- 21 Posts
I have an HTC Rezound and it will charge fine from the charging cable, but I've tried two MHL cables and the phone shows it is charging, but the battery% keeps dropping as though it is not connected to the charger.
With one MHL cable the voltage to the cable that goes to the phone was 4.6 Vdc and the phone of course wouldn't charge at all.
I had built my own USB charger into a radio and found that unless the voltage is 4.9-5 Vdc at the phone itself it will not charge at all, but the screes shows it charging.
Is that just a problem with the phone?
I do know that I have to wiggle the charging cable on the micro USB end to make it work, but always charges my phone just fine. Could the extra current required by the circuitry in the MHL adapter be drawing enough to make the voltage drop more at the bad plug?
I bought this cable Amazon.com: Cable Matters Gold Plated Micro USB to HDMI MHL Cable For Samsung Galaxy S2/Note & HTC Evo 3D/4G - 6ft: Electronics
Upon dismantling the cable the power wire from the USB plug goes to the PC board and through a couple components before supplying the voltage to an 820 ohm resistor that is in series with the power wire that goes to the phone cable. Why the resistor is there I don't know. My plan is to connect the power wire from the USB cable directly to the power wire going to the phone. Provided it works I will have to re-epoxy the board and seal the case shut.
I've seen those MHL adapters with the little box and short cord, but that will not work for me as I don't like the short cord they have.
- 04-26-2013, 09:14 AM #2
Re: Charging issue
How much AMPERAGE is the home made charger able to apply? The Rezound should be charged with a power supply capable of delivering 1000ma at 4.9vdc-5.2vdc, amperages as low as 500ma SHOULD be able to charge it unless there are things running in the phone drawing of the battery faster than that (if that is the case then it should be getting very warm well charging). I would highly recommend NOT building your own charger, but it's your call.
- 21 Posts
Re: Charging issue
Charger is good for 2 amps.
The voltage you listed is what I figured I needed based on tests when I built the USB charger.
It uses a toroidal power transformer and a 2 amp switching regulator that is pin compatible to a 7805 regulator. Found out that the regulator had to be mounted directly to the USB jack power and ground pins to provide enough voltage.
Charger always worked fine with just the USB charging cable. Works fine with the MHL cable when the HDMI audio adapter is powered using its own power supply and when the phone is not playing music.
My guess is that MHL cable is dropping some voltage. What I am thinking of doing is using a mini USB panel mount jack, attaching the regulator to it then wiring it in to a micro USB jack that is MHL capable which will allow the MHL adapter and HDMI audio converter to be powered by the regulator while the mini USB port will just require a mini to micro USB cable.
That should work provided the mini USB to micro USB cable can support MHL which it IIRC has 5 pins so should be compatible, right?
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