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Bicycle dynamo circuit

N

nicknoxx

Jan 1, 1970
0
Hi All,

This is my first post to this group and my electronics are very rusty
having not been used since school some 30 years ago so I may have made
many errors.

This circuit
http://www.zen202900.zen.co.uk/bike/lights/Mk2/mk2.2.png
has been cobbled together from various sources so there may be
incompatibilities.
I'll try to describe it; comments and advice would be very welcome
especially as I'm not sure how some of the components will react to the
relatively unstable voltages produced by the dynamo. (Technically an
alternator as it produces AC but normally referred to as a dynamo)

There are four basic parts to the circuit:
1. A rectifier and smoothing capacitor
2. Dark detector to turn lights on. This can be overridden by switch 1:
Posn 1 - off
Posn 2 - detector
Posn 3 - On
3. A standlight which keeps one LED lit when stationary.
4. Momentary latch circuit to bypass three LEDs for when going slowly
(up-hill)

I sure you're aware that dynamos can be roughly considered as constant
current devices. Mine produces about 500mA without the booster caps C1 &
C2 but can go up to 1A. Designed to drive a 12 Ohm bulb so voltage is
quoted a 6v but will in fact rise to meet the Vf of the diode string
(plus any losses from other bits of the circuit) providing you're going
fast enough!

Specific thoughts:
C5 and it's resistor are there to stop car headlights turning my lights
off, are the values suitable?
Suggestions for specific parts, particularly mosfet and inverter chip
much appreciated
The LEDs are Cree XP-Gs which have a Vf of about 3.25v at 700mA so
maximum voltage reached should be about 13v

Any other comments ?

Thanks
 
R

Rich Grise

Jan 1, 1970
0
nicknoxx said:
C5 and it's resistor are there to stop car headlights turning my lights
off, are the values suitable?

I dunno, but you're supposed to be riding the bike the same direction as
the traffic (i.e. on the right-hand side in the USA), so headlights
shouldn't be a problem in the first place.

Good Luck!
Rich
 
J

John - KD5YI

Jan 1, 1970
0
I dunno, but you're supposed to be riding the bike the same direction as
the traffic (i.e. on the right-hand side in the USA), so headlights
shouldn't be a problem in the first place.

Good Luck!
Rich

Have you considered oncoming cars in the adjacent lane?

C'mon, Rich, I know you're smarter than that.

John
 
M

mike

Jan 1, 1970
0
nicknoxx said:
Hi All,

This is my first post to this group and my electronics are very rusty
having not been used since school some 30 years ago so I may have made
many errors.

This circuit
http://www.zen202900.zen.co.uk/bike/lights/Mk2/mk2.2.png
has been cobbled together from various sources so there may be
incompatibilities.
I'll try to describe it; comments and advice would be very welcome
especially as I'm not sure how some of the components will react to the
relatively unstable voltages produced by the dynamo. (Technically an
alternator as it produces AC but normally referred to as a dynamo)

There are four basic parts to the circuit:
1. A rectifier and smoothing capacitor
2. Dark detector to turn lights on. This can be overridden by switch 1:
Posn 1 - off
Posn 2 - detector
Posn 3 - On
3. A standlight which keeps one LED lit when stationary.
4. Momentary latch circuit to bypass three LEDs for when going slowly
(up-hill)

I sure you're aware that dynamos can be roughly considered as constant
current devices. Mine produces about 500mA without the booster caps C1 &
C2 but can go up to 1A. Designed to drive a 12 Ohm bulb so voltage is
quoted a 6v but will in fact rise to meet the Vf of the diode string
(plus any losses from other bits of the circuit) providing you're going
fast enough!

Specific thoughts:
C5 and it's resistor are there to stop car headlights turning my lights
off, are the values suitable?
Suggestions for specific parts, particularly mosfet and inverter chip
much appreciated
The LEDs are Cree XP-Gs which have a Vf of about 3.25v at 700mA so
maximum voltage reached should be about 13v

Any other comments ?

Thanks
Amazing how complicated things can get.
If my math is right, 6V 12 ohms is 3 watts.
3.25V x .7A is 2.275W x 4 = 9.1W
You sure you can get from here to there?
The cost/reward ratio of the photodetector is too high.
It's gonna be more grief than benefit.
Also think the light output from the supercaps will be too
dim or too short (depending on your choice of resistor) to be useful.
You don't just stop at an intersection. You slow gradually
and by the time you're stopped the caps are discharged...I think
the 1K is WAY too big to give useful light and your time constant
will be much shorter than you planned.

