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need HELP with creating an extremely simple BATTERY CHARGING circuit for an LED flower!

Hello,
Could you help me with a personal project that I am working on?
I need help creating a simple rechargable battery circuit.
I am making an acrylic flower with LEDs that make the head glow white.
This is a birthday present for a friend.
My original plan was to just have a wall adapter to power the LEDs, but
now I think it would be cool if I can use rechargable batteries, so
when the flower is unplugged, it will still light up for a short time.
I see a lot of charger controllers for batteries, but they're too
complex for me to understand and I don't know anything about charging
batteries. I'm just an architecture student, so my knowledge of
electronics is very basic. Im afraid to use them because I don't know
what to connect the pins to or how it works.
I also don't have much space to put the components in, so a simple
circuit would be better.
I was wondering will it work if I use a 6v wall adapter to directly
charge a depleted 7.2v battery? Suppose the batteries are drained to
2v. Will the 6v adapter bring the batteries up to 6v? Or will it not
work at all? Will the charging stop automatically or keep going and
overcharge the batteries?

Here is a diagram drawing of what I want to do.

http://www.thomashuang.net/project.gif

Thank you for any advice you can give me.
Thomas
 
E

ehsjr

Hello,
Could you help me with a personal project that I am working on?
I need help creating a simple rechargable battery circuit.
I am making an acrylic flower with LEDs that make the head glow white.
This is a birthday present for a friend.
My original plan was to just have a wall adapter to power the LEDs, but
now I think it would be cool if I can use rechargable batteries, so
when the flower is unplugged, it will still light up for a short time.
I see a lot of charger controllers for batteries, but they're too
complex for me to understand and I don't know anything about charging
batteries. I'm just an architecture student, so my knowledge of
electronics is very basic. Im afraid to use them because I don't know
what to connect the pins to or how it works.
I also don't have much space to put the components in, so a simple
circuit would be better.
I was wondering will it work if I use a 6v wall adapter to directly
charge a depleted 7.2v battery? Suppose the batteries are drained to
2v. Will the 6v adapter bring the batteries up to 6v? Or will it not
work at all? Will the charging stop automatically or keep going and
overcharge the batteries?

Here is a diagram drawing of what I want to do.

http://www.thomashuang.net/project.gif

Thank you for any advice you can give me.
Thomas

Groan - as drawn, nothing will work right.
You show 3 LEDs at 3.3 volts each in series,
so 9.9 volts would be needed, not 6 volts.
You should never let a 6 cell (7.2V) NiCd pack
discharge to 2 volts - that can ruin the cells.
Your switch circuit will prevent battery power
from reachingh the LEDs - and as mentioned before
6 volts is too low in any event.

Get a 12V DC adapter and do this:

----- 2N3906
+12V ---Vin|LM317|Vout---+ +---+---- ---+----+----+
----- | | | e\ /c | | |
Adj [R1] | [R2] - | | |
| | | | | [R3] [R4] [R5]
+----------+---+ +-----+ | | |
| | |+ |+ |+
[NiCd] [Zd] [LED][LED][LED]
| | | | |
Gnd ---------------------+-------+----------+----+----+

R1 = 10 ohms, R2 = 1.2K, R3,R4,R5 = 220 ohms
Zd = 5.6 volt zener diode.

When the 12 volt supply is available, the LM317 will
limit the current to ~ 125 mA, which will protect the
NiCd pack (assuming the cells are rated at 1200 mAh
or more) from overcharge. That 125 mA will provide
current for the LEDs and current to charge the NiCds.
The 220 ohm resistors will limit current through each
LED to ~ 23 mA when the batteries are fully charged
down to ~ 13 mA when they are almost fully discharged.
The 5.6 volt zener diode will hold the base of the 2N3906
at 5.6 volts, so the transistor will conduct as long as
the pack is above ~ 6.2 volts. When the pack discharges
to ~ 6.2 volts, the transistor will turn off and prevent
the pack from discharging too far.

