Arduino True Battery Capacity Tester (Li-Ion/NiMH/NiCD/Pb)

 If anyone saw my last instructable "Simple Li-Ion Battery Power Tester" they can now upgrade to a computerized hi-tech version that is capable of measuring almost any type of rechargeable or none rechargeable batteries (but it will drain one charge from them in the process).
It can even connect to a PC and give you a full "Data-sheet" graph of the discharge and total capacity.
Note that this is my first Arduino project (I am not counting my "blink LED").

Step 1 This is what you can get at the end...(just to get you interested)

This is the graph you can get from the text file sent to the PC during drain cycle.

Comments

[loopingz]

It sounds interesting as this the kind of thing I was thinking building.
But I would gain hours to get these curves for four batteries at the same time. Do you think it is possible to modify it this way?

[paulryanmini]

hi all
fixed the code after a long night. i can get the setup to start up and the lcd turns on. it will then pick up what type of battery is connected and will measure the voltage and current of the battery, but the led wont illuminate which leads me to believe the mosfet is not switching on. im using a irf540a with a rds on of .052 ohms. any ideas?

Ive been using a 1.3v 1200mah AA rechargeable battery nimh.

any ideas?
thanks

[monbeamdistilleries]

Im having the same problem with the same part. Also trying to reduce the required display size from a 24x2 to a 16x2. Great circuit as I have tons of recycled/scavanged Li-ion cells to test before I use them making a new E-Bike battery pack.

[paulryanmini]

hi
i copied the code above directly into ardunio 0022 program. i have the duemilanove clone.

it comes up with the following errors:

dunkbat.cpp:3:10: error: #include expects "FILENAME" or
dunkbat:3: error: 'LiquidCrystal' does not name a type
dunkbat.cpp: In function 'void CL2()':
dunkbat:23: error: 'lcd' was not declared in this scope
dunkbat.cpp: In function 'void setup()':
dunkbat:31: error: 'lcd' was not declared in this scope
dunkbat.cpp: In function 'void loop()':
dunkbat:76: error: 'lcd' was not declared in this scope
dunkbat:99: error: 'lcd' was not declared in this scope


any ideas im a complete noob
thanks
paul

[abosebkk]

Dear paul

This is because the include file is not mentioned at the start. if you do: Sketch> Import Library>liquidcrystal , it will add the necessary header file to the sketch and compile correctly.

[slvr00gt]

Here is more detailed diagram of the same thing

[m_boby_k]

Hi slvr00gt, I' have seen your diagram but that's something I don't understand.
The FET voltage terminal is seems don't have connection to the drain circuit, how it's can give analog input (FET voltage) to arduino?

[slvr00gt]

Adding better quality diagram

[paulryanmini]

hi
its a fantastic circuit and ive started to build it. have you by any chance got a higher resolution of the diagram above i cant zoom in enough? thanks

[moris_zen]

I see some one made a diagram - great work

[slvr00gt]

Just added powerpoint file above.... My diagram jpeg was originally high quality, but this forum compressed it into nothing. So I added original ppt file

[techwiz]

Less word more little picture comments!

Isn't that the power of Instructables?

[blast09]

Sorry but I miss something...It seems to me there's a typo in PPT diagram.
Pin "fetVoltage[plus]" on discharge circuit is left floating around. Could you confirm this? Thanks for great work anyway.

[paulryanmini]

thanks very much. im building it as part of a assignment for power electronics.

i will then alter it to work with 36v 14ah lithium polymer batteries somehow :-) if you have any ideas that would be great

[arnefl]

Sure I do :-)

[slvr00gt]

Here is my change to the code. Change adjusts the voltage when the test stops. It also prints out capacity over time to the serial port. and changes input pin numbers to what I end up using


