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Author Topic: Power capacitors  (Read 2582 times)

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Offline gamefreakTopic starter

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Power capacitors
« on: February 05, 2008, 11:00:57 AM »
On my bot I commonly use 9V batteries, but as the servos run my power light begins to blink, and if I stall my servos the light gets really dim, could I conteract the blinking by adding more capcitors between unreg and grn, reg and grn, or both?
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Offline Steve Joblin

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Re: Power capacitors
« Reply #1 on: February 05, 2008, 11:09:54 AM »
9V transistor batteries provide 9v, but not much amps... motors draw a lot of current, and you should use a separate power supply (not 9v transistor batteries) for the motors... make sure you tie the grounds together between the two power supplies!

Offline gamefreakTopic starter

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Re: Power capacitors
« Reply #2 on: February 05, 2008, 11:11:58 AM »
that another question of mine, what if I wired the positive together and kept the grounds seperate?
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Offline Admin

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Re: Power capacitors
« Reply #3 on: February 05, 2008, 11:20:06 AM »
it will result in negative voltages - bad!

Offline gamefreakTopic starter

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Re: Power capacitors
« Reply #4 on: February 05, 2008, 07:55:57 PM »
alright, so is it better to have the capacitors positive on unreg, or reg, if all of my robot uses reg?
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Re: Power capacitors
« Reply #5 on: February 05, 2008, 09:58:44 PM »
Hmmm I dont understand the question.

You want capacitors on both the regulated and unregulated lines, depending on how sensitive your electronics are to power noise. You need a regulated line for sensors and the microcontroller.

What I did for the $50 Robot is what I'll say is the bare minimum of what you need.

Offline gamefreakTopic starter

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Re: Power capacitors
« Reply #6 on: February 06, 2008, 10:15:22 AM »
is there such a thing as too many capacitors or too much capictance?

I know the more I have the longer it takes to power on and off, but the better he power source can handle large immediate current draws(like a motor turning on).
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Re: Power capacitors
« Reply #7 on: February 06, 2008, 10:35:56 AM »
Yeap, there is such a thing. Some microcontrollers won't turn on if the power ramps up too slowly. Check the datasheets . . .

Capacitors are only needed because your battery can only supply a certain amount of power at any instant, while capacitors can discharge energy much much faster. If you find you need too much capacitance, that means you really need a better battery.

Offline gamefreakTopic starter

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Re: Power capacitors
« Reply #8 on: February 06, 2008, 11:04:28 AM »
alright, and it wouldnt matter on the location of the capicitor, correct? ex. If I put one right on the microcontrollers positive and negative, it would be no different then if it was on my servos?(my servos are on the same regulation as the controller) But If I had to seperate circuits, two identical regulators one going to the brain and one to motors, then there would be no noise in the brains circuitry and it would require at the most a small capcitor just incase, while the circuit for the motors should have a fairly large one, correct?
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Re: Power capacitors
« Reply #9 on: February 06, 2008, 11:13:36 AM »
If your electronics are insensitive to noise, you don't need capacitors.

Voltage regulators do not eliminate noise.

Put caps close to anything you think is harmed by noise.

Servos and motors are very insensitive to noise.

Use ceramic caps for high frequency noise (sensors, microcontroller), electrolytic caps for low frequency noise (motors, actuators).

What I have on the $50 Robot is a perfect example of the bare minimum that you need. Use it as a guide.

hope that clears stuff up . . . ;D

 


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