Re: Replacing the current sense resistor of INA219

[ilario]

Just an update on this (locked) thread: viewtopic.php?t=206456

I tested various other methods for removing the shunt resistor from INA219 boards (in order to install one with higher resistance for measuring small currents) and I wanted to share here the method I consider to be the best.

I did not try using a drill press as I don't have one, I had some success with a side cutter, and finally the easiest option has been to hit it with a hammer and a with bit as the one you can see in the picture.
Hitting in the "parallel to the board", "towards the INA219 chip" direction has proven to be the easiest, with the result indicated with the red arrow in the picture.

For the readers who are going to use a shunt resistor with a larger resistance to measure small currents, please try the alternative configuration guide I proposed here (following the current documentation with a 10 Ohm shunt resistor resulted in wrong measurements): https://github.com/adafruit/Adafruit_Ci ... 19/pull/37

20241128-replacing_resistor_INA219.jpg (312.07 KiB) Viewed 67 times

[languer]

That seems pretty aggressive so I must assume you do not have a soldering iron. An easier way, and less destructive way, if you have a soldering iron is to apply extra solder to both ends so the two solder pards/terminals have googd wetting; then apply heat to one side and use solder wick to clean that side; then apply heat to the other side and with tweezers remove the resistor. The key is that both sides must be "hot" so solder is flowing when attempting to remove. A better way would be to have soldering iron tweezers that can heat both sides at the same time but that is not as common for hobbyist. The pictures you provided are pretty cool though and clearly show how it was done.

[T_Mo]

The hammer method is extremely likely to induce stress damage in circuit traces that the 0.1 ohm resistor is soldered to. So that creates a reliability issue.

Since you'll need soldering skills to install the new resistor, that seems a better method for removing the old one.

[Timeline]

I have to say, when I saw the photo, my first thought was "Are we being trolled?" ;)

[adafruit_support_mike]

A less forceful option is to use a piece of copper wire as a heating tool.

Strip a couple inches of insulation off the end of the wire, and bend the tip into a U whose edges come reasonably close to the ends of the resistor (or whatever component you want to remove).

Touch the ends of the U to both solder joints and heat the wire with your soldering iron. The copper will carry heat to both joints, melting them at the same time. Then slide or twist the wire to move the ends of the component off their pads.

There's a good chance the component will end up soldered to the wire, making to easy to lift off the board even in tight spaces.

With a hot iron and a large tip, you can heat the wire an inch back from the U and still melt the solder joints.

[ilario]

Hi all!
Thanks for all the answers!

I have to say, when I saw the photo, my first thought was "Are we being trolled?" ;)

Hehehe yes, it is unexpected that the best solution (for me) is a quite violent one.

apply extra solder to both ends so the two solder pards/terminals have googd wetting; then apply heat to one side and use solder wick to clean that side; then apply heat to the other side and with tweezers remove the resistor. The key is that both sides must be "hot" so solder is flowing when attempting to remove.

Thanks for the suggestion! In the past I used to do something like that, just that I did not use the wick, instead I added more solder. Citing myself:

quickly alternate melting one side and the other and, while doing that, push the resistor with the solder iron. If you added enough solder, you will melt the second side before the first will be solid, and the slight push will move the resistor away from the pads.

And it did work, but it was not easy at all.

A better way would be to have soldering iron tweezers that can heat both sides at the same time but that is not as common for hobbyist.

That would be very nice, but you guessed right: I don't have it...

A less forceful option is to use a piece of copper wire as a heating tool.

Strip a couple inches of insulation off the end of the wire, and bend the tip into a U whose edges come reasonably close to the ends of the resistor (or whatever component you want to remove).

Touch the ends of the U to both solder joints and heat the wire with your soldering iron. The copper will carry heat to both joints, melting them at the same time. Then slide or twist the wire to move the ends of the component off their pads.

There's a good chance the component will end up soldered to the wire, making to easy to lift off the board even in tight spaces.

With a hot iron and a large tip, you can heat the wire an inch back from the U and still melt the solder joints.

Thanks for the suggestion :)
I did find the wire trick recommended by you in another post on this forum :) and I already tried this, but with no luck. I couldn't make it work.

The hammer method is extremely likely to induce stress damage in circuit traces that the 0.1 ohm resistor is soldered to. So that creates a reliability issue.

The risk of damaging the board is real, of course.

Still, I replaced the shunt resistor on 18 INA219 Adafruit boards, using the various described methods, and all of them are still perfectly functional :D

[T_Mo]

and all of them are still perfectly functional

For now.