Monitoring\analysing a dual charging system ...
Posted: Fri Oct 10, 2014 8:20 pm
Time for the next episode of electrickery ….
Short recap of my electrical system in my Hilux camper:
2 x 80 W solar panels
Ctek 250 S dual charger (charging from the alternator and the solar panels)
105 A.h deep cycle battery
The following is run from the battery:
National Luna 50 liter Weekender twin (dual compartment fridge and freezer)
Four different sets of LED lights
12V water pump
Compressor
Inverter to charge laptops and camera batteries
I have since added the following measuring equipment to be able to bust some myths :
Three off Volt and Amm meters to measure the following circuits –
- Solar panel
- What the Ctek delivers to the battery (either from the alternator or the solar)
- What power is being drawn from the battery by the fridge, lights etc …
So how to log the data from this most basic monitoring system ?
Set your GoPro to timelapse photography, or use an intervalometer on your DSLR …. hehehehehe
Test 1 – WHAT is a “MPPT” regulator ?
A solar panel can deliver as much as 17 V – enough to damage a battery !
Thus a solar panel should be connected to a battery via a “regulator”. There are two basic types:
1) Shunt Regulator – this unit “cuts off” the extra volts and delivers a safe amount of Volts to the battery. In this process it “throws away” energy that could have been used to charge the battery.
2) Maximum Power Point Tracking (MPPT) Regulator – A solar panel harvests “power” from the sun. Mathematically this power is : Power = Volts x Amps. The MPPT regulator reduces the solar volts, AND increase the amps as it passes through the MPPT regulator. Thus providing the maximum amps to the battery.
This photo shows a MPPT regulator at work:
The solar panels are delivering the following power :
P = Vx I = 18,1 x 3,2 = 57,92 W
The MPPT regulator takes this power, then delivers a higher current by reducing the volts. The power supplied to the battery is :
P = V x I = 13,2 x 4,1 = 54,12 W
The process of increasing the current however does take some power, in this example it took 3,8 W. Thus the MPPT regulator was 93,4% effective in this case.
Looking at a larger sample of reading the MPPT regulator took an average of 6,8W, with an average efficiency of 89,1%.
Test 2 – Charging a deep cycle battery
There are various myths and facts around deep cycle batteries …..
This test aims to see what happens when you try to charge a deep cycle battery that has been discharged past 50% - testing what you would encounter in a camp when your fridge drew power from the battery until the safety cut out on the fridge shut it down.
I deliberately discharged the battery until it had a resting voltage of 11,5V. Then parked the Hilux in the sun for the solar system and the Ctek 250 S to charge the battery.
Do note that my solar panels are mounted horizontally and as such does not track the sun – this CAN be seen in the available power as the sun moves over.
Here are part of the data set I recorded for this test :
What can I conclude from this data?
- On 4 October at 12:47, in Cape Town, the angle of the sun onto the horizontally mounted solar panels were such that the maximum power I could get from 2x80W solar panels was 106W, ie about 66% of the rated value.
- As the sun moves over, this potential power constantly varies.
- It was noted that the Ctek250S operates as a constant voltage source, keeping the voltage supplied to the battery constant, while the current could be seen to slowly change to a point before the voltage would change by 0,1V. At 12,9V the charge current steadily dropped, then the Ctek upped the charge voltage to 13V. I then ran out of daylight to see this pattern through, but day two completed this pattern.
- Even though the battery was at a LOW state of charge it accepted the maximum available charge current. (proving some of my prior forum statements wrong …)
The Hilux was moved into the garage. The battery was not charged by any other means, nor was any power drawn from it. The next morning I parked it outside again to monitor the remainder of the charge cycle.
Observations :
- The charge volts started much higher than on day one.
- The same power-sun-angle pattern was observed, with the power peaking at mid day.
- From 12:30 it can be seen how the Ctek starts to limit the charging current as the battery reaches a high SOC (state of charge). The charging volts now stayed at 14,3V while the current was gradually reduced down to 1 A – while the high voltage on the solar panel confirms that more energy is available. The solar panel voltage steadily increased to 18,5V as the current delivered to the battery declined to 1A. Thus the Ctek actively protects the battery against over charging.
- Interesting to see how the charge voltage jumped from 13,9V to 14,3V. Clearly an interesting algorithm that controls the Ctek250S.
- These readings suggest that from such a low discharge to full my 105A.h deep cycle battery only absorbed 41,5A.h !
NOTE – these tests were done with ZERO load connected to the battery.
Conclusion – the Ctek 250 S delivered on its promise as a MPPT solar regulator.
The next series of tests will look at the charging characteristics when a variable load (fridge) is connected to the battery.
I will then also do tests to check the auto-switch-over between solar and alternator charging of this dual charging unit.
These are early days, and I will need to repeat these tests with other regulators and dual chargers before making any comparisons …. This will take months, possibly a year or two ….
