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I want to add an USB port on my APC UPB50 battery so i can charge my phone and laptop.

rayjai

I want to add an USB port on my APC UPB50 battery so I can charge my phone and laptop. Since the battery is seal, I can't open it up. I plan to make an adapter from the power out plug.

 

When I check the power from the outside and inside walls of the plug i get 19v.
From the outside wall and the pin inside, i get 5v, can i use the 5v to charge my phone.

 

Can I just hook up a wall charger to the power out plug and charge my phone?

 

I'm new to this kind of tinkering and it's a step up from what I normally make. I need guidance.


Thanks!

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  • 0

    Most likely not! Not safely anyway.

    Most mobile phones use li-po/li-ion batteries which run at 3.7v. They're easy to over-charge and a lithium battery can be dangerous if it's not charged correctly! I designed a PIC+screen type gadget about 12 months ago which recharged a li-po battery over USB. It used a battery charge controller (surface mount chip) from Microchip so I'll dig out the designs and post them here when I get a min (the Farnell website is down for maintenance so I can't get the part number just yet).

     

    I know this post isn't particularly helpful without schematics or part numbers, but as soon as I get them I'll post them here. What you're trying to do is quite easy - but there are some people who will say "put in some blocking diodes, everything will be ok". For the sake of a few pounds/dollars, you're better off using a dedicated charge controlling chip! (check out the charging graphs for li-po batteries, they're non-linear and need some intelligence to charge safely).

  • 0 in reply to e14 Contributor

    Thanks for the warning.

     

    but if i hook up the 19v plug to a HTC wall charger wouldn't the wall charger control it for me? This way I woldn't have to build anything.

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  • 0 in reply to rayjai

    I'm not familiar with the wall-charger you mentioned. Usually wall chargers go into the mains (AC) and use a transformer and diodes to generate a lower, DC voltage. The cheaper ones use "clipping" to do away with the transformer to create DC. The charger may have built-in over-voltage protection, or it may just pump out voltage and expect the control circuit to be in the device.

    I wouldn't expect you to be able to plug a wall charger (AC) into a battery (DC) output.

    What you could do is take the DC output from the battery - the 5v - and use it to charge the phone.

     

    Addressing the question - can I use the 5V to charge my phone?

    It's possible. If you can be sure that the phone has built-in charge control circuitry, then you could just put 5v into it and charge it up. But then again, the batteries might get a bit warm and start to expand - this is a sure sign of over-charging. Once your batteries start to swell, get rid: they could at best start leaking and at worst go bang! Unfortunately, the li-ion batteries tend to have rigid outer-casings so swelling/over charging is less obvious until they burst spectacularly!

     

    One thing you could try is to put a multi-meter onto the 5v and ground pins of the output of the phone's own wall charger. If the charger has a usb-type plug, these are usually the outermost of the five pins (pin 1=+5v, pin 4+5=ground). If the charger is giving out 5V it's likely that this is going into a charge-control circuit inside the phone. If it's a lower value, say 4.1V-4.4V it's likely that the wall charger contains the charge control circuitry and you'll need to recreate this between the output of your battery and the input socket on your phone.