More efficient? Single 9v battery or 4, AA batteries?

Discussion in 'General Electronics Chat' started by cosmotcat, Jan 16, 2019.

  1. cosmotcat

    Thread Starter New Member

    Jan 16, 2019
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    So... very simple project. No LED’s, no motors, etc. Small power consumption - no need for any big power, MUST run on 5v (yes, a 5v regulator circuit will be used) and must run for extended periods of time.

    Which is more efficient (and would last longer)? A single 9v battery, or 4, AA (or possibly AAA) batteries?

    Forget about Lipo or any rechargeables for now. Multiple units will make that cost-prohibitive.

    I’m scratching my head. Trying to go for smallest size with most efficiency/longest life.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The AAs or AAA's have more Ah capacity than a 9V, so will last longer.
    The 9V also wastes more energy when dropped to 5V.

    Note that if you run on four alkalines, which give 6V, you will need a very low dropout regulator for 5V output.
     
  3. cosmotcat

    Thread Starter New Member

    Jan 16, 2019
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  4. cosmotcat

    Thread Starter New Member

    Jan 16, 2019
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    Thank you. A quick, simple, easy reply.

    I was kind of thinking that but wanted to be certain.
     
  5. Norfindel

    AAC Fanatic!

    Mar 6, 2008
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  6. rsjsouza

    Member

    Apr 21, 2014
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    I know it is somewhat unrelated but, depending on the power consumption, AAs or AAAs tend to leak if used for a very prolonged time. 9V batteries (6LR61) have better resistance against leakage.

    I have been giving preference to 9V batteries if the product/equipment needs to be left alone for years.
     
  7. dl324

    AAC Fanatic!

    Mar 30, 2015
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    How can you expect any thoughtful recommendations unless you provide more details?

    You say it "must" run on 5V. Explain to us why? Just about everything has a tolerance with the supply voltage. Even 5V TTL can operate from 4.5-5.5V.

    If you use a voltage regulator, it "has" to dissipate (i.e. waste) power.

    What is the current to be drawn from the batteries? What does extended mean? Why are you precluding secondary batteries? I have literally saved thousands of dollars by using secondary batteries. Primary batteries end up in landfill after a single use. Secondary batteries can be recharged many dozens of times, it not hundreds.

    For 5V operation, selecting a 9V battery wouldn't be a reasonable solution and should be dropped from consideration. AAA batteries would give longer run time because 9V batteries are pretty wimpy to begin with.
     
  8. cosmotcat

    Thread Starter New Member

    Jan 16, 2019
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    Thanks, but it was answered. Your last paragraph backed it up. It’s all I need at this beginning, prototype stage.
     
  9. Norfindel

    AAC Fanatic!

    Mar 6, 2008
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    That's a very good point. Even more: if all the components can work with 6v (or the max battery voltage, which could be slightly larger), then maybe he doesn't even need a voltage regulator.
     
  10. paulktreg

    AAC Fanatic!

    Jun 2, 2008
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    ....or put one maybe two diodes in series with the batteries?
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Depending on your needs, two AAs with a DC-DC boost converter might be a good solution. It would maintain constant output 5V even as the battery voltage sags. There are many such converters available for cheap on eBay if you want to experiment.
     
    Kjeldgaard likes this.
  12. Audioguru

    Expert

    Dec 20, 2007
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    A 9V alkaline battery very quickly runs down to 6V. Energizer battery company rates its capacity when it has run down to 4.8V.
    Four alkaline cells begin at 6.2V but soon run down to 4V. Energizer rates the capacity of one cell when it has run down to 0.8V.
     
  13. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    Instead of four batteries, five. The added voltage will give you extra headroom. However, you're still wasting a lot of battery power by pushing it through a regulator.

    You MIGHT consider PWM (Pulse Width Modulation as a means of regulating the voltage. It wastes less energy. Unless your energy consumption is going to be extremely low. But then again, using a linear regulator that turns extra voltage into heat - that's going to use a lot of energy.

    Love these mysteries when the thread starter doesn't give us enough detail. Then after many posts it starts to become clear the person who is reluctant to tell us what they're trying to do is to build something that can't exist - such as an over-unity device. Now, I don't know that's what you're up to; I could be wrong. But if it is - tell us now so we can stop wasting our time.
     
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