My Battery Discharge Analyser Project - Page 1
Forum section: electronics / projects

author: andyg
author_rank: Regular Contributor
timestamp: January 23, 2011, 12:52:37 pm
content: This is my first post on the forums, I've watched all the awesome videos, and funny after watching the last post about the batteries, is that I am actually working on a open source project about analysing battery discharge curves. So I thought I'd post this and show it offA while ago, I thought I'd make my own battery discharge analyser, something that can discharge a battery and log the voltage curve. So I built my own based on the Arduino. I made one on prototype board with the Atmega chip in it, a MOSFET on a old fan cooled computer CPU heatsink, it works okay, theres a few issues to iron out, but in general it does what I want it to do.This is my first "real" project other than flashing LEDs etc, I do have a slight engineering education but I now work as a professional photographer and do some work in electronics manufacturing (assembly). But I like to tinker around a bit with electronics as a hobby.Heres some photos of the prototype:As part of my work in manufacturing, I have the pleasure of being able to use Altium Designer also, so I have made a SMD board of the project, that I might get made. I don't know how much interest there would be out there, so I was wondering if anyone out there had any input on whether this might be worth forking out the dollars for a real board etc, as-in, would anyone buy it? Is there a market potential here in the maker, hobbyist area?Heres a 3D render of the board:The PCB isn't ready yet, its just a preview of work in progress. Theres a few more things that need to be done (e.g double checking everything, cleaning up silkscreen, LCD mounting holes etc)Thanks!Andy

author: andyg
author_rank: Regular Contributor
timestamp: January 23, 2011, 12:55:32 pm
content: I forgot to add, what its suppose to do- Programmable battery discharge analyser- Analyses batteries 1V to 15V- Discharges 0-2500mA (about 10mA resolution)- Programmable termination by voltage, time, capacity, or dV/dt.- Logging of data (capacity, voltage etc) to SD card, to CSV file- Uses Arduino libraries for easy modification of firmware by hobbyists- Spare I/O ports broken out so users can add custom features- USB port access (via FT232RL chip), can be left empty if no USB required- TTL-UART terminals for serial interface (when built without USB)- Discharge in constant current, constant resistance, constant power modes- Internal resistance test (by multiple constant current discharge steps)- 16x2 LCD display showing current status- 4-way key pad navigation- Stand-alone operation, no need to connect to computer- Can be powered by USB or external DC jack- Calibration via serial port terminal- MOSFET mounted externally, using appropriate heatsink for battery voltage and current discharge. This is so the user can customise their own mounting options.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 23, 2011, 02:31:27 pm
content: man! thats the 1D battery, you dont have to hide. nice project! with SD Card capable. care to tell what chip do you use to read/write the card? i have maha charger with discharge capability telling it can improve/restore dead battery, i just say it a crap! my dead battery is still dead! face it! i ended up discharging battery the normal way... using it. so what promise can this device make? if it want to go to niche? to be specific, what we can save by using this product?

author: andyg
author_rank: Regular Contributor
timestamp: January 23, 2011, 03:05:43 pm
content: Good recognitionI originally decided to make this to test my third party battery packs for my 1Ds. As I believed I may have gotten a few dodgy ones from eBay and wanted to test its discharge characteristic.Unlike the Maha C9000 AA/AAA charger, it does not do any charging, only discharge. So it doesn't do cycling etc. I did think about this, and to do it would add considerable cost to it. I have one of those Maha chargers too! But I think the Maha charger is pretty good.I guess the people its targeted to, are people who rely on batteries a lot and need to check its condition regularly. Such as people using cameras, the RC crowd and their toys, hobbyists wanting to see a visual graph of the discharge characteristic. I doubt it has any real general-population commercial use.It would be nice to have a computer program to see the plot without having to import the files to Excel etc, but I couldn't write a Windows GUI program (e.g .NET, VB, etc) to save my life!So if I open source it, maybe some enthusiastic person could build on it.It uses an AVR Atmega328 chip, the SD read/write code is done using Arduino sdfatlib. I originally tried writing straight AVR code using Chan's FatFs and i couldn't get it working. PetitFS worked okay, but wasn't really suitable for writing data in a practical way. So to sdfatlib for Arduino it was. The output from the MCU (5V) is level converted to 3.3V and drives the SD card.On a practical note, I did use it and found some battery packs with a out of balance cell, which was discharging to zero (falling off the wall) before the rest and managed to improve it signficantly by doing a few cycles (charging manually 16hrs 0.1C, discharge 0.1C).

