Alternative power/energy saving comp

Discussion in 'General Electronics Chat' started by Little Ghostman, Jun 12, 2014.

  1. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    Hi, it's time for the annual energy saving contest, every year in Devon Uk a certain School runs a competition, although I now live in Scotland I am allowed to enter as I have won it twice :D.
    This year I am needing some guidance, first the rules.

    1) While it dosnt have to be practical it does have to work

    2) The big points are for novelty and taking what would be considered a waste product and making it useful.

    3) I have to build 3

    This year I want to build a +/- 15V PSU from dead batteries, the School collects dead batteries like AA,AAA pp9 etc etc, they have a huge numbers in a tub and they get sold for recycling. So I thought what if I make a 1A capable PSU from them that could adjust upto +/- 15V.

    On the face of it I see joule thief circuits, maybe germanium diodes to isolate each battery for monitoring and low drop out regulators.

    What problems do you see with this approach? Any sugestions which way to go with it?

    I will update some of what I have looked at so far later.

  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Welcome back LG! Hope everything went well and your feeling better.
  3. wayneh


    Sep 9, 2010
    Sometimes "dead" means dead, and you wouldn't get far with those. But sometimes "dead" just means it can't keep up with the load, whatever that is. I have a basket of "dead" batteries that I use in low current things like digital clocks. They'll go years sometimes, long after they were unable to even start my digital camera.

    Personally, I'd like to have a battery rating device. I'd like to stick a battery in and be told to trash it or keep it, and sort it for various duty levels. I'd especially like a device that could give me the state of charge of any rechargeable battery, and its capacity. I wouldn't mind if it was not an instant feedback, since it would probably take at least a few hours to determine the health of it. I have the data acquisition tools to build my own, but ....

    If you're hoping to win the competition again, consider the audience, the judges. I'm not sure many regular folks would see the value of your power supply. You've won before so you know what you're doing. I'm just suggesting that something with more "obvious" utility might get more notice. Something like a wifi router made from coffee grinds. :D
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007

    Here's a discharge circuit that I think came from Electronics Design magazine's Ideas for Design section. Adjustable discharge current and cut-off voltage. Uses a analog wall/desk clock to time. I was going to try it, but haven't yet. Could be scaled to any battery and current.

    wayneh likes this.
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Well you need 30v total, and "dead" AA and AAA cells are often under 1.2v each.

    So you would need a series string of 25(!) cells just to meet the 30v criteria, and of you wanted the thing to still be working when the cells were badly discharged (0.9v each?) that would need 33 cells. :eek:

    Then to get 1A output it depends on the weakest link because the cells are a series chain. And dead cells are notorious for having high internal resistance and not being able to supply much current.

    Even worse, once the current rises the cells in better condition tend to override the cells in poor condition, and push reverse current through them so the output voltage falls really badly.

    So having 25 to 33 cells in a series chain, where the cells are of different ability and different point sin their life cycle, makes a really bad power source. Sorry to say. :(

    I like Wayneh's idea of a good battery "rating" device.

    Maybe something with a microcontroller that could quickly pulse different load currents on a AA or AAA cell, and "rate" it for it's life and/or ability to still keep using it in a low current application.

    I often find that a pair of AA cells that fail in my remote control can still prove some months of use in a tiny household clock, or even another remote that gets used less frequently.

    The benefit of using a microcontroller is that it can use the minimum time at load, to reduce the drain on the battery caused by the test. And it can display more info and suggestions. And if you are really clever you can power the tester from the AA or AAA cell under test! (tiny 1.5v to 5.0v converter modules are available on ebay for a couple bucks).

    PS. Good to see you back! :D
  6. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    Hi Guy's, sorry. I originally posted alot more information, however when I clicked post it all froze. So I ended up posting a much shorter version!
    The ECO HUT as we call it, is a huge wooden science center/hut, it sits in a field and is used for ecology experiments, it does have solar etc for power but the competition each year is to design something that would enhance or be useful to have in or around the center.
    So the psu idea is to have a power source that uses something that would normally go straight to recycling, the psu is for use in experiments around the center where you need +/- power supply. The center has a drop bin for dead batteries that local people drop into, it is based at a local supermarket and gets around 500 batteries in t a month.
    I have tested around 300 AA/AAA and the voltage ranges from 300mV- 1.3V, so that got me thinking... not all the batteries are actually dead, if I build a PSU say the physical size of a car battery and stuff it with these dead batteries and a micro then it could be useful. So I was thinking banks of battery holders for different size batteries, each battery individually monitored etc and switched into the main feed say via joule thief to the output. The micro could swap in or out as many cells as it needs to meet the current/voltage demand when its needed.
    Not sure how to get there but my idea in a basic way goes like this...

    Starting backwards at the output

    Final output comes from 2 voltage regulators controlled via micro, these could have MOSFET bypass on them for the extra grunt, the regulators are fed from a DC-DC converter, this could be say 60V-20V, this is fed from a cap bank that is kept charged to around 60V.
    Now my problem is back from that point, I know this thing will need to have maybe upwards of 100 cells in it, and that isnt a problem, I would like to measure/monitor each cell independently by a micro. Any cell that drops below say 350-400mV gets replaced and is ready for the recycle man.

    The reason I think it would win is because it would use something that is currently wasted, the center just sends the cells off and gets paid for them, but most the cells still have at least 600mV in them so that is a waste and could be used.
    What I cant work out is how to go from cell to cap bank, at the moment the only option I can see is to have each cell behind something like a low drop diode (0.2V), then into a individual joule thief, this feeds into the main cap bank.
    Unless there is a better way. The main points I need to watch to win are,
    Each cell that leaves the PSU is finally dead and cant be used anymore in a reasonable manner, so I need to set a final Voltage point that the cell type is declared dead, I am thinking around 250mV-300mV.
    This way the center gets a unit for field work that uses something they get for free in large volume, they will still get the money for the dead cells anyway. The cost of the PSU matters, in order to win I have to use stuff I can beg,borrow or get donated. I am allowed to spend £10 on parts but can use any parts I take from things I find at the recycle center and from a sponsor.
    My sponsor this year is Linear Technology and they are allowed to donate £50 of parts. I know from an engineering point of view it seems stupid idea, but the criteria is innovation and to use something ideally that the center dosnt use, for example one group is making a small steam powered generator to produce 12V, the steam is produced from sunlight via a frenzel lens, (they will get good marks for some parts, but ultimately they will not win because it needs sunlight so cant be used at all times).
    We could use solar, but would get very low marks in some places because the center uses solar already. I know the scoring sounds complex but its easy once you have been through it a few times.
    The prize is really cool, because it is sponsored by C.A.T (center for alternative technology) and some universities, I get credits, this means that when I am older and go to university I get some of my tuition fees paid for, also I get £1000 for a charity of my choice.
    Size wise it needs to be no bigger than a car battery or a deep cycle battery (approx 2 car batteries ). I have access to around 2000 different cells at the moment, I would like to be able to use a mix of cells at the same time. I am working on a rough schematic that might give you a better idea of what I see
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Sorry to sound negative about your idea, but... It might be possible to do, but to me it looks like a fail from a practicality viewpoint.

    Cells so badly discharged will leak, so it will be a real mess. Then there is the issue with the operator workload of inserting all the cells, then getting feedback from the device about which cells need to be changed and then constantly changing cells within a big battery bank full of gooey leaky acid covered cells.

    Then you have the significant problem that you can't really connect differently discharged cells in series, it performs really bad. And you can't connect 0.3v cells in parallel with 1.3v cells either.

    So now you have "hundreds" of cells that each need their own joule thief...

    I think if you want to win, you need something practical, useful and desireable. And this idea (to me) looks like a bust on all three counts.

