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  • Author Author: jw0752
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Nominal VS Actual Power of USB Power Pack

jw0752

The other day I was reading a blog by raspjoenoob   about trying to run a Raspberry Pi with a USB Power Pack.   USB POWER BANK // PORTABLE POWER SUPPLY  Later the same day I was in Walmart where I noticed they had 2200 mAh Power Packs on sale for $5.00. I bought 2 of these with the intention to test them to see just how much power they would actually deliver.

 

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A while back I built a little battery duration tester that is used in conjunction with a Load Unit to test battery energy available under different loading conditions.

Battle of the Batteries - E*** vs D*** vs Bargain


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These are better pictures of the USB Power Packs that will be evaluated. The specifications say that they are 5 volts in for charging and that they will supply 5 volts output at 1 Amp. The power rating was of course 2200 mAh.


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I alternated between the two units in my tests. Each time the Power Pack was allowed to fully charge before testing. The units were tested under loads of 250 mA, 500 mA, 750 mA, 870 mA, and 1000 mA. In each test the unit was run until the internal circuitry of the Power Pack disconnected the unit from the load due to low battery condition. The time on the clock was then noted and a calculation of milli Amp hours was calculated. Here is how the test setup looked:


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As I have seen before in battery tests the Power Packs were able to do slightly better under a low load than they did at the upper end of their rated load capability. Of course we are not dealing with a pure battery situation here as there is internal monitoring circuitry as well as a boost converter to deliver the nominal 5 volt output. Quite a neat little package all things considered. I will post a graph of the results of the tests below. The best power out that I was able to obtain was 1388 mAh under a continuous load of 250 mA. This level was very linear until the load got in excess of 750 mA at which point it dropped quite quickly until it was down to 750 mAh at it full rated 1000 mA output. Here is the Graph:


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Obviously at $5.00 and clearly marked as Made in China this battery pack was not top of the line quality. It would be interesting however to see how well an expensive top brand would stack up against it.. When we tested the Alkaline AA batteries we were surprised to find little to no difference between the top brands and the dollar store cheapies. If I can get my hands on a better unit with the same specifications I will post an addendum to this blog.


John

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  • Excellent job John.

     

    You learn quickly in the engineering world that stated capabilities are often NOT met by the devices.

     

    On one large project I identified a problem with the selected processor and predicted that they would only support about 80% of the stated capability.

    The VP of the primary contractor got up and stated that THEY were satisfied with the stated capabilities.

     

    Six months later I went for a check up visit only to have the programmers complain about how the processor were only about 80% of their promised capabilities.  I just smiled.

     

    DAB

Comment

  • Excellent job John.

     

    You learn quickly in the engineering world that stated capabilities are often NOT met by the devices.

     

    On one large project I identified a problem with the selected processor and predicted that they would only support about 80% of the stated capability.

    The VP of the primary contractor got up and stated that THEY were satisfied with the stated capabilities.

     

    Six months later I went for a check up visit only to have the programmers complain about how the processor were only about 80% of their promised capabilities.  I just smiled.

     

    DAB

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