author: tyblu
author_rank: Frequent Contributor
timestamp: January 23, 2011, 04:32:55 pm
content: Nice project! I like it.Note: forum seems to be screwing my youtube embed.

author: sonicj
author_rank: Frequent Contributor
timestamp: January 26, 2011, 10:31:47 am
content: thats pretty cool! how much power can you dissipate and what mosfet did you use? i'd like to replace my west mountain discharger with something bigger at some point.you could use processing to write a quick gui. arduino spawned from processing and wiring so its very similar to work with.OR, u could use logview.http://www.logview.info/vBulletin/highly configurable, works great!

author: andyg
author_rank: Regular Contributor
timestamp: January 26, 2011, 12:07:00 pm
content: sonicj:I originally designed this to handle 2.5A and used a IRFI530N mosfet.However in reality, it can only pass through around 1.5A max with Vgs=5V (my Vcc), and Vds=12V. This was with the opamp saturated on the upper rail (+5V). This is somewhat contrary to the datasheets which i used when i first selected the MOSFET, as the datasheets say it should pass a lot more than that with Vgs < 5V.And if i run it off my USB port, which is only about 4.6-4.7V, the controlled current is even lower.So I either need to1. find a new mosfet with a lower threshold voltage Vgs(th), or2. run my opamps with a higher power voltage supplyThe current control method is the same technique as on one of Dave's earlier video blogs.Thanks for the tips about logview, i might try it out. It looks very handy.I'm actually making a few changes to my design for the PCB build, I've worked out a way to add charging capability to it, with a addition of a few extra parts (a mechanical relay and some small mosfets). Depending on what parts are loaded, it can be discharge only, or charge+discharge, thus turning it into a "hobby charger" style set up.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 26, 2011, 04:24:36 pm
content: Quote from: andyg on January 23, 2011, 03:05:43 pmin the name of hell! few you said? third party? why the 1Ds owner need a "few 3rd party" batteries? and built a discharger to find out the dodgy one. its funny and i dont get it, except if you just want to do it for hobby or have plan to sell it. my "late" 1D have 2 original pack, and i never needed the second one, in any of my projects, so i cannot imagine how big is your project that need a "few" battery pack. why dont you get original pack instead of 3rd party? dont tell me its expensive. well that an OT rant, i hope you are not offended.anyway, have you successfully distinguished between the good one and the dodgy one? my normal way of doing is fully charge it, and see how many charge (volt) left after 1 day to 1 week not used.Quote from: andyg on January 23, 2011, 03:05:43 pmyes it is good, except at restoring dead battery, even its own brand battery.Quote from: andyg on January 23, 2011, 03:05:43 pmi can help you with that. but more complicated graph needs more time to develop.Quote from: andyg on January 23, 2011, 03:05:43 pmthanx for the interesting info. looking forward to use the library in my next project.Quote from: andyg on January 23, 2011, 03:05:43 pmhave you done test on AA size NiMH?

author: andyg
author_rank: Regular Contributor
timestamp: January 28, 2011, 11:46:52 am
content: QuoteYes, the price of a Canon battery pack is a bit high.... ~$300 each?! While a 3rd party pack is around $30-80. No doubt I'm going to try the third party ones. No offence taken. I don't see why aproperly built3rd party pack would be worse than the original Canon pack.I found some out of balance packs which I was able to increase its capacity again by running it through a few cycles of charge/discharge at low current (0.1C).My latest battery I got is a 2200mAh pack which appears to be true and correct when tested (measured ~2000mAh @ 200mA constant current discharge, so thats pretty reasonable), so thats all okay. (original Canon packs are rated 1650 mAh)QuoteI originally designed it to test these batteries as I have no real way of testing it (yes, even OEM batteries can deteriorate or fail too), but I thought it might be something worth selling, thus the PCB, but haven't decided on that one yet, depends on the est. price.QuoteI haven't used it on a single AA yet, technically it should work, but I'll try it one day. I did open up a battery pack just to see whats inside, but it looked like too much trouble to try and break the cells apart... I've heard of people repacking these NP-E3 batteries with Eneloops with great success.

author: Polossatik
author_rank: Frequent Contributor
timestamp: January 28, 2011, 03:33:26 pm
content: Quote from: andyg on January 23, 2011, 12:52:37 pmit all depends on the pricepoint i geuss, you should be looking at least cost * 2 as pricepoint. most likely the RC market is the biggest potential.you havevery cheap chargers who do discharging, some of the more expensive arestill only 80 $ (can only discharge 20 watt)but those can be connected to logview and get you plots of charge/discharge cycles.The main selling point of yours would be that anyone can customize the firmware at their wishes of course.Nice project, i like it.