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Old 6th November 2012, 06:27 PM   #1
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Default joule thief (draw more power from a power supply?)

I have a 5 volt power supply putting out 800mA
and I have a simple amplifier (it's just a set of speakers bought cheap from walmart)
the original power supply puts out 7.5 volts
so I wanted to bring the 5 volts up to around 7 or more volts
I noticed if I wire a 10,000uF capacitor in parallel with the power supply
and then attach a really large coil of wire to positive and negative of the power supply (from a 120volt motor NOT PLUGGED IN) it makes the LED on the amplifier start to light up more brightly
and if i quickly attach /unattach the motor. the LED flashes a pretty bright blue for a quick second
is there some way to get the motor to continuously and super rapidly attach and unattach or something along the lines of that
so that my amplifier continuously gets enough power to fully light the blue LED up and power the speakers better?
since the power supply is only 5 volts the sound quality isnt good and the LED on the amplifier isnt getting enough power
but when I have the motor quickly attached and unattached it makes the sound quality much better for a really quick second and it makes the LED light up fully for a second.
how would I get this to work?
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Old 6th November 2012, 07:05 PM   #2
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We need to know how much current the amplfifier consumes. The set up you have won't do it as it sits, but there are ways Is this a "wall wart" supply? Like the kind of lumpy thing you plug into a socket and has a wire on it? If so the best answer is to find one with a bit more voltage output. Like say 12V and then with a couple of parts avaiable at Radio Shack you can regulated it down for the amp. Please check the amp and see if it lists the voltage and current and we can go from there.
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Old 6th November 2012, 07:09 PM   #3
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Yes: put a brother or a sister to continuously switch on and of the motor!
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Old 6th November 2012, 07:14 PM   #4
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Quote:
Originally Posted by Osvaldo de Banfield View Post
Yes: put a brother or a sister to continuously switch on and of the motor!
Pick a fast person.
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Old 6th November 2012, 07:15 PM   #5
Mooly is online now Mooly  United Kingdom
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That extra bright flash is caused by "back EMF" from the large inductance of the motor coil.

Be very very careful because that voltage could be a lot higher than you think... enough to give you a shock and more than enough to damage any electronic equipment.
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Old 6th November 2012, 07:29 PM   #6
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ok this idea is in the trash now
and O_O WHOA 12 volts would blow this amplifier to bits! thats far too much power for the little chip to handle it gets hot even with a measily 5 volts! even less than what the original power cord put out.
this idea is definitely in the dumpster now
power supply is originally a 7.5 volt AC adapter and now running off of only that.
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Old 6th November 2012, 07:37 PM   #7
Mooly is online now Mooly  United Kingdom
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Old 6th November 2012, 07:37 PM   #8
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This kind of motors has large winding resistances, and inductance, and high interwinding capacitance. In this case, the energy stored in the core is low, as 1/2 L IČ is also small. Then, when disconnect the winding from supply, there exist a exponentially damped sine wave which acts as a current source, then no so high voltage can be expected, and no risk to human life. I don't know any people killed from BEF from a coil of such size.
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Old 6th November 2012, 07:45 PM   #9
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Quote:
Originally Posted by Osvaldo de Banfield View Post
then no so high voltage can be expected, and no risk to human life. I don't know any people killed from BEF from a coil of such size.
Yes,

it will not kill any human, but the back EMF created even by a 5V small-signal relay coil is high enough to kill LEDs, transistors or other semiconductor parts - probably also true for amplifier ICs!

Greetings,
Andreas
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Old 6th November 2012, 07:46 PM   #10
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Quote:
Originally Posted by Mooly View Post
That extra bright flash is caused by "back EMF" from the large inductance of the motor coil.
Which is how a boost converter works. The one the OP made wasn't a very good one, but he had the right idea. With an appropriate sized coil, switching transistor and a diode you can convert 5V to 7, 10, or whatever until limited by how much current can be drawn. It could be the start of a fun and educational project if he digs into it.


I used to bring 'shockers' made from a coil and a 6V lantern battery to school back in the 70's. Nowadays that would get Homeland Security involved and earn one a trip to the Federal Pen.
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