Apple Video Ipod – Battery Life analysis HDD vs. CF
As promised I have been spending sleepless nights measuring and testing the battery life to bring you the ultimate and most comprehensive battery analysis for apples Video Ipod (5g & 5.5G) players ever!
My original intention was to just compare the run-time of the hard drive based iPod i.e. standard off the shelf video iPod with my compact flash based solution, but being slightly of the rails when it comes to things like this I really pushed the boat out and made some electrical Current measurements as well.
Method
First thing I needed to invent was a method of breaking out the battery supply, so I could insert my Current meter. The easiest solution I felt would be to make something which was similar to the battery fitting which I could then use to power up the iPod from my bench power supply.
So after some cutting and soldering I produced my own custom flexible PCB stick to fit in to the battery connector on iPod. I set my bench power supply to 3.7V the nominal voltage as supplied by the internal battery. In-line with the supply I attached my Current meter, which would show me current drawn from the power supply.
Playtime measuring was going to be a little more interesting as I was not about to stand around my iPod for 15 plus hours waiting for it to die while holding a stop watch. So after some racking of the brains, I came up with the simplest and most novel method you will ever witness.
I will record the audio output from the iPod using my computer and sound recorder software, till the player switches off from the low battery. I will then analyse the wave file to find when the music stopped to determine how long the playtime was. I said it was simple 
Obviously I will record at the smallest bit length and sampling frequency as I don’t want to end up with a 20Gb wav file.
To demonstrate my utter boredom, I even soldered in 47Ohm resistors to the output lead to mimic earphones!! (before the geeks amongst you starting commenting most earphones have lower DC resistance – around 30Ohms, but they are inductive loads, so resistance does change with frequency - being on the safe side I settled on 47Ohms, plus I had the resistor lying here!)
To improve accuracy of the data, I have devised this charging and measuring cycle.
- Charge battery till full
- Play Music till it switches off
- Charge for 6hours and start test
This will bring the battery up-to a known starting level, before the above is repeated while recording the output. This will be repeated twice and the average of the time will be used. I will also do these tests playing HQ Video files rather than MP3’s.
Once the timings have been noted the Hard drive will be removed and the Compact Flash adaptor and 8Gb card will be installed, and all the above testing will be repeated.
To maintain consistency, the 8gb CF card and HDD are loaded up with exactly the same MP3 and Video files, even the order of play will be the same – so don’t accuse me of not being meticulous.
Move on the next page to see the results.
Results
The iPod that was tested had been fitted with the new brighter 5.5G LCD, so I added extra data to show the effects of the back-light brightness setting. Also the battery on this iPod had been replaced couple of months back, so it is still very fresh and should provide consistent run times. These results will not relate to the 5.5g Ipod as it appears that is either running different chipset or power saving techniques which in theory will produce longer run-times than shown here.
Looking at the electrical current draw table, you notice a few interesting things. Playing video or audio does not change the amount of current required, which is very surprising as you would have expected higher drain for video decoding. The base current drawn is around 30mA without the back-light on, which is very good. The main draw after the hard drive is the back-light and at nearly 100mA at maximum brightness, you can see how the back-light setting will have a big effect on battery life.
You will notice the compact flash version suffers from an increase in current during the spin-up and read cycle, this is probably down to a) the CF card being initialized, b) the ipod activating the i/o systems, like the storage interface and processor.
As was to be expected the Hard drive needs up to 4 times the current required by the compact flash card. In my tests during high quality video playback the drive was spun up and read every 90 seconds, and the whole spin-up, read, and spin-down sequence would take about 4 seconds. Considering the battery is about 480maH in capacity the spin-up sequence is quite a heavy load.
For someone who likes to play with there ipod i.e. constantly scrolling through songs, fast forwarding video and music – making the hard drive spin up and down quite often will see amazing increase in battery life by switching to compact flash storage.
Lets move on to the battery life tests.
The results surprised me here, I was expecting video playback to have the biggest increase. However this is not the case and this is due to the fact the back-light is on all the time being a major current draw tends to level out the difference between the HDD and CF over long periods.
Video playback with the CF came in at 5hrs 49mins which is an amazing 1hrs 25mins increase over the hard drive, and if you can live with reducing the back-light a few notches I can imagine breaking the 7hr barrier.
Audio playback recorded the biggest increase in terms of actual usage time and as a percentage increase. As the back-light was off the battle was between the current draw of the storage mediums. The Compact Flash came in at 15hrs 20mins of playback and a very impressive increase of 42% equating to an extra 4hrs 30mins over the Hard Drive.
Conclusion
While the test results showed pretty good increases by the compact flash camp, I still think in real life usage the increases will be even more spectacular. The tests demonstrated continuous play, with no stopping / pausing / switching on and off, these increase current demand as the hard drive needs to be activated. These things are what saps power and with the compact flash installed these things do not draw anymore current than the back-light.
Video performance of the compact flash will enable you to fit another film in on a flight, on the audio front you can fit an extra 4 hours flight.
How the Video Ipod’s should have performed from the factory……
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