Here's a "picture" of an LM317
-----
| o |
|_____|
/______/|
| ||
|______|/
| | |
| | |
Adj Vin Vout

The + side of the LEDs is marked on the diagram,
and the emitter (e) and collector (c) of the
2N3906 transistor are also marked on the diagram.

Ed
 
E

ehsjr

Hello,
Could you help me with a personal project that I am working on?
I need help creating a simple rechargable battery circuit.
I am making an acrylic flower with LEDs that make the head glow white.
This is a birthday present for a friend.
My original plan was to just have a wall adapter to power the LEDs, but
now I think it would be cool if I can use rechargable batteries, so
when the flower is unplugged, it will still light up for a short time.
I see a lot of charger controllers for batteries, but they're too
complex for me to understand and I don't know anything about charging
batteries. I'm just an architecture student, so my knowledge of
electronics is very basic. Im afraid to use them because I don't know
what to connect the pins to or how it works.
I also don't have much space to put the components in, so a simple
circuit would be better.
I was wondering will it work if I use a 6v wall adapter to directly
charge a depleted 7.2v battery? Suppose the batteries are drained to
2v. Will the 6v adapter bring the batteries up to 6v? Or will it not
work at all? Will the charging stop automatically or keep going and
overcharge the batteries?

Here is a diagram drawing of what I want to do.

http://www.thomashuang.net/project.gif

Thank you for any advice you can give me.
Thomas

Oops - forgot to mark the zener diode for
you on the diagram. The end of the diode
that has a band on it gets connected to the
base of the transistor and the 1.2K resistor.

Ed
 
thanks!
oh, i was just too lazy to draw the LEDs correctly but i meant for them
to be in parallel.
so how does the circuit prevent the batteries from overcharging?
they're only 60mAh each.
 
S

Sambo

ehsjr said:
Hello,
Could you help me with a personal project that I am working on?
I need help creating a simple rechargable battery circuit.
I am making an acrylic flower with LEDs that make the head glow white.
This is a birthday present for a friend.
My original plan was to just have a wall adapter to power the LEDs, but
now I think it would be cool if I can use rechargable batteries, so
when the flower is unplugged, it will still light up for a short time.
I see a lot of charger controllers for batteries, but they're too
complex for me to understand and I don't know anything about charging
batteries. I'm just an architecture student, so my knowledge of
electronics is very basic. Im afraid to use them because I don't know
what to connect the pins to or how it works.
I also don't have much space to put the components in, so a simple
circuit would be better.
I was wondering will it work if I use a 6v wall adapter to directly
charge a depleted 7.2v battery? Suppose the batteries are drained to
2v. Will the 6v adapter bring the batteries up to 6v? Or will it not
work at all? Will the charging stop automatically or keep going and
overcharge the batteries?

Here is a diagram drawing of what I want to do.

http://www.thomashuang.net/project.gif

Thank you for any advice you can give me.
Thomas

Groan - as drawn, nothing will work right.
You show 3 LEDs at 3.3 volts each in series,
so 9.9 volts would be needed, not 6 volts.
You should never let a 6 cell (7.2V) NiCd pack
discharge to 2 volts - that can ruin the cells.
Your switch circuit will prevent battery power
from reachingh the LEDs - and as mentioned before
6 volts is too low in any event.

Get a 12V DC adapter and do this:

----- 2N3906
+12V ---Vin|LM317|Vout---+ +---+---- ---+----+----+
----- | | | e\ /c | | |
Adj [R1] | [R2] - | | |
| | | | | [R3] [R4] [R5]
+----------+---+ +-----+ | | |
| | |+ |+ |+
[NiCd] [Zd] [LED][LED][LED]
| | | | |
Gnd ---------------------+-------+----------+----+----+

R1 = 10 ohms, R2 = 1.2K, R3,R4,R5 = 220 ohms
Zd = 5.6 volt zener diode.

