So I'm new to the world of Arduino. We are using it for a project in school, but not being given any guidance, and I'm flummoxed. Just wondering if anyone could point me in the right direction.
So I'm using an old car alternator as a generator, driven just by a hand drill. It's a 3 phase alternator, with a separate 12V battery to power the electro-magnets in the rotor. There will be something as simple as a light bulb being powered from it, solely to draw current for measuring purposes.
I have to use the Arduino to measure; Voltage, Current, and Frequency. These have to be displayed online by way of a shield, I believe. Possibly also using a LCD screen for local display.
I'm not sure of the setup of the alternator. Should it be set up in Star or Delta for this type of project?
For rectification, it is best I assume to use one phase from the alternator, rectify that, and step it down to measure voltage in the Arduino?
For measuring of frequency, I'm assuming I should use another phase, bring it through a Schmitt trigger for measuring frequency?
Then use a final phase to power a lamp, and measure the current from that.
Does that sound like a good plan, or is there a more advisable method of doing this??
When you write "old car alternator" just how old do you mean. Seems like forever they have the regulator and diodes built into the case of the alternator and use the case as a heat sink.
You wrote "hand drill". Can we assume you really mean a hand-held electric drill?
Well I was thinking that if I used any of the single phases prior to the rectification diodes, then that might act as a voltage divider and mess up my output readings anyway. Possibly overthinking that part though.
The few alternators I find online are set up in delta, but I was solely leaning towards wye to give me the 3 separate phases and an easy neutral point. And the frequency.
But yeah, I guess as you point out frequency can still be measured from before the diodes, and run the lot in Delta.
Hey Paul, I should have clarified. The regulator was removed from the alternator specifically for this project. As in I have to re-build all that myself, to work the project from 3 phase AC.
Yeah the drill is an electric hand drill. Just as a convenient drive option.
End of the day the project is really about the coding involved to drive the Arduino Uno, so I've just got to throw together the build side of the project and get cracking on the code.
Guess you are good to go, then. I guess you have access to both ends of the three windings so you can wire it any way you want. Without the regulator, your voltage will vary with the speed of the drill. Probably be rather less than 12 volts. Experiment!
...That's in addition to a voltage divider (2-resistors) if you're expecting about 12V. (The resistors that make-up the voltage divider can also serve as the resistor in the protection circuit, so you just need to add a diode or two following the voltage divider.)
Measuring current is "tricky" since the Arduino ADC measures voltage, referenced to it's ground. A Hall effect current sensor is usually the easiest solution, although you can measure a "small" voltage across a "small" series resistor on the ground side.
Hey Paul, yes I have access to both ends of the windings, to set them as required. I'm getting a solid 12V out of the alternator.
Doug, I hadn't thought of a voltage limiter, that looks interesting thank you. I'm unsure what the 5V is at the zener diode though?
Is that just showing it's protection limit?
As for frequency measurement, I don't think the rectified voltage in a 6 diode rectifier will have any zero crossings in it's output.
As for the current measurement, yes that will be a hall effect sensor that I can purchase online, easy solution there.
As for frequency measurement, I don't think the rectified voltage in a 6 diode rectifier will have any zero crossings in it's output.
Correct, it will never contain a voltage of zero. But, frequency x3 is present in the peaks and of course pure ac on the other side of the diodes.
The easiest method would be to provide a resistor fed second rectifier feeding an opto coupler to detect the zero voltage points - from which you can accurately measure frequency.
With a 12v output level, something like the INA219 and a shunt to match your current range would provide a good measurement solution for volts and amps.