6V battery to power 6V devices

Discussion in 'General Electronics Chat' started by gregthegeek, May 7, 2013.

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  1. gregthegeek

    Thread Starter Member

    Apr 10, 2013
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    I have 5 devices. They all are the same, and they draw up to 500ma at 6V from 4 AA batteries. I'm sick of replacing 20 AA batteries every day.

    So, if I have five 6V devices that draw up to 500ma each, then that would be 6V at 2.5amps.

    Is there any reason why I can't just buy a huge 6V lead acid battery like this one, and just hard-wire my devices?

    If not, then lets move on to question 2.

    Since my five devices require 6V and I'm providing 6V, is there any need for any circuitry whatsoever between the battery and my devices?

    In case it's relivant, the five devices are police radios.. would capacitors be helpful when all the radios speakers are running because of the larger sudden draw of amps? I'd prefer to avoid circuitry to keep things simple, but if someone can give me a good reason otherwise, I'm all ears.
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Q1. - No

    Q2 - No

    But what is the minimum voltage at which the devices will operate properly? The batt voltage will decrease as it discharges.
     
  3. gregthegeek

    Thread Starter Member

    Apr 10, 2013
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    The radios operate on 4 AA batteries, either throw-away or rechargables. I've been using rechargeables for 3 years and they work great. Throw-aways are 1.5V each, and rechargables are 1.2V each. With that math, my radios operate (when fully charged) at 4.8V. I do not know how low they can still operate at (I'll measure next time I have a dead 4 pack).

    My radios are configured by default to show a battery icon, flash a battery icon, and then flash the battery icon plus play an audible alert sound. The voltages at which these initiate can be adjusted (see attachment).

    My radios shut down and display "Low Voltage" on the LCD shortly after the flashing icon and audible alert, which is (by default) configured at 4.31V. So possibly 4.2V is the cutoff point, if I had to guess.

    Now if I can go from 4.8V to 4.2V in 4-8 hours (with new AA rechargables, depending on radio use, backlight, speaker volume), I would think 6V should take much longer to drop to 4.2V.

    I guess the question is.. how low can I go before I start causing damage to the battery.
     
  4. Matter45

    New Member

    Dec 13, 2012
    26
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    you would have to watch the voltage of the lead acid battery. make sure it doesnt drop below 5.7v

    lead acid batteries develope graphite on the plates when they are undercharged (they loose there capacitor and max output). to charge the battery, you would need 7.2v. Id recommend leaving it on a trickle charge of 6.825v if you can. a fully charge lead acid battery is 6.3v after leaving it off charge for a couple of hours.

    There isnt anything wrong with hard wiring up multiple devices to the same power source. if it has a computer monitoring the battery, that might cause problems, but certainly not harmful to the devices.

    just make sure that those 4 AA batteries are definitely in series.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,783
    945
    lead acid batteries should NEVER be discharged below 1.8 volt per cell, or 5.4 volts for a 6 volt battery. That is a minimum voltage that should not be reached during discharge. Better to stop discharge when 5.9 or 6.0 volts is reached.(50% point)

    I do not think "Graphite" is the proper chemical compound the previous poster had in mind. Lead sulfate is the compound produced during discharge.

    I would recommend you use two 6 volt batteries, or even three and rotate them so they are not in use daily. Using two batteries in parallel would let you charge them with a standard CHEAP 12 volt charger, by connecting two in series.
     
  6. Matter45

    New Member

    Dec 13, 2012
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    Yes, sulfate. thanks for the correction. (graphite? what was i thinking?)
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    Lead acid batteries are specifically NOT happy being discharged very far. They provide high current, but they are not like NI-CD/NI-MH which you can deeply discharge hundreds or thousands of times.

    I recommend you go to Fry's and get some Ni-MH AA batteries which are rechargeable. You can get them in 2.5 A-hr rating for cheap price. Get one spare set for each unit and keep them in the charger. You will get about 5 hours running time @ 500 mA load so the back up sets will have time to recharge.

    TWELVE PACK of 2.6 A-hr NI-MH batteries for $17.40, that's about $1.50 each.

    http://www.batteryjunction.com/12po20aaba.html
     
    Last edited: May 9, 2013
  8. gregthegeek

    Thread Starter Member

    Apr 10, 2013
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    That's exactly what I'm trying to avoid. I have 2300mah Energizers right now, but I go through 20 a night. And rushing to a scene at 100MPH while swapping out AA batteries and steering with my knees is not safe. I want a battery so insanely huge that I can basically leave them on 24/7 for an entire week and not have to worry. A 100aH battery (or a 200aH, 300aH, etc) would be insane... and that's the insane I want.
     
  9. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
    304
    What kind of scanners are you using? I put a meter on one of my portable radios( Wouxun KG-UVD1p) and it only draws 66ma while scanning and 169ma when locked on a channel with the volume set at 75%.
    A battery like this : http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_317024_-1
    should last for a while ,provided your scanners don't draw a lot of current, which is why I asked what brand they are. I saw your 500ma figure, was that actually measured?

    edit: And as previously stated, these batteries do not like to be drawn down too low, but I believe your scanners will shut down letting you know.
     
    Last edited: May 9, 2013
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I thought these were supposed to be portable scanners?

    The solution is to make some "docks" or cable adapters so you can plug them into the vehicle electrical system so that it tops off the battery while you are driving.

    There is no such thing as a 200 A-H battery that can be lifted without a wheelbarrow. Just ask Tesla. Lithium - Ion are the most energy dense for power-weight ratio but they are dangerous (ask Boeing). No free lunch in the battery business.
     
  11. BillO

    Well-Known Member

    Nov 24, 2008
    985
    136
    Get one of these and power them off your car's 12V system. Problem solved for $3.
     
  12. tindel

    Active Member

    Sep 16, 2012
    568
    193
    I've been trying to tell this to this guy for 3 days now - It's no use. He'll just post another thread tomorrow about the same topic. Just like he's done the last three days.

    :mad::mad::mad:

    I think It's Split Infinity.
     
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  13. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    @ gregthegeek,

    You have started 4 different threads for the same project. This not only clutters the forum, but most importantly makes it very difficult for the other members to help you effectively.

    All threads will be closed, except for the original one. Please continue the discussion there.
    Do not open another thread for the same project.

    The threads were not merged, as it would cause confusion from the overlapping answers.
     
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