Electrolytic Capacitor Failure at 40°C: Why Did My Sensor Readings Become Unstable?

Hello everyone.
I was in Italy for vacation and brought some of my DIY sensors (temperature, pressure, magnetism, etc).
It was terribly hot in Italy and it was a good 40° C in my room.

The results of all my sensors were incorrect, the values were going up and down and no longer followed normal trends.

So, after some analysis, I removed all the electrolytic capacitors from the circuits and, magic, the systems worked correctly.

Why?

Thank you all for any response.
John

Electrolytic capacitors are commonly rated for 85 deg. C or 105 deg. C. So no reason that they should misbehave at 40 deg C. In fact unless something is thermally out of spec any electronics should work ok at 40 deg C.
I'd say something else would have caused your problem.
Did your circuit work OK with the electrolytics when used at a more reasonable temperature (say 25 deg. C)?
Can you post the circuit you are using?

40°C is not terribly hot, IMO. It's only 10-20° above normal. That's not much.

Did the electrolytics have a proper DC bias voltage? Electrolytics are not good capacitors without the right bias.

How did you use them? As bypass capacitors, or with signals through them? If as bypass capacitors, it's unlikely they affect the circuits in a visible way. If in the signal path, you should not have used electrolytics there.

My guess is, when you removed them, you got lucky and reflowed the solder and fixed a bad connection.

Hi John,

That’s an interesting observation! High temperatures can indeed impact electrolytic capacitors, especially if they exceed their rated temperature limits. When capacitors heat up, their capacitance values fluctuate, leading to instability in circuits. Removing them might have allowed your circuit to function without interference, but long-term operation without capacitors could affect performance.

To quantify the impact, you can calculate the percentage change in capacitance due to temperature variations. Many capacitor datasheets provide a temperature coefficient, which you can use to estimate how much their capacitance changes per degree Celsius.