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Thread: One for the electronic experts.

  1. #1

    One for the electronic experts.

    Right I am having battery issues. That is AA battery issues, rechargables to be exact.
    i think some of them are fubared. But how do I know?

    heres the scenario. I use them 4 at a time in my thermal (think the power is 9 volts) and in my fox pro. Sometimes the thermal switches on other times it doesn't. recently the fox pro is starting to play up and I think it is battery related as well.

    anyway. Research on tinterweb shows how to test AA battery's but not under load. I tried to do it with a 100 ohm resistor but don't think I did it right.

    anyone able to help? I getting fed up carrying 20 sets of batteries when I go out, they weigh a tonne. I need to be able to separate the dead ones and chuck them.

    disgruntled of Hampshire.
    I can speak in-depth and with great knowledge about most subjects until some bugger who actually knows what he is speaking about opens his gob .

  2. #2
    firstly, ignore the so called high capacity batteries from 7dayshop etc. Some of these batteries lose 50% of their charge per day.
    Ideally, buy Eneloop batteries, and get a proper charger. e.g. Techno BL700, or other intelligent charger. Maha are good too I believe. They both can do discharge tests, showing the capacity on an LCD screen.
    Or - Put all four in series & measure the voltage across the whole lot. Should be about 1.2v per cell x no of cells with no load.
    Then connect your 100 Ohm resistor & monitor the voltage. It should drop a bit, then steady to maybe 1.1V per call (guesstimate). 1V per cell can be considered flat. Check voltage across each one individually too.
    100 Ohms isn't much load. Say your batteries are 2000mAh - they should be able to deliver 2000mA for an hour - or 200mA for 10 hrs.
    That would be...
    R=1.2 / 0.2 = 6 Ohms (an old speaker might do...)
    Last edited by simonl; 20-11-2015 at 23:21.

  3. #3
    You don't have to test them directly under load. If you are using 4 batteries in an item, the important thing is that they are all of an equal state of discharge. I always try to keep batteries as a set together rather than mixing them up. So newer cells aren't used with older cells.
    Charge the batteries, run the unit for a while, then test the voltage on each battery. If you have one lower than the others put it to one side. This way you will have loaded the cells. The longer you run the unit the greater the variance in voltage. If old cells stay of equal voltage you will only have a shorter runtime. When one drops out of range you get problems.

  4. #4
    The problem with not testing under load is that you can't ascertain whether there's high internal resistance, the key indicator of a duff cell. Think of a cell as a battery in series with it's own inbuilt resistor, all packaged up. The only way to establish the size of that resistor is to pass current through it, ie apply load.

  5. #5
    A bit more information I should have added at the beginning.
    All batteries are kept in sets and not mixed.
    They range in power from 2300 to 3200.
    Most are well know names such as Annsman, energiser, Memorix and Varta.
    They all lose power so will be charged the day before as after a week I don't think they would work.
    I do use a Maha charger. Three of them to be exact. Because I have to bring a bucketload of batteries with me.
    Last night in five hours use. Half of the xxxxing things wouldn't fire up the thermal. The ones that do generally last about an hour and a quarter to an hour and a half which I think is about right.
    They charge the individual batteries but show blocks rather than numbers.

    should I get get a more powerful resistor to give me a more accurate or better result.
    i will try the running of the units tomorrow and start measuring drops. I don't expect this to be a easy fix cos I xxxxing electrickery.
    I can speak in-depth and with great knowledge about most subjects until some bugger who actually knows what he is speaking about opens his gob .

  6. #6
    Quote Originally Posted by simonl View Post
    The problem with not testing under load is that you can't ascertain whether there's high internal resistance, the key indicator of a duff cell. Think of a cell as a battery in series with it's own inbuilt resistor, all packaged up. The only way to establish the size of that resistor is to pass current through it, ie apply load.
    That was my thinking from what I saw on the web.... Did I mention I hate eleckertrickery? Lol
    I can speak in-depth and with great knowledge about most subjects until some bugger who actually knows what he is speaking about opens his gob .

  7. #7
    use a 6v bulb from a torch as a load, and buy a little 4 x AA holder from ebay
    In fact, duplicate that several times & test them all at once. Whilst under load measure each cell for reference at the start & measure again when you see the bulb starting to dim. That'll pick out the badduns & be easy to monitor. 3 per test rig

  8. #8
    Isn't the key here that a rechargeable AA cell has a lower cell voltage than a non-rechargeable type and therefore isn't truly compatible. 1.2V versus 1.5V
    I have never found even high capacity rechargeables to be suitable replacements in NV or thermal. Lithium AA batteries are expensive and don't seem to last longer than a high capacity duracell or equivalent. So I look out for bulk battery deals on Ultra's at the supermarket or petrol station.
    Last edited by Leadwasp; 21-11-2015 at 18:27.

  9. #9
    Quote Originally Posted by Leadwasp View Post
    Isn't the key here that a rechargeable AA cell has a lower cell voltage than a non-rechargeable type and therefore isn't truly compatible. 1.2V versus 1.5V
    I have never found even high capacity rechargeables to be suitable replacements in NV or thermal. Lithium AA batteries are expensive and don't seem to last longer than a high capacity duracell or equivalent. So I look out for bulk battery deals on Ultra's at the supermarket or petrol station.
    Frequently, yes. It really depends on whether the device has been designed to run from 4x1.2V as well as 4x1.5V. He gets 75-90 mins from the gooduns, so I think we're okay here.

  10. #10
    Quote Originally Posted by Leadwasp View Post
    Isn't the key here that a rechargeable AA cell has a lower cell voltage than a non-rechargeable type and therefore isn't truly compatible. 1.2V versus 1.5V
    I have never found even high capacity rechargeables to be suitable replacements in NV or thermal. Lithium AA batteries are expensive and don't seem to last longer than a high capacity duracell or equivalent. So I look out for bulk battery deals on Ultra's at the supermarket or petrol station.
    I've found that the batteries that Lidl sell are fantastic for the money. I'm not sure of the UK price, but over here you can get a pack of 8 AA batteries for the equivalent of about 1.90.

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