Sunday, July 10, 2011

portable phone charger (part 3)

It is time to conclude my thoughts on making a portable charger. In the end, I chanced upon one on sale that is sold at a really cheap price. The best part is that the charger works. It imitates the way USB charging works and delivers a slow, but not unreasonably slow, charge to the phone. I bought it USD$4.53 from Dealextreme and it took 2 weeks to arrive. It was quite a long wait and I never knew if it would ever arrive, considering the fact that it wasn't a registered package. Nevertheless, the postman popped a yellow package into my mailbox and I knew it has finally arrived!

First Impressions:
This gadget is made with cheap plastic - the kind that will disintegrate after a few years of use. But thats ok considering the price. Moreover, the important thing is the circuitry, which can be removed and placed in a better container if necessary.
It is a made-in-china gadget that actually works. The construction is actually quite sturdy and yet, it is easy to slide in the batteries to power up the charger. The switch is not very secure so I won't recommend leaving your batteries inside when you are not using it, lest it drains away your precious battery power.

The LED light is so dim that it is practically useless. I'm not kidding! Its so dim that I have to switch off all my room lights just for my eyes to register a dim glow that is coming out of that LED.

Does it work with the latest Iphone4?
According to the interwebs, iphones are very strict with the charging protocols. Either it takes in energy at the precise programmed rate or it takes nothing at all. This is also the case with other new smartphones and I am very glad to report that it does work. This means that the charger is set up to USB charging specifications, which is to supply 0.5A at 5V at the power terminals. The original wall charger provides the juice at 1A at 5V. Those who knows a bit of electricity will point out that this portable charger charges at half the speed of the wall charger.

Slow Charging is good charging!
Fortunately, slow charging equals efficient charging. It means that less energy is lost as heat and the batteries don't have to work as hard. This is important because the faster you try to drain energy from a battery, the faster it dies. This may sound reasonable, but the drain is not actually proportional! I measured the current going out of the batteries and it is at 1.1A. At this rate, NiMH rechargables will perform within their design parameters and work well. On the other hand, alkaline batteries will only be able to supply about 1/3 of their typical capacity. This is because alkaline batteries are outdated and were actually designed for low power drain (around 0.2 to 0.5mA) despite what their packaging may say. If you really have to use disposable batteries, go for the most expensive lithium AAs. They are worth the performance and the reliability in extreme temperatures and can be stored for 10years and more without failure.

Performance and tests:
The batteries I used are 2400mAh Powerex Imedions, which should provide about 5.8Wh. On the other hand, the Iphone 4's battery is said to be 5.3Wh. By right, that means that I should be able to charge the Iphone just slightly more than 1 full charge. However, that is not the case. Due to the inefficiencies involved, my pair of AA batteries can only charge up to about 35% before it stops. Also, it feels quite warm to the touch. Therefore, the efficiency is less than half! It is slightly less efficient than I expected but it doesn't make it a bad charger. Inefficiencies are always expected as part of a charging process. It is an emergency charger and not a full fledged replacement charger. Hence, it is reasonable to expect such a performance.

Drawbacks:
The only thing I don't like about this charger is the lack of battery indicators. You never know if you are overdraining your batteries. It is fine when you are using disposables, if you overdrain rechargables, its lifespan will be shortened and some damage will be incurred. Otherwise, I can see it being a lifesaver in a rural areas.


Conclusion:
If you have to recharge your phone regularly while on the go, you may prefer those portable chargers that make use of internal rechargable Li-ion batteries. These batteries are not removable but they pack a lot more power and it is more cost effective in the long run. Best of all, when the internal batteries die, we can always pry open the cover and replace it with a new one (if you can find a replacement).

Note: I am not affiliated to dealextreme or the charger. I paid for the charger myself. The reason why I am reviewing this is because a close friend of mine is going to India and will be spending some time in less-developed villages. I hope it helps you in keeping your smartphone working :)

No comments: