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Discharger, With A Microcontroller (arduino)

By murankar, Jul 22, 2018 | | |
  1. murankar
    If you have listened to RCHN towards the end then you know Justin Pucci has been working on such a thing for almost 4 years now. He has never posted the Tech tip due to the nature of the topic. This project if done wrong can be very dangerous. As of late I have been want to work with my 2 arduinos that I have. I posses 1 Uno and 1 leonardo. This project is being built on the Uno for now. I will need the Mega at some point for the analog pins. My issue with the Uno right now is that it has 6 analog ports and 4 are used for the new screen. This makes reading 6 cells impossible right now. That's the reason for a different arduino. The mega has I think 12 analog ports which will work really well for me.

    I have had these two arduinos for a couple years now just sitting around. I have done some simple projects just to learn the platform. Its been fun but boring because they were not my projects. So on Monday (20180716) I decided to dust off the micro-controllers and the 2.8 inch screen I bought with the units. I found out that the screen I got will work just not for what I want. So I headed to Micro Center yesterday (20180721) and bought an adafruit 2.8 resistive tft lcd screen. It was about $30 and could have been bought off of banggood for way cheaper. I wanted to ensure I got one that adafruit supports. I know their code and libraries work. They are not the most efficient code base but they work. I got the screen tested and all is well there.

    My next hurdle was the IDE onn linux. While i got it work I am still having issues with my user account and the tty communication. I assigned my user account to the correct group and set the read write permissions as per the web and still no worky. My root account works just fine so I use my root account to transfer the sketches to the arduino only.

    I spent most of yesterday getting the header pins soldered on and getting the basic user interface designed. It was very fiddly to say the least. Getting all the coordinates worked out, font size and colors. It took me hours without mapping anything out. When I was done I was happy with it and thought it would be enough. Well today (20180722) I decided that I wanted more screens for different things. I have a start screen, a discharge screen and a stopped discharge screen. I also built in a countdown to simulate a discharge till I get that part set up. So the discharge starts at 4.2 volts and counts down to 3.7 volts and then goes to the stopped discharge screen. Whats missing right now is the user terminated feature. I want a screen press to stop the charge if the user wants to terminate the discharge for any reason. I am still learning the software side so I don’t know how to code that part.

    All of that so that we can read the voltage of the battery through the balance leads. My biggest issue right now is separating the voltages out of the independent cells. Since the arduino cant handle more than 5VDC each cell will need to be isolated. This is something I will workout over the next few what evers till its done. The idea of this is to have the controller shut down the circuit once a condition is met. My goal is 3.8 volts per cell, storage or any other situation they may need to stop the discharge.

    As for how we are going to discharge the batteries my goal is a load bank. My approach to this is going to be fairly simple, a bunch of resistors. Not just any resistors, power resisters at 1 ohm 100 watts each times 7 resistors. My target amp draw is around 25 to 30 amps. I will add a google sheets doc that will help anyone figure out their own needs or dreams. For now I am aiming at 700 watts worth of resistors at 1 ohm each in parallel. Once I get to this portion of the project I will write a dedicated continuation article on the topic. At about $15 each it will take a few days for me to get them. This part of the setup will be built to be modular so it can be what ever the end user wants as a load bank.

    OHMS Law Google Sheets

    This is the current welcome or home screen:

    As the pack discharges this screen will show the voltages: dischargeScreenlowRes.jpg

    When the discharge is stopped this is the final screen. It stays for 5 seconds and returns to the home screen. dischargeStopped-lowRes.jpg

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  1. Tony
    I will see what I can do to put this into a series when I have more time. For now though, I have to hit the sack right now though. I guess I have to go do that work thing tomorrow.....
  2. murankar
    makes sense to me. I am going to be working this as hard as i can for the time being. I really want this to work. I am excited about this new ground.
  3. Tony
    I think maybe we should turn this into a series so you can post updates like it is a blog. I have never really tested the series deal on here, but might be worth a shot with this one.
  4. murankar
    I got my fluke and my EOS Sentery battery voltage reader. My fluke and arduino are off by .14 volts, my fluke and EOS are dead on the same. So the Arduino is reading .14 volts higher than it should. not sure what is causing this but there is a difference. Something else to add to the list of things to do.

    After doing some down and dirt searching it appears the Arduino is about .14 volts off in reading, to the high side. If I can test this to be true then I can write code to adjust for this in the future. In factr i think I might do it now and see what happens.

    Ended up writting an .21 Volt subtraction. THis is getting me to with in .02 Volts over three batteries. I have 4 more packs to ckeck. I am validating against my EOS Sentery.
  5. murankar
  6. murankar
    Update Number 1

    I got the equation to read the voltage from 1 cell on a pack. So I plug the negative into a common ground on my bread board. The First cell is plugged into A5 on the arduino. Before doing any math I am reading a raw number of 910 on a scale of 0-1023. My volt meter reads 4.15 volts and after the math the arduino is claiming 4.45 volts. So something is a miss right now. I also got the screen to update with the single cell info. Now to figure out what it correct, the multi meter or the arduino.

    Just did a new reading I am at 4.05 volts per cell. A mains reading of 8.1 volts.

    As for a build list I will be making that as I go. That way people will know what they need.

    New reading and now I have about .2 volts difference.

    Thank you guys for the likes and encouragement.
  7. Tony
    This is a fantastic little project! I know I have had more than a few times where I needed to discharge a battery and I didn't have a drained Pb battery to do a regenerative discharge into for about 20 amps and the pack sat for a month or more fully charged. Finally, I was able to put it into a helicopter and discharge it, then put it at storage charge.

    You and I have been talking about this, and I think if we can find a way to do it with cheaper components it would be absolute awesome! Can't wait to see thing thing come together.