If it were me, I'd use a 18650 lithium cell, they come with built-in
protection if you're so inclined.
Use a microcontroller to skip cycles of the AC to keep the lithium
cell at a constant, safe voltage.
Make lighting decisions based on the frequency of the AC and set delays
for the various modes.
When you ride, the light comes on. When you stop, after some time
the light goes off.
Don't charge at low speed if that's your intention.
Many fewer parts, near constant intensity, infinite flexibility.

And if you don't already know how to program a microcontroller, you learn
a marketable skill in the process.
 
R

Rich Grise

Jan 1, 1970
0
John said:
Have you considered oncoming cars in the adjacent lane?

C'mon, Rich, I know you're smarter than that.
Headlights are supposed to be aimed such that they don't blind the
drivers in the opposite lane.

Thanks,
Rich
 
K

Kevin McMurtrie

Jan 1, 1970
0
nicknoxx said:
Hi All,

This is my first post to this group and my electronics are very rusty
having not been used since school some 30 years ago so I may have made
many errors.

This circuit
http://www.zen202900.zen.co.uk/bike/lights/Mk2/mk2.2.png
has been cobbled together from various sources so there may be
incompatibilities.
I'll try to describe it; comments and advice would be very welcome
especially as I'm not sure how some of the components will react to the
relatively unstable voltages produced by the dynamo. (Technically an
alternator as it produces AC but normally referred to as a dynamo)

There are four basic parts to the circuit:
1. A rectifier and smoothing capacitor
2. Dark detector to turn lights on. This can be overridden by switch 1:
Posn 1 - off
Posn 2 - detector
Posn 3 - On
3. A standlight which keeps one LED lit when stationary.
4. Momentary latch circuit to bypass three LEDs for when going slowly
(up-hill)

I sure you're aware that dynamos can be roughly considered as constant
current devices. Mine produces about 500mA without the booster caps C1 &
C2 but can go up to 1A. Designed to drive a 12 Ohm bulb so voltage is
quoted a 6v but will in fact rise to meet the Vf of the diode string
(plus any losses from other bits of the circuit) providing you're going
fast enough!

Specific thoughts:
C5 and it's resistor are there to stop car headlights turning my lights
off, are the values suitable?
Suggestions for specific parts, particularly mosfet and inverter chip
much appreciated
The LEDs are Cree XP-Gs which have a Vf of about 3.25v at 700mA so
maximum voltage reached should be about 13v

Any other comments ?

Thanks

Are C1 and C2 of any value?

When you activate low speed mode, a surge from C3 may burn out D7.

Forget the photodetector. Use a switch.

Check the internal resistance on the ultracaps. A rating of 5.5V 1.5F
sounds like low current CMOS backup caps. You need mobile power supply
ultracaps.

Place an LED power supply module where the 1K trickle resistor is, then
ditch the whole low voltage bypass circuit. The power supply modules
are tiny, current regulated, and can reach 90% efficiency at low
voltage. When current through the LED string gets low, the LED power
module will activate to keep D7 on until your caps are down to about 4V.
Make sure you wire it up correctly so the module's current sense works
with the string feeding D7. RECOM Power and LuxDrive modules are
commonly sold online.
 
N

nicknoxx

Jan 1, 1970
0
I dunno, but you're supposed to be riding the bike the same direction as
the traffic (i.e. on the right-hand side in the USA), so headlights
shouldn't be a problem in the first place.

Good Luck!
Rich
Who said anything about riding on the road?
 
N

nicknoxx

Jan 1, 1970
0
Amazing how complicated things can get.

Can't it just?
If my math is right, 6V 12 ohms is 3 watts.
3.25V x .7A is 2.275W x 4 = 9.1W
You sure you can get from here to there?

People have been able to get 12W out of a hub dynamo. 3W is just a
nominal figure based on using incandescent bulbs; 2.4W at the front and
0.6W at the back.
The cost/reward ratio of the photodetector is too high.
It's gonna be more grief than benefit.

Yes, I'm beginning to come to that conclusion, especially as I realised
last night that it has to work at both 3v and 13v.
Also think the light output from the supercaps will be too
dim or too short (depending on your choice of resistor) to be useful.
You don't just stop at an intersection. You slow gradually
and by the time you're stopped the caps are discharged...I think
the 1K is WAY too big to give useful light and your time constant
will be much shorter than you planned.

Real life experience in other places (candlepowerforum) suggests it will
work, but I may have resistor value wrong.
If it were me, I'd use a 18650 lithium cell, they come with built-in
protection if you're so inclined.
Use a microcontroller to skip cycles of the AC to keep the lithium
cell at a constant, safe voltage.
Make lighting decisions based on the frequency of the AC and set delays
for the various modes.
When you ride, the light comes on. When you stop, after some time
the light goes off.
Don't charge at low speed if that's your intention.
Many fewer parts, near constant intensity, infinite flexibility.

