I've been approached by a local group who are interested in putting on some
'green' Christmas lights in the High Street this year using pedal power.
I was sent a document outlining the idea but, unfortunately, it seems to be
based on a lot of press reports of other schemes which I suspect have cost a
lot more than their nothing pence target ...
Now my background is electronics, so I've never had any dealings with
generators other than the Miller dynamo on my mum's old bike (pre-war, 28"
wheels, cast iron frame, no gears) which was handed down to me over half a
century ago. Oh yes! There was also the little motor from my Trix construction
set when I was about 10 which could be made to light a 2.5V torch bulb - just!
I've stripped out all the 'why we should do this' and so on bits out and a lot
at the end - which does mention the H&S aspect, by the way. What follows are
the sections I've commented on - including my comments, of course.
What does the team think? Has anybody ever got involved with anything like this
before? And is my car alternator idea worth pursuing?
The originator already confesses to having zero electrical knowledge, so I
don't think that point needs further elaboration!
] PRECEDENTS OF PEDAL POWERED LIGHTS
I do so love it when journalists get involved with technical matters – they
can be a constant source of mirth unless, of course, anybody makes the fatal
mistake of taking them seriously!
] - Belsize Park, London
Doesn't say they managed it - just an appeal for bits. "We are currently
looking for an old exercise bike, a small 12volt generator and a battery ..."
] - Chorlton, Greater Manchester
Better, but "The turbine costs £500 ..." etc.
] - Copenhagen - UN Climate Summit:
Hardly sounds like one 80V 300W generator (see below) ... "a number of bikes
are (each) connected to a different section of the tree ..."
] - Video of Copenhagen (larger-scale than ours will be - but same principles)
Unfortunately, you don't see what they are using for generators!
] - Make Your Own Xmas - Rob and Roberta Smith at Tate Britain
Reading between the lines, this was all done commercially (see last paragraph)
at an undisclosed cost. The only thing free about this is the cycling!
] - Electric Pedals bicycle generator: <http://electricpedals.com/shop/bicycle -
300W ...? One horsepower = 746W so 300W is nearly ½ hp! 300W is actually 0.4hp
but this is assuming 100% efficiency! If 80% efficiency could be achieved, the
physical input would be ½ hp.
I note they have a ‘shop’ but no pricing or any way to place the order ...
Delving further, we find: http://electricpedals.com/shop/bicycle-generator /
Ah! This bit mentions "a 10m high tree with 2400 LED lights powered by the
public using 10 bikes and generators ..." So that's 240 LEDs per bike - but no
mention of the power demand of each LED ...
There is some further info on the Tate tree, though: "an 11m high tree with 30
halogen bulbs powered by 8 bikes ..." but, again, no details of the bulbs'
consumption but if we assume 12V 10W bulbs, that's approx. 4 per bike, so 40W
per bike. Finding suitable bulbs in weatherproof enclosures won't be cheap,
Perhaps this will help? http://electricpedals.com/how-it-works /
At last, some more realistic figures! "An average human can maintain 40 to 50
watts for an hour or more ..." - a tad short on the previous 300W then! Oh yes,
the generators: "Recycled 250 watt electric-scooter motors work a treat ...".
Have you got a source for these ...?
] TECHNICAL SPECIFICATION FOR PEDAL POWERED LIGHTS
] - Motor - expect 0 to 80volts (the faster you pedal, the higher the voltage);
] can generate over 300watts.
Rubbish! No way can you expect an average person/bike to expend ½ hp
continuously (See above) As for 80V, I’d expect a 12V motor (under load) to
generate something more like 12V! You might also like to look into the H&S
aspects of generating anything above, I think, about 40V – bearing in mind
this is outside and almost certainly in wet/damp conditions!
] - If we want to store power, need a diode, DC/AC inverter and a battery
What is the inverter for? Assuming the generator voltage is matched to the
battery, a diode simply stops the battery attempting to drive the
motor/generator in the absence of physical energy (from the bike). If an AC
generator is used, it also rectifies the AC to produce DC to charge the battery
but note that this is a very simplified explanation though.
