ipod Power Pack. Get over 105 hours mp3 playback or 15 hour video

Description

I have just got a 5th Generation ipod, the 'ipod with video'. After seeing one in the Apple shop I had to get one, they are very nice!

Anyway as you know the player can play videos, and they are (in my opinion) very watchable...the main draw back is the battery life when watching, for my 30GB model it’s about 2.5 hours.

After looking on the web for a while, all I could find were homemade packs using standard AA and 9V batteries! Not only have these got a relatively low energy density, all the example I found were using linear regulators or diodes to get the correct voltage, which almost by definition are extremely inefficient. Also using non-rechargable batteries would be very expensive, and bad for teh environment.

So I decided to make my own pack, here is the criteria:

Size: The pack does NOT have to fit into a pocket. The times when I will be watching videos on my pod for any length of time will be when travelling, then I will almost certainly be carrying a bag.

Capacity: At least 2 times the internal. The internal is 3.7v at only something like 900mah.

Charging: Must be chargeable from 12V source.

Initial Plan:
Obviously the best choice of battery type is Li-ion. They have a very high energy to weight/size ratio. The disadvantage is, cost, charging procedure and high susceptibility to being destroyed.

My initial idea was to used 2 x 3.7v Li-ion cells in series to get 7.4v, then use a DC/DC convector to get to 5V and power the ipod though the USB cable.

However I noticed on the back of the ipod it says ‘Rated 5-30v DC 1A Max’. After some searching I found this refers to the Fire wire charging port. Apparently the USB and Firewire power pins are on different circuits, and over 5V on USB will kill it (I only found one case where this happened, but its enough for me!)

So I seems there is little need for the DC/DC, and I could use 7.4V direct, this should save about 10% efficiency.

Battery source:
I found some very cheap brand Li-ions at http://www.allelectronics.com/ , however they are in America, I emailed them to ask for an approx shipping price to the UK, but they never replied.

I found a supplier of unbranded li-ion camcorder batteries and li-ion chargers on eBay (seller: premiumdigital).

I purchased a 7.4v 4000ma battery and 12v charger with car adaptor, it came to just under £30.

Assuming the battery is as stated, and is 100% efficient, it should be 8-9 times the capacity of the internal battery :).

 

((7.4/3.7) x 4000) / 900 = 8.888

I dismantled the charger and have tapped it to the battery with a STDP switch, which switches the battery between the charger and the ipod. I also got a cheap Firewire cable and cut the computer end of. This can now provide power the ipod for charging or playing.

Above is the battery pack with charger attached.

Usage

To use, make sure the ipod itself is completely charged, this will prevent the external battery charging the ipod (inefficent). Then run off the external untill it has run out, then obviously use the ipods battery if you need more viewing/listening!

IMPORTANT, STILL TO DO....

Li-ion batteries are very sensitive to over discharge, if one cell goes below 3v it will be totally destroyed (I have seen this before). It is therefore vital I put some protection onto the battery pack.
I am going to put a simple voltage monitor and mosfet on the battery which will disconnect the load when it reaches below 6.5v.

TESTING:

Video:

The video played for over 13 hours, with the internal battery thats 15 hours videos playback

Audio:

There is no way I can leave my ipod playing contantly for the few days it would need to test the mp3 play back time. The next best test is to use the video to audio ratio. according to apple the player can play 14hours audio and 2 hours video, giving a ratio fo 1:7.

15 x 7 = 105 hours

 

IPOD Tips:

Get new headphones!

I got some Sennheiser PX-100's. They are about £30. Excelent sound and bass responce, the only touble is they are open so if you have them loud anyone within 10 feet can hear what your listening to!

 

Protect the Screen!

From Dixons I got a pack screen protectors for palm piolts, then can easily be cut down the put over the ipod screen. There were 13 in the pack for £10