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Old 05-04-2009, 06:41 AM   #21
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Ever get this functioning? I'm curious how the capacitor for peak loads worked out.
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Old 05-04-2009, 07:12 AM   #22
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Worked great!

The two bricks feed 3 capacitors directly, a 5v and two 12v. All of the caps are 16v 8,200uF caps. The voltage out of the bricks are .3v over what the normal rail is so it ended up being perfect (the motherboard runs off the bricks until it pulls their voltage equal to the power supply voltage where current demand swings quickly to the normal PS again). Across the caps I have 10k ohm resistors to apply a constant load and discharge the caps when I unplug the unit.

I have a sensor pin from the stock 12v supply voltage that gives me my on/off switch. The relay is after the capacitor so the regulators can keep the caps charged while the computer is off and then start-up current isn't having to be fed while also charging the caps(defeating the purpose of them).

Since they are switching supplies they don't go up in voltage beyond their rating as demand decreases like a lot of linear supplies with transformers do. I honestly don't think that I needed caps that large but it's better to be safe than sorry!
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Old 05-04-2009, 07:24 AM   #23
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That's great. Pretty big caps! I noticed that all electronics has some 1/3 F supercapacitors for $1.15 which is what reminded me of your project. Only 5.5V though but I guess one could use several.
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co de pen den cy
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Function: noun
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Old 05-04-2009, 07:39 AM   #24
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Unfortunately, you can't use several to increase voltage handling, that is a fixed limit. You can run them in parallel to increase capacitance though.

Yeah, they are big, I don't think the bricks like charging them either as they sound funny when they are first started driving those caps versus when they aren't on there. I've considered limiting the current from the bricks to the caps but I don't expect the regulators to be plugged in and unplugged a lot anyways.

Those super caps are sweet! They are meant for slow-discharge like in a solar powered LED torch or something similar... Project time!
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Old 05-04-2009, 09:06 AM   #25
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Placing the capacitors in series should allow higher voltages, although you may need parallel large resistances if the leakage current isn't high enough. Of course you'll be sacrificing capacitance with the series setup. And it's a pain.

What project have you got in mind?
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Function: noun
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Old 05-04-2009, 02:08 PM   #26
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The voltage rating of a capacitor is the voltage at which the capacitor can safely run before the dielectric begins to break down. Running them in series will still cause you to go over that because on the negative side of the most positive cap will have 0 volts and the positive side will be over. The dielectric will break down and then the next cap will be over and it'll continue til every one of them is dead.

Not sure on the project, I'll come up with something!
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Old 05-04-2009, 02:22 PM   #27
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Check it out, useful trick:

http://books.google.com/books?id=nMB...um=7#PPA339,M1
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Main Entry: co de pen dence - see codependency
co de pen den cy
Pronunciation: \kō-di-ˈpen-dən(t)-sē\
Function: noun
Date: 1979

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another
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Old 05-04-2009, 03:16 PM   #28
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I see what they did there, they made a voltage divider using the resistors across the caps. That will work, for small headphone amps I do that to create a virtual ground.

Just know that circuit won't work without the resistors. Without the resistors they'll die like I mentioned above.
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Old 05-04-2009, 03:37 PM   #29
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This is one of those tricks I learned in college that I've never had an opportunity to try out. Most of my stuff is digital.
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Main Entry: co de pen dence - see codependency
co de pen den cy
Pronunciation: \kō-di-ˈpen-dən(t)-sē\
Function: noun
Date: 1979

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another
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Old 05-04-2009, 03:42 PM   #30
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You could actually use varying ratings if you put some thought behind it. If you have a 100v(DC) line and you put a 5k and a 10k resistor across it you'll have 33.3v and 66.6v respectively. Almost perfect for a 35v cap and a 63v cap.
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