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kentquirk
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Joined: 27 Nov 2006
Posts: 2
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 Posted: Mon Nov 27, 2006 3:24 am Post subject: Solar Engine doesn't work right? |
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Hi. I just built this solarengine:
http://www.tombot.net/beam/pics/circuits/1381engine.jpg
It's pretty simple. But it doesn't quite work for me, and I'm wondering if someone can help.
Instead of a motor, I'm using a coil to generate a magnetic pulse (with an LED reverse-biased across the coil as a freewheeling diode).
It charges up the first time, discharges all the way to 0.78 volts...and then sits there. The 3906 never turns off. If I block the light momentarily so that the solar cell voltage drops below 0.7, then it recycles and works again...once.
The static resistance of the coil is about 11 ohms. It appears that continuous current flow from the solar cell through this coil is just enough to provide a voltage drop that keeps the 3906 turned on.
I tried changing the 3906 and the 3904, just in case they were bad, and the same thing happened. I also had someone else check my wiring.
After trying several other things, I connected a 2.2K resistor from the base of the 3906 to the positive rail. It makes the circuit sorta work. It now only discharges to about 2.0 volts (and it's robbing some of the power that should go to the coil), but at least it operates more than once.
Can anyone give me any better suggestions for making it work reliably in this circumstance?
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admin
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Joined: 22 Sep 2005
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| Posted: Mon Nov 27, 2006 10:22 am Post subject: |
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Hi Kentquirk,
Does this circuit work if you remove the freewheeling diode? I understand why you have a freewheeler but am curious as to if this is affecting the circuit.
Tom
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Tom Elner, BEAM robotics@ Liverpool Uni
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admin
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kentquirk
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Joined: 27 Nov 2006
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| Posted: Mon Nov 27, 2006 8:28 pm Post subject: |
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The circuit you specify is actually triggered by the magnet swinging over the coil (the reverse pulse actually causes the circuit to dump its load). That's definitely not what I want in this case; I have a magnet that I want to have stay at rest until a pulse is generated. Using the 1381 as the trigger makes sense for my needs.
The presence or absence of the freewheeling diode doesn't make a difference.
After seeing some comments regarding solar engines "latching up" I did get the circuit to work, mostly, by putting a small diode in series with the coil. I'm also going to try a couple of different circuits. |
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admin
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Jo C
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Joined: 01 Dec 2006
Posts: 1
Location: Australia
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| Posted: Fri Dec 01, 2006 11:32 am Post subject: |
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Kentquirk,
Try this variation of the original circuit.
http://i16.tinypic.com/2jdgnir.gif
The solar cell is shorted when the engine fires. Let us know if it has the desired effect.
Jo
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