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

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).

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.

You could use one of these:

http://uk.farnell.com/microchip/mcp73827-4-2vua/batt-charger-li-ion-4-2v-8-msop/dp/1852161

if you're only going to charge li-ion batteries. They take up to 4.2V

If you're likely to want to charge li-poly batteries too, there are dedicated chips for them too which charge up to 4.1V (li-po are cheaper/easier to manufacture but mobile devices tend to stick to li-ions)

They can be fiddly to hand-solder, but it's possible. Use plenty of flux, pre-tin your traces and use a tiny amount of solder on a very small tip. I used press-n-peel to create a breakout board, and make a converter to get the SOIC23 sized device onto a 0.1" pitch board (for breadboard/protoytyping)

Thanks again.

Are you telling to build something to lower the voltage?

if so could you explain why my way wouldn't work?

I'm using this as the power source:

http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=upb50&tab=documentation

and going to hook the 19v out to a HTC wall charger like this:

http://www.htcdepot.com/htc-micro-usb-travel-charger/5A17A7825.htm

wouldn't the 19v be converted to 5v through the Wall charger? in theory.

I'm sorry if i'm still not getting it, never took a engineering class and I'm just doing this as a hobby.

thanks

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.

Got your last reply after I posted mine! In short, the wall charger at http://www.htcdepot.com/htc-micro-usb-travel-charger/5A17A7825.htm takes AC power and converts it to DC. It's not suitable to connect to the battery output (because of the small size, it looks like it doesn't have an internal transformer either and "clips" the AC waveform to lower the voltage)

ok, so when I remove the laptop adapter, I see 5 pins.

1,2,3,4,5

checking pins 1 - 4 with pin 5 gives me a reading.

Pin 1,5 - 3.9

pin 2,5 - 3.9

pin 3,5 - 1.9

pin 4,5 - 2.5

Can I use these pins to my advantage? thanks