When the 12 volt supply is available, the LM317 will
limit the current to ~ 125 mA, which will protect the
NiCd pack (assuming the cells are rated at 1200 mAh
or more) from overcharge. That 125 mA will provide
current for the LEDs and current to charge the NiCds.
The 220 ohm resistors will limit current through each
LED to ~ 23 mA when the batteries are fully charged
down to ~ 13 mA when they are almost fully discharged.
The 5.6 volt zener diode will hold the base of the 2N3906
at 5.6 volts, so the transistor will conduct as long as
the pack is above ~ 6.2 volts. When the pack discharges
to ~ 6.2 volts, the transistor will turn off and prevent
the pack from discharging too far.

Here's a "picture" of an LM317
-----
| o |
|_____|
/______/|
| ||
|______|/
| | |
| | |
Adj Vin Vout

The + side of the LEDs is marked on the diagram,
and the emitter (e) and collector (c) of the
2N3906 transistor are also marked on the diagram.

Ed

The over discharge protection is nice but perhaps unnecessary, I am not sure how much
leds let trough bellow it's forward voltage but it must be very / extremely low and discharging NiCd down to 1.1V per cell is acceptable according to what I can remember reading.
If indeed the LEDS are 3.3V not 1.7 , putting the batteries in parallel (or just using 1 )
and driving the leds in parallel through about 18 or 20 ohm resistors will burn up lot less power (in the resistors.)
1200Ma? I am looking at similar 4.8V pack and it is only rated at 60mAh.
Oh yes I just looked at the circuit again and it says 60mAh, however if you put then in series
you don't get twice the capacity just twice the voltage.
Come to thing of it, at this low rating , 3 leds in parallel is stressing the 1 or 2
batteries too much, but if it is only really 1 time use .....
Maybe use only 2 LEDs in series. you will have to find out the led forward voltage.
As far as charging goes you should probably aim for 1.42 - 1.43 constant voltage per cell
(for simplicity). I am not sure how much I destroyed my 4.8V pack prior to taking measurement and coming to this conclusion of 1.43 V but I hope not too much.
Older batteries tend to have higher internal resistance and reach higher voltages faster
( DURING CHARGING ) than brand new ones, when that happens charging stops or slows down to a crawl. With my setup the current after long charging period was down to about 100 -200nA
which I considered perfect trickle charging situation.
I am not a fan of battery stacks but trickle charging is supposed to be able to charge embedded weak batteries.
Anyway..
So if you use the 2 batteries in parallel ( and all LEDs in parallel) ,
you will need 4.3V supply.
6V wall wart maybe sufficient but 7V to 12 would be better.
Now use the LM317 to build regulated 4.3V power supply.

Since the regulator maintains 1.2V between ADJ and Vout. using the prescribed 240ohm:
_____________
| | 1.2V / 240 = 5mA
| LM317 | 5 - 1.2 = 3.8V 4.3V - 1.2 = 3.1V
| | 3.8 / .005 = 760ohm (R2) 3.1 / .005 = 620ohm (R2)
-------------
" " "
| | | Vout
| | L---------------
Adj | | |
| Vin |
-------------- | (5V)
| | R1 | 4.3V out R3 R4a
| | |---------| | | |--------| |--------|
| L-----o--| 240ohm |----o------>| ----| 30 ohm |----o---| 43 ohm |--o
| | |---------| | |--------| | |--------| |
| ----- 1N4001 | |
| |R2 | | V LED 1a
O + | | 620 ohm BAT. 3.6V ===== ===
from | | --- |
O - wallwart| | | |
| ----- | |
| | | |
--------------o-o---------------------------------------------o---------------|
|
GND ===


I think to calculate the charging resistor from the 1/10 capacity charging current (6mA),
I would use 1.25V ( at which voltage the battery only holds fraction of it's capacity )
and start with 6mA from here.
So:
1.43V - 1.25V / .006 = 30 ohm

Now we need to account for the leds current( 2 in parallel? ) at the same time hmmm.
At this higher voltage 4.3V lets allow 23mA ( assuming the LEDs can handle it ).

