How to build a Li-Ion charger myself (windmill, generator, solar cells)??

[mike]

BZZZZZTT! Wrong. As anyone who has worked on the design of CC/CV chargers
would know, when transition from CC to CV occurs, the cell is about 60% charged.
Also, the current does not "drop to zero" at transition - rather it starts an
almost exponential decay from the CC value. Typically this will take 2 hours or
more to drop to 10% of the CC value.

OK, sanity check.
You are not gonna pack a windmill on your bicycle. File that under,
"sounded like a good idea at the time."

You are not gonna build fixtures to hold all your batteries for external
charging poking out all over your bike rugged enough to hang onto the
batteries when you ride down that mountain trail. File that the same place.

Get yourself 10 high capacity AA NiMH cells and pack them into a thing
that snaps on like a tire pump. Hook them up to your bike generator and
charge the crap out of them. Use a thermal cutout in series that opens
when they start to get warm. Do some experiments using your typical
riding speed to see if you are applying way too much charge current and
add a resistor as required.
Don't worry too much about properly charging the NiMH. Just let the
overtemp switch take care of it. Might want an indicator so you can
manually switch 'em off. Plan on throwing them out when your trip is done.

At night, snap off the cell pack and use adapters with fixed voltage
outpts to connect to your devices for charging. Let the device manage
its own charge/discharge. You can charge multiple devices
simultaneously until you run out of energy.

Not the most efficient way, but at least it's practical.
mike

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[przemek klosowski]

LiIon cells are "managed" both in charging AND discharging. It's not a
trivial task to build your own. I would suggest purchasing a commercial
unit.

http://www.stensat.org/Docs/battery_test_results.pdf describes an
actual test showing that they are surprisingly robust. I was surprised to
learn that discharging dead short didn't kill the pack. On the other hand,
long-term short (over a day) and overcharging tend to do Li-ions in.

 

[Nick.]

Sure it can be done, have a look at www.maximic.com, they make a whole
range of Li-Ion charger IC's, and you can even get free samples to play
with. As for the generator, you could regulate the output with a small
high efficiency switchmode regulator, National Semiconductor makes a
line of those which are very easy to work with, and again samples are
available.

If using a bike gen to power electronics, make sure you cater for input
overvoltage protection! My bike gen will quite happily produce 50V RMS
given enough speed (~30mph) and a light or no load.

 

[Jasen Betts]

Sandra wrote:

<<Charging your battery is like charging a lead-acid battery: Constant
voltage with current limiting.>>

Bzzt. You missed an important point.

A Li+ battery *can* be constant voltage charged (if you can live with
the loss of life - figure 60% vs. constant current / constant voltage),
but what you forgot is the voltage limiting. Never charge a Li+ to more
than 4.2V per cell unless you want to see interesting light and nasal
effects (I know this to be a fact - I have a charger where the voltage
management failed).

Will charging them at a lower voltage or current damage them ?


ISTM that if the poster correctly implements a current and voltage
limited charger using his portable windmill, then the worst that
can happen is that his batteries don't get charged when there's no
wind.

during periods of low wind the charge current may be less than optimum
(or the voltage may be below the limit) but is that goinmg to be a
problem?

Bye.
Jasen

 

[Jasen Betts]

["Followup-To:" header set to sci.electronics.design.]

To save long on-line discussions, got to:
http://www.batteryuniversity.com/
for all you need to know about batteries.

How often do you expect to use your camera, and will you need a flash. Once
you fill a card, you will have to store or send it somewhere: will you be
carrying a PC or PDA around too? If so, that is going to need power as well.
Theft is a risk, if you are travelling outside the first world - carrying
something worth say $600 is the same sort of temptation to a desperately
poor person as ten to a hundred times that amount is to someone in an
affluent country.

It is a bit strange that in 1990, I simply mailed my films home.

so email the photos home, or to an account on gmail.com etc...

public email terminals are a little harder to find that postoffices, but
only a little harder.

Bye.
Jasen

 

[[email protected]]

Building a Li-Ion charger certainly is not trivial for most people, but
you have an important advantage: this newsgroup. There is nothing
magical about Li-Ion batteries. Of course, if you are launching them
into space and you need them to work reliably for fifty years, you
could spend the next few years researching the topic, but if you need
them to work reliably for one bicycle tour at a time without exploding,
I'm sure you can come up with a suitable design.

Besides, there really can't be much of a commercial market for a
human-powered battery charger. Most people are too lazy to plug
rechargeable batteries in and just use the disposable ones. Imagine
having to pedal!

Are there currently any, or have you considered building,
bicycle-powered 110V generators? You could bring your wall-wart along
for the ride and charge other gadgets as well.

