Small 12V low RPM generator

[Brian Wood]

Learned ones:
I posted this request to another (non-usenet) forum and was referred to you
by a friend in that forum.
I did also cross-post this in alt.energy.homepower, at his suggestion. When
I posted there, I discovered that I am using a usenet account established by
my nephew several years ago. The account is his name (Brian Wood); my name
is Dennis McKim and I live in western Colorado. Sorry for any confusion that
causes...

It is difficult to present my current 'daydream' in a reasonably short post,
but allow me to try: I plan to purchase a recumbent tadpole-design tricycle
(see www.catrike.com/road.htm for photos). "Chain management" is often an
issue for recumbent trikes, and idler pulleys are often used to control the
chain as it passes under the seat. I enjoy riding before sunrise and after
sundown, and will need reasonably powerful lights on my trike. I plan to
install a 14.8 volt Li-Ion battery pack, with a (nominal) 12 V lighting
system (HID or multi-LED headlamp and tail lamp, and a 360° amber strobe
light mounted on a pole behind the seat).
I wish to consider a small 12 V generator driven by a toothed idler pulley,
mounted low behind the seat. It will serve for chain management and power
generation. My front chainring will be 32-tooth and the rear gearing will be
an internal hub, so the chain velocity will be constant (no rear
derailleur). My normal pedaling cadence is 80 RPM, so the 16-tooth idler
pulley will be driven at ~160 RPM. I need an output of only 3-4 amperes, and
might get by with only 2-3 amps. I don't need to power all of my lighting
exclusively from the generator; I need to keep the battery charged and then
extend its run-down time after dark when I turn on all the lights.
*****
Is it feasible to try to construct a generator, using rare-earth magnets and
copper wire, that will generate 15-18 volts, and have a package something
close to the size of a can of soda pop (2-2½" diameter, 4-5" long)?
*****
My research to date finds many designs for homemade generators, but all of
them are large diameter (6-10 inches). That is great for wind turbine
projects but not suitable for my dream. I've heard of using brushless DC
motors as generators, but all that I can find operate at very high RPM.
There are dynamo hubs available for bicycles, but they all generate 6 volts
and I am committed to a 12 V system. There are "bottle type" generators for
bicycles that drive against the lateral surface of the rubber tire, but I am
(at least for now) set on designing something driven from an idler pulley.
What do y'all think? Totally feasible? Impossible? Somewhere in between?
Just to keep the discussion on track, please understand that I am also
investigating the options of solar power to charge the battery, and of using
a larger battery and "home-charging" it. My purpose for posting here is only
to inquire about the technical feasibility of constructing a (very) small
12V generator being spun at only 160 RPM.
Thanks in advance,
Dennis

 

[Phil Scott]

Learned ones:
I posted this request to another (non-usenet) forum and was
referred to you
by a friend in that forum.
I did also cross-post this in alt.energy.homepower, at his
suggestion. When
I posted there, I discovered that I am using a usenet
account established by
my nephew several years ago. The account is his name (Brian
Wood); my name
is Dennis McKim and I live in western Colorado. Sorry for
any confusion that
causes...

It is difficult to present my current 'daydream' in a
reasonably short post,
but allow me to try: I plan to purchase a recumbent
tadpole-design tricycle
(see www.catrike.com/road.htm for photos). "Chain
management" is often an
issue for recumbent trikes, and idler pulleys are often used
to control the
chain as it passes under the seat. I enjoy riding before
sunrise and after
sundown, and will need reasonably powerful lights on my
trike. I plan to
install a 14.8 volt Li-Ion battery pack, with a (nominal) 12
V lighting
system (HID or multi-LED headlamp and tail lamp, and a 360°
amber strobe
light mounted on a pole behind the seat).
I wish to consider a small 12 V generator driven by a
toothed idler pulley,
mounted low behind the seat. It will serve for chain
management and power
generation. My front chainring will be 32-tooth and the rear
gearing will be
an internal hub, so the chain velocity will be constant (no
rear
derailleur). My normal pedaling cadence is 80 RPM, so the
16-tooth idler
pulley will be driven at ~160 RPM. I need an output of only
3-4 amperes, and
might get by with only 2-3 amps. I don't need to power all
of my lighting
exclusively from the generator; I need to keep the battery
charged and then
extend its run-down time after dark when I turn on all the
lights.
*****
Is it feasible to try to construct a generator, using
rare-earth magnets and
copper wire,

No...

purchase the item that will be cheapest. and since its DC
variable RPM is not a significant issue as far as battery
charging is concerned.. as long as the generator is large
enough... a bike shop will have a good selection.

Phil Scott




that will generate 15-18 volts, and have a package something

 

[Brian Wood]

No...
purchase the item that will be cheapest. and since its DC
variable RPM is not a significant issue as far as battery
charging is concerned.. as long as the generator is large
enough... a bike shop will have a good selection.

Thanks for replying. Alas, the 12V bicycle generators I have seen for sale
only produce ¼ - ½ amp (3-6 watts).
I'll keep searching, though.
Thanks again,
Dennis

 

[Phil Scott]

Thanks for replying. Alas, the 12V bicycle generators I have
seen for sale
only produce ¼ - ½ amp (3-6 watts).\

sounds like you want more like 20 watts..with a halogen
bulb, narrow spectrum as with some motorcycles thats a lot of
illumination.

The combination of the right halogen lighting and several of
these small generators might do it.. rolling yer own in this
area is of course possible but time and money make it
impractical imho. when you can adapt other options.

