Ambient temperature has external influences?

[DrTron]

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latest master

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Hello everyone,
My aircooled Generac (Evolution 2.0 controller) reports ambient temperature via Genmon.
So far, so good, but I see rather strange dips in the temperature reading. Incidentally, they align with the dips in battery voltage, which occur regularly and I assume are battery load tests the generator performs.

Here's what I mean, the drop in temperature starts when the generator starts the battery check. And no, external temperature certainly did not follow this pattern.

Ambient Temperature:

Battery Voltage:

No real issue, just curious what may be going on here.

Additional information

No response

[jgyates]

How often does this occur and when is your exercise cycle relative to this dip?

[DrTron]

I only have genmon running for a few days now, but so far it happened with every battery test.
Green is battery voltage and blue is Ambient Temperature.

Exercise is scheduled for Wednesday, so the generator did not exercise within that timeframe.

[jgyates]

Here is my guess: The temperature is read reading the voltage across a thermistor, which is a type temperature sensitive resistor. Normally you have a constant voltage applied to one side of the thermistor and the change is temp causes a change in the voltage spread across the resistance, however since the voltage is dropping for a battery test it is causing the input to the thermistor to dip as well. This is causing the change in the ambient temp reading. I assume the Evo 2.0 firmware could compensate for this but they probably don't think anyone is reading the temp this often.

[DrTron]

Possibly, but that would be a very bad implementation. Normally those thermistors are supplied by a stabilized voltage of either 3.3V or 5V, and the latter is probably what the whole Evolution controller runs on, which also needs a stabilized power source.
So using an unstabilized source for a thermistor is very uncommon.

True, the generator probably uses this for intake air temperature to calculate fuel injection duties via an air mass sensor or such, and obviously only needs that to be accurate when the engine is running and then the alternator provides a stable voltage.

But as I said, not really important, I just thought I could use that as an additional outdoor thermometer and found the spikes a bit odd.