$ diff my.cpp orig.cpp
7,8c8,9
< int ledPin = 8; // select the pin for the LED
< int SPKPin = 9;
---
> int ledPin = 13; // select the pin for the LED
> int SPKPin = 6;
18c19
< int FetVoltage = 0;
---
> int FetVoltage = 5000;
66,67d66
< Serial.print("\t");
< Serial.print("Capacity[mAH]");
75c74
< if ( (BatVoltage-FetVoltage) > SelectedMinThreshold && !done) {
---
> if (BatVoltage > SelectedMinThreshold && !done) {
86c85
< TotalCurrent=TotalCurrent+MillisPassed/1000*(BatVoltage-FetVoltage)/10/3.6;
---
> TotalCurrent=TotalCurrent+MillisPassed/1000*(BatVoltage-FetVoltage)/2.2/3.6;
98,99d96
< Serial.print("\t"); // prints a tab
< Serial.print(TotalCurrent/1000);

[slvr00gt]

In the code you have following if-statement, where you check whether or not battery has reached the minimum., but in the check, you don't factor FetVoltage.

Should this statement:
"if (BatVoltage > SelectedMinThreshold && !done) {"
be replaced with this:
"if ( (BatVoltage-FetVoltage) > SelectedMinThreshold && !done) {"

Thanks for the great instructable. I just finished building your design!

[moris_zen]

It makes me happy people do actually use my designs .
It has been a while a go and I dont remember exactly but as far as I do I connected two points on the battery as the voltage on the Bat is the difference between them (or was that over the resistor) .
Pls check if the voltage is not clearly just over the battery - If I got it wrong then there may have been a mistake yet the voltage drop over a good FET (< 40mohm) could be neglected- o that may be the reason .

[moris_zen]

OK .. correction - the voltage on the top of the resistor is the battery voltage - it is correct .

[slvr00gt]

Yes, the voltage drop over FET is negligible ( roughly 0.03V), but in your design it is measured and used in calculation:
TotalCurrent=TotalCurrent+MillisPassed/1000*(BatVoltage-FetVoltage)/2.2/3.6;

[slvr00gt]

My second question is how do you get drain data from microcontroller board to PC?

[moris_zen]

I sent the info over RS232 . if you connect your PC (same channel I use to program it) ad open a terminal in the correct baud rate - you should see the information just coming in .
Copy paste into excel and make a graph for it .

[TheBlackBird]

Hello.
I would like very much to build this, but can you please clarify some aspects.
Do you use one or two connections to the arduino, because in the schematic you only draw one (on pin 19), and in the code you mention pin 23
"int sensorPin = 0; // select the input pin for the potentiometer (pin 23)
int sensor2Pin = 2; // select the input pin for the potentiometer (pin 23)"
and what is the potentiometer ?

In short i don't understand what pin of the arduino i connect where.
Thank you.

[moris_zen]

Hi ,
Sorry for the late response ,
I don't really remember so much but I tried to review the code .
I used the ledpin as the output pin (all ground must be connected) . The ledpin activates the FET and thus the load .
There might be some mixup between the pins in the code and in the comments because I decided to make my own arduino (ot use the purchased board) and thus indicated the physical (chip) pin in the comments (and I did a copy paste mistake in the two lines of the sensors).
In any case I used two pins for sensing the voltage across the resistor . the difference if the voltage drop on the load resistor and when you divide this by the resistance you get the current flow .
I hope this helped .

[TheBlackBird]

Moris, it is great that you have made this instructable.
But because you did it in a haste there are things uncleat.
So preety please :) can you post some answers from time to time.
Don't let us hang.

[Euphorbium]

BatVoltage = sensorValue*4.887; Where does this 4.887 comes from? Is it some constant?

[Madrias357]

Yes, I read all of the little comments.

[mathman47]

Great job.  Finally something useful for the Arduino.   I can use as a ham radio operator with lots of batteries.  Keep up the good work and post more when you get a new project.  Oh, does the FET have a part number or any markings on it?

