Monday, March 2, 2020

Robert Forstemann struggles to toast bread via bicycle: AC resistance from the DVD player, 1.6 times higher than DC resistance

Tour Pros climb 15% slopes at speeds of 20 kmh outputing 400+ watts.
  Sure we can wind up a radio or keep those mini-screens on those gym bikes going but we quickly hit our limit when the energy demands get higher—anything involving heating for example.
By means of demonstrating this inconvenient truth, Robert Förstemann took on the challenge of heating a single slice of toast in a 700 Watt toaster with the incredible strength of his 74cm diameter thighs. Setting out at a steady 50km/h Förstemann battles with maintaining pace to keep the toaster going—the power required equivalent to climbing a 40 degree incline.
 I just don't know how they hooked up a generator to a monarch. Also there would be windage, bearing friction and AC/DC Inversion, at the very best he would need 15% more at source (cranks say 850 watts) Than load (toaster at 700 watts) 
https://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html

It is estimated about 50% of watts are lost due to resistance, converting, etc.
https://www.appropedia.org/CCAT_pedal_powered_energy_generator

The question here is this DC or AC power because if you're pedaling a bicycle, then the resistance is key. https://www.skoolie.net/forums/f49/dc-watts-vs-ac-watts-28596.html

 12vdc@6amp=72w or
120vac@0.6amp=72w
So same watts but dramatically different resistance!

The current I in amps (A) is equal to the voltage V in volts (V) divided by the resistance R in ohms (Ω)
6=12/x or 6x=12 so Ohms=2
.6=120/x or .6x=120 so X=120/.6  so 200 Ohms.
That's a HUGE resistance difference.

So maybe it was DC generator so then  .206 ohms since 700 watts/12 volts = 58 amps and ohms= 12/58

 For example, a 100 watt light bulb operating on 120 volts AC will have 144 ohms of resistance and will draw 0.833 Amps.
 

One thing not mentioned here. It is quite easy to safely wire AC from one end of your bus to the other to run any 120V appliance. Twelve gauge will run pretty much anything rated for 120V at that distance.
With DC you have to run increasingly larger wire as power requirements and distance increase. And the size requirements go up quite rapidly.
My fridge, microwave and induction cook tops are about 20 feet from the power source. Wouldn't have been feasible on DC.
A lower voltage system will require a higher amount of amps to deliver the same amount of power.

As an example, a 1000w load, will pull roughly:
83.3A @ 12v DC (common DC voltage)
41.7A @ 24v DC (common DC voltage)
20.8A @ 48v DC (common DC voltage)
8.33A @ 120v AC (US AC voltage)
4.54A @ 220v AC (EU AC voltage)
1.00A @ 1000V DC (common max string voltage for solar)

Your wire size is proportional to the amperage it will carry, and the round trip length of the wire run. For a given load, higher voltage = lower amperage = smaller gauge wire. I don't believe it makes any difference whether its an AC or DC circuit.
 yet:
 https://www.quora.com/Which-one-is-more-AC-resistance-or-DC-resistance



Due to skin effect AC exhibits more resistance than DC.

To reduce the resistance on AC wires with more thickness and high guage are used. The same resistance will cause a fuse to trip in cases of short circuit as fuse's conductive sting is thinner.

The puzzling part for begineers might be if AC already has high resistance then why high ohm resistors are used in series with AC ? . This is because due to skin effect and the conductors used to carry it to your equipment the amount of decrease in voltage with respect to resistance is never known exactly. So they will have to maintain an isolated voltage for their circuit Irrespective of external factors. The resistors helps maintaining isolated voltage.
 The tendency of an alternating current to flow near the surface of the conductor is known as skin effect. As the frequency of the current increases, the current tends to concentrate around the outer surface of the conductor. The current density is largest at the outer surface of the conductor. Thus, the effective area of the conductor decreases when alternating current flows in the conductor, therefore, the resistance gets increased.
 https://www.quora.com/Is-12-Volts-of-DC-the-same-power-as-120-Volts-of-AC
 But here is the reason that 120 V can deliver more power: wire size. Higher voltage requires thicker or better insulation, but higher amperage requires a thicker conductor. Amps is the measurement of how many electrons are travelling through a wire, so as it gets larger so does the wire.


So....

 converting slopes into ohms?

https://bicycles.stackexchange.com/questions/7774/how-do-i-calculate-the-power-required-to-climb-a-hill-at-a-given-cadence
This is the crucial question - whether it is AC or DC it's both a lot of Ohms. So Resistance as OHms is voltage squared divided by watts. We know the watts. If it is 120 volts then it's 14400/750= 19 ohms. The Toaster is 120 volts - so the bicycle generator is probably 120 volts. I have charged up at 3 ohm or 4 ohms - and I could barely pedal!!
 Actually the "pedal power" products are very misleading because they don't include the resistance. So you have to get up to a certain amount of volts to power 12 volts - and/or 120 volts. So if the RPM is alot then it can also change the resistance. So his resistance is very high - probably 19 ohms. You probably could not even turn the pedal at all. For example a 12 volt 60 watt light bulb has 5 ohms and it's very difficult to maintain pedaling at that resistance.
So Pedal-A-Watt is only producing 1 to 2 amps - at 12 volts - vid

78 bicyclists at full power cycling to power one hot electric powered shower  - BBC vid








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