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Post by tattoo on Aug 3, 2019 14:27:30 GMT
I'm sure they would say yes, since by definition to "overpower" would void the warranty. My point was that you can violate the voltage or current limits even while not violating the power specs. That's why you never plugin panels to the cc without a battery. Series connected panels under no load are giving you open circuit voltages X number of panels, which could exceed the voltage limits even if you never experience enough sun to overpower the unit while it is charging the battery. Yes sir I totally agree...........
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Post by bupkis on Aug 3, 2019 15:58:08 GMT
epever the maker of commander CC
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Post by tattoo on Aug 3, 2019 18:11:10 GMT
WOW 3 times is a LOT and yes there is a cap........ Thanks for the info....
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Post by jeffinseattle on Aug 8, 2019 20:19:43 GMT
Thank you for all the replies! For some clarity, I already have 3 100w panels and I can afford those...so adding 4 more is affordable and they are all the same spec. Not interested in changing my panel size at this time. So... It sounds like wiring each panel separately (same as parallel, right?) would be my best shot. Each panel will provide it's max and 7 won't overload my CC. Is this diagram and my math correct? (7th panel not shown in diagram, just imagine it is there) This would give me 22.5V 40.25A 700W My CC is: Max. Solar Input Power: 800W (12V), 1600W (24V) (I am assuming the 800w max) Max. Solar Input Voltage: 150VDC Max. Input Short Current: 75A Most of these numbers don't come near the MAX of the CC as to not overtax it. I should be good to go...yes? I am worried about wiring the panels together properly; planning on using the Renogy branch connectors. Is my wiring diagram below correct? (The above is just the + (pos) side of the panel, not the neg.) The longest run from the furthest panel will be approx 50ft. The drop is calculated to be: Voltage drop: 0.91 Voltage drop percentage: 4.06% Voltage at the end: 21.59 (using this site, www.calculator.net/voltage-drop-calculator.html)I appreciate everyone's patience with my over-cautiousness. Jeff
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Post by mediadogg on Aug 8, 2019 21:11:27 GMT
Three things:
(1) 50A is a LOT of current to be sending over 50 feet. (2) If you stick with your plan, I would reduce the number of branch connectors. Your calculations do not take into account the effect of less than perfect connections. The fewer the connections the better. They make 4-ways I think. (3) Remember you have 50 ft x 2 going to the panels. A circuit is round-trip. So, unless you have already done it, you need to multiply your losses by 2.
If I were doing it, I would series connect 2 panels, then use a 4-way to parallel 4 sets of 2, for 8 total. If you can't go 8, drop down to 6 for now, and add the other two later. Alternatively, series connect 3 panels, and parallel two strings for a total of 6. Later, you can add a 4th panel to both strings.
It is better to send a larger voltage over long distances, than to send large currents. Also, you don't know how the almost 2 volts of drop (round-trip) will affect the ability of your CC to correctly manage the panels using MPPT.
If you are using a MPPT controller, the more voltage you give it coming in, the better. Late in the day, when the panels are producing a smaller voltage, their combined voltage will still be enough for the buck converters in the CC to do useful work. They will be squeezing the most power they can from the panels even as the sun goes down.
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Post by jeffinseattle on Aug 8, 2019 21:55:51 GMT
1. Only sending 5.75A the 50 ft., not 50A. 2. 4 way connectors, GREAT! I Didn't know they made those.
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Post by mediadogg on Aug 8, 2019 22:50:11 GMT
1. Only sending 5.75A the 50 ft., not 50A. 2. 4 way connectors, GREAT! I Didn't know they made those. So, each panel has 50 ft of cable that you are joining at the controller end?
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Post by tattoo on Aug 8, 2019 23:54:04 GMT
So, each panel has 50 ft of cable that you are joining at the controller end? It could be because his panels aren't close enough to hook them together...... Since he said he hangs them on the walls....
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Post by bupkis on Aug 9, 2019 0:06:30 GMT
Where does 22.5v come from, Voc? Vmp (test conditions) is usually ~18v and less in the heat. With a MPPT controller the panels operate @ Vmp of say 18v in cold weather and 16v or less in the heat using the branch connectors makes it easy. series pairs makes it easy. I do agree that pairs of series would be the way to go (easier), but disagree on the higher the voltage the better. Series pairs will cut current in HALF cutting voltage drop, less branch connectors. Yes there is a trade off in voltage drop (power loss) with series vs parallel vs transformer loss. Also consider that the panels rarely make their 5.75 A rated power, but still produce nominal voltage. With your E, W & S orientation, pairs of panels seemed the best, 2 in each direction until you add another for 2 pair facing south.
