proposed circuit for bicycle battery recharger

[Tom (at tomsweb.net)]

Everyone,

Based on suggestions from the previous thread I came up with the
following simple circuit for charging 4 NiMH cells from my dynamo, it
is a full-wave voltage doubler with Schottky diodes:

4700uF
||+
.------------|---o--||----o-->|--o-----o-------------.
| | | || | | | |
| - | | | | |+
| ^ | | | | ---
.-. | '-->|--. | | |+ -
( ~ ) GND|-o | | | --- --- 4 cell
dynamo '-' | | | | --- 4700uF - NiMH
2.5-5V | - .-->|--|-' | | --- (4.8V)
RMS | ^ | | | | -
| | | | | | ---
| | | ||+ | | | -
'------------|---o--||--o---->|--' | |
|| | |
4700uF | |
=== ===
GND GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

All diodes are schottkies. I simulated this and it appears to work
relatively fine for the expected voltages >=2.5V RMS. The NiMH
batteries are fed a ripply and unregulated rectified DC and I am
relying on the cells themselves to regulate this to their required
voltage (the theory is that when the voltage wants to go higher, the
batteries will demand more current and limit the voltage, and vice
versa).

Any opinions about whether this simple circuit will work? Will my NiMH
batteries like it? I realize I will have to make sure the batteries are
not overcharged.

FYI, a quick repeat of the specs of the dynamo:
* biking speed 10 km/h: 5.6VRMS unloaded, drops to 2.5VRMS at 0.5 amp
load, available power 1.25W
* biking speed 20 km/h: 9.9VRMS unloaded, drops to ca. 4VRMS at 0.5 amp
load, available power 2W
* did not measure the AC frequency but I expect it to be in the range
10..200 Hz, and pretty much sinusoidal

greetings,
Tom

 

[Ross Herbert]

Everyone,

Based on suggestions from the previous thread I came up with the
following simple circuit for charging 4 NiMH cells from my dynamo, it
is a full-wave voltage doubler with Schottky diodes:

4700uF
||+
.------------|---o--||----o-->|--o-----o-------------.
| | | || | | | |
| - | | | | |+
| ^ | | | | ---
.-. | '-->|--. | | |+ -
( ~ ) GND|-o | | | --- --- 4 cell
dynamo '-' | | | | --- 4700uF - NiMH
2.5-5V | - .-->|--|-' | | --- (4.8V)
RMS | ^ | | | | -
| | | | | | ---
| | | ||+ | | | -
'------------|---o--||--o---->|--' | |
|| | |
4700uF | |
=== ===
GND GND

I am not too impressed with the way the schematic appears. What are
those two devices directly across the dynamo with the GND between
them?

If they are meant to be diodes then on every alternate half cycle they
will place a short directly across the dynamo output.

 

[Ross Herbert]

You might like to read this http://chezphil.org/bikelights/

 

[Tom (at tomsweb.net)]

I am not too impressed with the way the schematic appears. What are

those two devices directly across the dynamo with the GND between
them?
If they are meant to be diodes then on every alternate half cycle they
will place a short directly across the dynamo output.

Oops, sorry, the bottom diode should have been the other way round.
Messed it up when translating my schematic to ASCII. Corrected
schematic:



4700uF
||+
.------------|---o--||----o-->|--o-----o-------------.
| | | || | | | |
| - | | | | |+
| ^ | | | | ---
.-. | '-->|--. | | |+ -
( ~ ) GND|-o | | | --- --- 4 cell
dynamo '-' | | | | --- 4700uF - NiMH
2.5-5V | V .-->|--|-' | | --- (4.8V)
RMS | - | | | | -
| | | | | | ---
| | | ||+ | | | -
'------------|---o--||--o---->|--' | |
|| | |
4700uF | |
=== ===
GND GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

This doubler circuit I found at:
http://www.kwarc.org/bulletin/99-04/tech_corner.htm

greetings,
Tom

 

[Ross Herbert]

Something like this?
http://phred.org/~alex/pictures/bikes/bikecurrent/bbcr_schem.pdf
http://phred.org/~alex/pictures/bikes/bikecurrent/BDGT_BCR.JPG

 

[Ross Herbert]

Oops, sorry, the bottom diode should have been the other way round.
Messed it up when translating my schematic to ASCII. Corrected
schematic:

That's better, should work....

 

[Tom (at tomsweb.net)]

Ross,

Something like this?
http://phred.org/~alex/pictures/bikes/bikecurrent/bbcr_schem.pdf

That's a standard bridge rectifier followed by a 6.2V shunt regulator.

The difference in my schematic (besides the doubling rectifier) is that
there is no separate regulator but I'm using the cells itself for
regulation. Part of my question is if this is acceptable for NiMH
cells?

greetings,
Tom

 

[Fred Bloggs]

4700uF
||+
.------------|---o--||----o-->|--o-----o-------------.
| | | || | | | |
| - | | | | |+
| ^ | | | | ---
.-. | '-->|--. | | |+ -
( ~ ) GND|-o | | | --- --- 4 cell
dynamo '-' | | | | --- 4700uF - NiMH
2.5-5V | V .-->|--|-' | | --- (4.8V)
RMS | - | | | | -
| | | | | | ---
| | | ||+ | | | -
'------------|---o--||--o---->|--' | |
|| | |
4700uF | |
=== ===
GND GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

This doubler circuit I found at:
http://www.kwarc.org/bulletin/99-04/tech_corner.htm

What's the matter with the conventional full-wave doubler, not enough
diode drops? :

View in a fixed-width font such as Courier.
..
..
..
..
..
.. dynamo
.. 2.5-5V
.. RMS
.. .-------+--o-->|--o---+---------------o-------------.
.. | | | | |+
.. .-. | |+ | ---
.. ( ~ ) | --- | -
.. '-' | --- 4700uF |+ --- 4 cell
.. | | | --- - NiMH
.. '---------------------+ --- 4700uF --- (4.8V)
.. | |+ | -
.. | --- | ---
.. | --- 4700uF | -
.. | | | |
.. +--o--|<--o---+---------------+-------------+
.. |
.. |
.. ===
.. GND
..