So:
4.3 - 3.3 = 1
1 / .023 = 43ohm (resistors with each of the 2 leds )
When batterie supplies the current and is at it's nominal voltage of 3.6 - 3.75V the current will be .3 / 43 = 6.9mA

For 20mA at 3*1.25V ==> (3.75 - 3.3) / .02 = 22.5
at 3.6V 22ohm only gives 13.6mA which maybe way to dim
and at 4.3V there is 1 / 22 = 45mA flowing through them LEDs.
Can they handle that?

!!!!looks like we have a major problem.
Maybe burning the 4V on resistors is a better approach after all, that way the current difference ( with larget resistors ) between charging voltage (8.58 - 8.6 ) and the
operating voltage (7.2) is not as large percentage wise.
In this case you'll most likely want to use the transistor/resistor/zener protection so
that the batteries don't go bellow 6V. At first glance there is something fishy about that sub-circuit even if the 3906 is a PNP transistor, so I can't tell you wheather to use 6.2 or 6.8V zener.

Alternatively the LEDS could be disconnected when charging.
If you do that then you could use what I drew.
As an after thought I inserted a diode after the regulator ( because regulators don't like to see voltage on their output and not on input.) That brings the voltage requirement to 5V,
so instead of LM317 and R1 and R2 you could use (LM)7805.

|---------|
| L7805 |
| |
| |
|---------|
I I I
Vin GND Vout (5V)

I'd have to think about how to use additional transistor to turn off the leds when voltage is above or better yet current flows through R3.

Right now I have to run.

Ciao for now,
Sam.
 
im trying to follow the calculations and how the current flows to each
component, but i cant.
its too confusing for me. i keep thinking that the resistor that
limits the current to the battery to 6mA also limits the current to the
LEDs to 6mA since they are in series with the resistor, while plugged
in. actually, did you mean for the adapter to be only used for
charging? that would make sense then. i still dont get how the 317
limits takes the voltage down to 4.3v. i thought it only limits the
current through the adj pin. and how does this stop the batteries from
being overcharged?
i dont know. its too much for me.
maybe ill just leave out the battery part altogether.
thanks for helping out. i really appreciate it.
i wish i hadnt thought about using batteries in the first place. would
have saved me 20 hours of worthless internet browsing.
 
i found this diagram
http://www.owlnet.rice.edu/~elec201/Book/images/img130a.gif
on this website
http://www.owlnet.rice.edu/~elec201/Book/batteries.html#SECTION001330000000000000000

it claims that it will automatically shut off charging when the battery
equalizes with the charge voltage with the use of the zenner diode
shutting off the base. i dont know. im not following it completely.
this might work if i also put a switch between the battery, wall, and
LEDs so that only either the battery or the wall provides power to the
LEDs.

i dont know. it still doesnt make much sense to me how it works, and
how i can use it correctly. oh well.
 
E

ehsjr

thanks!
oh, i was just too lazy to draw the LEDs correctly but i meant for them
to be in parallel.
so how does the circuit prevent the batteries from overcharging?
they're only 60mAh each.

Yup - I missed that spec. The value of R1 would need
to be changed to 210 ohms, but that creates another
problem: there won't be enough current to light
the LEDs while the battery is charging. So a modified
circuit is needed:

Replace the LM317 with an LM7809, add
2 diodes, 2 caps and change the resistor
values (except R2)and the zener as shown below:



---- D1 2N3906
+12V -+-Vin|7809|Vout--+--->|---+---+---- ---+----+----+
| ---- | k | | e\ /c | | |
| Gnd +----+ | [R2] - | | |
| | | | | | | [R3] [R4] [R5]
| | | [R1] | +-----+ | | |
| | | | D2 | | | | |
[C1] | [C2] +--->|---+ | | | |
| | | |+ k |k |+ |+ |+
| | | [NiCd] [Zd] [LED][LED][LED]
| | | | | | | |
Gnd --+-------+---+----+------------+----------+----+----+

C1 = .33 uF, C2 = .1 uF
D1,D2 = 1N4001
R1 = 330 ohms, R2 = 1.2K, R3,R4,R5 = 240 ohms
Zd = 1N4732A (4.7 volt zener diode)

The banded ends of the diodes are marked
with the letter k

The circuit above will charge the batteries and
power the LEDs simultaneously.

