"Passive" battery drain in electrical devices???

Discussion in 'General Science & Technology' started by Giambattista, Nov 14, 2007.

Thread Status:
Not open for further replies.
  1. Giambattista sssssssssssssssssssssssss sssss Valued Senior Member

    Messages:
    4,878
    Wasn't sure what to call this thread.

    Please Register or Log in to view the hidden image!



    Basically, I first noticed this effect, if it is indeed for real, after buying a cheap little reading lamp at a thrift store that was powered by 3 AA batteries.

    The batteries were brand new when I put them in. It worked perfectly, and had a decent brightness for the little bulb. Just one of those portable reading lights, more or less. The bulb itself is only a few millimeters across, and probably a few watts as well.

    Anyhow, in the first week I had it, I tried it out basically, and it saw no more than between twenty and thirty minutes approximately of use. It was running at the same constant brightness/luminosity/what-have-you. About a week or two later, I turned it on again, and noticed that it was definitely dimmer than it had been before. I thought that was pretty strange. Didn't use it for another week still. When I did turn it on, it was a dull orange color, and then after a few seconds, the output cut quite dramatically, and it was barely giving off light. It was basically the filament glowing dimly, and it was definitely useless for any practical light output.

    So, to sum it up, we have good solid output at the same level for the first week and only about a half-hour of use. After about two weeks of non-use, it has become dimmer by about 50%. Only ran it for a minute or so during that period. Another week later, and it is practically dead.

    Seems to me that the batteries were definitely losing power to SOMETHING during that time, and it wasn't the lightbulb! My uncle is an electrical engineer, and he didn't seem to think that the batteries would just drain like that, but I'm really not sure, because they went really dim in a short time without any use.

    Is anyone familiar with this kind of thing? Is there some flaw in the circuit which would drain the batteries regardless of whether power is flowing to the lightbulbs or not. I mean, my portable cd player lasts longer than that on less batteries (I think it takes a single AA)!
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. leopold Valued Senior Member

    Messages:
    17,455
    batteries have what is called "internal resistance". this resistance is the cause of your battery drain.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. Fraggle Rocker Staff Member

    Messages:
    24,690
    Yes but that resistance is extremely low. A high-quality battery will usually last months or even years if it's not used. I've pulled "emergency" appliances like flashlights and radios out of closets where they've been stored for ten years and had them work just fine. These batteries wouldn't be much good for emergency use if they weren't built to that standard.

    Buy top-end batteries like Energizer or Duracell. They're worth the extra money in terms of sheer watt-hours delivered per dollar, much less shelf life. Places like Costco and Wal-Mart sell them pretty cheap.

    Rechargeable batteries can of course be a big pain in the tushie, if only because they're all different. The one in my auto jump-starter is good for about six months without use. The one in my portable cassette player will last about a month. The one in my cell phone runs down in about three days and is the reason I'm having trouble getting used to having a cell phone at all. Every time I want to use it the frelling battery is dead.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. Exhumed Self ******. Registered Senior Member

    Messages:
    2,373
    When you say "brand new" when you put them in do you mean you just bought them or that you just opened them? Batteries die even when not being used, sitting there in the package, because the resistance, although high, still allows a small amount of current. It shouldn't be significant after a few weeks, so it probably was that the batteries were actually old.

    Could just be some problems with the lamp though.
     
  8. greenberg until the end of the world Registered Senior Member

    Messages:
    3,811
    Similar happened to my Hi-Fi remote. It worked fine, with new batteries. Then I haven't used it for a couple of months, and now it's dead.
    And the same happened one time earlier with a VCR remote, too.
     
  9. Exhumed Self ******. Registered Senior Member

    Messages:
    2,373
    Probably just old ("bad") batteries, even if you had not put them to use yet.
     
  10. greenberg until the end of the world Registered Senior Member

    Messages:
    3,811
    They have been in the original package for months, yes. Original Philips batteries for the VCR, original Sony batteries for the HiFi.
    But they died over a year before the expiry date.
     
