Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Designing Encoder/Tach Circuit for Digital Display and CPU Interface
(OP)
Mechanical guy tackling electronics here. I'm looking to design and fab a consumer grade personal-use wind turbine with portability and cost being main design constraints. My main goal is to have a charge controller box that displays voltage from the DC motor, as well as the motor shaft RPM, on the top of the controller box. I've also toyed around with the idea of having USB interface with the controller to record data onto a laptop for efficiency measurements for various blade designs. What's the most effective means of monitoring motor shaft speed and displaying it on a box some far distance away from the motor in the wind turbine nacelle, and having the option open to record that data onto a PC? Colleagues have suggested using resistors to calibrate the voltage to correspond with RPM, but I'm not sure that's the most effective/accurate means. Would an encoder be better for this task? Outside my territory here, so any and all advice is appreciated!
Deisng criteria:
Perm DC Brushless motor, .38" shaft diameter, 5" diametrical area behind the motor for monitoring equipment/cabling
Calculated RPM speeds 0-300 RPM (furling device will be used as braking method)
Deisng criteria:
Perm DC Brushless motor, .38" shaft diameter, 5" diametrical area behind the motor for monitoring equipment/cabling
Calculated RPM speeds 0-300 RPM (furling device will be used as braking method)





RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Next step up is the SKF sensor bearing. Google Sensor Bearing GKE for a presentation that has been on the net for twelve years now. But still covers the basics.
Putting a full-blown encoder up a wind turbine that size is asking for trouble. But, it can be done - of course. But it will probably ruin the project cost-wise.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
http://www.electro-sensors.com/product_info.php/cP...
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
You probably already knew that.
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Another option that is quite cheap is to buy a $2.00 toy motor, a cheap milliammeter, a fixed resistor and a potentiometer. Arrange the toy motor to be driven by the main shaft. It will generate a voltage proportional to the RPM. Select a resistor value that limits the voltage to the meter to about 125% at full speed. Calibrate the reading with the potentiometer. You may use a digital milliammeter if you want digital displays.
We tried this solution on a printing press for a customer. It worked well but the customer didn't like the $2.00 toy motor, because it looked like a $2.00 toy motor. We bought a replacement $14.00 toy motor and he was happy.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Isn't the 'motor' being used as a generator?
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Right, should have thought of that before! I have the pole pair number of the motor, and I understand it's just calibrating to count the number of sync cycles per rotation. I've seen programmable rate meters through some prelim searches. Is this a good street to go down, and if so any product recommendations?
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Beware the end result where the control system requires more watt-hours per day than is generated by the renewable energy supply itself. It's easy to avoid, so long as you're a tiny bit careful.
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Any type sensor may be used like a thermisistor. The conversion is very easy using the MAP function. Through a diagnostic debug screen, just get the reading at room temperature (82deg with 7090 count) and in an ice bath (32deg with 7930 count). The linear interpolation mapping actually extends beyond those two points. Now you have a temperature in understandable terms. Note how this works even though increasing temperatur creates a decreasing voltage.
TEMP = map(Ctemp, 7090, 7930, 82, 32);
// For five small signal diodes with 2.2K pullup to +5V
Battery voltage works in much the same way. A voltage divider of 300K from the battery with a 10K pot in series is tapped with a 87K resistor. This gives about 25mv per count for a 4:1 divider. A . 22uF capacitor at the input pin adds a little filtering and gives a stable reading. The multiplyinjg effect creates a number that approximates the battery voltage. Adjusting the pot finishes the calibration. Make sure in normal operation that the voltahe at the analog pin does not exceed 2.5V for safe operation when monitoring other voltages.
analogRead (AI0);
battery = battery - battery / 26;
// Sum the readings by subtracting one average reading
battery = battery + AI0; // Add latest A/D reading
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
I propose that the volts->RPM route is highly error-prone because as others have said, the terminal volts will depend on load as well as RPM. The pulse count is a much more accurate way to go and isolates the measurement from your power conversion circuitry. Doing pulse count in Arduino is a lot trickier than voltage mapping. You can do it, but it'll take a little head scratching.
The good news is that pulse counting is exactly what a tacho does! If you buy any standard tacho (eg. an automotive tacho) it'll have a simple configuration for pulses per revolution. Then you just feed the pulse train in and it'll spit out RPM! There are analog and digital versions in every shape and size.
The question then is, how do you get a suitable pulse train out? I would first look to see if the signal from the Hall Effect sensor in the BLDC is available - that will be as close as you'll get to a ready-to-use signal. If that fails, then the voltage from one of the coils will do - you'll probably just have to threshold it to convert from the phase waveform to a pulse train. A simple Schmitt trigger ought to do the trick. Just be careful to consider the range of voltages that the generator will produce - a high input impedance Zener circuit will help clip the larger voltages.
And finally, to get motor volts, a voltmeter will do. Again, the display comes for free!
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
I haven't used it but pulsein is likely to be a little unstable. Average a number of them as I have shown and it should be a repeatable number. Afrer all you are likely only interested in the 200-300rpm range. I would transformer to couple one of the phases and detect any positive signal. This would just be a simple LM339 with the output tied to the UNO pin and a 1K pullup to 5V. Feed the input signal through a 300K resistor to one of the inputs of the 339. Limit the voltage by back to back diodes to common where the other input is tied. The rest of the 339 will find other uses in this project.
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
Have some questions:
Are you saying a 1K pullup to the LM339 Vcc? Also, not understanding what you meant to do with the diodes.
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface
They are often used with +/- 15V supplies.
The open collector output makes them useful for interfacing between analog and digital circuits.
This
http://my.ece.ucsb.edu/bobsclass/2C/tutorials/App%...
should get you started on understanding some of the things the 339 can do.
Mike Halloran
Pembroke Pines, FL, USA
RE: Designing Encoder/Tach Circuit for Digital Display and CPU Interface