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Bikepacking The Bikebacking forum is for discussion that relates directly to bikepacking (also known as bicycle camping). Subject matter should involve the backpacking/camping/bike gear and trip planning as it relates to mountain biking and bicycle touring.


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  #1  
Old 08-02-2011, 08:40 AM
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Tnhillwalker Tnhillwalker is offline
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Mechanical Power (Generator) vs Solar Power

Why are you trying to use solar power when it would be so much more efficient to use the mechanical energy in the tires on your bicycle to power a micro generator.
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  #2  
Old 08-02-2011, 07:10 PM
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dsuursoo dsuursoo is offline
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Quote:
Originally Posted by Tnhillwalker
Why are you trying to use solar power when it would be so much more efficient to use the mechanical energy in the tires on your bicycle to power a micro generator.

under anything other than a minor load, it's actually a fair bit of work to power a generator capable of charging more than a small battery. charging multiple devices at anything more than a trickle saps a surprising amount of power out of your pedaling. you're already hauling around a goodish bit of weight, so loading down with an active load like a generator seems a little much.

okay, no problem, pedal away in camp you say.

well, alright, there's that. of course you'll have to bring along a frame that takes your driven wheel off the ground and holds you upright while you pedal. so add that weight along with the weight of the generator AND charging system to your load. it's not much, maybe oh 4 kilos on the low total. the stand *could* be smaller if you were either camping on asphalt or you could guarantee a solid and level surface each time you wanted to charge up. and then there's the hour(or three depending on device and charge rate) and change you could expect to spend puffing away on the generator to get your various gadgetry back up(micro-generators are not very high-output devices) to snuff. you know, the time you'd spend setting up camp, cooking, taking a load off sore muscles...

sure it's not a bad idea, but there are factors weighing(no pun intended) that make solar a pretty viable option for most bikepackers. as always, tho'.

now a tiny wind turbine...
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  #3  
Old 08-02-2011, 07:35 PM
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Tnhillwalker Tnhillwalker is offline
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Actually, that post was pulled out of another thread but that beside the point.

All I was trying to do was offer an alternative form of power generation to someone that was bikepacking. It seemed to me they were heading towards some expensive custom solar equipment.

I remember years ago using small generators on our bicycles to power headlights, while there was an extra load on the tire we managed and we were 10yo riding Schwinns.

I am willing to bet there could be a niche market for someone with a small lightweight micro generator you could mount to a bicycle frame. The output would only need to be minimal to surpass what a small solar panel could deliver.

I was thinking something along the lines about the size of a 9v electric motor, the idea being to provide a trickle charge to a battery over the course of a day. It seems to me it would not put that much of a load on the rider and would be more efficient and effective than a solar system.
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Old 08-03-2011, 01:48 AM
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dsuursoo dsuursoo is offline
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potentially. though in truth solar is maintenance free. even if you were to use a permanent magnet design the points of failure in an alternator(being what you're suggesting) start adding up. as a mechanical unit it's going to be vulnerable to dust, debris, bearing failure... sure you can build to mitigate those things but you cannot eliminate them(not without the alternator becoming a fancy paperweight).

and to harness more than a watt or two(most solar units deliver something like 4w direct off the panel so we'll set our bar there) you're actually going to be mounting a fairly large item. even with the most powerful rare earth magnets you're looking at something easily the size of a beer can and much heavier.

don't get me wrong, wheel-driven alternators aren't a bad idea. they're just not as practical, from many viewpoints, as solar. the alternator won't be charging while you're eating lunch unless you're really nimble, for example.

for any mobile charging solution to be really usable you need a battery pack in between your source and your load(it's a conditioning and lifetime thing), with a load dump to prevent the battery pack from being over-charged. output on alternators are partially dependent on RPM, and as a consequence can vary, quite a bit, so the load dump(and shunt that switches between them) has to be over-built to match. sure that stuff's not that hard, but it's extra work, complexity, cost...
the price point on photocells has gone down a lot recently while efficiency keeps going up. i'm a pretty damn competent engineer, and even I would have problems coming under-cost on a mechanical alternative that's relatively 'gold plated'. okay, economics of scale disregarded, it'd still come in higher in cost, both in maintenance and complexity. which is a shame cause it'd be great to see options out there.

a lot of solar units that deliver 4watts will fit in your hand and weigh less than a pound. their setup and operation consists of strapping them somwhere where they get light exposure and plug them into your device. that's one seriously tough bar to clear without sacrificing something(or several somethings) along the way. if you're into mechanicals, setting stuff up, adjusting it for the sweet spot and getting all that right, an alternator is really going to appeal. it's got its selling points. trouble is, those selling points only do it for a fairly small portion of the market. the engineering isn't excessively difficult but there's plenty of it to do to make the system reliable AND long-lived AND easy to use AND safe for devices.

i'd love to see an alternator-based option on the market, if for no other reason than to have options. i just don't see it realistically happening because of how the bar is set with solar.
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  #5  
Old 08-03-2011, 12:04 PM
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Tnhillwalker Tnhillwalker is offline
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Your solar design seems way more efficient than anything I have ever had my hands on.