] - LED lights
I note that no specification is given for these! However, as the intention is
to use whatever is freely or cheaply available, this comes down to Hobson’s
choice, anyway ...
Environmental and physical constraints probably rule out any idea of building
anything with sufficient mechanical strength from component parts – which
also be extremely time consuming.
LEDs are intrinsically low voltage devices (2 – 3V typical) but care has to be
taken to limit the current through them or they can (and will!) instantly self-
Adapting available lights will depend on how they are designed to work in the
first place. Low voltage lights (intended to be driven from a ‘wall-wart’)
should be the easiest to match to the generator.
Mains driven strings might be a problem as it could be very difficult to sub-
divide them into lower voltage strings without causing considerable physical
damage. Each sub-string will then need to have its own current limiter added as
there is unlikely to be more than one in the original.
It may be easier to use a DC/AC inverter here to feed the string/s with 230V
AC. Note that most inverters are designed to work on 12V DC only. 24V and
12/24V types are available but less common. This has a bearing on the choice of
Provided thick low voltage cables are used to minimise energy loss, inverters
could be mounted high up out of reach (for safety purposes).
* Alternator alternative
If a suitable automotive expert is available, how about using a car alternator,
rather than a DC generator. A scrap car can supply a complete
alternator/regulator/battery set-up. (Virtually any old car battery should do
most get replaced because they can’t start a car but are still good enough for
the current purpose – if you’ll pardon the pun ...)
As an alternator, as its name suggests, generates AC, rather than DC, which
would ease the problem of producing a range of voltages, if required, using
] NECESSARY RESOURCES - (I've deleted this section except for one paragraph I
* Protective earth. Even a small DC generator can generate some nasty peak
voltages if inadvertently run unloaded. Overall, we’re looking at a fair bit
power here, so a PE may be mandatory, even if everything is kept to 12V. Can be
a bit awkward on a large paved area. Would the council let you lift one of the
paving slabs ...?
] The aim is that they should be free, with materials obtained through
] Freecycle or donations.
] Paul Allen says there may be a small cost. LED light strings cost c. £10 for
Exercise bike, either find one that the owner's bored with or through
freecycle, longish v-belt from a local supplier, (Probably FOC if you
out a plate on saying "Some parts supplied by...."), car dynamo and
regulator (Not an alternator) from a scrappie, a couple of pulleys and
an old car battery. If labour's free, you could even modfiy an old
pushbike without too much trouble. You'll need a roof of some sort to
keep the rain (And, hopefully, snow, if we get a White Christmas) off
the pedaller (And, incidentally, the delicate bits), too.
Protective earth via a spike made from a length of 6mm threaded rod
between a couple of slabs, as they're mostly just laid on a sand bed in
pedestrian areas. The hardest thing is going to be fastening it all down
so it doesn't "walk". Even that could be done with a couple of Fischer
fixings into a 2 metre by 1.2 metre by 100mm thick slab just laid on the
floor. You'd need to borrow a lorry with a Hiab or equivalent to
position the slab. Again, a "sponsored by" plate nay get it FOC.
The freecycle pushbike (rear tyre removed to use as a pulley) is already in the
plan. Interested that you prefer a dynamo to an alternator. Any particular
reason? I thought dynamos had been out of favour for so long that it would be
difficult to find one these days - how old does the scrappie have to be?
I like the slab anchor idea!
I bought a brand new dynamo and regulator ex-stock at my local Lucas
agent for my Land Rover last year for under fifty quid, no exchange
needed. Or speak to a scrappie that deals with old Land Rovers or Army
vehicles. Some of them have 24 Volt dynamos fitted, so you have a choice
I suggested a dynamo as they are self exciting, so will charge a totally
flat battery, and don't *need* the same warning light and associated
switchery as car alternators do. Just get on and pedal....
