How to charge a smartphone

We are trying to charge the phone from the crown through the KREN5A microcircuit.

Not so long ago, the post “ When the battery runs down ” slammed on the hub , striking with its illiteracy. Everything would be fine, but this post even managed to appear on the main page, as a result, a lot of people read it, and the author criminally misled them. To show the incorrectness of the post, the experiment was repeated with maximum meticulousness: registration of currents, voltages. It also explains why this is not possible, and what to do if you really want to charge the phone with batteries.
Welcome to cat.

What is the essence of the problem?

Let's immediately indicate the points that ne_kotin indicated in the post, and they are incorrect.
The author says

I want something powerful (1.5 - 2 amperes) and inexpensive - preferably up to 100 rubles. So that you can solder on your knee.
And I still have them!

This phrase is the main thing - that is misleading, and indicates the complete incompetence of the author. The KREN5A microcircuit itself can work with currents of 1.5-2 A, but the author left the frame behind the question of whether the crown battery can give them.

Further, the author gives a circuit that can be easily simplified by removing unnecessary capacitors (the battery itself is already the capacity). And after that, the author confidently claims that with this device he manages to charge phones. He confidently talks about absurd things, and attempts to convince him and remove the post were unsuccessful.
In the comments, a real holivar sprang up, serious electronics engineers made fun of this sharing. Even in the well-known LJ community dedicated to radio electronics, a flurry of indignation erupted in this post.

So our goal: check the theorem of the existence of the possibility of charging from the crown, through the chip KREN5A (or KREN5B) of the smartphone, and what current this battery will give when charging.

Sources and assembly

To verify the existence, we need not so much: a wiring, a USB connector, the microcircuit itself, a charging wire, a smartphone, a crown connector, a multimeter with the ability to measure current + optional straight arms and a soldering iron :).


Some sources

As the charged smartphone, not the one in the photo was chosen, but HTC HD2 with a bucket on board. It so happened that during the experiments it turned out that the smartphone above, after an unsuccessful flashing, is terribly buggy and does not allow installing third-party software. The charge-discharge control was carried out by the Battery Mix program.
For experiments, a new crown was purchased in the first newspaper stall at the exit of the metro.


Sealed battery

We assemble according to the scheme, as indicated in the criticized post, we do not put only capacitors.


The device is assembled. We

check that we have the required voltage at the output.


Five volts, as in a pharmacy. It

remains only to discharge the phone. To do this, all wireless communications were turned on in active mode, and a 10-hour video from YouTube was launched. The device was discharged after about 40 minutes. 4% of the charge was left so that at least somehow it was possible to communicate with the device and monitor its condition.


Discharged up to four percent smartphone.

You can see a sharp drop in the battery graph of the phone. So, now everything is ready for us to begin the experiments.

Getting to the Experiments

We connect the phone to our charge. Photograph on the article heading. The phone happily informs us that he saw the voltage and the charge process started.
However, it is interesting not only to see this label, which apparently misled the comrade ne_kotin , but to measure the current. We measure the current consumption immediately and after half an hour from the start of charging:


The beginning of the charge. The charge current is 300 mA.

At the beginning of charging, it’s quite a good charging current of 300 mA. But here the claimed 1.5-2 A didn’t even lie nearby! Significantly interesting results after half an hour:


After half an hour: the charging current dropped to 100 mA!

The irony is that despite the fact that I switched the phone to airplane mode, turned off everything, did not touch the display and tried to minimize consumption by strangling all applications, it persistently continued to discharge.
After an hour, 1% of the phone’s charge remained. It was decided to measure the charge voltage and voltage on the battery. Very interesting results.


The voltage going to the phone 3.7 V - obviously not enough to charge

I wonder how much is on the battery?


The battery voltage is only 5 V !!!!

After which it was decided to stop the experiment due to its meaninglessness and put the smartphone on normal charge.

Our Conditional Charge Results

You probably already guessed that I could not charge the phone in this way. The chart will tell us much more interesting about this.


Schedule of discharging, “charging” from the battery, and from the charger The

orange line - this is the charge from the crown. Apparently, at the very beginning there were even some attempts to charge. But then this circuit only slowed the inevitable death of the phone from discharge.

Results: it is not possible to use this scheme to charge the phone from the crown!

Why did this happen?

Let’s do a debriefing, why did it happen. To begin with, compare the parameters of our crown battery and the battery of the phone. A little googling led me to the website of the manufacturer of this battery, where I got its parameters:


Battery capacity 450 mAh, voltage 9 V.

Let's see the battery parameters of our phone:


Voltage 3.7, capacity 1230 mAh and the most important parameter is battery energy batteries 4.55 W * h

Pay attention to such a parameter as battery energy. The probable energy (if the manufacturer is not lying to us) of our battery will be equal to:

W * h = U * I * h = 9 * 0.45 = 4.05 W * h.

Those. in simple terms, even if we were able to “drink” the battery energy without loss, we would never be able to charge the phone! But note that it is impossible to take all the energy from the battery. At least a little, yes it will remain.

Now it’s worth considering the efficiency of our power converter and battery charging circuit power. Take the efficiency of the last chain of 80%, with the hope that manufacturers have made it as high-quality as possible. The efficiency of our converter is calculated simply: the ratio of output power to input power.

N = (Uout * Iout) / (Uin * Iin)

Since the input and output currents are almost equal (the consumption of the microcircuit is negligible), the ratio is quite simple:

N = 5/9 = 0.56

The final efficiency will be N = 80 * 0.56 = 44.8, i.e. almost like a good steam train. As a result, at best, less than half the battery capacity can reach the battery.

But there is more to it than that. As we remember above, the current that the smartphone consumed from the battery was measured. And in the best of times, it was 300 mA. For the purity of the experiment, you should measure the charge current when powered by USB and a charger. Modifying the scarf a little so that the crown does not participate in nutrition, such measurements were made.


Current from the USB port

It should be noted right away that the current consumption is stable. And according to the standard, a USB port can give up to a half amp!


Power Consumption from Charger

The last photo is very telling - the phone consumes up to a half-ampere while charging! And our battery quickly ran out and gave us 100 mA, which was clearly not enough for the charge.

What are the solutions to the problem?

Who is to blame, we found out, but what to do? After all, I want to charge on the road!
Well, for starters, use more capacious batteries. The same circuit with Krenka would have turned out to be working for itself when charging from a car power supply. The author of these lines in his institute years made himself a “portable” CD player from Sidirom, a battery from a cash register, and ONE CRANK. It was possible for two hours to listen to music.
Another and more racially correct option is to use a switching power supply. This is a cheaper and correct option. Even the cheapest Chinese cigarette lighter charges incorporate a switching power supply. For example, here:


A car charging scarf from Siemens phones

After a short googling, there is the documentation for the microcircuit, and there is practically a diagram of this charging

Charging circuit

The topic of pulse converters is huge and inexhaustible. For this we will not dwell on it in detail. I can only say that there are cheap Chinese converters that can be bought at well-known auctions and solve the problem of battery charging.
Readers of this post themselves can put links in the comments.

conclusions

It is sad when articles of incompetent people appear on the hub and most of them are perceived as useful and interesting. Although, thank God there are few such cases. The irony is that when a friend here told how he “suddenly” discovered the overflow of variables in B, and how he solved it, the post was wildly minuscated (to minus 100). And this post was recognized as quite suitable, although it describes a much larger and impractical nonsense.

Generally speaking, the author ne_kotin led people astray by offering to use the long-obsolete Krenki, and even more so by offering to use them to charge the phone.



Z.Y. I would greatly appreciate criticism of the post, as well as error messages in a personal message.