 

[Tom (at tomsweb.net)]

What's the matter with the conventional full-wave doubler, not enough

diode drops? :

You're right, that circuit is more efficient at low input voltages
because of fewer diode drops - thanks.

greetings,
Tom

 

[John Smith]

Tom:

I would think that "shunt regulator" does nothing to improve the effort
needed to peddle the bike...

John

 

[John Fields]

Tom:

I would think that "shunt regulator" does nothing to improve the effort
needed to peddle the bike...

 

[mike]

What's the matter with the conventional full-wave doubler, not enough
diode drops? :

View in a fixed-width font such as Courier.
.
.
.
.
.
. dynamo
. 2.5-5V
. RMS
. .-------+--o-->|--o---+---------------o-------------.
. | | | | |+
. .-. | |+ | ---
. ( ~ ) | --- | -
. '-' | --- 4700uF |+ --- 4 cell
. | | | --- - NiMH
. '---------------------+ --- 4700uF --- (4.8V)
. | |+ | -
. | --- | ---
. | --- 4700uF | -
. | | | |
. +--o--|<--o---+---------------+-------------+
. |
. |
. ===
. GND
.

Please explain the purpose of the rightmost cap????
Then explain why we need ANY of the caps????

Depending on the load vs available charge current, there may
still be the problem of overcharging and the pedaling effort
to just overheat the batteries.

Then there's overdischarging...
mike

--
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..
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MAKE THE OBVIOUS CHANGES TO THE LINK
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[Dr. Sisyphus Frankenstein]

Tom:

I would think that "shunt regulator" does nothing to improve the effort
needed to peddle the bike...

It does if the lamp is prevented from burning out (otherwise you crash
in the dark).

 

[John Smith]

ahhh, I see, so the shunt kicks in, causes to great a load to be able to
pedal against and the bulb is saved!!!

.... are you for real, or you just don't think--possibly not understand
what you read?

John

 

[Fred Bloggs]

Please explain the purpose of the rightmost cap????
Then explain why we need ANY of the caps????

Pleas explain how you can double the dynamo voltage without ANY caps????
If the dynamo wasn't the dynamo, the two series caps can function as
ballasts, limiting the current. But the dynamo is all wrong for this,
increasing output voltage with frequency.

Depending on the load vs available charge current, there may
still be the problem of overcharging and the pedaling effort
to just overheat the batteries.

Right- he needs to put an N-Channel in series with the return to doubler
and cut this off when the average Vbatt indicates full charge. That
would be an LMV431 type circuit with zero drain when the dynamo is not
charging the capacitors. Why don't you draw that up????

Then there's overdischarging...

I wouldn't worry about that- if the lights are a safety issue then you
don't want them to shut off.

 

[mike]

Pleas explain how you can double the dynamo voltage without ANY caps????

As I stated in my first post on the subject, you don't need to double
the voltage. You need to put the load where the voltage exists. All
you need do is split the battery into two pairs
of cells and put them where the series caps are. Delete the third cap too.

If the dynamo wasn't the dynamo, the two series caps can function as
ballasts, limiting the current.

HUH?? I'll need another (different) expression of the above sentence???

But the dynamo is all wrong for this,
increasing output voltage with frequency.

This has been used in motorcycles for decades...almost a century. The
source
is inductive, so the increased output at higher frequencies is
mitigated by the inductance. If it's not enough, you can always
add more.

mike

 

[Dr. Sisyphus Frankenstein]

ahhh, I see, so the shunt kicks in, causes to great a load to be able to
pedal against and the bulb is saved!!!

... are you for real, or you just don't think--possibly not understand
what you read?

Hey dumbass,

How would *any* lighting system "improve the effort needed to peddle the
bike?" I own generator/light systems that have shunt regulators
built-in, with no modification. What do you know about the generators
built for bikes? You think some 1/2 or 1 watt zener means squat in
terms of the power needed to pedal a bike? Even a slacker can put out a
100 watts with little problem. LANCE can put out over 400 watts for > 1
hr straight. The shunt is cost effective protection, not perfection,
and not important in terms of total efficiency.

And what is with the stupid top-posting?

 

[Fred Bloggs]

As I stated in my first post on the subject, you don't need to double
the voltage. You need to put the load where the voltage exists. All
you need do is split the battery into two pairs
of cells and put them where the series caps are. Delete the third cap too.

That works, but if you add current limiting then you will need two
circuits in place of one.

HUH?? I'll need another (different) expression of the above sentence???

In half wave, those stacked caps act as resistors of value 1/(8*F*C)
IIRC in so far as determining the average output DC voltage.

 

[John Smith]

.... my gawd, perhaps someone in this room will take pity on you and
explain to you what an A$$ you have just made of yourself...

I might of, but ya pi$$ed me off... <grin>

John

 

[Fred Bloggs]

In half wave, those stacked caps act as resistors of value 1/(8*F*C)
IIRC in so far as determining the average output DC voltage.

make that 1/(2FC)