What happens when I stop for a long time, do I need another switch to
prevent the cell from discharging all the way?
And if you don't already know how to program a microcontroller, you learn
a marketable skill in the process.

Quite tempted to do this anyway.

Thanks - very helpful

Nick
 
N

nicknoxx

Jan 1, 1970
0
Are C1 and C2 of any value?

Oh yes, they can double the maximum current output from the dynamo. See
http://pilom.com/BicycleElectronics/DynamoCircuits.htm#Basics for deatils
When you activate low speed mode, a surge from C3 may burn out D7.

Yes, I can see that could happen, especially if I accidentally switched
from Hi to Lo at speed. Got any suggestions as to how I could prevent
this happening?
Forget the photodetector. Use a switch.

Seems to be the consensus.
Check the internal resistance on the ultracaps. A rating of 5.5V 1.5F
sounds like low current CMOS backup caps. You need mobile power supply
ultracaps.

Ah, they're going to be physically bigger aren't they?
Place an LED power supply module where the 1K trickle resistor is, then
ditch the whole low voltage bypass circuit. The power supply modules
are tiny, current regulated, and can reach 90% efficiency at low
voltage. When current through the LED string gets low, the LED power
module will activate to keep D7 on until your caps are down to about 4V.
Make sure you wire it up correctly so the module's current sense works
with the string feeding D7. RECOM Power and LuxDrive modules are
commonly sold online.

The current through the LED string almost never gets low. It's the odd
nature of the dynamo that it produces approx 500mA almost as soon as the
wheel turns but the available voltage rises with speed. Going up a steep
hill my speed will slow to the point where there isn't enough voltage to
light more than a single LEDs (about 6mph) (it's hilly here).
Very interesting idea to put LED driver in place of resistor. I really
like the idea of having an auto swithcing circuit based on
speed/voltage. The problem is the LED string won't light at all until
I'm going fast enough to power the whole string and charge the caps.

Tiny is relative, this is my mark 1 light.
http://www.zen202900.zen.co.uk/bike/lights/mk1/IMG_2296.JPG
Just room for 2 LEDs, a regulator, smoothing cap and switch,

Thanks very much for taking the time to think about this.
 
R

Rich Grise

Jan 1, 1970
0
nicknoxx said:
Who said anything about riding on the road?

I dunno - I guess I just ass-u-me-d that that was what you meant by
mentioning "headlights."

Thanks,
Rich
 
N

nicknoxx

Jan 1, 1970
0
I dunno - I guess I just ass-u-me-d that that was what you meant by
mentioning "headlights."

Thanks,
Rich
Oh yeah, fair point!
 
J

John - KD5YI

Jan 1, 1970
0
Headlights are supposed to be aimed such that they don't blind the
drivers in the opposite lane.

Thanks,
Rich

Did it occur to you that if you can see the oncoming lights that it
means light is coming into your eyes? Sure, I know that most of the
light is aimed down their own lane. But not all of it goes there.

You're welcome,
John
 
M

mike

Jan 1, 1970
0
nicknoxx said:
Can't it just?


People have been able to get 12W out of a hub dynamo. 3W is just a
nominal figure based on using incandescent bulbs; 2.4W at the front and
0.6W at the back.


Yes, I'm beginning to come to that conclusion, especially as I realised
last night that it has to work at both 3v and 13v.


Real life experience in other places (candlepowerforum) suggests it will
work, but I may have resistor value wrong.

Memory backup supercaps ain't gonna be much good. 4.5F of real low esr
supercaps is gonna be huge and expensive. yes?
What happens when I stop for a long time, do I need another switch to
prevent the cell from discharging all the way?
Possibilities are endless.
I'd have it dim some seconds after you stop, then turn off some time later.
Modern processors can sleep on half a microamp and wake up on the first rev
of the generator. Same reason there's no hardware on/off swtich on your
calculator, tv remote, etc.

For me, the biggest obstacle to the project would be the worry that
someone would steal it.
Quite tempted to do this anyway.
I'm a microchip guy. Startup effort can be daunting. Not hard, just
complicated getting all the hardware and software together and working.

I picked up one of these at a TI seminar
http://processors.wiki.ti.com/index.php/EZ430-F2013
Retails for $20 for processor, programmer, development system/compiler etc.
Looks like a relatively painless alternative.
This thread has motivated me to take it out of the drawer and
see what it can do.

I'm a big fan of the minimalist approach.
I have zero experience with hub generators, but depending on the number
of poles/frequencies involved, there's an old motorcycle trick that might
apply.
Put the leds in parallel, but two of them backwards so they run
alternatively on opposite half-cycles of the ac input. Or maybe two
in series parallel with the other two backwards, depending of
generator output characteristics.
Put an inductor in series. At low speed, the inductor looks like
a short. As the speed increases and the frequencies go up, the
inductor impedance goes up and limits the current. Depending on
the characteristics of the generator output this can greatly reduce
the change in intensity with speed. But the devil is in the details.
You may find that the inductor required weighs 5 pounds. Do the math.
The generator leakage inductance may already provide what you need
because you need the same function for the incandescent.

