to a 50A shunt to measure the current/voltage going to the battery. The INA219 is on a Adafruit breakout board (onboard 100R resistor removed) soldered to the prototyping area of an Adafruit log shield which provides a RTC and SD card reader. It allows me to log data to SD card for plotting later, e.g.:

I left it running overnight as you can see from the blog article above and it was all working fine. It's actually a Xino Basic (bare bones arduino clone) powered via a 5v regulator from the battery itself (so could go up to 14.5v). I went out to the garage where the setup is and switched it off this morning to retrieve the SD card to do the plot in the blog post above. I then went back out half an hour later to switch it on again to get more results and nothing. No blinky lights :frowning:

I pulled the shield off the top and tested the Arduino itself and the power light came on. I pushed the shield back on with just half the pins connected (the digital side) and the SD card light started to blink in the pattern it should, so the the SD card appears fine. When I pushed it the whole way in so the analog/power side of the shield connected, all lights went off. Plugging this side in connects the +5V, +3.3V, GND, and the two Analog pins used by the INA219 (A4, A5, aka SDA and SCL).

So I'm suspecting that somehow I've damaged the INA219 board/chip.

Things I've noted

  1. Disconnecting the shunt from the board makes no difference
  2. When connected but with no lights coming on, it draws 0.17A according to my DMM
  3. When just the Arduino is plugged in, with no shield, it draws 0.02A
  4. When I connect the shield, the voltage across +5V to GND drops to around 1V
  5. The voltage across GND to the battery negative itself is 0V

The only thing I think I may have accidentally done in the experiment above is that it is possible I may have switched the battery isolator off before the mains charger, this would result in the Arduino being powered directly by the 12V mains charger. This shouldn't cause an issue as it shouldn't go that high a voltage to be damaging. What do fixed voltage regulators do if you overvolt them? Do they just stop working? Do they fail passing the full voltage across?

So what do you guys think? Doesn't look like I have a ground short to positive voltage as the pd from GND to the battery negative is 0V. What kind of failure would cause the pd from 0 to +5V on the board to drop to 1V? 0.17A seems like quite a high current to be drawing when not doing much.

I've triple checked all the cabling and visually inspected the board and shield and don't see anything melting, bridging etc.

-Matt

2

It looks like the voltage regulator for that specific board is an option extra, so you may be right that it got exposed to 12V at the microchip and died by electrocution.

Never nice to have a board die :confused:

Edit: Looks like even with the voltage regulator it can only handle 5-9V, so even then it probably would have died.

3

I have the optional voltage regulators installed. The 5V regulator is this one, rated to 30V:

http://uk.farnell.com/texas-instruments/lp2950-50lpre3/ic-v-reg-ldo-5-0v-to-92-3-2950/dp/1262363

And I am definitely feeding the voltage regulator, not the 5V line directly. I made that mistake on a previous board and fed 9V from a battery directly to the 5V line by misunderstanding the power system.

As I said above the board itself all works fine. It is just the INA219 that seems to have stopped working.

-Matt