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Help with a battery pack design

Discussion in 'Electronic Design' started by Ryan, May 29, 2005.

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  1. Ryan

    Ryan Guest

    Ok so I have a wireless device the plugs into the wall with no option to
    make it completely wireless (darn..guess I have to do it).

    What I know is that the power supply outputs is DC 5V/2.5A, switching
    type. Also the tech specs say "Power Communication 4.5W (900mA x 5v)"
    which I don't know what they mean by power communication.

    I'm thinking of going to Radio Shack and getting some AAA, AA packs and
    testing the output and then just putting some diodes on until I get the
    desired output.

    Can anyone help and elevate some of the guess work with some tips for
    me? Should I be working for an output of 5v/2.5a from the battery pack?

    Thanks for any information.
  2. Ken Taylor

    Ken Taylor Guest

    Does your plug-pack supply 5V DC @ 2.5A, and your wireless device require 5V
    (DC?) @ 900mA ?

    If so then you can use this plug-pack for this device.

  3. Dan Hollands

    Dan Hollands Guest

    4 Batteries in series will probably make it work but the batteries will not
    last long enough to be useful.

    I think the label may say power consumption not communication.


    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
  4. Ryan

    Ryan Guest

    I don't have a plug-pack. I have the power supply for the device which
    states Output 5V @ 2.5A. But I also look at the tech specs online which
    stated "Power Communication 4.5W (900mA x 5v)" which I have know clue
    what they mean by this?

    Do it mean the device can operate at 5v @ 900mA? Can I test this any way?
  5. Ryan

    Ryan Guest

    4 AA? How long would they last? And how can I calculate how long so I
    can type in differet numbers for different batteries?
    Thats what I though as well but its not. It might be a typo in the doc
  6. Luhan Monat

    Luhan Monat Guest

    You need to supply 5V at 900ma to power the device. A set of 4 2400mah
    NiMH will give you 4.8volts for less than 3 hours.
  7. Ryan

    Ryan Guest

    So if I go with something like 6v @ 2900mah with a 5v zener diode would
    I be ok?
  8. Ken Taylor

    Ken Taylor Guest

    No, just use the power supply you have for the device. It has plenty of
    capacity for the task.

  9. Ken Taylor

    Ken Taylor Guest

    Yeah, that's spell-check for you. It's a typo - it should be 'consumption'.
    Like I said, use the supply you have, it's fine.

  10. Ryan

    Ryan Guest

    The problem is I don't have a battery pack. I only have the power
    supply that plugs into the wall. I'm looking to make one from parts. I
    just don't know enough of the engineering to do it correctly the first
    time. (Trying not to destroy my device)

    Thanks for the replys.
  11. Ken Taylor

    Ken Taylor Guest

    Sorry, I lost track of what you were asking. Get four Lithium or other
    hi-capacity rechargeables and use them. You'll probably find that four will
    do the trick (4.8V versus 5V required) or if needs be get a fifth and use
    that as well, and a diode (say, 1N4001 or virtually any other power diode)
    and put that in series.

    Sorry about the side-tracks. That sorta day. :-(

  12. Ken Taylor

    Ken Taylor Guest

    What the......

    Not Lithium, NiMH. Sheesh! Or the newer Alkaline rechargeables, for that
    matter. There's some pretty beefy types out there (1800mAh or more).


  13. Pooh Bear

    Pooh Bear Guest

    It's probably a convenient inexpensive 'off the shelf' unit that made sense to
    package with the device.

    It can cost *more* to make a 'special' with a lower rating !
    That sounds like the actual power consumption.

    It doesn't matter if the power supply is capable of delivering a bit more.

    That's what it sounds like to me.

  14. Pooh Bear

    Pooh Bear Guest


    I think you need to do electricity 101 first !

  15. Pooh Bear

    Pooh Bear Guest

    Chinese English I suspect ! I've seen far worse. ;-)

  16. Ryan

    Ryan Guest

    I agree, but I'm trying to learn as I go. I got 4 NmH AAs to work
    with, no I just need to get battery life to last longer. I guess the
    question I'm asking what does the 5.1v zener diode do? Does the diode
    only allow the 5.1v to pass through? And if so how much tolerance would
    it have, 6v ok 20v bad.

    5v @ 10000mah would be ok, right, it would just mean the battery power
    would last longer?

    Thanks for the patients and help.

  17. Pooh Bear

    Pooh Bear Guest

    4 NiMhs or indeed 4 Nicads will give around 4.8 ~ 4.9 V terminal voltage (
    close enought to 5 V ) when fully charged - which is clearly enough to make
    your device operate. Trouble is - when discharging - the voltage will
    gradually drop.

    This may or may not - depending on the design of your device - prove to be
    problematic or not.
    If you put a zener in parallel with the batteries - it'll simply exhaust them
    faster. It'll take current ( charge ) that that could be usefully used by the
    There's no chance of 20V so why are you worrying ?
    The more mAh you have - the longer your battery pack will last. As long as you
    don't put any zeners in there !

    Pls report back !

  18. All batteries have a capacity in mAh (milliAmphours). This is marked on
    the battery and you can read it in the specifications for a certain

    A big battery like you will need can have a capacity of 4000 mAh. Which
    means it can deliver 4000 mAmps for 1 hour, or 1 Amp for 4 hours. Or 2
    Amps for 8 hours. You need 2.5 Amps so it will run for 6 hours, or so.

    You need recharchable batteries, of the biggest sort you can afford, 4
    of them in series will probably work.

    If your device really needs carefully regulated 5Volt DC you may need
    to use a few more batteries and build a 5Volt 2.5 Amp regulator.

    If this battery needs to work 24/7 you may want to consider a 12Volt
    car battery, and a 5Volt regulator, because you need really big
    batteries if this is going to run without being recharched for days and

    2.5Amps is a lot of current to take out continously.

    A typical car battery can have 70Ah capacity. That is 70 Amps for 1
    hour, or 1 Amp for 70 hours. 2 Amps for 35 hours. 2.5 Amps for...?
  19. ehsjr

    ehsjr Guest

    No. A zener is the wrong choice for you, unless you have
    one that is rated at over 5 watts at 5 volts. Don't know
    where you'll find a zener like that. You would not get a
    huge increase in run time, even if you could get the 2900
    mah cells and a proper zener. With a 6 volts supply, and
    a zener shunt regulator, you have to waste about a watt
    of power.

    The solution Luhan proposed - 4.8 volts using NiMh cells
    rated at 2400 mAh - would work, and wastes no power. You
    might be able to use a 6 volt battery with a 1N540x diode
    in series to drop the voltage to about 5.4 (wasting a bit
    over 1/2 watt). Or you could use a battery with a high
    efficiency (up to 95% efficient) DC-DC converter. But, if
    you need more run time than Luhan's solution, your battery
    capacity *must* be increased, no matter what configuration
    you use.

    So - how much run time do you need?

  20. Ryan

    Ryan Guest

    Pooh Bear wrote:

    So, I used 4 NiMhs that tested at 5.1v fully charged. The device ran
    for about 25min, I added a simple toggle switch so I could kill the use
    of the batteries. I turn the device on and off a couple of time to
    change settings. I'm recharging now to do a constant run to get a
    better time. When I took them out they tested at 4.6v. So indeed you
    are right when the voltage drop it wasn't able to run the device.
    My question was more geared to learn the function of a diode. So I get
    now that it takes (wastes) current but if I passed 20v to a 5.1v diode
    would to still function or would it burn?
    So this brings up the question what can I do to make the life last
    longer now. Different batteries but I don't know of any that run a 5v
    that provide more mAh, thus the need to bring the voltage down.
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