Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I AA batteries in parallel

  1. Jun 19, 2018 #1
    Hey, so I tried to get a lot of Amps and primarly my tool are batteries, so I have 3 batteries that I have connected together in parallel (+ with the + and then - with the -) they are 1.6V Kirkland batteries that are all brand new. So when I took a machine I have to calculate the voltage and amps from a single batter i got 1.6 V which is what was supposed to be and I got 0.3 amps which is I guess normal for a AA battery? However when i connected them with a stripped down telephone wire (copper) and measured the same quantities I was expecting to get 1.6V and 0.9 amps... You know, pretty simple math there... However I got 1.6V and 0.3amps... My batteries are well connected but I keep getting a reading of 0.3 amps... What is happening? P.S the machine I was refering to is a multimeter.
     
  2. jcsd
  3. Jun 19, 2018 #2

    anorlunda

    Staff: Mentor

    Connected them how? Please show a diagram of all the connections, and the load, and where you make measurements. You can use the UPLOAD button next to POST REPLY and PREVIEW to insert pictures into your post.
     
  4. Jun 19, 2018 #3
    Ok so in the pic you can see (could be a bad pic but enough details tbh)
     

    Attached Files:

  5. Jun 19, 2018 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I can't be certain of the circuit you are describing but it doesn't surprise me that the current that your battery or batteries were supplying would have been the battery volts divided by the resistance of the "machine" you were using. (possibly 1.6/0.3 = 5.33Ω) This would be the same for any number of batteries in parallel and it suggests that your batteries are each quite capable of delivering 0.3A without dropping any significant volts.
    So I reckon that your Multimeter is the thing that's limiting the current. Its internal resistance makes it unsuitable for doing the measurement that way.
    If you want to find how much current your batteries can supply, you need a range of known resistances lower than 5.5Ω and you need to measure the Voltage across the resistor. You can then do I = V/R to find the current that the battery is supplying. I'd imagine that an AA battery could supply up to 2A for a brief time.

    What current can you get with two batteries in series? I would think you could expect higher than 0.3A; possibly 0.6A but the internal resistance of the batteries may limit the current to a bit below 0.6A.

    PS You should make sure that you cave good contacts around your circuit it's no good just holding meter probes and juggling around with multiple batteries (sorry if that is obvious for you). Also you should take care that components don't get hot with high currents and burn your fingers.
     
  6. Jun 19, 2018 #5
    Ah that might be why to be honest... And yes lol I do know about the connections it's because I took it apart not too long ago and I hadn't put it back together so when he asked for the picture I just put them side by side, and in series you'll get the same current but different volts... However looking at the machine I do think there is a cap of current it will measure as there seems to be a 320mA logo but seems to be faded, so quite possibly it does have a cap. Thank you!
     
  7. Jun 19, 2018 #6

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    That's just an assertion which will only apply if the batteries are going into current limit (which I doubt, for AA cells). If the resistance of the meter is the main resistance in the circuit then the current should go up with the volts - unless there is something else going on that you haven't mentioned.
     
  8. Jun 19, 2018 #7
    Oh I didn't know about that, will read/research more about that. Thank you!
     
  9. Jun 19, 2018 #8

    russ_watters

    User Avatar

    Staff: Mentor

    Amperage is something you measure in a circuit. You don't have a circuit, you just have a bunch of batteries. Sitting there by themselves, the amperage is zero.

    So what you really did is short them with the multi-meter. You are lucky you were only using batteries and weak ones at that, otherwise you would have burned-out or burned the fuse out of your multi-meter.
     
  10. Jun 19, 2018 #9
    No no, I do have a circuit, that picture was just the set up of how the batteries were connected...
     
  11. Jun 19, 2018 #10

    russ_watters

    User Avatar

    Staff: Mentor

    Right. So measuring amperage is meaningless. A bunch of batteries doesn't have an amperage.
     
  12. Jun 19, 2018 #11
    Well it's to build an electromagnet... But I need a lot of amps.
     
  13. Jun 20, 2018 #12

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award


    so have you built your coil ?
    if so, how many turns on what size former and what wire gauge ?
     
  14. Jun 20, 2018 #13

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    This can be a difficult exercise for someone not familiar with the business. @davenn wants that information so that you can work out the resistance as well as the magnetic field it can produce.
    If you have a battery then the coil needs to have as many turns as possible, consistent with the battery volts and the available current. It's best to have some idea of a plan for coil winding or you can have too few turns and less Field than you could get - plus you could be taking more current than the battery can supply comfortably. Too many turns and the battery will not have the Volts to put sufficient through the coil.
    This is not highly critical but it's worth while getting somewhere near an optimum.
     
  15. Jun 20, 2018 #14
    I've been testing more... So far I've got around a bunch of iron nails together around a cm in radius and I've wrapped around 600 times on it. I'm just trying to figure out the best option
     
  16. Jun 20, 2018 #15

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    You will certainly benefit from choosing things 'right'. That will involve having an idea about the resistance per metre of the wire you are using so that you can get the maximum sustainable current from your batteries.
    If you can find just how much current the battery (or several in parallel) can supply (with the procedure I was describing above), you can use the best number of turns for the job.
     
  17. Jun 20, 2018 #16
    I more dont have the skills/knowledge for that.. Im more doing a project to keep myself busy/hobby. I'm a young man who gets ideas of how to possibly help people and then try to pursue it...
     
  18. Jun 20, 2018 #17

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    It is worth while trying to get somewhere near the 'best' performance from anything you are making - for yourself or others. It's a simple matter of finding the diameter of the wire first and estimating the length that you used for the coil. I can help you to find what the resistance of that coil is. We can then decide, on the basis of that, whether it's better to use more or fewer turns of wire. If you could also measure the battery volts with and without the coil connected, that should be enough to work with.
     
  19. Jun 20, 2018 #18

    russ_watters

    User Avatar

    Staff: Mentor

    Fair enough. You can learn at least something by just randomly wrapping a bunch of wire around a nail and attaching a battery. Odds are good you'll run your batteries dead quickly, but that's a small price to pay.
     
  20. Jun 20, 2018 #19
    I have 20 meteres of wire, 22 gauge and the volts is 1.6V
     
  21. Jun 20, 2018 #20

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award


    you have a little misunderstanding about current. Current isn't something you supply, it is something that is "drawn" from a PSU ( batteries etc)
    and it will depend on the resistance of the load ( circuit) in this case your coil

    So measure the resistance of your 20 metres of 22 gauge wire. it may be around 1 Ohm, 2 Ohms at most
    After initial experiments ... you should consider increasing that to 2 or 3 times that length and possibly dropping to 26 or 28 gauge

    Amps = Volts / Resistance
    Amps = 1.6V / 2 Ohms
    Amps = 0.8 A

    several AA batteries in parallel will handle that current for a short while but as @russ_watters said, they wont last long

    cheers
    Dave
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted