Maybe the simplest thing is to get a speaker that can directly handle the amount of power that the dynamo can put out, and get rid of the audio amp.<div><br></div><div>Barring that, do you have a series capacitor (say 100 uF) between the dynamo output and the audio amp input to block DC? You shouldn't be feeding any constant (DC) current into the audio amp, lest it blow up. <div>
<br></div><div>Another way to get it to blow up would be to feed the audio amp (or the aforementioned 100 uF cap) too high a voltage. Instead, load the dynamo with a (relatively high valued so it doesn't get hot) resistor across its terminals to keep the voltage in a sane range, then use a voltage divider to bring that maximum output voltage down to whatever your audio amp can handle.<br>
<br>Less critical issues: Do you want it to get louder as (the dynamo rotates faster and) it gets higher pitched, or do you want to keep the volume somewhat constant? You might find that the dynamo will make a lot more power at high RPMs, so when you scale down the voltage as needed to not blow things up, the audio might not be audible at low RPMs without amplification. (This is easy to fix, if it is what you want.)<div>
<div><br></div><div>Hope this helps a bit!</div><div>Dennis</div><div>P.S. Anyone know a good way to quickly draw and send circuit diagrams in email?</div><div><br></div><div><br><div class="gmail_quote">On Sun, Jul 21, 2013 at 11:14 AM, Johny Radio <span dir="ltr"><<a href="mailto:johnyradio@gmail.com" target="_blank">johnyradio@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Hello<br>
<br>
Can anyone suggest how to limit the voltage and/or current coming
out of a dynamo, before audio amp? <br>
<br>
Actually, I'm not sure if this is a dynamo or alternator-- i'm
cranking the shaft of a DC motor, and tapping the electric
terminals. I'm trying to amplify the AC sine coming off the
terminals through a loudspeaker. <br>
<br>
It basically works-- i can hear the motor oscillation from the
speaker driver, which is my goal. But i've blown two audio
amplifiers doing this. The motor is not large (about 2" long, 1"
diameter), but i'm spinning it at thousands of cycles per second.
According to one article, as frequency increases, so does output
current. <br>
<br>
I'm not sure if the issue is too much current or too much voltage. i
believe i'm not getting clipping, so i suspect the problem is too
much current. A couple fat resistors in series with one of the
terminals did not prevent the amp from blowing. Also, the speaker
driver heaves, which suggests to me either an impedance issue,
grounding issue, or low-frequency content. <br>
<br>
I've found a couple ways of possibly handling too much current,
using circuits mostly designed for charging batteries off a
generator. I found solutions based on BJT transistors, CMOS, power
regulator chips, or diodes. Links below. <br>
<br>
I'm not charging batteries, so i wonder if i can eliminate the
reverse current protection? Actually, the motor no longer spins when
i apply voltage to it's terminals, so i think i blew the motor in
some way. Strangely, it still outputs a sinewave when i turn it's
crank. So maybe the reverse current protection IS needed. <br>
<br>
One solution employs a pair of diodes, wired back to back, between
the motor terminals (i think). This is intended to clip the voltage,
resulting in a square wave. This solution is not desirable, because
i want to preserve the sine shape coming off the DC motor. <br>
<br>
How can I limit current (or is it voltage?), without squaring the
original sinewave? As always, seeking a lowest-parts-count solution,
passive if possible. Any help is appreciated!<br>
<br>
<a href="http://islandcastaway.com/alternator-secrets/" target="_blank">http://islandcastaway.com/alternator-secrets/</a><br>
<a href="http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/?ALLSTEPS" target="_blank">http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/?ALLSTEPS</a><br>
<a href="http://goo.gl/MG4mF" target="_blank">http://goo.gl/MG4mF</a><br>
<a href="http://forum.allaboutcircuits.com/showpost.php?p=331463&postcount=52" target="_blank">http://forum.allaboutcircuits.com/showpost.php?p=331463&postcount=52</a><br>
<a href="http://ludens.cl/Electron/dynareg/dynareg.htm" target="_blank">http://ludens.cl/Electron/dynareg/dynareg.htm</a><span class="HOEnZb"><font color="#888888"><br>
<br>
<div>-- <br>
<font size="+1"><br>
Johny Radio<br>
<img alt="" src="http://us.123rf.com/400wm/400/400/robodread/robodread1201/robodread120100030/11882514-ear-and-sound-waves.jpg" width="150"><br>
Stick It In Your Ear!<br>
</font> <br>
</div>
</font></span></div>
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