Phone charger circuit.

Thread Starter

Deanwood

Joined Mar 26, 2020
5
Hi, I am currently undergoing a project to build a mobile power bank. I will charge a 12v battery via a solar panel then charge a phone from the battery. I am at the stage of trying to get a phone charging via the battery and I am getting a stable 5v output from the regulator. However it is still not charging the phone and when measuring the current it seems to keep dropping down rapidly, I have posted a picture below. Can anyone help or give me some advice please?EAAAE8E1-B036-47AB-99C1-4C97934D4FF2.jpeg
 

djsfantasi

Joined Apr 11, 2010
6,196
What type of phone are you using? Is it restricted to a proprietary charger? Do you have its battery specifications, such as charging voltage range and the recommended charging rate?

That’s a pretty picture, but what is it?You can’t tell what the circuit is. Please attach a schematic of the circuit. If you don’t have software to draw the schematic, use a pre-word processor from the 60s. That is, use a blank piece of paper and a pencil. Annotate all component values.

And can you specifically state how you can tell that the phone is not charging? Does it never charge? Or does it charge too slowly to be practical?
 

Dodgydave

Joined Jun 22, 2012
8,866
What phone is it, Apple (rubbish) or Android..

If it's Android short the D + and D - pins ( green and white wires) together for high speed charge.
 
Last edited:

MrAl

Joined Jun 17, 2014
7,179
Hi, I am currently undergoing a project to build a mobile power bank. I will charge a 12v battery via a solar panel then charge a phone from the battery. I am at the stage of trying to get a phone charging via the battery and I am getting a stable 5v output from the regulator. However it is still not charging the phone and when measuring the current it seems to keep dropping down rapidly, I have posted a picture below. Can anyone help or give me some advice please?View attachment 202439
Is it mandatory that you build this?
I ask because there are 100's of USB charger adapters that plug into the cigar lighter that means 12vdc to USB 5v female A. All you need then is a USB A male to micro or mini or C or Apple depending on the phone port type. That makes it really simple.
There is a chance for Apple you need a special cable though that comes from Apple.
 

Thread Starter

Deanwood

Joined Mar 26, 2020
5
3E327977-F3BF-4941-825D-9F359A64246D.jpeg
hi all, thanks for your fast responses. I have posted a pic of the schematic above. I a trying to charge either an old iPhone or old android from it and after shorting out the d+ and d- pins it is charging both devices but at a pretty low efficiency. Is there any simple way of boosting the current? any help much appreciated as I am a novice in this field (obviously) but have been tasked with this as part of my training. Thanks again for your help. Dean
 

ebeowulf17

Joined Aug 12, 2014
3,172
Is the regulator getting hot? I wonder about thermal protection built in to the regulator. When dropping 7V, even the lower of the standard charge rates (0.5A) would result in 3.5W dissipation. Putting out that much heat, without a heatsink, might throw the regulator into self protection mode.
 

Thread Starter

Deanwood

Joined Mar 26, 2020
5
Yeh I did buy a small heatsink for it but it is still getting incredibly hot so have purchased a larger one from rapid online. Will the efficiency improve with the larger heatsink do you think?
 

BobTPH

Joined Jun 5, 2013
2,264
You need to use a switching regulator to avoid wasting 60% of the battery power to produce heat.

Also, Apple phones require specific voltages on the data lines to get fast charging.

Bob
 

ebeowulf17

Joined Aug 12, 2014
3,172
when measuring the current it seems to keep dropping down rapidly
I forgot that you had mentioned getting current measurements. What range of currents were you seeing? What did it look like before it dropped rapidly? What lower level did it drop to? When it dropped, did it stay low, or was there a pattern of alternating between higher and lower currents periodically? Did any of these drops occur when the phone was approaching 100% charge, or were you seeing this behavior with the phone at low charge levels?
 

kaindub

Joined Oct 28, 2019
9
Deanwood
what are you expecting to see?
The external chargers for phones are not really chargers. they supply a constant 5V (usually) to the phone and the phone uses an internal regulator to charge the battery. In default the charge rate will be less than 150mA which is the maximum current a standard USB supplies (Thats the standard for USB ports)
The chargers you buy from the phone manufacturers usually manipulate the D+ and D- lines by applying a voltage to these pins as others have noted. The phone recognises these voltages and the internal regulator then demands more current from the charger.
Unless you correctly manipulate the D+ and D- voltages, then you wont get better than what you have
 

djsfantasi

Joined Apr 11, 2010
6,196
There are several resources, from the simple, to the complex, to a commercial circuit which will resolve your problem.

The issue is that different devices use different schemes of connecting D- and D+. Plus, the cables themselves may be built differently, based on the charging scheme and whether or not they support operations other than charging.

Take a look at these three articles and see if they help you solve your problem. Good luck!

https://www.instructables.com/id/Simple-USB-Socket-Charger/

https://electronics.stackexchange.com/questions/123172/what-is-the-ideal-way-to-handle-data-pins-d-and-d-on-a-usb-power-adapter-to-be

https://www.adafruit.com/product/14

https://learn.adafruit.com/minty-boost
 
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