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/sci/ - Science & Math

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4686534 No.4686534 [Reply] [Original]

Ok I admit it. I don't understand capacitors. I would like to but Wikipedia isn't helping much. Now, I understand that the voltage of a discharging capacitor lessens as it discharges, but that can be handled by a voltage regulator, can't it? What I would like is to buy some of these 1000+ farad capacitors from teh intarwebz and build myself a rechargeable power supply.

According to wikipedia, 1 farad = 1 watt-second / volt^2 so if I did my math right, 75 watts for 8 hours at 110 volts comes to just under 180 farads. Is that right?

P.S.

Not homework

>> No.4686552

never thought about that before but suddenly relevant to my interests. If that turns out to be right I can power my laptop on one of these

http://compare.ebay.com/like/270825328358?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_l
wgsi=y&cbt=y

for quite a while on a single charge.

>> No.4686567

I don't really know anything about capacitors except that they traditionally have had lower energy densities than batteries. I have a hard time believing you could run a laptop for over 8 hours on a capacitor that size, "ultra" or otherwise.

Still I can't find anything wrong with your calculation.

>> No.4686578

They have these things called capacitor banks. Banks. Like, fuckloads of capacitors. You need a fuckload to do anything useful, so the costs are way too high. Also, the continuous discharge makes them useless as batteries. Have fun setting up 5000+ capacitors is series for 20 minutes of battery life though.

>> No.4686602

it depends on what you're trying to do. A fuck ton has been done in the field of capacitors lately. The idea of a 1 farad capacitor used to be ridiculous. Now they have 3000 Farad capacitor, but shit that's just how tech works.

As far as I can tell, capacitors are still looking at a 3-5 Wh/kg energy density, compared to lithion ion which can have 150 Wh/kg easily. On the other hand, Lithium Ion batteries are notorious for their shitty number of cycles before they become unusable, so I can see the attraction of using a capacitors. Not sure about the math though.

>> No.4686624

hmm, you know, a single capacitor in the 500 farad range could probably start a car engine. That actually the kind of application capacitors were invented for. High current for a short period of time.

>> No.4686986

they leak after a time though

>> No.4687006

>>4686624

If a human being can step outside the car and turn a crank to start it, is the human being some kind of capacitor and what are its farads?

>> No.4687029

>>4686534 180 farads
This would be the size of a fridge using electrolytic or ceramic capacitors. With supercapacitors the size of a toaster, and costing tens of thousands of dollars.

> can be handled by a voltage regulator, can't it
Voltage regulators drop the voltage by burning excess off as heat. One won't reduce how much power is actually coming out of the capacitor so it lasts longer, and it will only work so long as the capacitor voltage is above the regulation level. A Buck–boost converter is more what you're looking for.


> 110 volts
You mean you're trying to generate AC?

>> No.4687043

......right.

I know exactly what you are trying to do and let me save you the trouble right now by telling you it's not going to work.

>> No.4687044

Gravity is quantized just as qualia are.