Arduino misconceptions 6: a 9V battery is a good power source

This one has come up a lot recently on the Arduino subreddit and Electronics stackexchange – can I power my Arduino with a 9V battery?

The quick answer is yes, you can.

The long answer is yes, but only if your goal is to chose the most expensive and short lived batteries possible.

9V PP3 battery (Ashley Pomeroy, Wikipedia)

I think the boards and documentation should have an explicit warning about 9V PP3s for this reason!

9V is not a good input voltage to produce 5V through a linear regulator

The first problem is how to reduce that 9V to 5V that the Arduino board can use. Most Arduino boards have an external voltage input, and a range of 7-12V is recommended. So 9V seems perfect.

The problem is that most Arduino boards use a linear regulator to drop that 9V to 5V. If you are drawing a mere 50mA, 0.2W is being burnt in this linear regulator with 0.25W being used by the Arduno itself. This is very inefficient!

To solve this, either another battery should be used, or a switch-mode regulator used – these are much, much more efficient.

Even worse is if you try to draw large currents – say 250mA – from the 9V source. The regulator needs to now burn 1W of power. It will fry in no time!

9V batteries are very low capacity

An alkaline 9V PP3 has a capacity of between 500 and 600mAh. This really isn’t very high – a typical alkaline AA battery will be at least 2000mAh. 6 series AA cells will provide the same voltage, but a capacity at least 4 times the size!

This gets even worse if you look at rechargeable 9V batteries. A typical 9V PP3 NiMH battery has a capacity of less than 200mAh. This is so low it is hardly worth bothering with.

No matter how efficient the regulation is, these batteries are not going to last very long.

Ideal solution

First thing first, you need to ditch that linear regulator. It is meant to regulate external voltages when power loss is not an issue.

Use one of the modern switching regulators like the LTC3525 – this can take an input voltage of between 1.0V and 5.5V and convert it to 3.3V or 5V as required. Bypass the linear regulator on the board.

Couple this new regulator with high capacity AA batteries. The LTC3525 is so versatile it can take one, two or three batteries and drain the last drop out of them.

AA batteries are common, cheap, and high capacity. There are excellent rechargeable batteries available as well. Please stop using the 9V PP3s!

16 thoughts on “Arduino misconceptions 6: a 9V battery is a good power source

  1. Permalink  ⋅ Reply

    Vitor

    July 4, 2013 at 10:30pm

    Nice article, however it’s a bit misleading telling that a 9V battery is low capacity. Yes, it has less mAh than the AA battery, but also a higher voltage. In fact, based on your numbers, the 9V battery stores more energy than the AA one.
    Still, this doesn’t invalidates your point: it’s really ineficient to use them to power a stock arduino.

    • Permalink  ⋅ Reply

      cybergibbons

      July 5, 2013 at 7:28am

      I agree, I could be more clear. Will edit! Thanks for the comment.

      • Permalink  ⋅ Reply

        cybergibbons

        July 5, 2013 at 7:29am

        I certainly will keep blogging!

        • Permalink  ⋅ Reply

          Vitor

          July 5, 2013 at 11:16am

          Keep going! It’s an awesome way to teach and learn at the same time :D

          • cybergibbons

            July 6, 2013 at 6:52am

            Yes, I find blogging is a great way to solidify ideas, especially ones you yourself haven’t 100% grasped!

  2. Permalink  ⋅ Reply

    john errington

    July 6, 2013 at 9:52pm

    The simple fact is that a bank of 4 AA NiMH cells (1.3V each) will provide a very usable 5V (within the Arduino’s voltage requirement). 4 2200mAh cells store 5V * 2.2Ah = 11 watt hours of energy, and this is used efficiently.
    A 9V battery provides 9 * 600mAh = 5.4Wh of energy – of which 3Wh is used by the circuit and 2.4Wh wasted in the regulator.

    DONT use one of the modern switching regulators … you dont need it. NiMH cells have good regulation.