IF the voltage is too low, say 6 volts when you want 18 you
can series wind these probably,

with slot cars we used to send the motors out and have the 4
pole motors rewound to two pole motors to get twice the
speed... there will be someone who will rewind a bicycle
generator for you somewhere in the world...that wouldnt be
expensive.

 

[Brian Wood]

several of these small generators might do it..

That may be a viable option, especially if I find the need for more than one
idler pulley for chain management. Thanks very much for the idea.
Regards,
Dennis

 

[Phil Scott]

That may be a viable option, especially if I find the need
for more than one
idler pulley for chain management. Thanks very much for the
idea.
Regards,
Dennis

bzzzzzzzzzzzzzztttt. the idler pulley is a bad idea as it
spins yer mini gen too slowly, you would need a very large gen
to make the juice you need going that slow.

the cheapies that ride on the side of the tire would be
spinning perhaps 1,000 rpm..(a direct ratio of the
circumference of the tire and the circumference of the gen
driver wheel thingie. probably at least 100 to 1...

you dont get that leverage with your idler sprocket set up...
you are a man looking for complexity where none exists... then
arriving at non solutions when actual solutions abound.


Phil Scott

 

[TimPerry]

That may be a viable option, especially if I find the need for more than one
idler pulley for chain management. Thanks very much for the idea.
Regards,
Dennis

here is one kit with headlight and tail light
http://sportsbay.com/genligset.html

here is one that is built into the hub
http://www.peterwhitecycles.com/Schmidt-Lumotec.asp

if it was me i'd use a 6 or 12 volt gel cell and not bother with the
generator (if somone forced me to ride a bike at night) and use lots of
reflector strips.

 

[Brian Wood]

here is one kit with headlight and tail light
http://sportsbay.com/genligset.html
here is one that is built into the hub
http://www.peterwhitecycles.com/Schmidt-Lumotec.asp

Thanks. Unfortunately, both of those are 6V systems, and also have
insufficient lighting power for my needs. Thanks for checking them, though.

Regards,
Dennis

 

[Phil Scott]

Thanks. Unfortunately, both of those are 6V systems, and
also have
insufficient lighting power for my needs. Thanks for
checking them, though.

errrr Dennis... the voltage, 6 or 12v is irrelevant ..my
guess is that your notion of what you need in total wattage is
similarly founded.

whats relevant is what is the most practical in the
situation... if you want more light than what the kits
provide... fit more of them.. nothing complex about that, nor
expensive... you are creating problems for yourself.,,, unless
you are trying to learn something...in that case there are
books on these issues and kits you can buy or instructions to
build whatever you want... it wont be cost effective though as
far as the job is concerned.

 

[Brian Wood]

errrr Dennis... the voltage, 6 or 12v is irrelevant ..my
guess is that your notion of what you need in total wattage is
similarly founded.

You misunderstood my statement. Those are two independent clauses:
1. Both of those are 6V systems, and
2. They both have insufficient lighting power for my needs.

I am aware of the difference between (and the relationships among) voltage,
current, power and work.

Thanks,

Dennis

 

[Phil Scott]

You misunderstood my statement. Those are two independent
clauses:
1. Both of those are 6V systems, and
2. They both have insufficient lighting power for my needs.

We have to say goodby now Bob.... I will leave you with the
notion of applying two or three such systems in parallel to
reach the net wattage you want. You have been ignoring that
remark..

Thats impolite from someone asking for advice.

your earlier remarks about how it has to be a 12v system are
likewise loopy... any of those voltages can be stepped up
or down etc.

I am aware of the difference between (and the relationships
among) voltage,
current, power and work.

Not impressive then to be asking such a range of less
competent questions.... in the past I have found in cases like
yours the guy has invented a dynamo for his washing machine
that will power the entire western world and is fishing around
to see if 'anyone else thought of it'... these types have
obtuse requirements, and while tossing terms around
demonstrate no clue on the basics.

 

[Dean Hoffman]

Learned ones:
I posted this request to another (non-usenet) forum and was referred to you
by a friend in that forum.
I did also cross-post this in alt.energy.homepower, at his suggestion. When
I posted there, I discovered that I am using a usenet account established by
my nephew several years ago. The account is his name (Brian Wood); my name
is Dennis McKim and I live in western Colorado. Sorry for any confusion that
causes...

It is difficult to present my current 'daydream' in a reasonably short post,
but allow me to try: I plan to purchase a recumbent tadpole-design tricycle
(see www.catrike.com/road.htm for photos). "Chain management" is often an
issue for recumbent trikes, and idler pulleys are often used to control the
chain as it passes under the seat. I enjoy riding before sunrise and after
sundown, and will need reasonably powerful lights on my trike. I plan to
install a 14.8 volt Li-Ion battery pack, with a (nominal) 12 V lighting
system (HID or multi-LED headlamp and tail lamp, and a 360° amber strobe
light mounted on a pole behind the seat).

Not what you asked about but something like this might be an
alternative:
http://www.webbikeworld.com/r3/safety-vest/

Dean

 

[TimPerry]

Thanks. Unfortunately, both of those are 6V systems, and also have
insufficient lighting power for my needs. Thanks for checking them, though.

Regards,
Dennis

wouldnt a recliner have at least 2 hubs? two 6V gens in series is 12 V. 3
units will be 18 V

at 6W / 12V = .5 A

this would be sutable for charging a battery of about 5 AH (5000 mAH)