  11. leopold Valued Senior Member

    Messages:
    17,455
    you mean extremely high.
    the "shelf life" of a battery is on the order of years.
    a typical "D" cell will last a minimum of 5 years "on the shelf"
    not recommended because of corrosion.
    batteries should be removed from the appliance when stored for 6 months or longer.

    some brands even have a use before date.

    also because the dry cells have 0.3 less volts than a disposable.
    a disposable puts out ~1.5V when fresh. a rechargable, on the order of 1.2 to 1.3. that doesn't sound like much, but it adds up in series cells
     
  12. Giambattista sssssssssssssssssssssssss sssss Valued Senior Member

    Messages:
    4,878
    Batteries were for all purposes brandnew. The date on the batteries (the use-before-date) was 2012. Underneath the date, it said that all batteries will be obsolete after this date... just a metaphysical joke there about 2012.

    That WAS the date though. Never seen three AAs go completely dead in less than a month when they were practically unused during that whole time. In fact, one of the batteries is corroded now. I've also never seen brand-new batteries corrode so quickly.

    LIke I said, I get more use from one AA in my Sony Discman than these three AAs in this light which couldn't have been more than 1 or 2 watts. Watt-hours in AA batteries is around 2.5. With 3 of them, this little light should have lasted much longer than a half hour.

    What I really want to know is if there is ever anything about a circuit that could possibly drain batteries regardless of whether or not it is switched-on or "closed".
     
  13. quadraphonics Bloodthirsty Barbarian Valued Senior Member

    Messages:
    9,391
    Yes, absolutely. No practical circuit is a perfect open circuit.

    Which is to say that it's not the batteries themselves, it's the device you're using them in. Some small amount of current is draining from the batteries even when the device is in the "off" setting, and so, over the course of weeks, the batteries run down. This tends to be worse in cheap devices, which employ crappy switches and generally don't fine-tune little things like off-state consumption, but I've seen it happen in every flashlight I own (and I own a lot). Digital cameras are also very bad about this.

    I do notice that it seems to be worse in compact flashlights, presumably because the small dimensions make quality switches much more expensive. Big plastic clunker flashlights whose switches have 1/2-inch or more of travel seem to cut off the current pretty well.

    And, yes, I am an Electrical Engineer.
     
  14. Giambattista sssssssssssssssssssssssss sssss Valued Senior Member

    Messages:
    4,878
    Thank YOU for this most helpful response! I was suspecting as much. One month to drain batteries with hardly any use was just too unbelievable for me.

    I also bought a cheap LED bike headlight, and I have suspected much the same with this. In fact, I KNOW it has a problem. The biggest hint of unintended battery drain: when I turn it off, I still see a faint glow coming from the outer ring of LEDs!!!

    Please Register or Log in to view the hidden image!


    It lasts for about a minute and then fades. At first I was removing the battery cap (has a 3-battery cartridge that you can slide out) and the glow immediately dissipated. However, I became careless and stopped doing that, and it seemed to be a lot dimmer just a few weeks later, again, with not a lot of use in between.

    I'm going to be diligent in always removing the cartridge and see how long it lasts then.

    Would the battery cartridge possibly also constitute a potential drain? I have doubts that it would, but one never knows. At least, I don't.

    Well, for ten bucks, it's a great all around flashlight/headlight. Very bright, 3 different levels of brightness. As long as I can keep it from killing my batteries before their time, it's a great item.
     
  15. quadraphonics Bloodthirsty Barbarian Valued Senior Member

    Messages:
    9,391
    Yeah, it's this kind of thing that alerted me to how badly my headlamps were about off-state current. Three years ago, a friend and I both purchased identical flashlights, but I never bother to remove the batteries when not using it. He, meanwhile, is extremely diligent and takes the batteries out, even if it's only for a few hours. The result is that I typically need a fresh set of batteries every few weeks, whereas he's still using the set that came included with the flashlight.

    It's hard to say without knowing how it's built and how it's integrated into the rest of the device, but my guess would be no.
     
Thread Status:
Not open for further replies.

Share This Page