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Checking voltage of batteries

Discussion in 'Sound, Music, and Intercom' started by Anonymous067, Jun 28, 2009.

  1. Anonymous067

    Anonymous067 BANNED USER

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    I've been told I can't use a standard volt meter because it doesn't have resistance or something.

    But here's my problem. I don't like battery testers because they just say "good" "bad" and "check". Well first of all, what does check actually mean, and what are their standards of good and bad. My standards of good are much higher than theirs are.

    so whats so wrong about using a standard volt meter??
     
  2. aminorking

    aminorking Member

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    The voltage of the battery can still be high, especially if it has been sitting around for a while, but it has very little charge stored in it. Therefore when you go to use it, you actually get very little out of it. A voltmeter cannot identify the charge that the battery actually contains.
    The multimeter test therefore is good to a point, and useful for identifying which bunches of batteries came out of a device together, in a crowd of lots more batteries, as they will have same voltage, but can not be relied on.
    Really you should be using new batteries in at least radio mics every show. You could use the used ones in torches etc to use them fully instead of just "disposing of them responsibly"
     
  3. Stookeybrd

    Stookeybrd Active Member

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    How do you know? :confused:


    There is more to electricity than just Volts. Amps, like mentioned in your other battery thread, are also important to measure. So as -aminorking- said, a multimeter may give a "false positive" result so-to-speak, of a battery's health.
     
  4. jkowtko

    jkowtko Active Member

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    Is whatever test you are doing working for you?

    I use a simple voltmeter, have the transmitters turned on for 3-4 hours per show, and will use the batteries a second time if they are over 1.38v for ensemble and 1.42v for leads (these are AAs, Duracell or Energizer). I have never had a battery outage during its second show, so whether or not the voltmeter measures differently from the battery tester really doesn't matter for me. (i.e., I've found a measurement threshold that works).
     
  5. Chris15

    Chris15 CBMod CB Mods Premium Member

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    From memory, as batteries die, their internal resistance increases. So with next to no load, as a voltmeter should have, you can't see the effect of that internal resistance.

    Now if you want to make a simple jig, just add a light bulb across the voltmeter...
     
  6. rwhealey

    rwhealey Active Member

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    The reason that almost dead batteries have voltages similar to new batteries has to do with electrochemestry and the fundamental way batteries work.

    I remember learning exactly why, but I can't remember off the top of my head.
     
  7. Anonymous067

    Anonymous067 BANNED USER

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    This is my philosophy too...but it was brought to my attention and therefore wanted to ask around.
     
  8. jkowtko

    jkowtko Active Member

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    I should also add -- I mentioned Energizer and Duracell because they seem to have a much slower voltage dropoff towards the end of their charge, vs cheap batteries like the Costco "Kirkland" brand. I would probably not use the Kirklands a second time unless their voltage was close to 1.50v.
     
  9. epimetheus

    epimetheus Well-Known Member

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    Using voltage as a singular metric for determining whether a battery is "good" or not is a completely flawed process. If I pick a used battery and test it with a voltmeter, which has a very high impedance, the measurement I'll get will not be the same as if i put that same battery in a device, power it on, then measure the voltage. The "load" that a voltmeter puts on a battery is much less than the device most of us are powering with the battery (wireless mics and IEM's).

    My current method is based on time. If I mic has been on for more than about 4 hours, the batteries do not get used again, in a mic at least. There are a lot of variables to consider here as well. I'm using Shure UHF-R and UHF-P mics. I would imagine that the older the system, the less effecient it is in battery life, but even that's not always accurate.
     
  10. Anonymous067

    Anonymous067 BANNED USER

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    So I should be able to test with a voltmeter a battery by placing it in the device it will be used at, powering that device on, and then getting a volt level? This would be the same as figuring out the resistance on the device and just putting a capacitor on one side of the voltmeter right?
     
  11. Anonymous067

    Anonymous067 BANNED USER

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    Yes, I do know how electricity works (to a point it is necessary in my field of work...).
     
  12. felixm

    felixm Member

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    Volts/Ohms=amps

    Remember the static shock is around 10kv or 10,000 volts and it may hurt but wont kill you but touch a live 120v AC line and it could kill you. A static shock last just for an instant where an AC power line can supply that voltage all day long. Volts is just electrical potential. Amps is the amount of power behind that voltage.

    When testing a battery for a car they test the amp output capability or cold cranking amps not the voltage of the battery.

    When something can't fail I change the batteries every set and let my mini Mag figure out when that are really done.
     
  13. NickJones

    NickJones Active Member

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    Which could lead to a new thread: Uses for used Mic Batteries.
    I did a show over Christmas with a high school with no real tech experience past 2 speakers and a 58, and they took great delight in joining two used batteries together, waiting for them to heat up and sticking them into each others pockets when they weren't looking. Amusing to see them jump if the battery exploded but not entirely safe.
    Nick
     
  14. aminorking

    aminorking Member

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    Just a few corrections
    1. Potential difference/Resistance=Current
    2. Amps is a unit of current not power. Power is measured in Watts (Joule/second)
     
  15. Anonymous067

    Anonymous067 BANNED USER

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    Thanks for clarifying that, I was just about to correct that myself.
     
  16. Chris15

    Chris15 CBMod CB Mods Premium Member

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    UHF-R systems have a battery level transmitted with the audio and viewable on the receivers and via wireless workbench. It's reasonably accurate, but needs to be told the chemistry of the battery in order to have any hope of giving an accurate run time prediction.

    Do we need to talk about what sorts of battery chemistries are appropriate for wireless audio usage?

    You want to insert the equivalent impedance which will consist of a resistor and depending on the nature of the load, perhaps an inductor or capacitor (if the load has inductive or capacitive characteristics). But for the most part, just an equivalent resistance will be fine - after all the complex impedance will only come into play with a non DC source...

    Note however that because of battery chemistry (galvanic cells), you may get a false voltage to start with anyway - just think about how the battery meter on your mobile can change if you switch it off and then back on again...

    Landfill.

    Or torches, remote controls, rehearsals, lectures and such things that don't matter if you need a battery change midway through. But NOT smoke alarms or other such critical devices.
     
  17. Anonymous067

    Anonymous067 BANNED USER

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    Whoops...too late...
     
  18. Chris15

    Chris15 CBMod CB Mods Premium Member

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    You do so at your own risk then... Whilst it will matter less for mains powered battery backed devices, it's still unwise to use a second hand battery for a life safety application...
     
  19. Wolf

    Wolf Active Member

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    here is an actual battery tester kinda expensive since most people just replace them after every show. but if you're interested BATTERY TESTERS
     

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