building a 12v solar power battery pack
They have become very affordable and portable.
However, they all have a major flaw, which is related to how the charging circuit in the phone and tablet can charge its internal battery.
So now that you find your perfect solar panel, it comes with the perfect USB connector for your phone, puts it in the sun and the phone starts charging as expected.
However, unless you live in the desert, there will always be something in the sky that will spoil your perfect charging system. . .
Clouds, birds, shaking trees, and even planes passing.
The charging circuit of the phone is designed to protect itself when the power supply becomes unreliable, and when it detects a power drop, it does so by cutting off the current of the internal battery.
However, for solar power, sudden power outages always occur.
As long as someone comes over and casts a shadow on the solar panel, it is enough to cut off the charging process.
While you have the perfect system, come back in an hour and find that the phone is not charging, sometimes even worse than not charging, the phone starts all the circuits to lock the fluctuating power supply, it actually ended up using more power from the battery.
This is a note on how to build a small power pack to store overcharging in all solar conditions and use overcharging to get past the time when there is a shadow on the panel.
I designed this system for 12 v operation because it is a universal voltage commercial solar panel.
The basic specifications I designed are: nominal voltage. . . . . . . . . . . . . . . . 13.
0 v battery capacity. . . . . . . . . . . . . . . . . 3.
Energy capacity of 3Ah specification. . . . . . . .
> 40 Wh battery chemistry. . . . . . . . . . . . . . .
The maximum charging current of lithium phosphate. . . . . . . . . . .
3A maximum discharge current. . . . . . 7A (continuous)
Pulse discharge current. . . 27A (10s)
The charging voltage drops. . .
1 v full charging pressure. . . . . . . . . . . . 14.
The output of the 4 V battery ended up being much stronger than I originally expected, and it was strong enough to power small inverters, run lights and other small appliances.
The lithium iron phosphate battery chemistry was selected for its good match with the solar panel output voltage, excellent power properties and long cycle life.
A good battery should provide a charging cycle of more than 1000 times.
Materials needed for the battery :(
All parts are available from www. batteryspace. com)
4 X lithium ion battery, either purchased as pre-order product
Assemble the battery pack, or build the lithium battery protection circuit of pack1x 12 v on its own. I use PCM-
Due to the low idle current of the battery charging controller, I packed the LFP7A4S myself: TL431-
Band gap regulator vn2222-
Can be replaced with any small signal N-
Red LED channel-
Type is not important ltv-816 -
Optical isolator with BJT output, can be replaced with similar type irf9z24nHigh power P-
Channel MOSFET, can use a larger current device to reduce loss
Any diode with a low forward voltage can work in a fine-tuning tank of 100 k, and the multi-turn unit is ideal, but the conventional fine-tuning tank only works on resistance: 4.
7 k, 100 k, 510 k, 1 k.
The regular 1/8 w perforated type works fine, or if you like connectors, SMD: I connect to the solar panel using the regular 5mm barrel connector and the output watt-hour meter using the car power connector: amazon has sold many LED or LCD-based voltmeter at a fairly low cost, and here is some basic background information that helps drive the design of the battery pack.
Solar panels are devices with constant voltage and constant current.
They have specific design voltages for each panel design work.
As the load draws more and more current from the panel, the output voltage drops slightly, but not significantly.
At a certain point, the current consumption exceeds the electrical flow that can be generated by the panel (
Directly related to the amount of light on the panel. )
This is called the maximum power point.
Through the maximum power point, the voltage of the panel starts to drop and the power output drops.
Therefore, in order to maximize the power generated by the solar panel, it is necessary to run the solar panel to the position as close as possible to the maximum power point.
The diagram of the solar panels I plan to use for this project illustrates this.
While the final design will work with many different solar panels, this will be most effective when the voltage at the maximum power point of the solar panel matches the design voltage.
In this project, I used the Mercury 27 foldable solar panels made by Instapark.
From the power chart, the maximum power point of this special panel looks like 14 v. The design consists of a charging controller, a battery pack, a voltmeter for observing the state of the battery\'s charging and a connector for power input and output.
The most complex part of the design is the charging controller.
Several design requirements must be met by the charging controller: 1.
Low voltage difference because the solar panel voltage is a bit more than 14 v and the nominal battery voltage is 13. 4V (3. 35V per cell)
, The allowable voltage drop of the charging controller must be as small as possible. 2.
High current capability.
At the maximum power output, the solar panel will go out near the current 2A.
Therefore, passing through a transistor should be able to pass through a current of at least 2A at a minimum voltage drop and should not overheat. 3.
When the solar panel has no current, the minimum current consumption on the battery.
In order to prevent the charging circuit from discharging the battery during storage, it is necessary. 4.
Current regulation is not needed.
Since the solar panel is a device with constant current, there is no need to adjust the current flowing through, only the voltage needs to be adjusted. 5.
Adjustable voltage regulation.
Ideally set to the maximum charging voltage of the lithium battery.
This design is 14. 4V (3. 6V per cell).
The schematic diagram is displayed at the top of the page.
Although the main passage of the transistor is the power P-MOS.
The MOS transistor is driven above the threshold in normal working condition to ensure minimal conduction
State resistance (Linear mode. )
Voltage regulation is achieved by using a TL431 bandwidth regulator.
The output of the MOS transistor is connected to the schottky diode to prevent the current from returning from the battery to the charging controller.
To minimize the on-state voltage drop, a Schottky diode was used.
Use the optical isolator to cut off the connection between the battery and the TL431 feedback circuit.
Even if the voltage divider has a fairly high resistance (100kohm)
, When the battery is not in use, it will still show unwanted leakage current.
Therefore, when there is no solar energy, the optical isolator connected to the power supply voltage of the solar panel can effectively disconnect the voltage divider to ensure minimal power loss.
The battery pack is made of four 26650 lithium ion batteries in series. I used a 3.
The 3Ah unit obtained from batteryspace. com.
The battery pack is connected to the 8A Battery Monitor, which will protect the battery from overcharging, undercharging, and short circuit conditions.
There are other pre-
Battery packs that can also be used.
For people who have no experience in battery pack manufacturing, I would recommend buying a pre-
There is a built-in battery pack in the battery monitoring circuit.
The battery pack building is dangerous because these are very high power lithium batteries that can cause an explosion if they are short-circuited. The pre-
The battery pack manufactured contains a monitoring circuit that will protect the battery when a short circuit is detected.
The charging controller is built using breadboard technology with wire wrapping.
I put the whole design in a box.
In addition to the power level of about 40 x, the design is very similar to the minimum boost.
A ready-made voltmeter purchased from Amazon is added to the top, allowing users to monitor battery voltage during charging and discharging.
For the initial adjustment, it is necessary to trim the output voltage to the set point of the design before using it.
The best way to do this is to fully charge the battery to 14 using a lab power supply.
4 V, the voltage should drop to about 14 V than let the battery rest for 5 minutes.
Connect the power supply (
Solar or laboratory power supplies)
And adjust the trim pan until the battery is charged back to 14. 4V again. The P-
MOS transistors do get a bit hot during use, I put a small radiator on it to help cool it in hot weather.