Is designing and producing a dirt cheap charger really that hard?

Question

Recently one blog service (all text is in Russian) published a curious post. The author proposes to add mobile phone charging capability to each 4-pieces pack of AA alkaline batteries.

The idea is that very thin aluminum foil wires are "drawn" right on the inner side of the cardboard pack to interconnect the batteries and a "dirt chip" very short micro-USB cable is connected and hidden inside the pack.

One of the comments says it won't fly for a number of reasons, including

• need for spring-loaded contacts, which also implies stronger pack
• need for pack sealing to prevent contacts corrosion
• need for a certified USB cable which is not dirt cheap
• extra circuits to prevent shorting, overcurrent and overcharging protection

What I want to ask is - is it really that hard? Is it really near impossible to produce a disposable dirt cheap charger?

Answer 1

• viable

• Not ideal

AA Alkaline batteries may be assumed to have a capacity somewhat in excess of 2000 mAh. This varies with load but at C/2 rate (see below) they will have most of that. [ Carbon-inc - inc Chloride or 'Le Clanche' have less capacity and ability to suppo high discharge and will do poorly here]

USB spec is ~ 5V and you are charging LiIon that reach 4.2V at full charge.

Alkaline cells start at almost 1.6V, rapidly drop under 1.5V and the discharge at very very approximately linearly decreasing voltage down to say 1V.

At 1.6 x 4 = 6.4 V some badly designed devices that do meet USB spec MAY be damaged. Not usual.

At 1.25V x 4 = 5V you drop under nominal USB spec voltage, and allowance for voltage drop in pack wiring and connectors takes you lower quicker. Charging at a possibly reducing rate will continue down to say 4.7V - maybe lower.
4.7/4 = say 1.2V/cell.
So available range is (1.5-1.2)/(1.5-1.0) = 0.6 = say about 60% of capacity - maybe more.
So you may get 60% x 2000 mAh+ = 1200 - 1500 mAh out of a pack of AA Alkalines.

Many cellphones have battery capacities under 1200 mAh and LiIon current charging efficiency is excellent (as opposed to energy efficincy which is good but lower) so you'll fully charge many cvellphones.

LiIon with as much energy available as desired charge at typically 1C for about40 minutes and then tail off at reducing current for 2 to 3 hours total. Total time also affected by current cutoff decisions. As peak current into a say 1000 mAh cell will be 1000 mA this is about C/2 for Alkaline cells so while capacity will be down it will not be terrible compared with nominal capacity.

NimH - will be less satisfactory. Vout ~= 1.3V oc when fully chaarged. Drops into 1.1V to 1.2V across most of range depending on discharge rate. At C/2 it should be closer to 1.2V for a lot of the ime. This gives 4 x 1.2 = 4.8V before resistance drops. Under USB spec and very marginal. May work in selected cases but no guarantee in any one case.

Connector: will be able to be done cheaply despite non-standardness. Chinese can and do implement almost anything they wish that will "almost work well enough most of the time" at a throwaway price if they want to. (I have reasonably extensive first hand Chinese factory experience of the general willingness to do anything if they want to - and not to do so if they choose not to).

Answer 2

The two main areas that I can forsee are the contacts and the power.

Yes, spring-loaded contacts will be essential. And yes, that means a stronger pack. And that means more cost to the manufacturer. At the moment the cardboard and plastic blister-pack style of packaging is a fraction of the overall cost of the product. To replace that with something able to withstand the contact springiness would increase its cost many times over. It would be hard to make it economically viable as a pack of batteries any more. As a disposable charger the costs would probably out weigh the benefits.

Secondly, the power. Modern mobile phones use quite a large amount of power. It is unlikely that a pack of 4 AA batteries will be able to charge a phone to its full capacity - in fact you will be lucky to get 50% capacity.

In a dire emergency, yes, this could be of use, but there are already products out there that allow you to charge your phone from external batteries, such as the Thumbs Up Emergency Charger and similar. There are also solar powered ones which have an integral battery. Just leave it in the sun and you have the emergency charge at your finger tips. Much greener (and cheaper in the long run) than 4 disposable AA batteries each time you want to charge.

Answer 3

I've seen in stores packs of 4 rechargeable AA batteries with charge contacts embedded in the package. Those packages are kept in a special shelf that keeps the batteries charged and ready to use. So, contacts are apparently not an issue...

(Manufacturer is Beghelli, an Italian brand)