<s>
A	O
bottle	B-Algorithm
dynamo	I-Algorithm
or	O
sidewall	B-Algorithm
dynamo	I-Algorithm
is	O
a	O
small	O
electrical	O
generator	O
for	O
bicycles	O
employed	O
to	O
power	O
a	O
bicycle	O
's	O
lights	O
.	O
</s>
<s>
The	O
traditional	O
bottle	B-Algorithm
dynamo	I-Algorithm
(	O
pictured	O
)	O
is	O
not	O
actually	O
a	O
dynamo	B-Language
at	O
all	O
(	O
which	O
creates	O
DC	O
power	O
)	O
,	O
but	O
a	O
low-power	O
magneto	B-Algorithm
that	O
generates	O
AC	O
.	O
</s>
<s>
Newer	O
models	O
can	O
include	O
a	O
rectifier	B-Algorithm
to	O
create	O
DC	O
output	O
to	O
charge	O
batteries	O
for	O
electronic	O
devices	O
including	O
cellphones	O
or	O
GPS	O
receivers	O
.	O
</s>
<s>
Named	O
after	O
their	O
resemblance	O
to	O
bottles	O
,	O
these	O
generators	O
are	O
also	O
called	O
sidewall	B-Algorithm
dynamos	I-Algorithm
because	O
they	O
operate	O
using	O
a	O
roller	O
placed	O
on	O
the	O
sidewall	O
of	O
a	O
bicycle	O
tire	O
.	O
</s>
<s>
When	O
the	O
bicycle	O
is	O
in	O
motion	O
and	O
the	O
dynamo	B-Language
roller	O
is	O
engaged	O
,	O
electricity	O
is	O
generated	O
as	O
the	O
tire	O
spins	O
the	O
roller	O
.	O
</s>
<s>
Two	O
other	O
dynamo	B-Language
systems	O
used	O
on	O
bicycles	O
are	O
hub	O
dynamos	B-Language
and	O
bottom	O
bracket	O
dynamos	B-Language
.	O
</s>
<s>
No	O
extra	O
resistance	O
when	O
disengaged	O
When	O
engaged	O
,	O
a	O
dynamo	B-Language
requires	O
the	O
bicycle	O
rider	O
to	O
exert	O
more	O
effort	O
to	O
maintain	O
a	O
given	O
speed	O
than	O
would	O
otherwise	O
be	O
necessary	O
when	O
the	O
dynamo	B-Language
is	O
not	O
present	O
or	O
disengaged	O
.	O
</s>
<s>
Bottle	B-Algorithm
dynamos	I-Algorithm
can	O
be	O
completely	O
disengaged	O
when	O
they	O
are	O
not	O
in	O
use	O
,	O
whereas	O
a	O
hub	O
dynamo	B-Language
will	O
always	O
have	O
added	O
drag	O
(	O
though	O
it	O
may	O
be	O
so	O
low	O
as	O
to	O
be	O
irrelevant	O
or	O
unnoticeable	O
to	O
the	O
rider	O
,	O
and	O
it	O
is	O
reduced	O
significantly	O
when	O
lights	O
are	O
not	O
being	O
powered	O
by	O
the	O
hub	O
)	O
.	O
</s>
<s>
Easy	O
retrofitting	O
A	O
bottle	B-Algorithm
dynamo	I-Algorithm
may	O
be	O
more	O
feasible	O
than	O
a	O
hub	O
dynamo	B-Language
to	O
add	O
to	O
an	O
existing	O
bicycle	O
,	O
as	O
it	O
does	O
not	O
require	O
a	O
replacement	O
or	O
rebuilt	O
wheel	O
.	O
</s>
<s>
Price	O
A	O
bottle	B-Algorithm
dynamo	I-Algorithm
is	O
generally	O
cheaper	O
than	O
a	O
hub	O
dynamo	B-Language
,	O
but	O
not	O
always	O
.	O
</s>
<s>
Slippage	O
In	O
wet	O
conditions	O
,	O
the	O
roller	O
on	O
a	O
bottle	B-Algorithm
dynamo	I-Algorithm
can	O
slip	O
against	O
the	O
surface	O
of	O
a	O
tire	O
,	O
which	O
interrupts	O
or	O
reduces	O
the	O
amount	O
of	O
electricity	O
generated	O
.	O
</s>
<s>
Hub	O
dynamos	B-Language
do	O
not	O
need	O
traction	O
and	O
are	O
sealed	O
from	O
the	O
elements	O
.	O
</s>
<s>
Increased	O
resistance	O
Bottle	B-Algorithm
dynamos	I-Algorithm
typically	O
create	O
more	O
drag	O
than	O
hub	O
dynamos	B-Language
.	O
</s>
<s>
However	O
,	O
when	O
they	O
are	O
properly	O
adjusted	O
,	O
the	O
drag	O
may	O
be	O
so	O
low	O
as	O
to	O
be	O
trivial	O
,	O
and	O
there	O
is	O
no	O
resistance	O
when	O
the	O
bottle	B-Algorithm
dynamo	I-Algorithm
is	O
disengaged	O
.	O
</s>
<s>
Tire	O
wear	O
Because	O
bottle	B-Algorithm
dynamos	I-Algorithm
rub	O
against	O
the	O
sidewall	O
of	O
a	O
tire	O
to	O
generate	O
electricity	O
,	O
they	O
cause	O
added	O
wear	O
on	O
the	O
side	O
of	O
tire	O
.	O
</s>
<s>
Hub	O
dynamos	B-Language
do	O
not	O
.	O
</s>
<s>
Noise	O
Bottle	B-Algorithm
dynamos	I-Algorithm
make	O
an	O
easily	O
audible	O
mechanical	O
humming	O
or	O
whirring	O
sound	O
when	O
engaged	O
.	O
</s>
<s>
Hub	O
dynamos	B-Language
are	O
silent	O
.	O
</s>
<s>
Switching	O
Bottle	B-Algorithm
dynamos	I-Algorithm
must	O
be	O
physically	O
repositioned	O
to	O
engage	O
them	O
,	O
to	O
turn	O
on	O
the	O
lamps	O
.	O
</s>
<s>
Hub	O
dynamos	B-Language
are	O
switched	O
on	O
electrically	O
.	O
</s>
<s>
Hub	O
dynamos	B-Language
can	O
be	O
engaged	O
automatically	O
by	O
using	O
electronic	O
ambient	O
light	O
detection	O
,	O
providing	O
zero-effort	O
activation	O
.	O
</s>
<s>
Positioning	O
Bottle	B-Algorithm
dynamos	I-Algorithm
must	O
be	O
carefully	O
adjusted	O
to	O
touch	O
the	O
sidewall	O
at	O
correct	O
angles	O
,	O
height	O
and	O
pressure	O
.	O
</s>
<s>
Bottle	B-Algorithm
dynamos	I-Algorithm
can	O
be	O
knocked	O
out	O
of	O
position	O
if	O
the	O
bike	O
falls	O
,	O
or	O
if	O
the	O
mounting	O
screws	O
are	O
too	O
loose	O
.	O
</s>
<s>
A	O
badly	O
positioned	O
bottle	B-Algorithm
dynamo	I-Algorithm
will	O
make	O
more	O
noise	O
and	O
drag	O
,	O
slip	O
more	O
easily	O
,	O
and	O
can	O
in	O
worst	O
case	O
fall	O
into	O
the	O
spokes	O
.	O
</s>
<s>
Some	O
dynamo	B-Language
mounts	O
have	O
tabs	O
to	O
try	O
to	O
prevent	O
the	O
latter	O
.	O
</s>
