How to restore old cells…..for spying project :-)

[junglemike]

Hello folks. This is a good site. I enjoy reading it.
I can ask a question right away, but I would like to tell the "behind" story first. In case it's really boring, and you still want to help me – see the questions at the bottom.

I have some very old crappy camera (Aiptek Pocket cam 3mega). It is very old cheap toy, doesn't have any moving parts (not even focus) and is basically useless as camera (greedy pays twice?  --- I learned it hard way…)
But it has some remarkable useful feature. It can act as a web cam and it can record video. It records video in 320x200@15fps, in MJPEG format. Most modern cameras (including my Canon A610) can also record video in MJPEG format in much higher resolution , fps and quality.
But, my canon and just about any modern camera, can put not more than 30 minutes on 1gb SD card. (with good settings, my canon does only 8 minutes per 1gb SD card)
This old crappy camera uses very high compression and can record literally hours on just 1gb CF card (it's a pity it can't accept cards >1gb) Maximum I managed was 7 hours of non-stop video and card wasn't even half full. My DIY battery died. It makes this ideal for spying purposes. My good friend thinks some bad stuff happening in his house. So I'm trying to make this solution for him. I know there are surveillance solutions available but they are light years away from my budget (we are poor students :-( ). I'm not worried about battery size, I can hide this battery behind a book shelf or put whole project inside some sort of toy..

GOAL: I need this camera to record 10-20 hours of non-stop video!! And then repeat 2-3 times on single charge. It takes in 2x AA cells. With my best 2700mah AA's it can record only about 2-2.5 hours top (while encoding and recording video, camera is very hot, it probably consumes lots of power). I made a custom battery of four C-size 2400mah (ni-mh cells).(2s2p). Here's the picture:



It does some 5 hours or so on these cells. (these cells not new but they are in quite good shape)
I need from 4 to 10 times this much!!(to be able to record 2-3 days total) And I don't have any other batteries available.

I recently bought Maha-c9000 charger that I wanted for a long time (not connected to this project)
I played with it a bit and discovered that it can restore completely dead cells quite remarkably.
** I also discovered that my new GP 2700 were only 1200mah but that's another story***
There is this box in public places where you throw away dead batteries, right? There is one in our university. First, I took dead AAA 3s pack (300mah, ni-cd) for old cordless phones. I made 3 cycles on those cells. I know that 300mah is little low for Maha c9000, and you would probably recommend dong break-in cycle, but I didn't want to wait 40 hours
Anyway, capacities after 3 cycles are:
First cycle……56mah………..Second cycle…….214mah………….Third cycle……..306mah
!!!! That was really impressive. I don't know if I can trust these numbers, b/c even new 300mah cell isn't supposed to do 306mah@ 100ma discharge current (lowest setting Maha gives)
I also read at batteryuniversity.com that ni-cd cells have very large restoring capabilities (much more than ni-mh)
Anyway, I was so impressed, that I went to my campus and took any rechargeable battery I could find out of the garbage.
Here's what I got:\


They are all completely dead (as was that 300mah pack I restored) and worse still they are mostly unknown capacity and chemistry. These cells are from very very old laptops (before they used li-ion ).
I would like to try to restore them but I have couple of problems and questions. First , none of them fit Maha c9000, So I had to improvise on how to connect them. This is what I got: 1st slot uses strong conductive magnets to hold the wires, and 3rd slot uses dummy plastic cell with wires coming out.

This solution has very big disadvantage – THERE IS NO TEMPERATURE SENSING AT ALL!!!!!
And I really need it. When I played with some old cells after I got Maha, many of them missed the –delta V termination and were severly overcharged and overheated!!
Q1) How do I solve this??
U understand that I need large charge and discharge currents to try to restore those cells, but those cells were lying around for many years with 0v on them. I'm pretty sure they'll miss –deltaV.
Q2) I have no idea about the capacities (somewhere from 500mah to 4500mah) What charge/discharge currents to choose?
Q3) Let's say I find and restore 10 cells out of this crap, can I connect Ni-cd and Ni-mh cells in parallel?
Q4) How connecting Ni-mh or ni-cd cells in parallel would affect –deltaV charge termination?
Q5) Suppose I make a working pack out of all this. There is no way I will be able to charge this 2S pack with Maha, right? Do I need to disconnect this 2.4v pack into 2 sets of paralleled cells (each 1.2v) and charge them in 2 slots .
Maybe some sort of switch that would have 2 states (charge and discharge) – It would connect them in series (for discharge in camera) and in parallel (to charge in maha). What do you think?
Q6) Let's Imagine that all above problems are solved, how do I balance this 2S pack while in constant use?
TIA.

