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Old 17-01-2017, 18:36   #61
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Re: Turn calories into electricity?

At my best five years ago at age 55 and 140 pounds, I could produce 300w continuous for one hour on a track bike, which was enough to come extremely close to setting a new Hour world record on the velodrome averaging 28.3mph. A couple of solar panels or running a generator for five minutes could easily beat me and everyone else here on the forum. It's not worth the effort.

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Old 17-01-2017, 18:43   #62
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Re: Turn calories into electricity?

OK let's look at it this way I have a generator that maxes at 400 watts at 250 rpm so I have a 20 inch diameter wheel and a circumference of 63 inches turning a pully of 3 inches diameter and a 9.5 inch circumference means if my math is correct I need to turn the big wheel at 42 rpm to get about 250 rpm on the small pully on my pm Genny . Producing 400 watts or approx 26.5 amps and for one hours peddling I have produced 26+ ah . I ride my bike about 3 hours aday on the beach so ..........
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Old 17-01-2017, 21:00   #63
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Re: Turn calories into electricity?

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Originally Posted by newhaul View Post
OK let's look at it this way I have a generator that maxes at 400 watts at 250 rpm so I have a 20 inch diameter wheel and a circumference of 63 inches turning a pully of 3 inches diameter and a 9.5 inch circumference means if my math is correct I need to turn the big wheel at 42 rpm to get about 250 rpm on the small pully on my pm Genny . Producing 400 watts or approx 26.5 amps and for one hours peddling I have produced 26+ ah . I ride my bike about 3 hours aday on the beach so ..........
So this is kind of what I was figuring, though that is more output than I had figured I'd need. I was not imagining this to be the sole source of power nor was I figuring on trying to power appliances or a fridge. ( Btw why not just hook up the belt you are pedaling to the compressor?) so I think I have in mind something easily put together and that fits in some convenient way in the cockpit to burn off some fat and/or top off batteries on a cloudy day. I got the oars already! It is very humbling to find out how little one has in the way of hp on those things too! Oh, and this strategy may be better for higher lat where you need to keep warm!
Btw that guy on the bike, if I had his physique I'd probably just be doing a Jack LaLane and tow my boat everywhere! To be fair, the position he is in is not the most efficient is it? I'd think seated with a backrest would yield better results.
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Old 17-01-2017, 21:37   #64
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Re: Turn calories into electricity?

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OK let's look at it this way I have a generator that maxes at 400 watts at 250 rpm so I have a 20 inch diameter wheel and a circumference of 63 inches turning a pully of 3 inches diameter and a 9.5 inch circumference means if my math is correct I need to turn the big wheel at 42 rpm to get about 250 rpm on the small pully on my pm Genny . Producing 400 watts or approx 26.5 amps and for one hours peddling I have produced 26+ ah . I ride my bike about 3 hours aday on the beach so ..........
Did the math on this and to get top rpm out of Genny I would be doing approx 30 mph with a 20 inch rim. But with a 26 inch rim hat drops to about 25 mph. Which is easily obtainable on flat ground with a conventional 21 speed bicycle without a problem. ( got a speeding ticket one time doing 35 in a 25 on flat ground ) ( trick is toe clips )
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Old 17-01-2017, 23:45   #65
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Re: Turn calories into electricity?

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Did the math on this and to get top rpm out of Genny I would be doing approx 30 mph with a 20 inch rim. But with a 26 inch rim hat drops to about 25 mph. Which is easily obtainable on flat ground with a conventional 21 speed bicycle without a problem. ( got a speeding ticket one time doing 35 in a 25 on flat ground ) ( trick is toe clips )
What is the torque you need to maintain that?

400w at 250rpm, you need about 11.5ft-lb of torque. Reality with friction and losses, closer to 14ft-lb.

The gearing requires about 8.7 times the torque applied to the 26in rim or about 121ft-lb.

The pedal crank is only about 7in radius resulting in a need for around 225lb of force applied to the pedal.

But that only works when the crank is perpendicular to the force your foot applies. The rest of the time the force must be significantly higher (or you need to apply even more force when perpendicular so you can coast thru the top and bottom of the cranking).

That's a lot of force to apply 42 times per second.
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Old 18-01-2017, 06:11   #66
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Re: Turn calories into electricity?

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Did the math on this and to get top rpm out of Genny I would be doing approx 30 mph with a 20 inch rim. But with a 26 inch rim hat drops to about 25 mph. Which is easily obtainable on flat ground with a conventional 21 speed bicycle without a problem. ( got a speeding ticket one time doing 35 in a 25 on flat ground ) ( trick is toe clips )
If I'm understanding your thought process, you've sorted out the operating RPMs you need, but neglected the actual load of the generator and assumed it'll somehow be just like bicycling on flat ground.

I doubt that is the case, on flat ground at target velocity all you are fighting is your wind resistance and some friction. I'm guess thats a *lot* less power per stroke than your generator requires.
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Old 18-01-2017, 06:39   #67
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Re: Turn calories into electricity?

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What is the torque you need to maintain that?

400w at 250rpm, you need about 11.5ft-lb of torque. Reality with friction and losses, closer to 14ft-lb.

The gearing requires about 8.7 times the torque applied to the 26in rim or about 121ft-lb.

The pedal crank is only about 7in radius resulting in a need for around 225lb of force applied to the pedal.

But that only works when the crank is perpendicular to the force your foot applies. The rest of the time the force must be significantly higher (or you need to apply even more force when perpendicular so you can coast thru the top and bottom of the cranking).