Use a 20mA led with a battery for the low intensity (please don't run
over me) light when you stop.
You can use some small NiMh and charge 'em at low rate from the generator
if you like. Just keep the current low and replace 'em every few
years when the abuse takes its toll.
 
N

nicknoxx

Jan 1, 1970
0
I'm a microchip guy. Startup effort can be daunting. Not hard, just
complicated getting all the hardware and software together and working.

Yes, I have often considered making the effort to get into PIC stuff but
have always been daunted by the steep learning curve.
snip

I'm a big fan of the minimalist approach.
I have zero experience with hub generators, but depending on the number
of poles/frequencies involved, there's an old motorcycle trick that might
apply.
Put the leds in parallel, but two of them backwards so they run
alternatively on opposite half-cycles of the ac input. Or maybe two
in series parallel with the other two backwards, depending of
generator output characteristics.
Put an inductor in series. At low speed, the inductor looks like
a short. As the speed increases and the frequencies go up, the
inductor impedance goes up and limits the current. Depending on
the characteristics of the generator output this can greatly reduce
the change in intensity with speed. But the devil is in the details.
You may find that the inductor required weighs 5 pounds. Do the math.
The generator leakage inductance may already provide what you need
because you need the same function for the incandescent.
The problem with hub dynamos in bicycles is that they don't spin very
fast. This is particularly true in my case because I've bought the
latest, lightest hub which is really designed for 20" wheels and I'm
using it in a 29" wheel. It only works at all because LEDs are so much
more efficient than incandescents.

Unless you go down the rectified, smoothed voltage route, the flicker is
unbearable even though the losses are greater this way.

My hub is inherently limited to somewhere between 500mA and 1A.
 
G

Grant

Jan 1, 1970
0
Yes, I have often considered making the effort to get into PIC stuff but
have always been daunted by the steep learning curve.
The problem with hub dynamos in bicycles is that they don't spin very
fast. This is particularly true in my case because I've bought the
latest, lightest hub which is really designed for 20" wheels and I'm
using it in a 29" wheel. It only works at all because LEDs are so much
more efficient than incandescents.

Unless you go down the rectified, smoothed voltage route, the flicker is
unbearable even though the losses are greater this way.

Rather than do the classic bridge -> cap -> load, instead try bridge ->
switcher -> load, perhaps with battery standby for minimal lighting when
you stop?

I've been making various LED drivers with the NCP3063 chip (much better
than the 33063/34063 chips it supercedes) recently and it works down to
low voltage, as well as up to 40V. On the output side I've run parallel
strings of LEDs with current mirrors (>200 LEDs with external switch MOSFET)
and even a voltage multiplier to run a single string of 50 LEDs with >100V.

There's a lot you can do with simple electronics before you go play with
microcontrollers. Which is also a place I play too, but not yet with
the LEDs. Yes, steep learning curve. I have the PIC chips as well as some
TI 430 whatsits that cost only USD4.30 each on an intro offer at the start
of the year to play with.
My hub is inherently limited to somewhere between 500mA and 1A.

Switchers can extract the maximum available power, transforming the load
to suit the dynamo, within large limits.

Grant.
 
J

John - KD5YI

Jan 1, 1970
0
Rather than do the classic bridge -> cap -> load, instead try bridge ->
switcher -> load, perhaps with battery standby for minimal lighting when
you stop?

I've been making various LED drivers with the NCP3063 chip (much better
than the 33063/34063 chips it supercedes) recently and it works down to
low voltage, as well as up to 40V. On the output side I've run parallel
strings of LEDs with current mirrors (>200 LEDs with external switch MOSFET)
and even a voltage multiplier to run a single string of 50 LEDs with>100V.

There's a lot you can do with simple electronics before you go play with
microcontrollers. Which is also a place I play too, but not yet with
the LEDs. Yes, steep learning curve. I have the PIC chips as well as some
TI 430 whatsits that cost only USD4.30 each on an intro offer at the start
of the year to play with.

Switchers can extract the maximum available power, transforming the load
to suit the dynamo, within large limits.

Grant.

Good suggestion, Grant.

The LED traffic signals I worked on work similarly. The input is a
bridge feeding a flyback switcher whose secondary gets rectified and
applied to a series/parallel string of LEDs. Feedback is LED current
converted to volts for the switcher. Proper tailoring of the feedback
(low pass) gives a power factor correction.

This was done with a current-mode switcher chip rather than a true power
factor controller.

Cheers,
John
 
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