How much energy does it take to toast a slice of bread? - Page 1
Forum section: electronics / general

author: halexa
author_rank: Regular Contributor
timestamp: November 25, 2015, 05:48:10 am
content: https://youtu.be/S4O5voOCqAQ

author: Stonent
author_rank: Super Contributor
timestamp: November 25, 2015, 05:58:08 am
content: To be fair, they required him to produce twice as much needed as they were only toasting one slice.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: November 25, 2015, 06:04:28 am
content: They have a bicycle generator like that at a science museum. The light it powered was 100W. That was more than difficult enough.I don't know what the efficiency is of the chemical conversion of sugar energy to muscle force is. Let's call it 50% at best. Let's also call the bicycle generator 50% at best. Then he has to dissipate 700W * 2 * 2 - 700W= 2100W to make that go.

author: timb
author_rank: Super Contributor
timestamp: November 25, 2015, 09:08:04 am
content: What if you like your toast burnt, or maybe not quite brown? How many Roberts does that take?Also, how many slices of toast does he need to eat, to have the calories to produce enough energy to toast a slice?Sent from my Tablet

author: VK5RC
author_rank: Unknown
timestamp: November 25, 2015, 10:33:30 am
content: Slice of white bread approx = 250kJoules = 250,000 wattsecsat 700 wats out (assume 80% of calories taken in by mouth get absorbed, of those absorbed 50% get out as energy i.e. 40% of intake can come out)250, 000 x 0.4 = 100,000ws at 700w out a slice of bread should last 142s. Ballpark.

author: SL4P
author_rank: Super Contributor
timestamp: November 25, 2015, 10:48:13 am
content: I'm glad you wrote that...I was going to post, but thought 'how am I going to make that sound sensible?'I concur with your estimate!

author: djQUAN
author_rank: Frequent Contributor
timestamp: November 25, 2015, 11:28:31 am
content: I keep seeing this regurgitated on my facebook wall.http://www.elitereaders.com/free-electric-hybrid-bicycle/1hr on the so called pedal generator could power your home for 24hrs. Supposedly.

author: Maxlor
author_rank: Frequent Contributor
timestamp: November 25, 2015, 12:12:25 pm
content: Quote from: djQUAN on November 25, 2015, 11:28:31 amHeh, no.The power output I can keep up for an hour is about 140W, according to various exercise machines I've used over the years. With that, I can power my fridge for about 4 hours! And if I do it every day, it'll save me a grand total of... $6 per year. I Better hope all the exercise doesn't make me want to eat more...

author: djQUAN
author_rank: Frequent Contributor
timestamp: November 25, 2015, 12:19:39 pm
content: I was actually thinking of making a bike generator to augment the home off grid solar system during cloudy days but if most people could do 100w for 1hr is 100wh. Not sure how much dent it could make as the solar array does 3-4kwh per day when it is sunny.

author: Muttley Snickers
author_rank: Unknown
timestamp: November 25, 2015, 12:43:23 pm
content: There is a big gymnasium about 150 meters away at the end of our street and I have a big roll of cable, an untapped resource perhaps....Also rumour has it that Robert can simultaneously cook crumpets with just the friction generated between his thighs and they have an extinguisher on permanent standby....

author: SL4P
author_rank: Super Contributor
timestamp: November 25, 2015, 12:48:28 pm
content: Will it generate more power if the bike is sloping downhill?

author: Mechanical Menace
author_rank: Super Contributor
timestamp: November 25, 2015, 01:23:43 pm
content: Wholemeal bread takes less energy to toast. Tastier too :/

author: Dave
author_rank: Super Contributor
timestamp: November 25, 2015, 01:33:53 pm
content: Quote from: Tomorokoshi on November 25, 2015, 06:04:28 amMuscles aren't that efficient.Wikipediasays 18 to 26 percent.That's a lot of energy for a slice of toast.

author: Gyro
author_rank: Super Contributor
timestamp: November 25, 2015, 05:37:04 pm
content: At that efficiency that's a hell of a lot of waste heat generation in the muscles - amazing that it's possible at all given the very narrow permissible temperature range of the human body!