[moris_zen]

It is all closed in a box now but I will give you a tip to how I select my components ...
when I have old electronics I take a torch and burn the back side very well - then when all solder is solf I hit it many times on the other sides and the components just fall off . I colect and sotrt them (Just did it with an old TV set) .
The when I need a FET or any other components I just search the net for the PNs on the components and take whatever is best suited .
So back to your question - you can use almost any FET that can withstand the current (most will do the job .. you need low impedance .. check out their DS from the net)
good luck .

[moris_zen]

The box is shut tight and I cant get to the PN of the FET but I just open old TVs and look around then search the PN on the net and see if they can meet the current .. here I really over did it :-)

[guyfrom7up]

very nice and well done!  This is an arduino project I actually like!  It used a real schematic (thankyou! lol) and it was interfaced with a computer, which is one of the main convienient part of the arduino (otherwise i strongly suggest a plain microcontroller).  I'm currently working on a "supermeter" which is pretty much like a multimeter with a whole bunch more functions.  The current model i'm designing has about 40 functions and I'm adding some code (I'll be using an avr, not an arduino, even though they are both avr :P) so that it'll now test battery capacity.  Great instructable, and 5 stars!

[moris_zen]

Thanks for the FB .
I would love to see your instructable - pls post it when you are done.
I was thinking of adding charging capability to it but after finding a micro controller multi charger for 35$ I decided to just buy it ....
I don't think it tests for the actual capacity .. I should get it soon from Ebay

[moris_zen]

Thanks .
The schematics is real simple and is based on the original Arduino Delicima and then just a fet with a load .. tx rx from arduino to pc (you actualy only need tx) and you get a clear table for excel.
post you project when you are done!
good luck.

[cipriti]

I used a BUZ11 fet and it's not working. Any ideeas?

[megapix]

Most likely reason would be connecting it wrong. Another possibility is that the threshold voltage for a BUZ11 (the voltage where it just starts to turn on) can be as high as 4 Volts. So it could be that the 5 Volt drive from the Arduino is not turning it fully on. When they measure the resistance in the data sheet they put 20 Volts on the gate (Vgs).

[MattSum1]

Can you provide some more info on the non processor electronics?  In one step you mention "a FET with "on" resistance of ~8mOHM" in which I'm not sure what the ~ means. Then later you say "This FET was removed from a TV set - it has 4mOhm on-resistance.cool!" which is different.  Any info on what different resistances does in this case would be very helpful.  Also, besides the 2.2 ohm 10w, I see another resistor, a couple led's, a "reset" button, and of course the LCD.  Can you maybe provide some info on the "non arduino" components & possibly a schematic showing the non arduino stuff?

[moris_zen]

 I will try to answer the best I can - you have many questions .
1. The 4-8 mili Ohm is approximately the "on" resistance of the FET - use an N channel FET any kind you find (try Wikipedia for info on FETs if you don't know what they are .... basically it is an electronic switch with low resistance).
2. all Arduinos have a reset Switch used to restart the device / program it . if you are not familiar with Arduino - pls go to the web page I placed in the article . I can't pass 2 weeks of learning in a sentence - you must o the web page and read about it - what it does and how .
3. I just used a led to indicate when the FET is "ON" with a resistor in series so not to over load it (1K ohm will do the trick).
4. to connect an LCD you need to use the library in the Arduino (see SW include file) . you can find all the info and an example on the Arduino web page .
I hope I helped - I know not completely but I can't copy all Arduino site here .
I hope you understand.

[amidar]

Hello,
just a simple question. :-)

What for is division with 3.6 in this formula ?

TotalCurrent=TotalCurrent+MillisPassed/1000*(BatVoltage-FetVoltage)/2.2/3.6; 

[moris_zen]

 Nice to see someone actualy read the code - way to go!
3.6 is 3600 seconds (an hour) 60x 60 - I put 3.6 due to removing 1000 from the (what do you call the upper part divisor divider .. whatever)
:-)

[amidar]

I figured that just about 10ps after i pressed "post comment" button ! :-)
Anyway, here is one very  instructive site releted to battery charging/recharging.
I learned a lot especially from schematic part of the project. :-)

www.avr-asm-tutorial.net/akkuload/en/index.html