Ed
 
S

Sambo

No wonder I have been convinced what crap rechargeble batteries are all this time.
that circuit cannot charge NiCd or Lead/acid battery to any reasonable capacity, maybe 2%
Most recently I started with Ni-Mh batteries when I got a digital camera which came with charger and 2 batteries. after the first 2 or 3 times recharges I started noticing that I can't make more
than 5-7 pictures before it shuts down because the batteries are weak. I don't think I ever had a charger that was any good.
I think I measured the current while using the ZOOM it was sucking nearly an amp
if the camera draws that much current then they should at least make room for 4 batteries but I haven't seen a camera that takes 4 batteries yet.
 
S

Sambo

im trying to follow the calculations and how the current flows to each
component, but i cant.
its too confusing for me. i keep thinking that the resistor that
limits the current to the battery to 6mA also limits the current to the
LEDs to 6mA since they are in series with the resistor, while plugged
in. actually, did you mean for the adapter to be only used for
You are righ that only 6mA are available with that circuit but if the batteries still
have charge , They'll supply most power less the 6mA.
charging? that would make sense then. i still dont get how the 317
limits takes the voltage down to 4.3v. i thought it only limits the
current through the adj pin. and how does this stop the batteries from
being overcharged?
while the 317 can be used to supply constant current I don't know any way of terminating
charging besides using microprocessor.
After finally reading something and seeing the 1.42V figure I have decided to try and let the voltage go that high with my 4.8V stack. I set the voltage source to 1.43 * 4 and used resistor that would allow around 7 mA and it took about 14 hours for the current fall down to lot less than 1mA. Then I discharged it (starting with 7 or 8 mA) and got about 9 hours before the voltage dropped to about 1.1v per cell.
The charging doesn't realy stop but is passing wery little current through the battery,
small enough not to cause any damage to it.
As the battery charges the voltage rises, it takes relatively short time to reach into
the 1.30 range and then about 14 hours to rise the additional .1V, when finally the battery is
1.42 and supply 1.43 you only have .01/ 20ohm = 500nA

i dont know. its too much for me.
maybe ill just leave out the battery part altogether.
thanks for helping out. i really appreciate it.
i wish i hadnt thought about using batteries in the first place. would
have saved me 20 hours of worthless internet browsing.

Cheers
 
E

ehsjr

Sambo said:
while the 317 can be used to supply constant current I don't know any
way of terminating charging besides using microprocessor.

Same way I terminated discharging: compare the voltage
to a reference voltage and take the appropriate
action (shut off the power supply, disconnect the
battery, interrupt the circuit, whatever.)

Ed
 
LEDS require voltage and current to work to where you may see them. so now lets git rid of one thing voltage and still use the lm117 to regulate power or current now you only need to know LED current and add a 1 one resistor to limit the current from adj to output. let say 15ma the you add 75 to 82 ohms resistor and you got it. a 9v battery will not last long. now you may choose any DC voltage source from 3 to 60v and it will work. of course i assume 1 LED @.015 amps to a maximun 1.5 amps out total.any combination will work provided the source is there solid.
 
J

John Fields

i finished the website, and a video too. there are more pics up now.
please to go http://www.thomashuang.net
thanks!

---
That video made me cry.

In a world as full of hate as ours is now, you made me feel that
there's still hope.

I wish you a long, long, happy life.


BTW, you might want to put your video on youtube.
 
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