It's also easy to adjust the maximum current output to match the likely
energy levels of the participants and protect the mechanical bits from
K.I.S.S. You could also potentially just crane the lot away afterwards
and store it somewhere for next year as a unit.
1) Nick a Boris Bike (they have the genny built in);
2) Jack it so back wheel off the road;
3) Add one tree hugger;
4) Hang PV FIT contract exactly 3ft in front of treehugger's nose;
5) When treehugger expires, replace and start at 4)
Oops - not really in the spirit of Xmas???
But I'd pay to see it on youtube!
Nearer 200W for a few hours.
Have a look at this near the bottom of the page, two of these bikes ran the
sound system all night, The rear wheel jacked up and the tyre driving the
250W electric scooter motor into 2 one farad capacitors with a green led
indicating how hard to pedal. Even I maintained a constant 100W.
BTW if anyone comes across the horsebox with its hand made kitchen let the
girls know as it was stolen in July. With it went some bright leds donated
by a pv sceptic on this group and I suspect my panaflow fans ( where can I
get these now Dorothy Bradbury seems to have stopped trading?).
If you mean 10W halogen bulbs, possibly though, in the example quoted, the
number worked out to 4 per generator.
However, the stated intention is to use LEDs which increases the numbers
If the performance of the 7 LEDs in my 3 x AAA cell torch is anything to go by,
that would be very considerably ...
Of course, there is a vast variety available and it all depends on what LEDs
can be sourced in suitable physical form ...
Yes there was a bit on the telly last Christmas of where a group of
cyclists tried to power an average family home for the day, seemed it
needed some 60 or more of them to run an electric kettle;!..
I remember in the science museum downstairs in the domestic section
there is a handle to crank and light up a 30 watt IIRC bulb and thats
bloody hard work for any length of time;!...
I remmebr that I thought it was 80 cyclists when the pout the otaster
on too i.e breakfast time.
True the thing is that this energy isn;t free, people tend to forget
that, if you have these cyslists cycling
they need food water to enable them to continue and with the price of
food nowadays well........
Why can't we run off politicians hot air or lies, surely those sources
would be truely endless ;-)
Hardly relevant unless you've got a way of attracting the world's top cyclists
to the local High Street to keep the illuminations going!
"Armstrong can ride up the mountains in France generating about 500 watts of
power for 20 minutes ..."
Hardly relates to Christmas shoppers and enthusiastic children, does it?
"...something a typical 25-year-old could do for only 30 seconds ..."
So, brilliant lighting for 30 seconds - then nothing. It's a bit like a
firework display with one firework - momentarily brilliant but disappointing
A casual look around would indicate that you are correct..
an electric bike with a 250 watt motor will run at about 10-15 mph, a top
cyclist would be able to manage more than that indicating that they generate
around 400+ watts.
I doubt if I could manage 250 watts for an hour though and I doubt if there
are any cycle dynamos that generate more than about 20 watts.
i wonder how much power they generate on the hill sections of that toure in
France (or was it Germany?).
Almost all are nominally 2.4W for front light only, or 3W for front and rear,
but the hub dynamos are actually roughly constant current devices which will
deliver 6W at reasonable cycling speeds if you give them twice the load.
There are secondary dynamo lights designed to be switched in at speed
(with the switch shorting across them when not used), but there's less
point with modern LED lights.
On 16 Aug 2011 18:43:42 +0100 (BST), Alan Braggins wrote:
All of mine are 3W, usually run as 2.4W and O.6W, and most are modded
systems to have LED rear and 3W front.
My only hub dynamo was a Sturmey-Archer, built back-to-back with a hub brake
and with a Campag. rear QR axle all in the front wheel of a trike. Bloody
good light front and rear!
Modern hub dynos are much better.
My Father had a Miller 12V dynamo on his tandem in the late '30s - cars used
to pull in and stop as their headlights just weren't competitive!
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