Hi guys

I was discussing the need for a lipo to usb adaptor with my local electronics vendor from whom I source my electronic components. He has an electronics shop and does college projects for students.

So after coaxing him enough he agreed to design and get fabricated a similar circuit for me. I have successfully charged my keychain cam and an indoor IR heli with it. Couldn't check my phone as I don't have a usb charger cable for it.

I asked him not to solder any connector as he didn't have xt60 or deans. He gave the bare bones circuit to me and I soldered a deans onto it. It also has a led for power indication. You can power it up with a 3s lipo too as compared to the Hk one where you need to use a 2s only. Paid 400 for it (its a little pricey i know)

All in all happy with it. Now will try to make a case for it. Will put pics shortly.

That should not have been a big design challenge. A common place 78LM05 regulator would have done the job, even handling 3S lipos. If you dont want any loss in the Lipos due to heat, a better DC-DC step down converter could be used , even our regular 5volt BEC would have done the job.

http://www.ebay.com/itm/1PCS-LM2596-DC-Step-Down-Adjustable-Converter-Power-Module-/251088690509?pt=LH_DefaultDomain_0&hash=item3a760d5d4d

Hobby King recently added exactly the same thing you want in a neat package...
http://www.hobbyking.com/hobbyking/store/__24405__Hobbyking_Lipo_to_USB_Charging_Adapter.html

Hi Ujjwaana

My electronic skills are way below average. Soldering skill is a tad better. If you ask to me solder a component I will do that but if you ask me to choose a component..you will see a blank face.

Yes I saw the product at HK but its consistently out of stock. Hence coaxed my vendor to make one for me. It costs approx same as HK (tad cheaper) and I get to build a custom case for it out of balsa. 

Ankur

Pics

So now you are playing with fire everywhere you go... not just when you are going flying

Just kidding... many (most?) newer cell phones use lipos.

I would like to HIGHLY discourage you from using this  converter. The regulator used to pull down the voltage is in  TO-92 package which can max give you current rating of 100mA max.... I would again recommend you to use a 2Amp BEC instead, or at least use the 78L085 regulator in TO-220 which would give you 500mA. 

Good effort Ankur Sir.IMHO i think it will overload the circuit if using it for a mobile charger(Required current is minimum 500ma). LM7805 (05 Defines the output voltage,7809 will give a constant 9V) would really be great in these kind of applications as Ujjwal Sir suggested.Also if you are using a Dean connector(where polarity reversal is not possible even by mistake) the diode can be removed from the package saving you some .3-.8 Volts.
 I guess HK also has used 7805 Positive voltage regulator.That'why there max current is 1A.If making DIY Current can be increased if necessary by using multiple 7805's in parallel.

Pankaj

I am afraid that using a 9V supply is a no-no. The USB standard specifies a 5V output voltage and the phone's internal charging circuit would, perforce, be designed around that.

Yes 5V is standard and we should use LM7805 in this case ,i was telling that LM78XX Series are positive voltage regulators and 7809 can be used if we need a 9V constant.

Pankaj