Intelligent battery charger circuit

[Dexter Dude]

16f877 nicd charger

This is the complete schematic:
**broken link removed**

The software was written in both ASM and in PIC-Basic .The ADC routine is from AN700 Microchip AppNote . The RS232 interface was only used in the develpement stage.I also used this schematic (striped away unnecessary parts ) as an PC DataLogger.

RS232 settings:
"9600baud Parity None 8 bits driven inverted " ( also known in RealTerminal as "9600 8N1 none" )

 

[RenatoBR]

sla battery charger circuit

Dude,

How to calibrate the 2k5 pot?


Renato

 

[Dexter Dude]

intelligent nicd charger atmega8

There are several ways to calibrate the Pot.

Met1:
Power up the charger with 12V dc , no batt in it.
Use the RS232 connection to watch the voltage readings of ADC .I used "RealTem" software to do this.
http://realterm.sourceforge.net/.

Also connect an Digital Voltmeter on charger Output (Cathode of 1N5401 diode)
Adjust the 2k5 POT till readings from DV and RealTerm match .An error of adjustment of less then 90mV is quite OK.
This is the most accurate adjustment.


Met2:
Feed 12V dc to the charger , no batt in it .
Adjust the POT to min value.Display will read E . Slowly adjust the POT untill display show I , then go back a little till display shows again E .
This method is less accurate but works just fine .

Now put 1 acc in and power up .
The display will show for 2 sec the number of elements to be charged (in this case I and then discharge the acc till 1V (pulse discharging , aprox 300mA for 1 element , 500mA for 2 elements , 600mA for 3 or 4 elements ) . Remember to use 0.8ohmi /10W 1.25ohm/10w resistors .

Normal operation mode :
- first connect the rechargeable batteries to the charger
- power up charger
Reset = Power off charger

 

[wizpic]

bq2004 charger

so dexter you going to share code or not

we understand if you say no

wizpic

 

[RenatoBR]

atmega charger

Hi all,

I built the circuit on a potoboard using IRF540, I don't have IRF530.
Display, I have only common catode, no possible to calibrate the circuit, I´ll buy the correct this week.
Each time I power the charger it works for about five minutes (pulse discharge) and then stops using battery full charged or discharged.
I don´t know how to prepare the RS232 to conect to PC, anyone can help me?
Can I use only one display and one BC251?


Rgds


Renato

 

[Dexter Dude]

battery charging circuit

After discharge to 1V/element the charger rests for 35sec (cool down battery) and then start slow charge for aprox. 6min. So I guess your charger is working but you still need to calibrate . If you do not calibrate , the charger could work but the discharge voltage will be off .I think that's what happening in your case .
The MOS-FET it is not critical but it is better to use one with low "Vgs threshold voltage " like those in PC motherboards .This tipe of fet is important only if you are planning to use only one rechargeable element at a time (so that reflex charging keep working normal at low voltages ).

Actually you could connect the display like this (no need for transistors) :
**broken link removed**

I used 2 digits becouse I intended to display more information , but that is for future development .

The RS232 terminal should display something like this :
**broken link removed**

For RS232 connection you could use this :
http://picprojects.org.uk/projects/simpleSIO/ssio.htm
or
http://www.kmitl.ac.th/~kswichit%20/MAX232/MAX232.htm

I used MAX232 , but the transistor version should work fine.

 

[RenatoBR]

atmel battery charging

Tanks Dude,

You're helping a lot.
I'll build the RS232 with transistors, but I have one more question:
+3 to +5 volts conect on LM7805 (out).
PIC TxD conect on RB7.
PIC RxD where to conect??
GND conect on ground from charger.

Sorry for asking a lot of question, I'm not expert in pics.


Rgds


Renato

 

[Dexter Dude]

avr battery charger reflex mode

"+3 to +5 volts conect on LM7805 (out). " <- correct
You don't need PIC_RXD .The communication is unidirectional : from PIC to PC.
"GND conect on ground from charger. " <- correct

 

[RenatoBR]

intelligent battery charger circuits

I built the RS232 interface with transistors and did the calibration.
On the screen of the RealTerm after the calibration I read:

V=7791 mv read=742 status=err, and on multimeter 0.773 volts, is it correct?
The value to compare with multimeter is read?
What means V=7791?

