Electronics > Beginners
is it possible to mechanically trim resistors?
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exe:
Hello forum!

I wonder if it is possible to increase/trim value of a resistor by mechanically removing part of conductive layer. What do you think about this? I keep in mind two cases: 1) through-hole (or melf) round resistors 2) square smd package. The latter can be particularly difficult.

Application scenarios:

1) sometimes I need an "odd" value (like 50 Ohms, while only 47 or 51 are available)

2) To better match resistors. Matched resistors / networks can cost quite a bit.

I'd love to give it a try, but don't have access to the lab at the moment. Asking now because this questions bothers me since a long time ago.
Brumby:
Sure, you could do it - but getting an accurate result would be a challenge.

Even if you were able to 'dial in' a value, there's the question of stability.  Mechanical abrasion may cause weakness in parts of the component that may crack or fail.  Add to that age, thermal cycling and moisture ingress and drift and/or failure will be higher than a regular component.

Then there's the issue of uneven heating for a resistor that's dissipating a significant amount of power.


Personally, I'm a big fan of series/parallel connection of multiple, intact resistors to achieve a similar result.
Gyro:
I agree, your carefully trimmed resistor is unlikely to stay that way. Over-coating with lacquer or epoxy might help an little, but not when you get down to smd sizes.

As Brumby says, resistor combinations are the way to go. Two parallel 100R for 50R, 2x150R for 75R etc. You get twice the power rating and half the inductance (some applications even use 4x200R for these reasons).

There are programs linked on this forum somewhere that make calculation of Exx resistor combinations really easy.
DannyTheGhost:
All standard resistor values were designed in such a way, so you can easily use them for typical applications like voltage divider, or get any other possible resistor value, so this type of trimming is unnecessary
Muxr:
You could make your own wirewound resistors to your own spec. There are tutorials on how to do it on youtube as well.
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