Performance
The ideal diodes work as intended for the most part - the output voltage is approximately equal to the supply voltage for all voltages >0V.
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Nomura Ideal Diode Images:
Parallel Ideal Diode Testing
2 ideal diodes, powered from 2 different power supplies, connected to a common DC load. Current measurements were taken with the clamp meter, so are not 100% accurate.
Test Setup:
Test Results:
| Test # | Test Conditions | Test For | PSU 1 V | PSU 1 I | PSU 2 V | PSU 2 I | Load Mode | Load 1 V | Load 1 I | Results |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Matched PSU Voltage (20V), Current Limit, not hitting CC limit (0.9A each) | 19.98 | 0.7 | 19.99 | 0.6 | CC | 19.85 | 1.4 | Both PSU in CV | |
| 2 | Matched PSU Voltage (20V), Current Limit (0.9A), load at lower CV | Battery Charging | 18.14 | 0.86 | 18.18 | 0.86 | CV | 18 | 1.818 | Both PSU in CC |
| 3 | PSU 1 higher V (21V), PSU 2 20V, Matched Current Limit (0.9A), load at lower CV | Unbalanced V Set Points | 18.14 | 0.87 | 18.18 | 0.87 | CV | 18 | 1.818 | Both PSU in CC |
| 4 | Matched PSU Voltage (20V), PSU 1 higher CC (1.2A), PSU 2 0.9A, load at lower CV | Unbalanced Panels | 18.18 | 1.2 | 18.18 | 0.85 | CV | 18 | 2.125 | Both PSU in CC |
| 5 | Mismatched V and I PSU 1 (22V, 1.2A), PSU 2 (20V, 0.9A), load at lower CV | Unbalanced Panels and Set Points | 18.18 | 1.2 | 18.18 | 0.85 | CV | 18 | 2.123 | Both in CC |
| 6 | PSU1 (22V, 1.2A), PSU2 (20V, 0.9A), Load at CV 19.8V | Batteries charging with mismatched panels and set point | 19.98 | 1.2 | 19.98 | 0.9 | CV | 19.80 | 2.120 | Both PSU in CC |
| 7 | PSU1 (22V, 1.2A), PSU2 (20V, 0.9A), Load at CV 20V | Batteries charging with mismatched panels and set point | 20.18 | 1.2 | 20 | 0 | CV | 20 | 1.22 | PSU 1 in CV, PSU 2 in CC |
| 8 | PSU1 (22V, 1.2A) PSU2 (20V, 0.5A), Load in CC of 0.3A | Single panel can provide the requested current (mismatched voltages) | 21.99 | 0.3 | 20 | 0 | CC | 21.93 | 0.3 | Draws all current from higher voltage panel |
| 9 | PSU1 (20V, 1.2A) PSU2 (20V, 0.5A), Load in CC of 0.3A | Single panel can provide requested current, matched voltages | 19.98 | 0.2 | 19.99 | 0.1 | CC | 19.92 | 0.3 | Uneven load sharing |
| 10 | PSU1 (20V, 1.0A) PSU2 (20V, 0.5A), Load in CC of 0.8A | Single panel (or both panels) can provide requested current, matched voltages | 19.98 | 0.5 | 19.99 | 0.3 | CC | 19.89 | 0.8 | Uneven load sharing |
RESULTS:
Load is shared evenly when the power supplies are in CC mode.
This is best achieved by setting the voltage limit of the power supplies higher than the DC load's CV setting (Tests 2-6).
If one of the PSUs voltages is at or lower than the DC load CV set point, then the power supply transitions to CV mode and outputs nothing.
If the requested current is low, only the higher voltage panel will be providing power, as long as the power is sufficient.
In our application, we do not care about uneven load sharing for a small load, we care only about getting the maximum power when requested - e.g. if the batteries only want 2A, and one panel can provide all 2A, then it does not matter if it is provided by that one panel or by a combination of both.
For a load that is larger than the panels can provide, then the maximum is drawn from both panels. This was tested by setting the CV of the DC load lower than the PSUs. Both PSUs were fully loaded into CC mode, and we were drawing the maximum current. With the MPPTs, they will adjust to provide higher current at the lower output voltage.
PLAN:
Set the MPPT voltage set points higher than the maximum voltage of the battery. This way, we will be able to charge in all conditions, but will not be able to taper the charge at the end. We will be able to achieve 98.5% charge (ish), but never 100% charge through solar. I think this is acceptable. We will set the MPPT voltage to somewhere around 155V, leaving room for 4V of drop along the wiring. We should look into how much voltage drop we expect over the length of the wiring and all the relays, etc. when charging at full power through solar. Keep in mind the 2 different set points for Over Voltage and Set Voltage of the MPPTs.
Layout
Layout is probably based on the layout above, judging by the parts on the board.
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