I connected one cell and start dischargin, when finished, the RealTerm showed
"no B" and did not start charging.
My calibration is correct?

May be I have a problem because no all parts available:

For 27k using 22k
For 0.8R using 2.2R
For 1.25R using 4.7R
For pot 2k5 using 2k2
For IRF 530 using IRF540

The resistors for charge and discharge are criticals or I can change the values?

What do you say.


Renato

 

[Dexter Dude]

avr inteligent charger

"The value to compare with multimeter is read? "
No.That is the 10bit value ADC reads (0-1023 max).You calibrated the wrong way.You should use V=xxxxmV variable instead (not read variable from RealTerm.( I guess you also changed the POT or the 2k2 resistor connected to it )


The ADC is 10bit precision but it it feed thru an voltage divider aprox 2:1 (2k5 Pot and 2k2 resistor. The resistor needs to be a little lower value then the POT )


* For 27k using 22k (OK values 22K-56K )
* For 0.8R using 2.2R (important for discharge current , not critical but direct proportional with charge resistor , in order to correctly use the "reflex charging technique"
* For 1.25R using 4.7R see above , not critical
* For pot 2k5 using 2k2 not critical
* For IRF 530 using IRF540 not critical

This are the voltage thresholds used by charger :
V_batt read
0.877V ----- 90(units) <-you need to adjust the pot to read this value 90 +- 5
1V ----- 100 (units)
2V ----- 200 (units)
3V ----- 300
4V ----- 410
8V ----- 850 ....................(1023 units max)


V=7791 <- the voltage ADC sense (or 742 x ADC_resolution )
So 7791/742 ~10mV resolution.

How exactly did you calibrate ? Where did you connect DV? If DV reads 0.773 volts then you should adjust the POT until Realterm reads 0.77-0.8V or "read=77" .Then if you put a batt in the DV and Realterm readings should match.
It is impossible to get 7.791V reading with no batt atached .Check the LM317 , the BC173 and the resistor connected to its base (decrease 1K5 resistor).
Also , if you power up the charger with no batt attached , the display should read E
Check protection diode orientation.

"Met1:
Power up the charger with 12V dc , no batt in it.
Use the RS232 connection to watch the voltage readings of ADC .I used "RealTem" software to do this.
http://realterm.sourceforge.net/.

Also connect an Digital Voltmeter on charger Output (Cathode of 1N5401 diode)
Adjust the 2k5 POT till readings from DV and RealTerm match .An error of adjustment of less then 90mV is quite OK.
This is the most accurate adjustment. "

 

[wizpic]

battery charger circuit schematic

you can use a better routine for A/D conversion, I have one that read 1MV resalution, Sure this would be a better way of doing it.

I've yet to build this charger,

Dexter I persume that you use PWM for the outputs is that HPWM or the 10bit PWM ?

wizpic

 

[Dexter Dude]

regulator irf530

There is no need for more resolution .Tried with 8bits resolution and it is working for more then 2 elements .I increase the resolution so only one element could be used.

I do no use HPWM , just some carefully timing for ON and OFF periods .The result is a signal like this :
**broken link removed** .

Do you have a link(s) for that better routine for AD conversion ? .Right now I am experimenting with such AD routines but this one (AN700) seems to work the best .

 

[wizpic]

burp charging

I have no link it's my own routine I made

It is done in Proton I tajke you said yours was done in PBP ?

wizpic

 

[Dexter Dude]

intelligent charger schematic

My AD routine was done in .asm but used in a PicBasic program.I tried a PWM based AD in PicBasic but I was getting only 8Bits of resolution and a conversion time of approx 100ms . The .asm routine takes only 20ms for 10bit resolution. My current project is an PIC16F628A thermometer (using 3X1n4148 diodes as sensors) .I am trying to figure out how to implement two ADC using internal comparators of PIC16f628. Also the speed of conversion is important .

