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STECA Solar battery charger - regulator for solar panels
Tuesday, 29 January 2008
For a mobile home nowadays it’s a must to have a solar power system. It’s free electricity at locations where there is none – although the initial investment is quite significant. An important part of the solar power system is the solar power regulator. It chargers the battery with solar electricity. There are many on the market – we use the STECA PR 2020 Regulator for Photovoltaic systems. It does it’s job well although it has a somewhat peculiar behavior.

The STECA PR 2020 Regulator comes with a LCD display. Two buttons on the front control the functions of the regulator. It’s a simple device to use and shows all the info needed to determine the state of charge (SoC) of the batteries. The SoC is a reflection of how much electric power is available in the batteries.

Steca solar battery charger - regulator
20 Amps Solar Battery Charger
We use the voltage indicator of the STECA PR 2020 to determine the state of charge. Battery voltage is a reflection of how much power is left in the battery. It takes a while to get used to this number ranging somewhere between 24 and 28 volts. It depends on what type of battery (Acid, Gell) is used and it’s quality. With a simple table we convert the voltage into a percentage ranging between 40 and 80 %. For instance a voltage of 25.5 volts during the evening (with lights on) we associate with full. A voltage of 23.4 volts indicates 40 %. Normally we don’t let the voltage drop under 24 volts (65 %).

During the day the STECA PR 2020 shows the actual amount of current coming from the solar panels and what’s being fed to the batteries. On a bright sunny day it can shoot up to 7 Amps but normally hovers round 3 to 4 Amps round noon when the sun is out. At that time it has an average voltage between 26 and 27 Volts. That’s at least 78 Watts coming in. The calculation of what’s being fed to the battery is most of the time a little off. When it shows 3.5 Amps coming in, it says 3.4 Amps going to the batteries. It’s probably because of a small component variation in the shunt resistors measuring the current going through.

The regulator comes with two power counters. One for the solar power coming in, one for what’s being consumed. We only use the counter for the solar power coming in. It shows the total Ampere hours collected by the solar panels since the last reset. The counter can be used to count for instance the daily or weekly charge. On a bright sunny day we collect 28 Amp hours in a 24 Volt system. That’s the equivalent of a 672 Watt light bulb turned on for 1 hour. Or a 80 watt laptop used for about 8 hours. When the counter is used for a longer time it switches to kAh with one decimal point. For instance 12.4 kAh, meaning  12400 Amps Hour. With 28 Amps coming in on a daily basis, it takes at least 3 days to see a decimal point change in the counter.

The STECA PR 2020 comes with a night light function. A separate power output is switched on by the regulator after sunset. It stays on for an amount of hours set in the device setup. We have connected a big white LED to this output to light the display when its dark. During the evening the voltage indicator of the PR2020 matters the most. With the LED light the display can be read easily when dark.

The regulator uses a smiley with a happy or sad face to indicate good or faulty status. A separate error code shows the exact fault when the sad face shows. Connecting an 300 watt inverter to the separate power output sometimes shows the sad face. The error code says E11 – short circuit at the output. This while the inverter has nothing connected to its output. Switching the inverter on and off a few times shows the happy face again.
Looking a bit closer, the STECA PR2020 has a load sensing function. It slowly increases the voltage on the output when switched on and probably measure the current at the same time. When the current goes up too fast the sad faces shows. The inverter has a peak current when starting – during the load-sensing stage (voltage ramp-up) the short-circuit calculation trips and shows the sad face. Switching the inverter off-on a few times reduces the peak current. The sad face stays on for several minutes although the error condition has disappeared already. (inverter running)

In all the STECA PR 2020 Regulator performs well in our case. So far we collected 14600 Amps in approximately 3 years. That’s about 350 kW of solar power. It would be nice if the display was fitted with backlight so it could easily be read in the dark. A revolving feature which automatically alternates battery voltage with the charging current would be a nice addition.

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