RPM Measurement

[SparWeb]

An idea I thought I'd share.

After hunting for ways to accurately measure the RPM of my turbine (including considering the 88 cent calculator idea), I realized that my digital camera provided what I needed.  I have a Nikon with video capability, therefore playing video of the turbine a frame at a time allows me to count the number of frames per turn.  Divide that into the number of frames per second (15 fps on my camera) and out drops RPM.

One of those things that are obvious once you think of them.  It seems that many of you already have digital cam's judging by the many photos on the site.  If they can take video, you're up and running.

[GeoJohn]

Except if your generator is spinning at 1800 rpm and your video camera shoots at 30 frames per second, then the blades will not move on the video. You are essentialy shooting with a strobe light.

[shockwind]

A simple RPM gauge that I made uses an earphone from a regular walkman headset. I place a magnet on the bottom of my magnet disk and plug the earphone into to my mic jack on my computer and turn the mic volume all the way down. As the magnet passes over the earphone, a voltage is induced in the coil and can be recorded. I turn the volume all the way down so as not to get sound coming through the earphone, however, the pulse of the magnet will still show on the screen.

I then use some audio recording software (or an oscilloscope) to record the pulses as the magnet passes over the earphone. Then I just count the number of pulses in 10 seconds and multiply by 6.

[kitno455]

another way is to wrap a few turns of wire around one of the wires carrying one of the phases of the gen, before the rectifiers. this will inductively pickup the pulses in the wire. if course, the signal is going to get stronger as the current rises, and you will have to deal with multiplying by some factor to deal with number of pulses per rev. there have been a couple posts on this lately...

try this one, about 2/3 of the way down...

http://www.fieldlines.com/story/2005/7/20/153456/453

allan

[SparWeb]

Actually in my case, the camera shoots at 15 frames per second, so the turbine would appear to stand still at 900 RPM.  Worse, with a 2-blade model, the magic number is 450 RPM, and so on.  Since I've been building 2-bladed VAWT's, I don't expect that limit to be a problem.

[Norm]

  Ah....SparWeb I see you must have seen my diary entry....another person had suggested

putting a clicker and counting the clicks for

a minute...I've tried that, the fastest I can count is about 200 per minute... the next best

thing is the old threaded rod and nut method..

  I've never heard it mentioned on this board,

but what about the good old fashioned speedometer

...you find them on some old pedal exercise

bicycles completely mechanical...no wires...

just a flexible cable that spins a magnet by

a metal disk?

                    ( :>)Norm

[MelTx]

  I found a hobby shop that has model airplane part and stuff.They have a small hand helt meter that had settings for 2 or 3 or 4 props.It was about $30.00..

                                   Hope this helps    MelTx

[pyrocasto]

Or for you lazy people who just want to be able to tell instantly how many rpm you've got: http://www.allelectronics.com/cgi-bin/category.cgi?category=760&item=TCH-4&type=store

[SparWeb]

Had a 70 kph wind this weekend. The thing was going fast enough that, you guessed it, it looks like it's turning backwards in the videos.  450 RPM was well exceeded... that is, until the bearing mounts failed...

[SparWeb]

I ultimately have gone the way of digital bicycle tachs.  With a bike speedo, I can have instantaneous measurements, and the thing comes with Max, Avg, and cumulative data features that really ice the cake.