 

[Yucca Patrol]

This may not be the answer you are looking for, but it sounds like your best solution would be to use an old AC/DC adapter and plug it into the wall for uninterrupted limitless power.

If you don't have a box/drawer/closet/garage full of old AC adapters, go to your local thrift store and look through their junk until you find one with the power output you need. Clip the tip off of it and connect the wires to your camera.

 

[Darkpower]

This may not be the answer you are looking for, but it sounds like your best solution would be to use an old AC/DC adapter and plug it into the wall for uninterrupted limitless power.

If you don't have a box/drawer/closet/garage full of old AC adapters, go to your local thrift store and look through their junk until you find one with the power output you need. Clip the tip off of it and connect the wires to your camera.

I think the idea behind a spy cam is that there are no leads running to it that can be seen. Most spy cams used to catch nannys abusing children or roommates rifling through someone elses drawers generally have to be concealed in a self contained item without any wires giving it away. I once many years ago caught a maintenance worker at a apartment complex going into my apartment and using my phone and going through my unit without my permission. Hiding the camera, powering it up for an all day-recording session and connecting it to a VCR took lots of effort.

 

[Jarl]

The charger missed charge termination most likely because the cells weren't being charged hard enough- the -delta V termination is stronger the harder you're charging the cells. To start, do a break in with the capacity at 1
1000mah (yes, it's 40 hours, but so what). Use the capacity ratings it gives (write it on a sticker on the cell) as the charge current (i.e, if a battery has a capacity after break-in of 855 mah, go with 0.8 amps charging current). Run a few charge/discharge cycles, and adjust the charging current- you want it to be around, or just under, 1C for the strongest -delta V signal, and the best chance of it terminating properly.

Eventually, you should have final capacities for all the batteries written on stickers (final capacities means the capacity where more discharge/charge cycles have little effect on the capacity you C9000 gives you). Only use those within about 5 or 10% of each other, or else the pack will be damaged badly by deep discharge (which it seems you're planning to do). When it comes to charging the batteries again, it's a bit tricker. If I were doing it, i'd wire it as 2s/6p (say you have 12 cells in total) and 4s/3p. Attach each of the parallel batteries to each of the 4 ports on the C9000 (so you have 3 cells in parallel on each port) and set charge to 2A, or 1C for the combined battery (i.e, the capacity of each cell is about 1000mah, so 1C for 3 cells would be 3 amps, which the C9000 is unable to give, so using a 2A charge current is the closest you can get to 1C).


Alternatively, you could use 2 10,000mah D cells- probably a lot easier.


As for mixing chemistries, it's generally a "don't do it!" thing, but it should be ok when you consider how much of a bodge job this is. Try to keep all Ni-CD in one parallel string while charging, and all NiMH in another parallel string while charging as they have slightly different charging characteristics.


Of course, this is all "I think" and I accept no responsibility if it all goes poof on you

 

[shadowjk]

Also test the self discharge rate of these cells. Charge and let them sit for awhile, you were aiming for 10-20, so let them sit 24 hours and see how much capacity is left after that. You don't want a bad cell becoming a load on good cells in your pack.

 

[junglemike]

Thanks for answers guys.
Jarl, your Idea to try to charge them at 1C sounds good, but isn't it a double-edged sword?
From one side charging with larger current will increase probability of -deltaV charge termination. But from other side it will more overcharge/ overheat the battery (with no temp sensing) in case -deltaV fails?
2 D 10Ah cells , won't be enough, i'm afraid, maybe 2 of them or 3 of them in parallel.....
But this in case this pile of crap fails, i will have to buy them
You convinced me to do a break-in cycle, even though it takes ages.
Can anybody answer question 4)?

Yucca Patrol, this project has to be concealed and portable, If i could use AC adapter, making 2.4v 1A output would be piece of case of course!

 

[shadowjk]

As for question 4, I don't think parallell charging works very well even if you just have nimh in parallell...

 

[Jarl]

From one side charging with larger current will increase probability of -deltaV charge termination. But from other side it will more overcharge/ overheat the battery (with no temp sensing) in case -deltaV fails?

Kind of, but the C9000 is a decent charger, so it won't miss the -delta V signal at 1C- it's rated to not miss it at 0.33C, so 1C is making extra sure.

What were you charging at when it missed the termination before?

 

[Mr Happy]

Kind of, but the C9000 is a decent charger, so it won't miss the -delta V signal at 1C- it's rated to not miss it at 0.33C, so 1C is making extra sure.

I don't know that this is guaranteed. I think it's possible that some cells in very poor condition may fail to exhibit a -delta V signal at all and then the charger must fall back on some other termination method like max temperature.