 

[Funfly3]

Will charging them at a lower voltage or current damage them ?


ISTM that if the poster correctly implements a current and voltage
limited charger using his portable windmill, then the worst that
can happen is that his batteries don't get charged when there's no
wind.

during periods of low wind the charge current may be less than optimum
(or the voltage may be below the limit) but is that goinmg to be a
problem?

Bye.
Jasen

the only problem at low speed is if the cells start to discharge rather than
charge and if you go below 2,8v a cell most will just give up and die

 

[clifto]

http://www.stensat.org/Docs/battery_test_results.pdf describes an
actual test showing that they are surprisingly robust. I was surprised to
learn that discharging dead short didn't kill the pack. On the other hand,
long-term short (over a day) and overcharging tend to do Li-ions in.

I have a pair of packs (old cell phones) that aren't worth their weight
in potato chips after being stored mostly charged for a couple of years.
They were rather good when in regular use.

 

[Rich Grise]

OK, sanity check.
You are not gonna pack a windmill on your bicycle. File that under,
"sounded like a good idea at the time." ....
At night, snap off the cell pack and use adapters with fixed voltage
outpts to connect to your devices for charging. Let the device manage
its own charge/discharge. You can charge multiple devices
simultaneously until you run out of energy.

Not the most efficient way, but at least it's practical.

Or, he could even get one of those stands that lifts the back tire off
the ground, and pedal while he watches TV at camp.

Cheers!
Rich

 

[Rich Grise]

Building a Li-Ion charger certainly is not trivial for most people, but
you have an important advantage: this newsgroup. There is nothing
magical about Li-Ion batteries. Of course, if you are launching them
into space and you need them to work reliably for fifty years, you
could spend the next few years researching the topic, but if you need
them to work reliably for one bicycle tour at a time without exploding,
I'm sure you can come up with a suitable design.

Besides, there really can't be much of a commercial market for a
human-powered battery charger. Most people are too lazy to plug
rechargeable batteries in and just use the disposable ones. Imagine
having to pedal!

Are there currently any, or have you considered building,
bicycle-powered 110V generators? You could bring your wall-wart along
for the ride and charge other gadgets as well.

Just rectify and filter the 12V from the generator and use a 110V
inverter. You could probably build a 25-watt inverter in about the
space of a couple of packs of cigarettes.

Cheers!
Rich

 

[Chris Jones]

You should use a set of solar cells. A windmill would be pretty annoying,
and probably powered by your legs rather than the sun.

If you only want to charge a single cell (4.2V) you can use a 6V solar
cell pad. Limiting the current to 0.5C won't be an issue with solar cells,
assuming you don't go nuts and buy too many. The cells are generally
speced for a particular current. The voltage limit will be the main issue.
Use a regulator, like an LM317 (see the datasheet at www.national.com for
an appropriate circuit). You can get these at radio shack, where the
packages have schematics on the back. A small 1 hour timer would be a good
thing.

Look here and elsewhere for information on solar cells:

http://www.siliconsolar.com/portable_power_system.htm

---
Regards,
Bob Monsen

It is mathematics that offers the exact mathematical sciences a certain
measure of security which, without mathematics, they could not obtain.
- Albert Einstein

Better to use a low-dropout regulator rather than the LM317, otherwise
you'll waste a good fraction of your hard-won solar power in the regulator.

Chris

 

[Chris Jones]

[...]
Just rectify and filter the 12V from the generator and use a 110V
inverter. You could probably build a 25-watt inverter in about the
space of a couple of packs of cigarettes.

Cheers!
Rich

This isn't a very efficient arrangement. One really appreciate how much
energy is wasted in a wall-wart or cheap inverter when one must generate
that power through one's own muscles.

Chris

 

[[email protected]]

On trips of my own I plan on using a homemade 12 volt battery pack made
from 10 AA NimH rechargable batteries. I'll charge them at anyplace I
can..ie restaurant, hostel, local's willing to trade a few cents worth
of power for some stories of the road. I'll get a universal smart
charger that is good for 110-240 volt..good for the whole world.
Charge the pack up and power your camera for hours or use the pack to
recharge your cameras batteries several times. You'll pedel by power
sources daily..even in africa, bolivia, mongolia. It gives you a
chance to meet more people. Cycling is a lonely hobby. Does anyone
out there forsee any problems with this project...besides a little more
weight? I plan to hook the battery pack up to a female car cigarrett
lighter adapter so I can plug my cameras male adapter or mp3's male
adapter into it easily...this will cut the 12 volts down to the 4 or
the 5 needed for my different devices. Will this be inefficient? any
help would be great.
Good luck on your trip. May tail winds be with you.
Jay

