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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  A fundamental question about power 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: A fundamental question about power  (Read 535 times)
chromesphere
Posts: 1128


Paul - Australia


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A fundamental question about power
« on: March 14, 2012, 04:51:56 PM »

Yo dudes!

I was thinking about this, this morning and couldnt work out the answer.  Its a back to basics sort of question about power.   

The input jack of a guitar pedal has the battery power neg connected to it, which is broken unless a cable is plugged in.  The plus is connected to the circuit.  The question is, why cant the power flow from the plus of the battery to the ground of circuit, even if the negative is disconnected?  Ground is still there. I have 2 possible answers not sure if either are correct although im leaning toward 2):  1) makes no difference if the battery has a connection from plus of the battery to ground, there has to be a completed circuit between the + and - of the battery terminals before current flows or 2) i have read current flows in reverse, therefore if the negative lead is disconnected from the battery, current wont flow 'out of the battery'.
Or a 3) option if both are the wrong answer?

Thanks for your help as always Cheesy
Paul
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R.G.
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Re: A fundamental question about power
« Reply #1 on: March 14, 2012, 05:04:12 PM »

1) makes no difference if the battery has a connection from plus of the battery to ground, there has to be a completed circuit between the + and - of the battery terminals before current flows or 2) i have read current flows in reverse, therefore if the negative lead is disconnected from the battery, current wont flow 'out of the battery'.
Or a 3) option if both are the wrong answer?
It's a mix of 1 and 3. A battery with only one terminal connected can't provide current at all. Electricity must have completed conducting (or semiconducting, or resistive) loops to flow. This is why they call them "circuits" - there has to be a full circuit available or nothing flows. The battery + is connected without the input plug plugged in. The battery (-) is not connected to anything, whether it's called "ground" or not, so no current flows from the battery.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
chromesphere
Posts: 1128


Paul - Australia


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Re: A fundamental question about power
« Reply #2 on: March 14, 2012, 05:31:09 PM »

Thanks for the reponse RG i think im getting it.  I think i had this idea that 'ground' was interchangable; if the negative of the battery wasnt available you could use the 'ground' of the circuit instead.  Which as you explained is not the case.  The negative terminal must be connected to the circuit.  Cheers!
Paul
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R.G.
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Re: A fundamental question about power
« Reply #3 on: March 14, 2012, 08:47:13 PM »

"Ground" is s concept that throws people. It used to mean a wire to the actual dirt of the planet; folks from the UK call it "earth".

Later it was found that circuits don't need a connection to actual dirt to work. Instead, you can define any point and call it "ground", meaning " the voltage reference against which all other voltages are measured: the defined position of 0.0000000V for all measurements.".

It carries no implication about power connections at all any more, just a reference point. At least part of the confusion is that it is common, almost universal, to attach the most negative power supply lead to the reference point. It's easy to confuse that practice into being how it must be.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
chromesphere
Posts: 1128


Paul - Australia


WWW
Re: A fundamental question about power
« Reply #4 on: March 14, 2012, 09:04:47 PM »

Ok, i think i get it now RG!  I've gotten into the habit of thinking that there is a connection to physical ground / dirt when looking at schematics / thinking theoretically, through the guitar cable or something, but of course there isnt, the circuit still works, with or without a guitar cable plugged in.  Or that, if the battery negative is removed from the circuit, it can just use any negative (like the negative from the DC jack for instance) like a rubbish bin or something.  But as you have explained, it doesnt work like that.  You have to have a circuit from the 2 terminals before power will be supplied.
Thanks for the explanation!
Paul
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