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My Battery Discharge Analyser Project

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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!


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 to
1. find a new mosfet with a lower threshold voltage Vgs(th), or
2. run my opamps with a higher power voltage supply

The 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.


--- Quote from: andyg on January 23, 2011, 03:05:43 pm ---I 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.

--- End quote ---
in 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 pm ---But I think the Maha charger is pretty good.

--- End quote ---
yes it is good, except at restoring dead battery, even its own brand battery.

--- Quote from: andyg on January 23, 2011, 03:05:43 pm ---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.

--- End quote ---
i can help you with that. but more complicated graph needs more time to develop.

--- Quote from: andyg on January 23, 2011, 03:05:43 pm ---It uses an AVR Atmega328 chip, the SD read/write code is done using Arduino sdfatlib...

--- End quote ---
thanx for the interesting info. looking forward to use the library in my next project.

--- Quote from: andyg on January 23, 2011, 03:05:43 pm ---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).

--- End quote ---
have you done test on AA size NiMH?


--- Quote ---why dont you get original pack instead of 3rd party? dont tell me its expensive. well that an OT rant
--- End quote ---
Yes, 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 a properly built 3rd 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)

--- Quote ---except if you just want to do it for hobby or have plan to sell it
--- End quote ---
I 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.

--- Quote ---have you done test on AA size NiMH?
--- End quote ---

I 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.


--- Quote from: andyg on January 23, 2011, 12:52:37 pm --- 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?

--- End quote ---

it 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 have very cheap chargers who do discharging , some of the more expensive are still 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.


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