...
The following table should outline results from varying the E-load and intensity of the sunlight. The first cell in series was isolated, and attached to an E-load.
| Light Source | V(in)oc | E-Load Setting | Measured Voltage Output | Measured Current | extra notes |
|---|---|---|---|---|---|
| Sunlight | 25.131 | ||||
| Clouds | 16.2 | 7.0kohm | 10.03 | 0.0014 | |
| Clouds | 16.2 | 10ohm | 0.155 | 0.0152 | |
| Clouds | 16.2 | 70W | basically 0 | 0.015 | |
| 240W light | 9V | 5ohm | 0.227 | 0.0422 | reading the vout from mppt was 0.56V while output from solarsenseslave was 0.056V |
| 240W light | .866 (dmm) 25V(eload off) | 5ohm | .285 | 0.0566 | |
Note: when the Mppts are lit by the light outside on a fully cloudy day, the mppt goes into short circuit mode where it provides basically no output voltage increase for a normal resistance on the line. However, using the 240W flashlights provided by Micah, we are able to see a huge increase in the voltage input and the voltage out on the line (from 15V(out)oc when cloudy to 25V(out)oc). On a sunny day outside the voltage output from the mppt is still 25V which is pretty good.
...
Due to the variance in the measuremntes, each mppt was taken out of the holders and tested with the bench supply and DC E-Load. The following table summarizes the results. Note that the input open circuit voltage was set to 27V by the output voltage setting potentiometer. The input open circuit voltage (voltage from power supply) should also always start at 20V (unless modified in the notes).
| MPPT# | DC E-Load Settings | V(in)oc | V(out)oc | Vin | Vout | Iin | Iout | max temp (deg C) | Notes |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 6ohm | 15.98 | 25.245 | 10.01 | 18.516 | 6.264 | 3.087 | 44 | 24-25V has audible frequency oscillations (can hear) |
| 1 | 7ohm | 15.98 | 25.245 | 33.01 | 32.339 | 4.608 | 4.62 | 31.3 | When in audible range, heat increases really quickly. With an increase in resistance on the E-load is a increase in the voltage output with a significant decrease in the output current for a total less amount of output power (of course its following the inverse exponential curve until open circuit voltage in this case → infinite impedance). |
| 1 | 6ohm | - | - | - | 25.622 | 5.768 | 4.27 | 49 | during the time of this testing I also wanted to test the efficiency loss from running the mppt with an input voltage of 25-27V, in which the DCDC operates at an audible frequency of oscillations. Before the testing, I noticed that there was an increase in temperature at this frequency, so I wanted to find out the loss in efficiency. It was concluded that the loss in about 6 watts at this point, which was about the same power loss as at 20V input. It seems that the audible noise comes from the fact that the input voltage matches the upper limit of the output voltage determined by the output potentiometer. |
| 2 | 6ohm | - | - | - | 25.721 | 5.87 | 4.289 | 50 | preformed similarily to mppt #1 except that running it at 27V was 1W less efficient than under 27V. |
| 3 | 5ohm | - | - | - | 25.606 | 6.938 | 5.1206 | 43 | The power drop for this testing (as outlined) was 7W (about 1W more than normal) |
| 4 | 6ohm | - | - | - | 25.549 | 5.743 | 4.256 | 49 | About a 6.5W drop in efficiency. |
| 5 | 6ohm | - | - | - | 25.696 | 5.793 | 4.283 | 55 | Preforms similarly to the others, except gets to a higher temperature even though just 6W drop |
| 6 | 6ohm | - | - | - | 25.706 | 5.816 | 4.284 | 55 | Preforms similarly to the others, (6W drop) |
V(in)oc & V(out)oc were measured without an electronic load connected.
...
The following table outlines the results:
| Current input MPPT1 | Current Input MPPT2 | DC Load Voltage | DC Load Current | DC Load Resistance | Max Temperature | Notes |
|---|---|---|---|---|---|---|
| 0.906 | 0.985 | 50.543 | 0.7218 | 70 | negligible | When the resistance is decreased so that one of the mppts goes into constant current mode, the mppt cannot stabilize itself at a specific voltage, and instead fluctuates like crazy. This may be an issue if a mppt needs to maintain a certain current output, and one mppt lags behind others. Also in any case, one (or both) of the mppts will have fluctuating current (before current limit is met) in order to keep a constant current from the constant resistance. |
| 2.819 | 2.595 | 49.907 | 2.0787 | 24 | 32.5 | was using two power supplies limited to 3A output (still decreased CR value until one of them went into constant current mode) 20V input for this and above on power supplies |
| 2.818 | 2.605 | 57.759 | 2.595 | 20 | 30 | Input on mppt 1 is 25V and on 2 is 32V (limits of the power supplies) |
Array testing
| MPPT # | Resistance (Load) | Voltage | Current |
|---|---|---|---|
| 1 | 1000 | 15.918 | 0.01533 |
| 1 | 10 | 0.671 | 0.0667 |
| 2 | 1000 | 15.937 | 0.1553 |
| 2 | 10 | 0.731 | 0.073 |
| 3 | 1000 | 16.332 | 0.0161 |
| 3 | 10 | 0.745 | 0.0742 |
| 4 | 1000 | 16.437 | 0.0161 |
| 4 | 10 | 0.866 | 0.0863 |
| 5 | 1000 | 16.591 | 0.0159 |
| 5 | 10 | 0.833 | 0.0831 |
| 6 | 1000 | 16.563 | 0.0159 |
| 6 | 10 | 0.931 | 0.0929 |
To conclude this testing, the only way that the cells are the point of failure is if in direct sunlight they still do not have a sufficient power output. I will try to test this, however it is winter so getting the car outside may be a little tricky.
...
SPI Communication Testing of MPPTs
...