Short recap of my electrical system in my Hilux camper:
2 x 80 W solar panels
Ctek 250 S dual charger (charging from the alternator and the solar panels)
105 A.h deep cycle battery
- 6.jpg (29.92 KiB) Viewed 4905 times
National Luna 50 liter Weekender twin (dual compartment fridge and freezer)
Four different sets of LED lights
12V water pump
Compressor
Inverter to charge laptops and camera batteries
I have since added the following measuring equipment to be able to bust some myths :
Three off Volt and Amm meters to measure the following circuits –
- Solar panel
- What the Ctek delivers to the battery (either from the alternator or the solar)
- What power is being drawn from the battery by the fridge, lights etc …
- DSCN1434 (Small).JPG (56.48 KiB) Viewed 4905 times
So how to log the data from this most basic monitoring system ?
Set your GoPro to timelapse photography, or use an intervalometer on your DSLR …. hehehehehe
- DSCN1625.JPG (39.77 KiB) Viewed 4905 times
Test 1 – WHAT is a “MPPT” regulator ?
A solar panel can deliver as much as 17 V – enough to damage a battery !
Thus a solar panel should be connected to a battery via a “regulator”. There are two basic types:
1) Shunt Regulator – this unit “cuts off” the extra volts and delivers a safe amount of Volts to the battery. In this process it “throws away” energy that could have been used to charge the battery.
2) Maximum Power Point Tracking (MPPT) Regulator – A solar panel harvests “power” from the sun. Mathematically this power is : Power = Volts x Amps. The MPPT regulator reduces the solar volts, AND increase the amps as it passes through the MPPT regulator. Thus providing the maximum amps to the battery.
This photo shows a MPPT regulator at work:
- DSCN1501.JPG (35.35 KiB) Viewed 4905 times
P = Vx I = 18,1 x 3,2 = 57,92 W
The MPPT regulator takes this power, then delivers a higher current by reducing the volts. The power supplied to the battery is :
P = V x I = 13,2 x 4,1 = 54,12 W
The process of increasing the current however does take some power, in this example it took 3,8 W. Thus the MPPT regulator was 93,4% effective in this case.
Looking at a larger sample of reading the MPPT regulator took an average of 6,8W, with an average efficiency of 89,1%.
Test 2 – Charging a deep cycle battery
There are various myths and facts around deep cycle batteries …..
This test aims to see what happens when you try to charge a deep cycle battery that has been discharged past 50% - testing what you would encounter in a camp when your fridge drew power from the battery until the safety cut out on the fridge shut it down.
I deliberately discharged the battery until it had a resting voltage of 11,5V. Then parked the Hilux in the sun for the solar system and the Ctek 250 S to charge the battery.
Do note that my solar panels are mounted horizontally and as such does not track the sun – this CAN be seen in the available power as the sun moves over.
Here are part of the data set I recorded for this test :
- test 1.jpg (11.89 KiB) Viewed 4905 times
- On 4 October at 12:47, in Cape Town, the angle of the sun onto the horizontally mounted solar panels were such that the maximum power I could get from 2x80W solar panels was 106W, ie about 66% of the rated value.
- As the sun moves over, this potential power constantly varies.
- It was noted that the Ctek250S operates as a constant voltage source, keeping the voltage supplied to the battery constant, while the current could be seen to slowly change to a point before the voltage would change by 0,1V. At 12,9V the charge current steadily dropped, then the Ctek upped the charge voltage to 13V. I then ran out of daylight to see this pattern through, but day two completed this pattern.
- Even though the battery was at a LOW state of charge it accepted the maximum available charge current. (proving some of my prior forum statements wrong …)
The Hilux was moved into the garage. The battery was not charged by any other means, nor was any power drawn from it. The next morning I parked it outside again to monitor the remainder of the charge cycle.
- test 2.jpg (12.98 KiB) Viewed 4905 times
Observations :
- The charge volts started much higher than on day one.
- The same power-sun-angle pattern was observed, with the power peaking at mid day.
- From 12:30 it can be seen how the Ctek starts to limit the charging current as the battery reaches a high SOC (state of charge). The charging volts now stayed at 14,3V while the current was gradually reduced down to 1 A – while the high voltage on the solar panel confirms that more energy is available. The solar panel voltage steadily increased to 18,5V as the current delivered to the battery declined to 1A. Thus the Ctek actively protects the battery against over charging.
- Interesting to see how the charge voltage jumped from 13,9V to 14,3V. Clearly an interesting algorithm that controls the Ctek250S.
- These readings suggest that from such a low discharge to full my 105A.h deep cycle battery only absorbed 41,5A.h !
NOTE – these tests were done with ZERO load connected to the battery.
Conclusion – the Ctek 250 S delivered on its promise as a MPPT solar regulator.
The next series of tests will look at the charging characteristics when a variable load (fridge) is connected to the battery.
I will then also do tests to check the auto-switch-over between solar and alternator charging of this dual charging unit.
These are early days, and I will need to repeat these tests with other regulators and dual chargers before making any comparisons …. This will take months, possibly a year or two ….
