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### Topic: Measureing Above 9V. (Read 543 times)previous topic - next topic

#### Peterfoxflick

##### Jan 30, 2013, 01:13 am
I need some way to measure the volts being produced by a dc motor. It can produce anywhere between 0-24v dc. The part I can't figure out is how to do it without greatly changing the volts. The motor is being used to charge a battery and I want to be able to record how many volts are being produced without taking away anything from the battery.

The project in full is a bike that produces electricity with a motor that then charges a car battery that then charges a laptop. I have it worked out so that students at the high school can pick their grade. Then the grade with the most volts at the end of the month wins something. So far I have an Arduino Leonardo hooked up to a Data Logger then to a 16x2 monitor. I want them to be able to select their class, then the monitor to display how many volts are being producing. Also I want it to record this number with a time stamp so that we can add them up at the end of the month. It doesn't have to be volts, ideally it would be mAmps but that sounded harder. It just has to record anything that would be compeatable like distance or speed.

#### arduinoPi

#1
##### Jan 30, 2013, 01:21 am
you would either have to get an Ardunio SD card shield so the Ardunio can save data when it is powered off. another option you could do is send all the data to a computer and save the results their.
As for getting the amount of volts the motor is producing you would need a voltage divider  http://en.wikipedia.org/wiki/Voltage_divider  to bring the motors voltage down to 0-5 volts and have the Ardunio read it with an analog pin.
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#### johnwasser

#2
##### Jan 30, 2013, 01:27 am
One easy measurement of bicycle 'progress' is a revolution counter on the wheel.  Often this is done with a magnet on the spokes and a reed switch or Hall-effect switch on the fork.  If you know the wheel circumference you can convert the wheel pulses to both distance and speed.
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#### PeterH

#3
##### Jan 30, 2013, 01:39 am
Monitoring voltage doesn't give you a very good indication of how much energy is being produced - it's really only telling you the state of charge of the battery. Measuring the current would be a far better indication of the work being done, and monitoring voltage and current would be ideal because voltage times current gives you the instantaneous power output.

To monitor the current you would measure the voltage drop across a small series resistor.

I'd recommend storing the data in a relational database, and if you're running on Windows you can use GoBetwino to make the database updates for you. The database also gives you the capability to store and change any other relevent information such as the relationship between individuals and teams, so you can calculate the team scores in a way that copes fine with changes to the team compositions.
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#### Peterfoxflick

#4
##### Jan 31, 2013, 12:18 am

One easy measurement of bicycle 'progress' is a revolution counter on the wheel.  Often this is done with a magnet on the spokes and a reed switch or Hall-effect switch on the fork.  If you know the wheel circumference you can convert the wheel pulses to both distance and speed.

Thanks that sounds a lot easier.

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