I have a 12in x 12in solar collector mounted on the tongue of one of my trailers to trickle charge a deep cycle battery, its not that effective.

I was just thinking the old tried and true 12v generators we had on our bikes as being a more reliable power source.

Best of luck in your ventures.
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  #6  
Old 08-03-2011, 04:07 PM
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dsuursoo dsuursoo is offline
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actually 4w is setting the bar pretty low. a trailer's deep cycle battery is going to be extremely high capacity compared to the batteries used in backpacker's/bikepacker's solar units. its amp-hours capability is in an entirely different weight class. a 10-15w panel(which is probably more like it for your trickle charger) is going to be kind of marginal for any sort of significant amount of charging(of course, a trickle charger isn't meant to charge a battery but keep it topped off).

the other part of that is the driving voltage. a lot of the portable kits run at 6v on the upper end(they can deliver 12v but current is pretty low). your trailer battery unit had to run probably to the tune of 14-15v AND had to deliver above a certain level of current to even begin to charge the battery, which is what accounted for its size(you have to run lots of cells in series and parallel to reach a given output).
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  #7  
Old 08-03-2011, 06:42 PM
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Ralph Ralph is offline
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As an alternative to solar power I did find this:

Power generator makes electricity from heat

The PG-1 thermoelectric power generator allows users to generate electricity with canned fuel or other heat source. This self-contained device is suitable for demonstrating the Seebeck effect. The thermoelectric power generation effect occurs when there is a temperature difference across the thermoelectric module located inside the unit, producing electrical power.

The device has a net output of approximately 0.75 W is adjustable from 3 to 14 Vdc with a built-in voltage converter. Consumer applications include thermoelectric cup holders that heat and cool beverages. Other applications include thermoelectric modules for cooling and electric power generation.

Any heat source can be used and it seems to be a compact unit (the picture in the reference shows a box not much bigger than a large Sterno can) but I've never seen one and don't know what they weigh.

FWIW I carry a small 12VDC variable voltage converter that plugs into the lighter outlet in the truck and have used it to charge up or run small devices while driving.
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  #8  
Old 08-03-2011, 09:59 PM
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dsuursoo dsuursoo is offline
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Quote:
Originally Posted by Ralph
As an alternative to solar power I did find this:

Power generator makes electricity from heat

The PG-1 thermoelectric power generator allows users to generate electricity with canned fuel or other heat source. This self-contained device is suitable for demonstrating the Seebeck effect. The thermoelectric power generation effect occurs when there is a temperature difference across the thermoelectric module located inside the unit, producing electrical power.

The device has a net output of approximately 0.75 W is adjustable from 3 to 14 Vdc with a built-in voltage converter. Consumer applications include thermoelectric cup holders that heat and cool beverages. Other applications include thermoelectric modules for cooling and electric power generation.

Any heat source can be used and it seems to be a compact unit (the picture in the reference shows a box not much bigger than a large Sterno can) but I've never seen one and don't know what they weigh.

FWIW I carry a small 12VDC variable voltage converter that plugs into the lighter outlet in the truck and have used it to charge up or run small devices while driving.


those are neat toys. not a ton of output but they run on very little temperature difference and they run for as long as the difference is there.

if you're going somewhere hot there's not much use you can get out of them, but they are awfully cool.
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  #9  
Old 08-06-2011, 10:31 PM
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WildlifeNate WildlifeNate is offline
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the question I have is when are we gonna see regenerative braking scaled down to bicycle size?
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  #10  
Old 08-07-2011, 11:38 AM
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dsuursoo dsuursoo is offline
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Quote:
Originally Posted by WildlifeNate
the question I have is when are we gonna see regenerative braking scaled down to bicycle size?

they have that on a lot of the electric-assist/powered bicycles.

granted, those bikes are heavy and you prolly won't see a lot of bikepackers using them...

/had a coworker with an electric bike that didn't have regenerative braking. the day he let it wear down, was the day he was basically a warm puddle at work.

//waiting on the 'battery in frame' technology.
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