CygoLite Rover II light coupled to a roller dynamo?

[Sir Ridesalot]

Hi there.

Been following with interest the dynamo roller slippage thread.

I have a CygoLite Rover II system and I like the light it throws onto
the road. I'll be doing some longer tours this year and will most
likely be doing a fair bit of night riding on them. The only problem I
have with the Rover II is the 6 to 8 hours recharge time. he shop I
bought the light from said they'd get me the quick-charger for it but
I haven't seen it yet since I bought the light a few years ago now.

Therefore I seem to have three main options if I want to use the
CygoLite Rover II system on a week to two weeks tour.

Option 1. Buy an extra battery or two of the same 4.8 volts but with
higher amp hours.
Option 2. Get a used Soubitez or Sony roller dynamo and run the light
off of that whilst riding and keep the battery for backupor when
stopped.
Otion 3. Buy a Quick-Charger that's compatible with that lights
battery and charge the battery at a coffee shop or other stop along
the way.

I like Option 2 the best but wonder if it will require a lot of work
to adapt the light to run on a roller dynamo. I am not electricity
literate as I haven't studied the subject since high school. The
CygoLite Quick-Charger for the Rover II recharges a fully drained
battery in 2.5 hours. That's a long time to be sitting in a coffee
shop or other place during daylight hours on a multi-day tour just to
recharge the battery.

What would I need to do to use a Sanyo or Soubitez roller dynamo to
run my CygoLite Rover II headlight? If I recall correctly both of
those dynamos put out 6 volts. So I guess that means that I'd need a
1.2 volt resistor in the system somewhere. Is tht correct?

All perinent advice to this topic is immensely appreciated.

Thanks and cheers

[James]

If you want the simplest solution, carry a spare battery.

If you want a dynamo solution, don't carry any batteries and use a
light designed for use with a dynamo.

If you really want to use the existing light with a dynamo, it would
be nice to be able to drop the battery completely, effectively
replacing the battery with a dynamo. This would be possible by
building or buying a small power supply that can convert the 6V AC
output from the dynamo to the required 4.8 V DC that powers the light
- assuming the LED driver is in the light. This would be a little
wasteful of energy, as electrical voltage converters are normally only
about 90% efficient, and you'll end up with two in series.

--
JS.

[Frank Krygowski]

The electrical theory is a bit more complicated. First, although
almost all dynamos are rated 6V 3W, that's an oversimplification
that's approximately valid only when they're fitted with the load
(i.e. bulbs) for which they were designed. It's more accurate to say
they put out half an Amp. The physics of the design causes it to
automatically adjust the voltage to whatever value is needed to push
out half an amp.

Second, a resistor's characteristic property (called "resistance"_) is
measured in Ohms, not Volts. The number of volts you'd drop through a
resistor depends on its rating in Ohms, but also on the amount of
current measured in Amps. So that part is a bit more complicated.
Look up "Ohm's Law," which is a very simple equation, to see how the
variables tie together.

Now about the practicalities: I don't know much about the design of
the light you're using. But there's a (small?) chance you could get
by much more simply. If the light naturally drew about half an amp
out of the battery, you could expect the dynamo to put about half an
amp into the battery, and you might be done. But a bike dynamo puts
out AC, while the battery both produces DC, and needs DC for
charging. So you need a full-wave rectifier, which costs maybe $3
from Radio Shack.

For a little more explanation, see Sheldon's explanation of his
system, at
http://sheldonbrown.com/dynohubs.html It's mostly correct. He was
talking about antique Sturmey-Archer Dynohubs but it applies to almost
any dynamo.

Here's a partial quote of the pertinent part:
"I used to have a Dynohub on a tandem, and the bulb consumption was
unacceptable. I solved the problem (and some others) by running the
Dyno's output through a full-wave bridge rectifier and then hooking
the DC in parallel with a 6 volt (5 x 1.2v cell) nickel cadmium
battery. This not only provided light when I was stopped, the Dyno
would re-charge the nicads, and, when we went so fast that the voltage
rose above 6 volts, the low internal resistance of the nicads sucked
up the excess, gaining a bit of extra charge and saving the bulb.

"The rectified output of the Dynohub was always connected to the
lights. There was no way to turn the light off while you were in
motion. It would have been easy enough to rig a switch for that
purpose, but I didn't see the need. The Dynohub has _very_ low drag.

"I had a three way switch connecting the battery pack to the lights.
In the "night" position, the nicads were in parallel with the
rectified output of the Dynohub, as described above..."

But I think you'll find your headlight draws more current than half an
amp. If so, engaging the dynamo/rectifier system might extend running
time, but not make it infinite, as with a proper generator system.
There may be ways around that (e.g. reducing current to the headlamp)
but I suspect that's more than you'd want to attempt.

If the battery is a Ni-Cad or lead acid, I wouldn't worry about the
difference between the supposed 6V dynamo output and the 4.8V of the
battery. To charge a battery, you need a bit of excess voltage. But
if it's lithium or Ni-MH, I think recharging needs more
sophistication. Look up accounts of laptop batteries catching fire.
(I've never seen a bicycle fire, but you wouldn't want to be the
first!)

