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# I want to power a laptop on supercapacitors. How would i do it with 2.5-2.7 v caps? what capacitance will i need? Answered

battery: 10.8 v, 47 whr
the charger says 18.5 v output, 3.5 A

Laptop: Presario f500, Turion 64 Mk-36 2.0 ghz (800 mhz or less for most tasks) 2 gb ram, 100 gb hdd, ubuntu 9.10. i think its supposed to last aroun 2 1/2 hours on a charge, but the battery's really old so I can't know for certain. i want to switch to capacitors so i don't have to buy a new battery every couple of years.

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## 8 Replies

Lemonie's right, but for the hell of it, here's some rough maths.

Assume the thing pulls 25 Watts, and it takes 18V from the supply and a current of 25/18 amps. Assume you're right, and it'd last 2.5 hours, or 9000 seconds.

Current = Charge/time, 1A is one Couloumb per second  - we need 25/18 C / sec, so for 9000 seconds we need 25 x 9000/18 Couloumb - 12500 Couloumb

For a capacitor, Q = CV, 12500 = C x 18 .....rearrangel for C = 694 Farads.

694 Farads at 18V is some supercap bank.

Steve

sillyn00b (author)2009-11-22

but if I still wanted to do it, how would I?

steveastrouk (author)2009-11-23

You'd need 20 of these
http://www.nesscap.com/data_nesscap/spec_sheets/ESHSR-3000C0-002R7A5.pdf

10 in series, in parallel with another 10.
Then you'd need to build a buck/boost inverter, to keep the output stable as the caps discharge, or an inverted output inverter would work.

Steve

Bigev (author)2009-11-10
For something like that, You'd practically need a room to keep them in.

lemonie (author)2009-11-09

Thanks for doing the maths, hard day: I had to sum it up like that.

L

lemonie (author)2009-11-09

It'd be cheaper and easier to replace the battery.

L

Re-design (author)2009-11-09

But he's got these 300 throw away cameras just sitting there and he don't know what to do with them.

lemonie (author)2009-11-09

Make a "nuclear" flash-gun, is the obvious project (to me)

L