 

[wizpic]

charger atmega

I did not think that the 16f628 has A/D converter ?

I know it can be done by other means but sure it would be better to use a pic with A/D converter on it.

That's what I like about Proton you can do 10bit PWM easily and the A/D conversion is very quick
I'll PM it you if you like to have a look at it

wizpic

 

[RenatoBR]

pic battery charging circuit

Hi All,

Dude, my charger did not work yet.
Now I'm using the correct parts like your project except for the 2k5 pot that is not comercial use here in Brazil.
I got one with 3k that measured 2.56k on my DV Fluke 189, I'm using this pot now.
For BC173 I'm using BC549 that is equivalent.
I put a display in the circuit.
Making a correct calibration with Realterm and display inserted in the charger:

If pot totaly closed, Realterm show that big number for mv like 6000 to 7000 or so and display pulse the letters E and A.
IF I open totaly continue the same.
Wath I need to do, open the pot +- 3/4, power up the charger and then is possible to make a calibration, but display only show E.

If I try to calibrate only using the display it show E, not change to I.

I have cheked all the components, circuit and changed LM 317, 1N5401, IRF530 and inserted more capacitors on LM 7805.
I did a test without pic inserted like your procedure and it's ok.

Do you have voltages on pins pic during the calibration?
May you share your pcb lay out?
As told you, I'm using a protoboard.


Rgds


Renato

 

[Dexter Dude]

battery charger+16f877

Hello .
If you power up the charger with no batt in it will display E A .

Let' try a different calibration method :
1. First burn the PIC with "charger calibrate.hex" .Use the configuration bits mentioned before .
This is a stripped version of the charger program .It only enables to measure(Delta Sigma ADC using comparators) the voltage across charger's outputs (using RealTerm ).LM317 is "put to sleep" and the discharge is OFF .

2. Connect 1 2 3 or 4 batt. to the charger . Also connect an Digital Voltmeter on charger Output (Cathode of 1N5401 diode)
Adjust the 2k5 POT till readings from DV and RealTerm match .An error of adjustment of less then 90mV is quite OK (pot allows a brute adjustment )

3. Remove the batteries .The Realterm should display a value approx between 700mV-945mV or 70-90 units.(If you have 0.773V on DV then you must read 773mV in Realterm .)

4. If you succeeded so far then the calibration is done

5. Finally. Burn burn the PIC with "charger SAR 10 fin.hex" .Use the configuration bits mentioned before .

The hex files and the PCB is here :
http://depositfiles.com/files/2721725

 

[RenatoBR]

atmel battery charger code

Tank you Dude,

Before this new procedure I have made one more test with the display:

Calibration on RealTerm, inserted one battery and power up the charger.
The display showed I and then 0 (discharging).
After finished the discharge the display showed I for some seconds and S for one second +- and then the letters E and A.
It's not start charging again.

I have measured some voltages on pins 2 and 17:

Pin 2 - 4.34 to 4.40v. and 4.39 to 4.45v.
Pin 17 - 2.51 to 2.52 and 2.51 to 2.52v.




Renato

 

[Dexter Dude]

lm7805 charging circuit

"The display showed I and then 0 (discharging). " <- detect one element (measure a voltage between 1V-1.95V).


"After finished the discharge the display showed I for some seconds and S for one second +- and then the letters E and A. " <- Battery IN and start Slow Charging

I think you may have a loose connection (between charger and batt. ).The charger display E A only when senses a voltage lower than 0.925V witch is lower than discharge voltage /element .

 

[RenatoBR]

pic battery charger circuit

Not working,

Unfotunately the new procedure didn't work, I have made several tests.
Discharged till 0.9v, show: I then S for a second and then E/A.
Sure I have problem with the ADC, but I don't konw how to resolve it.
I'm using 2.56k pot. and and 2.17k resistor measured on my DV, can I choose another value for resistor to make a test?

I think you may have a loose connection (between charger and batt. ).The charger display E A only when senses a voltage lower than 0.925V witch is lower than discharge voltage /element .

I believe no bad conection, where can I test if the voltage is correct to start charging?


Renato