Sunday, 1-November-2020

Small mod for Voltmeter - Thermometer from Aliexpress

That story is dedicated to modification of small chinese produced voltage thermometer, which main purpose is to be inside the car. As additional option it have 5V charging ability which I think is highly unlikely to be good at.
My intent was to make it a bit more precise and to add some extra capacitors, so that I can measure some voltage drop during the engine start. That voltage drop is based on the fact, that all energy to additional sockets is cut off because of the starter motor need it.

So, here is how the original was:
voltmeter_2.jpg voltmeter_1.jpg
with blue is marked the adjustment for the temp probe, and with red the voltage correcting. Unfortunately that unit is made for 12-24V, so it correction didn`t wish to go properly , and didn`t show exact voltage.
For that reason I replace the both resistor and variable resistor on the income line with 200kOhms rotary precise potentiometer.
Now sorted that out, I measure the thermistor probe with laser thermometer, and correct it a bit.

Next in the list was to add bigger capacitors what was not so much possible due the lack of much free space.
voltmeter_3.jpg voltmeter_4.jpg

Used capacitors are the original one of 100uF , and added one 470uF and two of 220uF (front). Seems it still work.. and doing what was intended.
Still, I consider better option - to make my own with some small OLED display and Attiny85. But that one .. some another day.