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Post by mediadogg on Aug 9, 2019 0:29:25 GMT
This was what I said exactly: "It is better to send a larger voltage over long distances, than to send large currents." (I meant relative to power losses from resistance.)
Ever wonder why power grids transmit power over miles and miles use 10'000s or 100,000s of volts? Why don't they use 100,000 amps?
But of course there are limits to everything. The CC voltage limit is one, and local electrical codes are another. I read somewhere that 80V was listed in some building codes. Of course, you might want to check your own.
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Post by bupkis on Aug 9, 2019 12:20:10 GMT
This was what I said exactly: "It is better to send a larger voltage over long distances, than to send large currents." (I meant relative to power losses from resistance.) I'm talking transformer losses from high voltage input into the CC transformed to battery voltage, the higher the less eff. I'm sure the utility companies know the sweet spot based on MILES of transmission, stepping up then down. Renogy does not include CC eff curves but I've linked manuals that do and they would be similar. All these different compromises beginning with crappy panel orientation, shade, series/parallel, wire gauge, distance, temp and the rest.
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Post by mediadogg on Aug 9, 2019 13:32:59 GMT
This was what I said exactly: "It is better to send a larger voltage over long distances, than to send large currents." (I meant relative to power losses from resistance.) I'm talking transformer losses from high voltage input into the CC transformed to battery voltage, the higher the less eff. I'm sure the utility companies know the sweet spot based on MILES of transmission, stepping up then down. Renogy does not include CC eff curves but I've linked manuals that do and they would be similar. All these different compromises beginning with crappy panel orientation, shade, series/parallel, wire gauge, distance, temp and the rest. Today's new "buck" circuits are not simple transformers. In fact they tend to be more efficient when the input DC voltage is higher than the target DC voltage (again, up to the design limit), and can be over 90%. If the panel voltage drops below the voltage required to charge the battery, then the CC has to "boost" instead. I think MPPT controllers can do that, but I don't think the typical PWM controller has boost circuitry. That's why I like to have at least two panels in series, so regardless of what CC I have hooked up, there is a wider range of times of the day when the input voltage from the panels to the CC is higher than the required charging voltage.
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Post by bupkis on Aug 9, 2019 13:36:55 GMT
No mppt controller I know of can buck voltage. (please note that transform does not always mean transformer!) I did find in the newer Rover manuals a generic PV controller eff curves, they are not too bad. Others go higher and lower and are extreme at either low or high wattage. Trying to limit power loss to 3% panel to CC and then the CC looses another 8%! pair low voltage panels '12v' is a must to stay @mppt cuz of heat issues, not only from the sun but from poor install. Even when Vmp is low, voltage drop (and other losses) can force the panel to operate well above Vmp in a very ineff region of the power curve.
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Post by tattoo on Aug 9, 2019 14:07:26 GMT
Thank you for all the replies! For some clarity, I already have 3 100w panels and I can afford those...so adding 4 more is affordable and they are all the same spec. Not interested in changing my panel size at this time. I don't blame you...... Yes they are affordable and a much easier size to deal with......
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Post by mediadogg on Aug 9, 2019 14:51:36 GMT
No mppt controller I know of can buck voltage. (please note that transform does not always mean transformer!) I did find in the newer Rover manuals a generic PV controller eff curves, they are not too bad. Others go higher and lower and are extreme at either low or high wattage. Trying to limit power loss to 3% panel to CC and then the CC looses another 8%! pair low voltage panels '12v' is a must to stay @mppt cuz of heat issues, not only from the sun but from poor install. Even when Vmp is low, voltage drop (and other losses) can force the panel to operate well above Vmp in a very ineff region of the power curve. Good point about the word "transform." I don't profess to know all about anything, certainly not all designs for all controllers - so, I'm with you there. Here is what I would agree to, and I think these statements are true: (1) MPPT algorithms do not specifically depend on the use of buck / boost converters (2) Sone sort of DC - DC conversion or transformation, however is needed inside a solar charge controller (3) Some charge controllers use buck and boost circuits to perform the DC - DC conversion ( theory and chipset for ti SolarMagic smart panels ) From here: Notice they talk about "stepping down" a high voltage from the PV to a lower voltage used for charging the battery, and then "boosting" the current to compensate for the lower voltage (power out + losses = power in) at over 90% efficiency. This task, at that efficiency is typically done today by what are called buck converters. There may be other ways to do it. Boost converters do the opposite: they convert a lower DC voltage to a higher DC voltage, at a reduced current (again, Power out = approximately Power In). MPPT controllers for battery voltages greater than 48 Volts might need both "buck" and "boost" circuits (this use of the word "boost" is totally different from "boost mode" as a stage of charging a battery).
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