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Old 26-01-2014, 10:08 PM   #1
BrownDog
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Self Sustaining Radio

Had an inventive thought last night, what if I build a portable radio that uses car components, add a battery, an alternator and an electric motor.

Now what I need to is a electric motor with the right sized pully and the right sized pully for the alt, I'm thinking bigger on the motor and smaller on the alt, how ever the opposite way might work if the motor can spin fast enough.

I did google it and saw all these paragraphs about perpetual motion ( finally got the funny bit about PMS "perpetual motion squad"), however I am persistNt and prefer to have it proven Infront of me rather than someone just say it can't happen

Need someone a bit more advanced with physics

Discuss
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Old 26-01-2014, 10:37 PM   #2
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If its perpetual motion why do you need a battery to feed the engine?

I dont understand how you can not realise its not possible? Why does your car come to a stop if you push it?

Why do batteries die? Why do electrical circuits produce heat?

How much physics do you want?
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Old 26-01-2014, 10:41 PM   #3
BrownDog
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Need the batt to spin the motor until the alt can take over the power needed.

I get the car part, friction, gravity and memetic energy(i think)

But I just feel that there is a motor and pully combination that will spin the alt and leave enough output to charge the batt and run the stereo
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Old 27-01-2014, 06:37 AM   #4
Drakh
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I think the most you can ask for is just extending the time the radio will work before running out of batterys. Physics basically says you can't get more energy out then you put in.
In regards to having the right motor and pulley combo/ratio, the way I understand it is if you could find a combination that would work, the pulleys end up being large, and if you were to disconnect the battery after starting it up, the motor ends up not having the grunt to turn the pulleys, and comes to a stop. Get a bigger motor, need bigger pulley to drive it.
On to efficiencies. electric motors are about 90%, alternators are about 50%, so that can be a bit to overcome.
But I don't really know- been a long time since school.
I just imagine that if you could get 'free' power out of a motor and alternator with the right pulleys, than that technology would be everywhere, being put in all the latest electric cars, being retrofitted on electric motors worldwide, powerplants would be a joke.
Thats my 2c anywho
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Old 27-01-2014, 11:38 AM   #5
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Here you go: http://en.wikipedia.org/wiki/Crystal_radio
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Old 27-01-2014, 01:15 PM   #6
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WTF

I understand our school system is going to the Dogs but someone needs to back and sit in science class. Or Buy a bible and Follow that.

The basic laws of Physics answer all these questions.
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Old 30-01-2014, 05:31 PM   #7
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Just in case this is a genuine question (although it's hard to believe) ...

Forgeting the radio for the moment and picking efficiency figures out of thin air ...
Lets say a motor is 80% efficient at turning the electrical energy from the battery into mechanical energy.
Lets say an alternator is 80% efficient at turning the mechanical energy from the motor into electrical energy.

Lets say the motor draws 500W of electrical energy from the battery.
500W x 80% = 400W of mechanical energy.
400W of mechanical energy drives the alternator, which puts out 400W x 80% = 320W of electrical energy.

Where does the 180W shortfall come from? ... The solar panel of course!
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Old 12-02-2014, 11:22 AM   #8
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The school system these days is practically stuffed mainly because most kids these days in my area have this "I don't whatever the **** I want" attitude and well some people are trying to learn but unfortunately there are some dunce's that just disrupt and stop the teacher from doing his/her job and we end up having half an hour of listening to the teacher try to control the class, I say bring back the cane

I'm sure a few people on this site got the cane back in the day and they don't seem to be negatively affected by it, there will none of this "can't hit a child" in my house, nothing wrong with a slap on the backside I had frequent floggings and well I'm fairly behaved, well sort of
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Old 12-02-2014, 11:25 AM   #9
BrownDog
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Back on topic I have an old alternator from a cortina I think and I was spinning it with my hand and managed 6v, no idea how many amps as my multimeter only goes up to 1A

Maybe I should just get a treadmill and get the dog onto it
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Old 12-02-2014, 01:07 PM   #10
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I learnt alot of this in grade 9. Granted alot of detailed stuff I learnt was in physics.

Once you get past the mechanical inefficiencies theres things like Ohms law to consider for ohmic items like wires and resistors. Then theres the resistance for non ohmic sources such as diodes and batteries.

Then theres temperature to take into account etc etc.

Its been so long since ive done this stuff I honestly can't really contribute much more without getting my phsyics text book out.
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Old 12-02-2014, 02:24 PM   #11
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Hmm, I never got far in physics, It all made sense in my head but just couldn't write it down, kept trying to work it out in my head but kept loosing tracking

I'll say this now btw, this radio won't be very portable, but still moveable
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Old 12-02-2014, 06:05 PM   #12
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I had a crystal radio. It was awesome. Obviously it'd need an amplifier to be louder than headphones...
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