Power distabution problem

[Skylinegodzilla]

so I'm building a bot with my raspberry Pi it's earley stages and I have run into a issue. This issue is power distribution.
After some testing of my bot I have worked out that my Pi can spare 1.4 amps of power while plugged into my power bank (this is not counting the the posable 1.2-2.2 boost I could get if I used the second port on the bank)
The problem is that whatever I wirer up on my breadboard that 1.4 amps gets devided up evenly among them.
This is not very economical Expsaley when I have 2 motors that have to carry the load of the bot getting the same amount of power as a survo that's just turning a sonic seancer.
I also decovered that the l293d chip that I am using counts as 4 things (I would guess it's two parts for the motors, one for the power source and one for the logic calculation)
So keeping that in mind with 1.4 amps and just the motors the power each Motor gets is only 350 mA. And as I add new things that number just keeps decreasing.

So my question is does anyone know how to manage what component gets how much power? There must be some way to do it or else the Pi would not be able to give us its remaining 1.4 amps that it's not using.

[drgeoff]

You don't seem to understand basic electricity. When you wire n different loads to a supply that can provide A amps each load does NOT get A/n amps.

Loads try to take the current they require. Something like a low current servo will take less current than a high current motor.

Just the same as with the mains electricity in your house. If you plug in a 3 kilowatt electric kettle and a 60 watt light bulb, which of the following do you think is correct..

1. They both take the same current.

2. The kettle takes 50 times as much current as the light bulb.

[SonOfAMotherlessGoat]

Super simplified, but to help you get a bigger picture:

If you look at the power supply that you are using for the Pi, it will have a listing/rating for the Amperage that it will provide. The Pi takes that amperage and sips off what it needs to do it's own internal functions. What's left after that is what you've found as 1.4A (I think the Pi is set to provide a max of 1.2A via USB but I'd have to check to make absolutely sure.). So the Pi doesn't decide that it's going to provide you with 1.4A, that's just what is left 'in the glass' after the Pi has had it's turn drinking. And there are sites that have comparisons of the different models of Pi and differing loads along with the amperage that is used in those scenarios.

So, then you have your other devices, and they in turn will siphon off the amperage they require. Until there is no more.

The way to look at it then is to reverse your thinking. Take the devices on the robot and start adding up the rated amperage. You'll get a total that is your needed amperage. If that is over the power budget you're allowed, then you need to look at powering the bot via another method and controlling with the Pi instead of powering with the Pi.

Starting point is http://chrisgammell.com/what-is-a-power-budget/ and just go from there. Read up on whatever you can get your hands on and you'll find a way to accomplish your goals.

[stderr]

So my question is does anyone know how to manage what component gets how much power? There must be some way to do it or else the Pi would not be able to give us its remaining 1.4 amps that it's not using.

What is causing you to imagine all the above data to be the case? Are you measuring something? You may find that motors and that sort of thing cause such a drag on your battery that you need a separate dedicated system to power your pi. The pi might reboot unless it is given good power all the time, the motor might be more demanding for start up, say.

[Skylinegodzilla]

You don't seem to understand basic electricity. When you wire n different loads to a supply that can provide A amps each load does NOT get A/n amps.

Loads try to take the current they require. Something like a low current servo will take less current than a high current motor.

Just the same as with the mains electricity in your house. If you plug in a 3 kilowatt electric kettle and a 60 watt light bulb, which of the following do you think is correct..

Aparentley not.
I'm confused because as far as I am awear if I put somthing in a circuit like say a led it will chew up as much current that it can at once intill it pops. Hence why you have to use a resister to controll the current.

So how is it that the componits can use what they need and leave what's left over if they just use as mutch current that they can get intill its to mutch and they break?

Yes I am awear I am missing some understanding here that's why I'm asking


So say I have two dc moters, a servo, a sonic sencer a thurmastat. And more then enougth amps to run them all. And are all set up in parrall with eatchother.
Will they
A) use Onley current they need and leave the rest of the current that they did not use untouched
B) use all the current but in a ratio of what they need (like the servo using Onley a fraction of the current the motors are using)
C) all break because they are using to mutch current that's not controlled by resisters?

[bensimmo]

All components behave differently and that why you sometime need to know a little bit about them

The resistor you out before that LED is suddenly not burning out.
The current they take is also linked to the voltage you feed them, but for a bulb or resistor they move in a simple way. Increase the voltage and it will use a greater current, so is effectively controlled by the voltage under normal circumstances, increase the voltage and the current increases and it total power will make them get hair and then blow.

On an LED it can do the same but the current profile is different and ramp up suddenly on a small increase, you get to a point and it starts to emit light, but the current suddenly increases, tap it a little bit more voltage and the current increases but in a controlled manner. Get to another point and the current just rushed through pulling as much if not all it can and it goes pop. I.e the resistor set the working voltage of the led and hence limits the current it can pull.
Do a quick search on Google for some basic info on them and you'll see the difference.


Motors are at their simplest a winding a wire and hence just a resistor, you set the voltage and can control that.


Simplified but I think you need to go have a read on the basics.

[drgeoff]

You don't seem to understand basic electricity. When you wire n different loads to a supply that can provide A amps each load does NOT get A/n amps.

Loads try to take the current they require. Something like a low current servo will take less current than a high current motor.

Just the same as with the mains electricity in your house. If you plug in a 3 kilowatt electric kettle and a 60 watt light bulb, which of the following do you think is correct..

Aparentley not.
I'm confused because as far as I am awear if I put somthing in a circuit like say a led it will chew up as much current that it can at once intill it pops. Hence why you have to use a resister to controll the current.

So how is it that the componits can use what they need and leave what's left over if they just use as mutch current that they can get intill its to mutch and they break?

Yes I am awear I am missing some understanding here that's why I'm asking


So say I have two dc moters, a servo, a sonic sencer a thurmastat. And more then enougth amps to run them all. And are all set up in parrall with eatchother.
Will they
A) use Onley current they need and leave the rest of the current that they did not use untouched
B) use all the current but in a ratio of what they need (like the servo using Onley a fraction of the current the motors are using)
C) all break because they are using to mutch current that's not controlled by resisters?

A