    If they have hundreds of dead cells what about an automated sorter? You stack cells in the top of a hopper and it measures each cell in turn and a motor pops it into "good" or "bad" bins? That has some benefit that the 1.3v cells can be automatically removed and allowed to be re-used. It's useful AND cool. Winner material. ;)
  8. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    Hmmmmm, back to the drawing board! There is little point sorting the cells as they wouldnt be used much without some kind of application for them.
    I might have a total rethink and go with something simpler, It's really hard to explain the scoring system, its the kind of thing you need to have attended a couple of times and actually see the projects and there scores.
    I have another idea, but I am having trouble working out roughly where I think I would gain or loose points on it. Like at home they have a compact tractor exactly th same as my old Kabota, its around 15hp and 2 cylinder. VERY basic tractor that once started only has a couple of head lights that you can switch on, so most the time once you have started the machine and it has topped the battery back up from the starting process, the alternator isnt doing anything.
    So I thought about adding a couple of leisure battery holders on the back platform, they use a number of these batteries around the center to power most things, they are normally topped up via solar spaniels or a couple of homemade wind turbines (tiny ones).
    Despite this the batteries have to be regularly charged via a normal mains powered battery charger. So seeing as the tractor is used most days my idea is to have a switch to change over to the batteries that need charging, start the tractor on its own battery, wait 10 mins until its topped up then flick a switch and have the alternator charge the other battery in the cradle.
    Its not great point wise but would be useful for charging the spare batteries and a bit more reliable that the wind and solar chargers they use. I am ging to the center today, so I will have a walk about and see what I can come up with idea wise. I would love to build a hydro charger and power unit, but I dont have enough time, the center has a long slope that would be ideal for laying a 1/4 mile pipe down to a turbine. Also I dont have the money for the pipe, but that would get killer points, all I would need to do is tap into the top drainage ditch and discharge into the bottom one. plenty of water for a small hydro unit.
    I was going to do a methane bio reactor, but this year they changed the rules, so now I cant use 'EXPLOSIVE' Gasses :(.
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Welcome back, LG.
    Will the judges take into account the extra tractor fuel needed to provide the energy to charge the batteries? That could lose points if the scoring system is eco-biased.
  10. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    Thats the whole point, there is no extra fuel used, the tractor when in use has no electrics (unless its dark and lights are on), there are no gauges or anything else electrical on these tractors.
    So once started and being used the tractor just charges up the battery that started it, after a while the battery will reach full charge, then the alternator is still spinning but the juice isnt going anywhere as such. So if I add another battery on a cradle that is switched in once the starting one is charged, then the tractor isnt going to use very much to charge it. These tractors run all day on £5 of fuel, so even if you were to factor in the extra pull on the motor because the alternator is actually charging rather than just spinning, the cost would be tiny. Far cheaper than using a battery charger connected to the mains.
    Dont get me wrong, it isnt a great winner, I dont think points wise it would score much for innovation or execution, it would score well for resource use and cost saving, but it isnt MY kind of project its too bland :D. I am still wondering about a small scale hydro :D, they have a large pond with a small waterfall, just maybe it might run a small wheel to charge a battery via say a alternator.
    Its caught me off guard because I was sure the dead battery one was a goer, now I have wasted 3 weeks thinking time, so time to crank up the brain and find plan B
  11. Markd77

    Senior Member

    Sep 7, 2009
    Unfortunately the power to charge the battery does cause extra load on the engine, and engines are very inefficient. It's much more environmentally friendly to charge them from the mains.
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    You can easily confirm that. With engine idling just watch the rev counter drop back when you switch on a heavy electrical load (in your Dad's car, if not in the tractor :)).
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
    That works better in old cars as a demonstration. New fuel injected cars quickly respond between no headlights and high beams.

    You might get a more noticeable effect on a small tractor with a carburetor.