Beginners Guide to Processing 18650 Cells | Cell Database


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64/128 cells - DIY Multi Battery Tester Charger / Discharger
#11
(09-13-2017, 06:28 PM)srk Wrote:
(09-13-2017, 03:54 AM)SimonW Wrote:
(09-12-2017, 07:19 PM)mrconstantin Wrote: Yes i will make the other 32 module with constant current discharge. in few days. And after that i will make an comparation.

Cool, I look forward to seeing how you go.
Just one extra resistor and an NPN transistor, maybe also change the 10 ohm so you get a higher current draw toward the end(say 500mA instead of your 250mA with the 10 ohm), and you're set.
The mosfet will go from being a switch to an automatic variable resistor Big Grin
Would need some heatsinking, but it's only a few watts per mosfet.

Simon, would you be willing to sketch out the placement of the additional resistor and transistor based on his initial design? I have all the parts coming my way to build out his initial design. Thanks!

hi

    tomorrow i will make an other movie with the constant current version. 
    In theory Ohm Low is : 
              I=U/R 
    So u know the U will be changing from 4.2 to 2.5V on discharge of the cell.
    For I to be constant u have tow option:

             1 - to change the R value : this can be done like that use an fixed R + RDSon of MOSFET so if u want to discharge with max 1A at 2.5V u will need an 2.5Ohm resistor at the end of the cycle. So u will need an 2.5ohm 5W at end and 2.5ohm + RDSon of MOSFET  4.2ohm on start. So will need to control the mosfet to have a resistor of 1.7 ohm. 
            Because IRLZ44n is an logic mosfet u will need few mV to have that resistance because if u look to data sheet u will have less then 0.8 ohm on 2V and at 5V u have 0.028 ohm.
            Also the RDSon will depend of the temperature of the MOSFET, so from my point of view cant be done with an logic mosfet!!!

             2 - the second option is to control the voltage to make that U/R constant. so if u will have same 2.5ohm 5W resistor and can make an voltage regulator controlled by the microcontroler u can also have an constant current discharge. 
 
             I will try the second version an i will make the presentation video tomorrow. All the parts u brought are ok but on constant discharge will discharge with only 250mA. if u want to reach 500mW put 2 resistors 10 ohm in parallel to reach 5ohm and if u want 1A u need 2.5ohm resistor or 4 10 ohm in parallel.
 
            Also form other test is better to use  different MUX one for Vbat reading and one of Vres reading, in my presentation i use the odd inputs (0,2,4,6,8,10,12,14)  of mux for Vbat and even inputs (1,3,5,7,9,11,13,15) for Vres. I use also 2 mux but was easy to wiring with odd and even but better is to be separate one mux all 16 inputs for Vres and one mux for Vbat.  Because I see the circuit need few millisec after the mux change the input to drop the voltage from 4V (battery voltage) to 0.018V (voltage droped on mosfet), for that i need to ad an 50milisec delay on each reading. when u have 32 batttery will and some sec of delay.


best regards
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#12
(09-13-2017, 06:28 PM)srk Wrote: Simon, would you be willing to sketch out the placement of the additional resistor and transistor based on his initial design? I have all the parts coming my way to build out his initial design. Thanks!
Google is your friend Big Grin
Mosfet dummy load: https://www.google.com.au/search?q=mosfe...4&bih=1192
Mosfet Constant current : https://www.google.com.au/search?client=...UyL2b3MA9Q
While you can use an NPN transistor to drive the Mosfet, as you can see at the links, an Op Amp is the preferred method.
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#13
Constant Current programabile Discharger:

Constant Current vs Constant Load

       

Constant Current with variabile resistor theory

        


Constant Current with constant voltage controlled by arduino PWM  - Parts & Schematics 

       
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#14
Constant Current Complete Boards

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#15
So nice setup you got there. Thats proper DIY Smile
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#16
30 Cells Constant Current Tester

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