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Old 09-11-2019, 05:59 AM   #15
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Aren't you worried about putting 140V into a 150V controller when the temperature drops?
It should be worried. On my system, I run 84v on one string and 42v on another, but I have the second level control - BMS on battery would cut off incoming current above 45v. In certain conditions, high voltage could strike the controller, and controller could fail, whatever voltage on the array would be applied to the battery directly. Per Murphy's law, if it could it will, I believe the second protection is necessary.
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Old 09-11-2019, 01:16 PM   #16
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Aren't you worried about putting 140V into a 150V controller when the temperature drops?
This is a good question and after my observations since installing them, my answer would be no.

There are 6 panels in series.
Normal Vmpp voltage is at 19.67v.
Max Open Circuit Voltage per panel (Voc) is 24.06v.



If we multiply mpp voltage by 6 we get a normal loaded voltage of 118.02v.
Then if we multiply the Voc by 6 we get a max Voc voltage of 144.36v.

But since I too was curious, I've been tracking this via Victrons VRM. I especially like to do so on those partly cloudy days when the the cloud edge effect would have the highest potential.

The below day/graph is the highest that I've ever seen them register.
These would be considered cold panels as this was shortly after a hailstorm and also during partly cloudy conditions, in June (June 8th), right after 12-noon, and only a couple weeks away from a near the solar maximum (June 21st.)




You can see that they reached 144.07v which is fortunately still under the 150v max for the controllers. The output amps was Zero because my batteries were full, so there was no load allowing the volts to be at their very highest.

With the temp coefficient being +.04% they 'might' get a little more output during a cold freeze (aka over winter) but by then then sun's angle would have changed (even if I tilted the panels) and the atmosphere would be thicker so the over all number of photons reaching the cells would be less.

But the 144.36v should be the very maximum that these panels could ever produce even under the best of conditions and I can say that we normally see somewhere in between these two (118-144) voltages.

Great question though!
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Old 09-12-2019, 09:25 AM   #17
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I have a new AM Solar combiner box on order (now, for over week! Sigh.), and will manually control each panel's connection to avoid overload in parallel mode until I get the Victron MPPT controller installed. MC4 connectors throughout.
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Old 09-12-2019, 10:21 AM   #18
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Would not worry either. One string I have is 126 open circuit volts, and even at full sun on a cold day, have never seen it above 140 volts, with full batteries. Victron told me controller will derate if it sees voltage or amperage too high.
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Old 09-13-2019, 10:16 AM   #19
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The first phase of my installation effort will be using the old Zamp PWM controller with up to 4 x 12v @ 200 watt panels manually selectable in parallel. Next phase is to add the Victron MPPT controller and wire the other electronics to support a 24v bus, wire the four panels in series/parallel, and temporarily wire the existing 2 x 12v FLA house batteries in series. Final phase will be creating the temperature controlled box to hold 2 x 24v Tesla batteries, yielding 10 kwh.
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Old 09-13-2019, 02:20 PM   #20
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The first phase of my installation effort will be using the old Zamp PWM controller with up to 4 x 12v @ 200 watt panels manually selectable in parallel. Next phase is to add the Victron MPPT controller and wire the other electronics to support a 24v bus, wire the four panels in series/parallel, and temporarily wire the existing 2 x 12v FLA house batteries in series. Final phase will be creating the temperature controlled box to hold 2 x 24v Tesla batteries, yielding 10 kwh.
The Zamp controller is limited to 30-amps. You are limited to ~400 watts of solar panels because of that.
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Old 09-15-2019, 12:15 PM   #21
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According to my Zamp manual, "suitable for solar panels up to 510 watts". If there is less than 100% insolation, then there is less than full wattage provided by any panel. Thus all four panels can be safely connected on a cloudy day and only two panels if directly pointing at sun, zero humidity, dust, etc. This is only a temp setup for occasional travel while I rewired and install MPPT controller system.
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