I tried to make a power bank with little knowledge but I am facing some problem.
I have a lithium cell with maximum voltage of 4.1V and 16Ah capacity. I want the cell to be charged by both solar energy and by a phone charger. Hence, I have a charger from solar panel side that output 4.1V. The phone charger voltage is 5.1, so I am using a DCDC step down converter to make 4.1V. Finally, for the load which would be 5V, I am using a DCDC step up converter. With this setup, the cell has successfully charged upto 4.1V, but when I tried to connect a small 12V lamp to the output where the output current was 900mA, the IC on the DCDC converter was getting hot very quickly. May I know how to improve my setup?
I am using this type of DCDC step up and down converters.
Below is the schematic of my setup. Thank you for assistance.
You can't just apply 4.1V to the cell. You have to use a charger which will charge properly, then automatically terminate. What device is the "Charger" in your diagram?
Also, what lithium cell are you using with 16Ah capacity?
I'm thinking you might feed both the phone charger 5V and the 7V panel into the charger input, each through a diode, and then have a normal circuit after that. But we don't know how much current is involved with either the final load or the charger. The diodes could get toasty.
Yes. The lamp is normally designed for 12VDC, however, I connected it to 5V output of DCDC boost converter. The current I measured was 900 mA. The dcdc module has adjustable voltage regulator (XL6009), which can take input from 3-32V and output 5-35V. The maximum it can deliver is 3A.
The technical detail of the module are:
Small powerful DC/DC converter module with adjustable voltage regulator (XL6009).
Ideal for simple and universal voltage adjustment for countless applications in the electronics sector.
Testing to the sample:
In: 3V Out: 12V 0.4A 4.8W
In: 5V Out: 12V 0.8A 9.6W
In: 7.4V Out: 12V 1.5A 18W
In: 12 V, out: 15 V, 2 A, 30 W
In: 12 V, out: 16 V, 2 A, 32 W
In: 12V Out: 18V 1.6A 28.8W
In: 12 V, out: 19 V, 1.5 A, 28.5 W
In: 12 V, out: 24 V, 1 A, 24 W
Powerful power supply for as it can withstand up to 3 amps.
Powerful tension smoothing in case of fluctuations.
Technical data:
Input voltage: 3.2V-32V
Output voltage: 5V-35V
Maximum efficiency: 94%
Voltage regulation: ± 0.5%.
Operating temperature: -40 to +85 °C.
Frequency: 400 kHz.
The charger has a LM317 IC with TL431. The input to charger from PV panel is 6V. And the output of the charger has been adjusted to a maximum of 4.1V as the battery cell has the maximum 4.1V. The battery cell doesn't overcharge.
I have a kind of flate lithium polymer cell, and it has a capacity of 16Ah.
As the output maximum current rating of DCDC module is 3A, so I will restrict the load to draw a maximum of 1 or 1.5A.
That's what I am also thinking to put a diode on output of both the charger and the DCDC stepdown module so that none of them feed each other. However, during a test, when I was charging the battery with a phone charger, without the diode on the output of the DCDC stepdown module, the current to the battery was 1A, but after inserting a diode, the current reduced down to only 300mA. I had inserted a 3A diode, the drop across the diode was 0.7V.
But, the question I asked can't be answered based only on information from the diagram. It only shows that the devices are connected. I acknowledged that fact, and asked if the connection was legitimate. That is a question about the modules themselves, which can only be answered with knowledge of the modules.
Well, what you are doing violates everything I've learned about proper charging of a lithium cell. If the cell is a 4.1V cell, you cannot continue to feed it with 4.1V after it has fully charged. You must terminate charging. See the datasheet for the TP4056, which uses constant current, then constant voltage, then termination. If it's a 4.2V cell, I don't know what happens if you apply 4.1V continuously.
With respect to load, remember that you have to provide for both the load current and the charging current if your device will be powered up while you are charging.
As the charger output is 4.1 volt and similarly if the battery voltage rises up to 4.1 volt, the charging current would automatically becomes 0. Yes, in my case, there is no termination but I don't if it is required. The module you sugget is of course great and cheap as well. The problem is, it will charge the cell upto 4.2 volts and I want the cell to be charged not more than 4.1 volts. The cell I use is also a 4.2 volt cell, but it is now quite old and the manufacturer recommends to charge it not more than 4.15 volt. So, to be on the safe side, I want to keep it at 4.1 volts.
Secondly, if the termination is required, then I can take two of the TP4056 modules, one for PV module and the other for charging by the phone charger. And connect their output to the cell. But question is, would I require diode on the output of these modules?
Generally, the load would require 5V and 1 to 1.5A max.
But I am more worried about stepping up the 4.1V to 5V. I tested two different step-up DCDC modules and two different loads but both of the modules got really hot. For the test purpose, first, I used a 12V light which was drawing 900mA and then in the second test, I used a 4.7 ohm 1000 watt big resistor as a load. Both the modules can handle a maximum of 3A of output current.
According to the data sheet of the XL6009 http://beriled.biz/data/files/XL6009.pdf, the minimum input voltage to step up is 3.6volts. That, even though some Amazon/Ebay retailers make more generous claims. Your 4.1 volts is very close to that minimum and it is likely to be very inefficient at the fringes of its operating range.
For your test with the "12v" light (driven at 5v ?), measure also the input current. From that you will be able to determine the efficiency of the device under those input/load conditions and see why the device is getting hot.
You should NOT be trying to charge a lithium battery except using a properly designed charger. Consequences of mis-operation can be a battery fire which is very nasty. Both the PV and UAB power sources should feed into the charger, with a boost converter on the 5V and diodes for current steering. Then connect the load to the battery via the step-up.
