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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(outin)oc | E-Load Setting | Measured Voltage input (using dmm on input terminals of mppt)Measured Voltage Output | Measured Current | extra notes | |
|---|---|---|---|---|---|---|
| Sunlight | 25.131 | |||||
| Clouds | 16.2 | 7.0kohm | 0.171 | 10.03 | 0.0014 | |
| Clouds | 16.2 | 10ohm0.171 | 0.155 | 0.0152 | ||
| Clouds | 16.2 | 70W | basically 0 | 0.015 | ||
| 240W light | 9V | 5ohm | 0.068V0.227 | 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 | .316.285 | 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.
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Another note: the voltage on the input of the mppt changes drastically when the outside environment does not even change. For example, the voltage output(oc) was 15V, which changed to 25V after several minutes and changed to 8.8V after several more minutes of doing nothing (same light source and intensity).
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.
| 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 tehb output current for a total less amount of output power. Maybe this has to be configured so the output voltage we want will get drawn, and the |
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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.
Note, the maximum output power for any mppt is determined by decreasing the resistance on the DC load until the power supply goes into Constant current mode. This limits the maximum input power knowing the mppts are limited to 7A on input
what is the minimum power out that we expect from each mppt?
what is the maximum power out that we expect form each mppt?
were each of them meeting this requirement?
String Testing of MPPTs
Each MPPT once unit tested, will be tested in series for the total array output power, and continuity. Like unit testing, this will be run for at least half an hour for full validation.
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