 

[[email protected]]

This is what I plan to build:
http://www.hotmp3gear.com/powerrunner.htm

I'd buy it, but I'm cheap..and yes the sad truth is that theft is a
great possiblity on long distance cycle trips. Back up those picks at
every cyber cafe you come to (there are thousands in Central South
America and South East Asia...people in those countries cant afford a
home pc so they go to cafes that charge 20 cents an hour) Cafes are
harder to find in the first world. Send the cds home via airmail.
This device is heavy. Lighter if you dont need the charger and can use
the generator to charge the Nimh battery pack. Just pack well. People
pack way too much junk they dont need on trips like this. Cut weight
in other places. You only need a few changes of clothes...you WILL
stink no matter how many undies you have.
Sorry if this has turned into a backpacker/Cycler forum.
Jay

 

[Eric R Snow]

I have a crazy idea:

1. On my self suppored bicycle trips around the world I want to use a
digital camera.
2. I have faced reality and accepted that most digital cameras use
Li-Ion batteries, which makes them very small and handy.
3. Currently I'm interested in a Sony DSC-T7 which uses a Li-Ion
battery. The battery specs can be found here:
http://www.calcellular.com/np-fe1.html
4. I don't want to carry a regular charger but I want to use either a
regular bike generator (the ones powering for front and rear light on a
bicycle), solar cells or a home-built mini wind mill which can be
mounted on the bicycle and produce electricity during the night.

So the question is:
Is it possible to build my own Li-ion charger if I have a varying power
source such as a wind mill? I know that Li-ion batteries are difficult
to charge and that they may be damaged if treated wrongly. I have seen
in some other threads that companies such as Texas Instruments are
offering special ICs. What about the small motor/generator for such a
mini wind mill application - does anybody have recommendations? Are
there some published circuits on the internet which I could use?

Regards, Lucas Jensen

Lucas,
I have been reading some of the posts here and have a suggestion.
First, I'm not very knowledgeable in electronics so take what I say
with a grain of salt. Anyway, here's what I found when researching
battery chargers and batteries for use in digital cameras. Buy a
camera that can use AA size batteries. Many cameras that do will
accept alakiline batteries, NiMh batteries, and lithium ion batteries.
Buy a charger that will charge NiMH batteries and power this charger
from the bicycle charger. Keep a lithium battery or two in you
backpack as backup. These batteries are light and have a very long
shelf life. If you get in a situation where the Nimh batteries are
dead and the LI ion batteries are dead, then you should be able to buy
batteries to tide you over until the charging situation is fixed.
Since you will have up to 4 choices of batteries to choose from your
power needs are quite flexible. Finally, NiMH batteries are much more
tolerant of bad charging situations. Li polymer and Li ion batteries
can explode or catch fire. Because of this some (maybe all) Li
batteries have a device built in to prevent overheating the battery.
I buy batteries and chargers from Thomas Distributing. This company
was well recommended by more than one person and web site. I have no
interest in this company, just a satisfied customer.
Cheers,
Eric

 

[peter]

Lucas,
I have been reading some of the posts here and have a suggestion.
First, I'm not very knowledgeable in electronics so take what I say
with a grain of salt. Anyway, here's what I found when researching
battery chargers and batteries for use in digital cameras. Buy a
camera that can use AA size batteries. Many cameras that do will
accept alakiline batteries, NiMh batteries, and lithium ion batteries.
Buy a charger that will charge NiMH batteries and power this charger
from the bicycle charger. Keep a lithium battery or two in you
backpack as backup. These batteries are light and have a very long
shelf life. If you get in a situation where the Nimh batteries are
dead and the LI ion batteries are dead, then you should be able to buy
batteries to tide you over until the charging situation is fixed.
Since you will have up to 4 choices of batteries to choose from your
power needs are quite flexible. Finally, NiMH batteries are much more
tolerant of bad charging situations. Li polymer and Li ion batteries
can explode or catch fire. Because of this some (maybe all) Li
batteries have a device built in to prevent overheating the battery.
I buy batteries and chargers from Thomas Distributing. This company
was well recommended by more than one person and web site. I have no
interest in this company, just a satisfied customer.
Cheers,
Eric

There are a number of Li-ion chargers available that have a 12 volt
input for in-car use. Of course these could be powered from any 12v
source, so you could charge a bullet proof pack of nicads from your
cycle generator, I suggest a simple full wave rectifier charging 2 or 3
cells in series at a time and then power the Li-ion charger from 9 or 10
cells in series. I suggest nicads because they have the best tolerance
to abuse. I know it's a 2 step process, but it's simple and the tricky
bit can be handled by a professionally manufactured gizmo.