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| 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) |
Note: I started testing in constant current mode to match the following diagram in terms of power out and in.
I found that the output voltage started fluctuating and making the input also fluctuate to maintain the current. Not sure if it is supposed to operate like this, but it may be an issue if other mppts in the string force one mppt to be at a constant current. I will continue testing this issue by looking into the suggestions on the user manual of the mppt:
V(in)oc & V(out)oc were measured without an electronic load connected.
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I will start by connecting 2 mppts in series, with an output voltage predicted to be about 50 volts with a current limited by the power supply/.
The first part of the process involved combining both mppts in series, and based on the resources in the bay, testing was limited to the 1A output from one of the power supplies. Both mppts were set for a V(out)oc of about 27V, and limited to a current out of 1A. The dc load was set to constant resistance mode, and decreased from 100ohms until the resistance before either power supply would go into constant current mode.
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. |
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SPI Communication Testing of MPPTs
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