Tips/Tricks

USB OTG: Sharing the Charge!

11 Jan , 2012  

When Nokia N8 was announced, people came up with different usage about USB OTG and showing different capabilities of this feature.  USB OTG can let you attach an external HDD, attach a USB mouse or keyboard, some attached barcode reader, etc. Nokia N8 and similar S^3 phones comes with the USB Charging. You may charge a phone using its microUSB port. I wonder, why nobody thought (or at least put attention to ) charging one phone with another phone using USB OTG and microUSB charging. I had this in mind since after I bought N8 but having no other phone to test it, just  left the thought. After having the Nokia E7 from @Nokia_Connects for trial, I finally got a chance to try it and test if this really works?


Nokia already have an accessory named Nokia Extra Power DC-11 which can be used to charge phone On-the-go, however, if you own two devices, having USB OTG and microUSB charging, did you ever thought you can share charge of one battery with another? No? Then try it. 😛

First I connected Nokia E7 to Nokia N8 in mass storage as shown in above picture and it started charging the Nokia E7. You may notice LED glowing near USB port of Nokia E7 indicating Nokia E7 is being charged. Then here I applied the reverse:

Again, you may see Nokia N8 being charged from it LED indicator.

Another Use Case you can consider for this thing is when you are having Nokia’s 2 mm traditional charger and want to charge Nokia E7 along with your Nokia N8, you may use it as shown above and you will be charging those devices together.

The biggest question that you may have is how efficient this thing is? Well, surely, I was also interested in knowing this thing also. Being a non Electronic person, I was not really able to check how much this thing is technically efficient but as far as I know, USB OTG allow phone to draw about 500mAh according to specifications of USB OTG. Typical Nokia’s high-efficiency charger has rating of 800 mAh and considering this, 500mAh isn’t bad. However, not having much knowledge in electronics part, I thought to test from perspective of a layman. I connected Nokia N8 and E7 such that E7 get charged through N8. I noted the stats battery in Nokia N8 and E7 using Nokia Battery Monitor and after around 10 min, N8 had lost 9% of battery and Nokia E7 had received 5% of battery charge. This was more than 50% efficiency. However, I thought to give it one more shot, I kept them like this for about an hour and N8 lost 23% of battery while E7 was charged around 8% only! This really confused me. Nokia Battery Monitor does not show accurate info also and this made me confused as a layman.

I will really like to know more info regarding this from some expert or those who got knowledge in this area. How efficient this can be?

You guys may think this as a useless thing, but rather than a technical thing, I took this thing as more like fun and to share one more thing that USB OTG can do! 🙂

Do let me know what do you think about this.

Source: http://go.ksg91.com/vOqobR

Kishan Gor is a Co-Founder of NokiaTips. He is Software Developer by profession and have a great passion for Programming and Gadgets.

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  • Hashan Gayasri

    The phone must be using a boost converter or a inductor-less capacitor switching circuit to get a 5V output from its 3.1v to 4.2v battery. As I’ve noticed when using the Nokia Power Profiler, the phone can cope up till the battery drops to 3.1v.s So most, if not all modern Nokia phones should be having a step-up converter internally. Since its very important for phones battery consumption, I assume the efficiency to be between 93%-97%. But thats only the 5V out efficiency of the USB OTG port. The charging circuitry of the receiving end may not be very efficient.It could be as worse as (3.7/5)*100%=74% (Assuming the a switching method isn’t used). So when the efficiencies are combined it could be around 70%-90%. Which is not THAT bad 🙂