That's a lot of force to apply 42 times per second.
Correction applied 42 times per minute or about 0.75 per downstroke.
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Old 18-01-2017, 07:15   #68
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Re: Turn calories into electricity?

I have some land based experience with this. Teaching High School shop we rigged up a 12 volt generator to a bicycle wind trainer with the blowers removed and replaced with the generator. This arrangement meant that any bike could be mounted to the rig in seconds. For a generator we used a 100 watt electric fan motor from a VW Rabbit. It should be easy to rig up you once the generator is mounted to a plate the shafts can be mated with some fuel hose and clamps. If you have a bike this device takes up very little space and is portable you can use it above and below deck.
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Old 18-01-2017, 07:58   #69
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Re: Turn calories into electricity?

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Correction applied 42 times per minute or about 0.75 per downstroke.
One little omition on your part. Gearing on the crank side we have a 12inch ring gear on the wheel side we have a 1.5 inch gear so to turn the wheel at 42 rpm would require the crank to rotate at about 4.2 rpm now on the down stroke ( with toe clips) you can.exert about 130% of your body weight while on the upstroke you can exert many times your body weight.
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Old 18-01-2017, 08:29   #70
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Re: Turn calories into electricity?

Toe clips? Is is the 60's again?
Clipless pedals were invented in 1895 it seems but didn't get poplar until 1971.
I was surprised to see clips on that Video, nobody rides toe clips since, well a long time ago. I like my Speedplays cause I have bad knees and they allow lots of float.
Average crank arm length is 170 mm too or 6.6"
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Old 18-01-2017, 08:34   #71
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Re: Turn calories into electricity?

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Toe clips? Is is the 60's again?
Clipless pedals were invented in 1895 it seems but didn't get poplar until 1971.
I was surprised to see clips on that Video, nobody rides toe clips since, well a long time ago. I like my Speedplays cause I have bad knees and they allow lots of float.
Average crank arm length is 170 mm too or 6.6"
I use toe clips because I can make my own for about a buck with scraps I find laying around . You can buy them for under 20 bucks in many places.
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Old 18-01-2017, 22:13   #72
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Re: Turn calories into electricity?

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One little omition on your part. Gearing on the crank side we have a 12inch ring gear on the wheel side we have a 1.5 inch gear so to turn the wheel at 42 rpm would require the crank to rotate at about 4.2 rpm now on the down stroke ( with toe clips) you can.exert about 130% of your body weight while on the upstroke you can exert many times your body weight.
If you have a 10-1 gearing between the 26" pulley and the crank, you just bumped up the force required on the pedal to about 2250lbs. There is no free ride. You either have to pedal at a furious rate (high RPM) or you can cut the RPM but the force needed to turn the system goes up proportionally.

Also, to gear it up with multiple pulleys/gears, introduces additional friction into the system further increasing the force needed to turn the crank.

Toe clips will help but you aren't going to apply many times your body weight on the up or down stroke. If you can brace your back, you can apply 2-3 times your body weight on the down stroke. With toe clips, you would be hard pressed to pull more than 50% of your body weight on the upstroke. Realistically, the combined force (up on one leg and down on the other, most people will peak at maybe 150% of body weight and at 42 RPM, they aren't going to be able to maintain it for more than a couple minutes)

To produce a meaningful amount of stored electricity, you have to put out this huge effort for maybe an hour.

This is completely different than cruising along at 25mph with your bike on a level road where power needs are much lower.
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Old 19-01-2017, 05:58   #73
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Re: Turn calories into electricity?

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If you have a 10-1 gearing between the 26" pulley and the crank, you just bumped up the force required on the pedal to about 2250lbs. There is no free ride. You either have to pedal at a furious rate (high RPM) or you can cut the RPM but the force needed to turn the system goes up proportionally.


I think this is why some of us harp on so much about units like amps vs amp hours, etc. Their incorrect usage shows an unfamiliarity with the concepts of ENERGY (work) and POWER (ENERGY per unit time) - and trivial problems like figuring out the impact of gearing up and down become very difficult to understand without that foundation.
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Old 19-01-2017, 06:16   #74
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Re: Turn calories into electricity?

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If you have a 10-1 gearing between the 26" pulley and the crank, you just bumped up the force required on the pedal to about 2250lbs. There is no free ride. You either have to pedal at a furious rate (high RPM) or you can cut the RPM but the force needed to turn the system goes up proportionally.

Also, to gear it up with multiple pulleys/gears, introduces additional friction into the system further increasing the force needed to turn the crank.

Toe clips will help but you aren't going to apply many times your body weight on the up or down stroke. If you can brace your back, you can apply 2-3 times your body weight on the down stroke. With toe clips, you would be hard pressed to pull more than 50% of your body weight on the upstroke. Realistically, the combined force (up on one leg and down on the other, most people will peak at maybe 150% of body weight and at 42 RPM, they aren't going to be able to maintain it for more than a couple minutes)

To produce a meaningful amount of stored electricity, you have to put out this huge effort for maybe an hour.

This is completely different than cruising along at 25mph with your bike on a level road where power needs are much lower.
When was the last time you rode a bike . I do it every day . I dont see myself exerting that many pounds of force just to pedal the hills around here.
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Old 19-01-2017, 06:27   #75
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Re: Turn calories into electricity?

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. I dont see myself exerting that many pounds of force just to pedal the hills around here.
Exactly my point, you aren't putting out 400w when cycling.
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