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Charging mobile with a 6V lead acid battery? Answered

I want to make something like power bank. i want to charge my mobile with a 6V 4.7Ah battery. My mobile charger is rated 5v 500mA. How to make this circuit?



2 years ago

I would take a standard 12v car charger and connect a positive and negative wire to it (the center post should be negative the outer should be positive). Once you do that use those and another wire to connect 2 6v baterries in series. The catch is you will have to disconnect whIle not in use. I have done this with to recharge able lead acid batteries. I even linked in a small 12v solar panel. If you go that route I recommend connecting the solar panels to only one 6v battery. Even in low light the 12v panel should produce 6v keeping your batteries charged. Again I've done this it 100% works.

Jack A Lopez

5 years ago

You know, 6 volts is pretty close to 5 volts. It might be the case that your phone is robust enough to charge itself from a 6 volt DC supply, or a 5 volt DC supply, or even a 4.5 volt supply. It kind of depends on the charger circuit in the phone and what input voltage range it is happy with.

So maybe your next question is how I change 6 volts DC to 5 volts DC? And I think the easiest way to do that would be to just put one or two rectifier diodes in series with the 6 volt supply.

The way that works is the voltage drop across a forward biased silicon diode is about 0.6 volts, over a very wide range of current, e.g. like 1 mA to 1000 mA. So at whatever the current is, the voltage drop across one diode is about 0.6 V. The voltage drop across two of them in series is 1.2 V. So if the battery voltage really was 6.0 V, and you've got it wired with two diodes in series with your charging phone, then the voltage drop across the phone is 6.0 - 1.2 = 4.8 V.

Also, on the subject of voltage drops, if you can find yourself a 1 ohm resistor, one rated at maybe 1 watt, that could be handy for actually measuring the current your phone is drawing while it is charging. That is to say, you put the 1 ohm resistor in series with your charging phone, and then measure the voltage across this resistor, using a voltmeter. Then (from Ohm's law) the voltage you measure (divided by 1 ohm) is the current your phone is drawing, in amperes. Note that you are expecting this voltage drop to be less than 0.5 V, since the power supply intended for charging your phone is rated at a maximum current of 500mA. (500mA*1ohm = 500mV=0.5V)

I am guessing the actual current draw of your phone while charging will be something less than 500 mA, like maybe 100mA or 200 mA? Meaning a drop of 0.1V or 0.2V, respectively, across your 1 ohm current sensing resistor.

Anyway, I don't know if the trick with adding a few diodes to drop the voltage will be necessary, or not. As I was saying before it might be the case that your phone is happy drawing current from a (nominally) 6 volt, sealed lead-acid battery.

Also I have seen inexpensive DC-to-DC converters which convert a 12 volt DC supply, like from a car's battery, to a 5 volt DC supply for charging phones, or basically anything made to be charged through a USB plug, which is 5 volt DC supply. Although going that route means you have to seek out one of those car-cigarette-lighter-socket-to-USB charger gizmos, plus a 12 volt, sealed lead acid battery to power it.

I am guessing a 6 volt battery, the 4.7 ampere*hour one you mentioned, is already in your possession.

panoramaBeatsJack A Lopez

Answer 3 years ago

I pretty much did exactly what you have said here for my almost identical project. (2x6V 4.7ah batteries in parallel, solar charge controlled power pack.)

I used the product linked below as my usb output, in series with a diode, which dropped me to about 5.7 V - still uncomfortably high, but after a lot of soldering and trying things was ready to accept. Like you mentioned, I pretty much trust my phone's internal charging regulation, etc.

One of the usb ports had been feeding an alarm clock rated for 4.5 V, seemingly fine. It's just something I have around that seemed good for testing.

Tragically, this hub stopped working for me after about 40 min. The lights in the hub had turned out, but the the voltage remained the same going to the hub, so it wasn't a wiring disconnect or short.

Maybe I fried one of the LEDs in the hub? Maybe the alarm clock drew too much current? The clock is ok, and has AAs to fall back on. It conveniently lights up when plugged into USB, so good for testing and powering it that way.

Anyway, my next fix is probably gonna be somewhere in this guy...


Jack A LopezpanoramaBeats

Answer 3 years ago

I guess you want to be able to plug in more than one load at once, and that is why you decided to use a USB hub.

I mean what you probably want is a bunch of USB jacks with their power pins all wired in parallel; i.e all the +5 pins tied together, and all the ground pins tied together.

I mean that's all you really need. Is it possible to find such a simple thing, already manufactured by someone. I dunno.

Of course the USB hub is designed to do things besides being a 5-volt power strip. It is designed to do complicated things like, switching data, and stuff.

I can only guess at why your USB hub died.

Maybe you are planning to take the dead hub apart and do some pruning? I mean, cutting out all the stuff that does not suit your goal of just having power jacks to plug loads into. I guess that's what you're saying with the words, "my next fix is probably gonna be somewhere in this guy..."

Honestly, I am not sure what you're saying, or why I had to reply to it.

However, I wish you luck with your projects, and I also offer my sincere and heartfelt condolences for the loss of your USB hub.


Answer 4 years ago

Discharge the batt to 5v is not good idea, really. A 6v batt discharged to 5v is already VERY discharged, almost EMPTY. If you start charging the phone when the 6V batt is discharged to 5v, it will drop below 5v very soon.

By the way, I agree with Jack Lopez´s solution. You could also use a analog regulator circuit with a power transistor and a 5.6v zener in the base, but most of times the easier diode solution would be better.

Since the voltage drop required is just 1V, IC regulators are out of question.


5 years ago

A very simple down-voltage circuit for your mobile !


5 years ago

Use 2 X 6v 4.7A battery in series, or better still a small 12V 5ah scooter batt, with a 12V inverter (100w will work) and plug your cell phone charger into the inverter putput.

The charger contains all the circuitry needed for your LiPo cellphone battery, therefore you cannot plug a battery directly to your cell phone and expect it to work safely.


5 years ago

Your mobile will have a lithium battery in it.

It is ESSENTIAL you use a charging circuit designed for that type of battery or the battery may well burst into flames either under charge or in your pocket.

This is not very easy to do and so my commendation is to use a commercial product you can have some confidence in or look for another way - say and inverter from the battery so you can use your normal charger.