I made a 250mA Solar battery charger previously, which is useful. But the charge current is not enough. So I made this high-current version, that can provide 800mA to the lead-acid battery. I am using a 7.2Ah battery to make my system.
This Solar charger is currently limited to about 800mA out of which 160mA is made available using the LM317T(130mA) and the TIP32C(30mA); the rest of the current is supplied by the TIP3055(640mA).
So a totally discharged battery with zero charge can be charged to full capacity in
7Ah/0.8A = 8.75h
The tip3055 will get heated up during the operations. So, a big heatsink is necessary to keep its junction temperature low.
How much the TIP3055 junction temperature will rise depend upon the following equation which I used to calculate.
Junction temp = Ambient Temp + (Power x junction-to-ambient temp of Tip3055)
so if your ambient temperature is 35 degrees Celsius.
and the power dissipated is 4W
the junction to ambient temp of tip3055 is 35.7 degrees Celsius
then, your junction temperature will be = 35 + (4 x 35.7) = 177 degree celsius
you can operate the tip3055 up to 150 degrees celsius only after that it will quickly degrade and go into thermal runaway.
To prevent it from going into a thermal runaway you need to put a heat sink that can take the extra 27 degrees celsius and make dissipate into the air. This is if the tip3055 can safely operate at 150 degrees Celsius.
In the real world, you do not want to reach the absolute maximum temperature of the transistor. In fact, you want it to be up to 80 degrees celsius only. A further increase will only cause trouble and it will surely go into thermal runaway.
Charging profile of lead acid solar charger
If the battery is discharged then it will start to charge from the constant charge constant voltage mode.
In constant charge constant voltage mode it will get about 800mA of constant current using a combination of Pass transistor TIP3055, TIP32C and LM317T voltage regulator. This continues till the battery voltage is near the voltage regulator set point.
As the battery voltage increases the current consumed by the battery decreases.
This marks the ending of the first stage and then the battery current decreases following a curve.
It will go from 800ma to 160mA. Till 160mA the TIP3055 is active and supplies the bulk current and from 160mA to 130mA the TIP32C will supply 30mA and the rest of the current, which is 130mA is supplied by the voltage regulator.
So it essentially becomes a two-stage charging profile.
Battery Voltage
Date Time Battery Voltage(V)
4/8 12:26 AM 8/4/2022 12.96
2:01 AM 8/4/2022 12.88
9:50 PM 8/4/2022 12.96
11:48 PM 8/4/2022 12.84
5/8 2:14 AM 8/5/2022 12.74
10:39 AM 8/5/2022 13.68
11:44 AM 8/5/2022 13.50
7:35 PM 8/5/2022 13.03
9:04 PM 8/5/2022 12.94
6/8 5:40 AM 8/6/2022 12:74
10:46 AM 8/6/2022 13.72
6:57 PM 8/6/2022 13.17
10:21 PM 8/6/2022 12.99
11:50 PM 8/6/2022 12.99
7/8 5:44 AM 8/7/2022 12.91
2:26 PM 8/7/2022 13.67You can clearly see that the battery is being charged during the day and it is being discharged at night.