I want to read the charge level on the capacitor bank for my coil gun. Since the capacitors charge up to 300 V each, I want to read in 300 V on my arduino. Since it only reads <5V, I decided to use a voltage divider.
I purchased the following resistors:
R1 = 450 ohms (5W, i think)
R2 = 7 ohms (10W)
According to my calculations, they should reduce it to levels just below 5V, but I just want to make sure that my setup is fine before I plug it into the arduino. I don't wanna fry my new UNO
No electro guru but Ohm's law state I = U/R = 300 / 457 = 0.66 Ampere. Watt = I * U = 0.66 * 300 = 200 Watt. The resistors will burn!
The good part is that the ratio is quite good. I would feel a lot safer safer with 1 M and and 15K => 0.3mA => 0.1W You can validate this with a voltmeter of course before connecting.
But even then the 0..5V out should drive an optocoupler, then there is less risk for the Arduino.
Out of curiosity, what part would be suitable here?
I am only aware of digital -- ie: on/off optical isolators.
I would have pegged this as a job for an isolation amplifier, which is a different sort of bear.
I have successfully measured 1200V with a 5V input using Ohms law and carefully selected (HIGH VALUE) 1% resistors. It's mainly down to doing some math.