    • Permalink  ⋅ Reply

      cybergibbons

      July 6, 2013 at 9:58pm

      You can get a lot more out of AAs with a switching regulator though. With NiMH, you are down to 1.25V per cell before you hit the drop-out of the normal 5V regulator. Those cells have a lot more to give. It also gives you the versatility of using 1, 2 or 3 cells.

      • Permalink  ⋅ Reply

        Zeph

        October 17, 2014 at 6:49pm

        I think the point was to use 4xAA NiMH without a regulator (ie: as Vcc), because the batteries themselves will have stable enough voltages in the right range. In that case you can drain the AA’s down to whatever the brownout fuses are set at (eg: do around 0.7v per cell for 2.7v brownout). Of course 2.7v is beyond sped at 16 MHz, but that’s a surprisingly conservative spec. In any case you can drain essentially all the usable power from 4x NiMH with an ATMega driven directly.

  3. Permalink  ⋅ Reply

    Apu

    August 23, 2013 at 12:00pm

    What kind of battery pack I need If I need to use all the below components:
    1> Rasberry Pi with camera
    2> Arduino 2560 Borad+ motor control grid
    3> 7 to 9 v dc motor 2
    4> 2 servo motor

    I want to run this whole system atleast 2 hour Un-Interrupted

    Regards
    Apu.

    • Permalink  ⋅ Reply

      cybergibbons

      August 23, 2013 at 12:06pm

      The Raspberry Pi requires a lot more power that an Arduino even when doing nothing, but it’s also quite variable when working.

      The motors and servos will use more or less power if they are on or off.

      You’d need to measure current consumption and work out how much power would be needed for 2 hours and then work back from that.

  4. Permalink  ⋅ Reply

    Fernando A.

    August 30, 2013 at 8:52am

    What’s your recomendation for an arduino pro mini 3.3V ? I’m considering 3x AA or 1x 9V
    3xAA is enought? 4.5V don’t don’t seem too much
    I dont want to use an external regulator.
    What’s about LiPos ?

  5. Permalink  ⋅ Reply

    Tim

    November 14, 2013 at 3:44pm

    Problem is you link to a very low power regulator that is useless for any power draw. the 7805 will let me do a full amp for the Arduino and strip of addressable RGB led’s therefore a 7805 is the perfect thing for such a setup with a tiny heat sink on it.

    Dont discount old tech, it has it’s uses in a lot of projects. Plus it is honestly dirt cheap and doesnt require hard to find coils to function like the LTC3525. in fact I use them in parallel to deliver a full hard 3 Amps for a nice large string of RGB led’s controlled by the arduino. 3, 9V batteries in parallel run almost the entire night while blinding people with my wearable project.

  6. Permalink  ⋅ Reply

    cybergibbons

    November 14, 2013 at 4:20pm

    The regulator linked to will do 100mA which enough for a lot of Arduino projects though – obviously if you are drawing more, you need to think about another regulator. The coils are easy to get from many places as well.

  7. Permalink  ⋅ Reply

    Koollife

    July 11, 2014 at 9:11am

    Nice Articles , Please Guide me,
    Firstly: i have TFT 7ich Lcd monitor that use 9v 3A power , I tried it with 9v battery, the LCD monitor blinks but the battery can’t power the lcd. How many 9v battery can i loop to able to power this LCD monitor?

    Secondly: i have a led light that use 6x AA 1.5 battery. i used 1x 9v battery but the led light was low. how many 9v can be loop to get a last long light on the LED light?

    Thanks

  8. […] when pushing either button and powering the LED indicator. Following the calculations presented in this post from CyberGibbons.com, this means that the Arduino Pro Mini is using a maximum of 0.0198 Watts = (3.3v x 6mA) after power […]

  9. Permalink  ⋅ Reply

    Mick

    September 20, 2014 at 12:19pm

    ‘6 series AA cells will provide the same voltage, but a capacity at least 4 times the size!’

    I had to re-read this to get your own meaning from this, but it isn’t very clear. It can be read to mean 6 series cells provide the same voltage as one cell but 4 times the capacity, when I know you really mean:-

    ‘6 series AA cells will provide the same voltage [as a PP3 9V], but a Ah capacity [of four or more times the PP3]!’

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