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Battery driven USB supply

Former Member

I have been working on rechargeable batteries and noticed that a rested dead cell comes back to life after about 5 mins.

I fully discharged and re-charged 4 AA cells in a small plug in rechargeable power pack...

I then connected a good quality 5V DC-DC converter to the output of the 4 cells, which were placed in a 4 cell battery holder.

The output from the DC-DC converter was connected to a USB socket.

An Acer Andriod mobile phone was connected to the USB socket and the dead phone started charging, an led indicator on the DC-DC converter lit up brightly.

The phone got to 38% charge in 1.5 hours at which point the led went out and the voltage on the batteries suddenly reduced to less than 0.5v.The batteries were warm at this point.

I then switched off the DC-DC converter from the batteries for ten minutes, I then measured the voltage on the batteries and found them to be around 4v, I switched on again, the mobile phone started charging again for a few seconds..

We all know that batteries work in this way and the fact that a rested battery replenishes itself has made me curious if this can be used to extend the charged supply time to the mobile phone..

I am looking for a simple no fuss solution to this so here is what i have come up with so far...

I was thinking of using a super capacitor between the batteries and the DC-DC converter.

The super capacitor supplies the DC-DC converter which has a min voltage requirement of say 3.6v.

The batteries are switched on to supply the super cap when the voltage on them fall to 3.7v.

I have also thought about just oscillating the switching between battery and super cap at a rate which changes frequency dependant on time and battery level. Gradually increasing the off time as the battery charge reduces.

This switching off of batteries and letting them settle may well help the batteries life span as well as the cells should never overheat or de-gas.

Your thoughts or links to relevant info on available products which use this idea would be helpfull..

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    You would do much better just to charge at a current more suitable for the batteries. If you look at the battery suppliers' data you'll notice that for any battery there is an optimum discharge profile (often a constant current but not always) which gives the best possible life. I think that if the batteries are getting warm you are taking far more current than that optimum.

    Of course the phone has a built in charger which was not (probably) designed with getting the most out of AA cells as a power source. I don't think you'll get far putting more complexity outside that charger.

     

    MK

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  • 0

    You would do much better just to charge at a current more suitable for the batteries. If you look at the battery suppliers' data you'll notice that for any battery there is an optimum discharge profile (often a constant current but not always) which gives the best possible life. I think that if the batteries are getting warm you are taking far more current than that optimum.

    Of course the phone has a built in charger which was not (probably) designed with getting the most out of AA cells as a power source. I don't think you'll get far putting more complexity outside that charger.

     

    MK

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