Those are initial thoughts. If you could post more technical details
on your lights, we could probably give further advice. How many watts
do they claim? What's the amp-hour capacity of the stock battery?
How many hours does the battery actually last? What chemistry is it?
Oh, and how much do you want to learn about working with electricity?

It would be simpler just to buy a good dynamo and headlight. But the
tinkering and the challenge can be fun.

- Frank Krygowski

[somebody]

On Fri, 6 Apr 2012 17:32:35 -0700 (PDT), Sir Ridesalot
<i_am_cyc...@yahoo.ca> wrote:

>Hi there.
>
>Been following with interest the dynamo roller slippage thread.
>
>I have a CygoLite Rover II system and I like the light it throws onto
>the road. I'll be doing some longer tours this year and will most
>likely be doing a fair bit of night riding on them. The only problem I
>have with the Rover II is the 6 to 8 hours recharge time. he shop I
>bought the light from said they'd get me the quick-charger for it but
>I haven't seen it yet since I bought the light a few years ago now.
>
>Therefore I seem to have three main options if I want to use the
>CygoLite Rover II system on a week to two weeks tour.
>
>Option 1. Buy an extra battery or two of the same 4.8 volts but with
>higher amp hours.
>Option 2. Get a used Soubitez or Sony roller dynamo and run the light
>off of that whilst riding and keep the battery for backupor when
>stopped.

I would go with the dynamo with a blocking diode (so it doesn't turn
into a motor when you are going slow) and a series resistor. Pick the
resistor to limit current to maximum safe charge rate when going fast.

Or get that second/third battery, parallel it with the first and then
use the dynamo. It can handle 2x or 3x the charging current. And you
get much longer run time.

[Sir Ridesalot]

On Apr 6, 8:32 pm, Sir Ridesalot <i_am_cycle_pat...@yahoo.ca> wrote:

Hi there.

Thanks for all the replies.

I guess I wasn't clear enough in my original post.

I want the roller dynamo to *ONLY* power the light. I will not have
any battery or batteries wired into the circuit. If I need the light
off the bike I'll disconectthe dynamo wire from the light and then
attach the battery to the light. I have a headband that the light can
be mounted to. SO again all I want is to be able to run the light from
a roller dynamo. \There are no batteries planned to be used with the
dynamo.

Thanks again and cheers

[Frank Krygowski]

On Apr 7, 6:27 pm, Sir Ridesalot <i_am_cycle_pat...@yahoo.ca> wrote:
>
> Hi there.
>

> Thanks for all the replies.
>
> I guess I wasn't clear enough in my original post.
>
> I want the roller dynamo to *ONLY* power the light. I will not have
> any battery or batteries wired into the circuit. If I need the light
> off the bike I'll disconectthe dynamo wire from the light and then
> attach the battery to the light. I have a headband that the light can
> be mounted to. SO again all I want is to be able to run the light from
> a roller dynamo. \There are no batteries planned to be used with the
> dynamo.
>
> Thanks again and cheers

OK, but we'd still need more technical information to tell you what
would likely be possible. But here's my guess: I think it's likely
that the number of Amps drawn by the headlamp is more than what the
dynamo will be able to produce. But there's a chance the lamp might
still be adequate for your use with just the half Amp output of a bike
generator. (LEDs are less sensitive to a drop in current than are
filament bulbs.)

How about trying this? Get yourself a full-wave rectifier from Radio
Shack:
http://www.radioshack.com/product/index.jsp?productId=12673815 You
should probably look for a plug connector to match the one that
connects to your headlamp, too. And some insulated wire, preferably
two conductor. Lamp cord or speaker wire works well.

Scrounge yourself a bike generator or dynamo. It doesn't have to be a
roller type; they all have pretty much the same electrical
characteristics. They're not easy to find, but I've gotten them cheap
at K-mart, used off junk bikes, in old stock bins at bike shops that
keep old parts, etc. Just make sure it (like almost all) is rated 6
Volts, 3 Watts.

The generator needs two wires. One goes to its obvious output
terminal. The other wire has to electrically connect to the metal
body, even if you just hold it in place. Connect those two wires to
the two inside pins of that rectifier. It doesn't matter which is
which. Just carefully wrap them around the pins, with each touching
only the intended pin.

The outer pins of the rectifier are marked plus and minus. Use wire
to connect those directly to your headlight, just temporarily, using
the matching connector plug. Polarity matters here, so if you can
tell what's positive out of your battery, wire the positive output of
the rectifier to match what the battery does. If you can't tell,
you'll have to do very careful trial and error.

Put your bike in a workstand, have someone turn the cranks to _slowly_
spin the rear wheel. Hold the generator to the rear tire to get it
spinning slowly. See if you get any light. If you don't get at least
some dim light, you may have plus and minus wrong between the
rectifier and headlight. Try it the other way.

If you do get some light, then your polarity is OK. Crank the rear
wheel up to speed and see what the headlight looks like. If it's
bright enough, you're good. Get a better generator (if necessary) and
learn how to solder and to use heat shrink tubing (to insulate
connections). Make your setup permanent.

Let us know how it goes.

- Frank Krygowski

[James]

You need to at least rectify the AC output from the dynamo with a full
wave bridge rectifier and employ some filter capacitors to reduce
ripple. Several hundred microfarads as electrolytic caps I should think.

Assuming the light has a DC-DC converter that regulates the current to
the LED, it is possible that you could then just connect the output of
the rectifier filter capacitors to the input of the light, replacing the
battery.

This assumes the input to the light can cope with more voltage than the
battery supplied, and if it is a switch mode DC-DC converter, it is
quite possible that it can. But without detailed knowledge of the light
circuitry, I couldn't tell you either way.

If it can't you'd need a DC-DC converter after the bridge rectifier and
filter caps to produce a regulated 4.8V output to replace the battery.

If you can take the light assembly apart and look to see if it has some
components that look like capacitors and at least one small coil, it is
likely a switch mode current controlled DC-DC converter driving the LED.

--
JS.

[Frank Krygowski]

I've wondered if a switch mode DC-DC converter can cope with the
inductance in a bike dynamo.


--
- Frank Krygowski

[James]

Another good reason for big electrolytic caps after the bridge rectifier.

Oh, a bridge rectifier makes a really good noise source. If yours or
your friends wireless sensors act up, you might need some more
sophisticated circuitry.

My mates Polar computer acted up the last couple of evenings only when
his front LED light was in flash mode.

--
JS

[SMS]

On 4/7/2012 3:27 PM, Sir Ridesalot wrote:

> I guess I wasn't clear enough in my original post.
>
> I want the roller dynamo to *ONLY* power the light. I will not have
> any battery or batteries wired into the circuit. If I need the light
> off the bike I'll disconectthe dynamo wire from the light and then
> attach the battery to the light. I have a headband that the light can
> be mounted to. SO again all I want is to be able to run the light from
> a roller dynamo. \There are no batteries planned to be used with the
> dynamo.

Rectify (bridge rectifier) and filter (1000 uF 16V electrolytic cap) the
output of the dynamo and feed it into this module:
<http://www.dealextreme.com/p/vmp3201-5v-high-efficiency-dc-dc-module-47813>.
The 5V output of the module will power the light.

You don't want to just use resistors or a linear regulator to drop the
voltage as this is wasteful. You don't want to feed the ~9VDC output
from the bridge rectifier directly into the Rover. It might be okay, it
might not. It depends on what kind of circuitry is inside the light housing.

Personally, I wouldn't do this. I'd get an Cree LED MR16 lamp or
<http://www.dealextreme.com/p/3w-3-led-270-lumen-waterproof-flood-light-projection-warm-white-lamp-12v-47572>
and connect it directly to the output of the dynamo. See
<http://nordicgroup.us/s78/mr16LED.htm>.

[SMS]

There are some cheap DC-DC modules that put out 5V which is close enough.

<http://www.dealextreme.com/p/vmp3201-5v-high-efficiency-dc-dc-module-47813>.
Much easier than cobbling together a switching regulator circuit yourself!

> If you can take the light assembly apart and look to see if it has some
> components that look like capacitors and at least one small coil, it is
> likely a switch mode current controlled DC-DC converter driving the LED.

I would suspect that this is the case, but I wonder what the maximum
input voltage of the circuit is. With a 4.8V pack they might not have
designed it for an input voltage of 9V or so (1.414 * the output voltage
of the dynamo).

[James]

On 12/04/12 08:54, SMS wrote:
> On 4/7/2012 3:27 PM, Sir Ridesalot wrote:
>
>> I guess I wasn't clear enough in my original post.
>>
>> I want the roller dynamo to *ONLY* power the light. I will not have
>> any battery or batteries wired into the circuit. If I need the light
>> off the bike I'll disconectthe dynamo wire from the light and then
>> attach the battery to the light. I have a headband that the light can
>> be mounted to. SO again all I want is to be able to run the light from
>> a roller dynamo. \There are no batteries planned to be used with the
>> dynamo.
>
> Rectify (bridge rectifier) and filter (1000 uF 16V electrolytic cap) the
> output of the dynamo and feed it into this module:
> <http://www.dealextreme.com/p/vmp3201-5v-high-efficiency-dc-dc-module-47813>.
> The 5V output of the module will power the light.

Unloaded (light off) the dynamo voltage may be more than 16V, I would
imagine.

There may be need for some disconnect if the light is off, or voltage
clamp, to save the caps.

--
JS

[SMS]

I didn't think it got up past about 12-13 VDC. But 25V caps might be safer.

[James]

Why don't you test it? AC volt meter and no load connected. If you
don't, I can this weekend. I'm busy the next 2 nights.

--
JS.

[James]

On 12/04/12 09:37, SMS wrote:

One website I read claims up to 100V open circuit even at reasonably low
speed.

http://www.ktverkko.fi/~msmakela/electronics/dynamo5v/

"I connected the input to a SON dynamo hub and measured the output. When
I rotated the wheel by hand (approximately 15 km/h), the unloaded output
reached almost 100 volts."

The open circuit voltage will be limited by the riders speed.

e = -N * d[phi] / dt

the d phi / dt bit is proportional to speed.

See http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

--
JS.