James,
That does clarify things a little, thank you for the reference.
However my main point was that this positive ground requirement is specific to this particular module design only. I'm pretty sure the old style modules with the gridlines in the sun, still have a negative ground whether you are stringing 2 or 20 of them together. So it's not just about an increase in the array's voltage, it's about an increase in an array voltage for THIS particular panel design.
Your original statement made it sound like any time you string more than 3 panels together you need to switch to a positive grounding system and I don't believe this is correct. Perhaps the old style modules experience this same ion buildup but it occurs on the negative side that is in the sun. Although I've never had occasion to string more than two panels together myself, it is my understanding that you still have a negative ground on the typical panel array even when it is putting out 300-600V, as is the case in some popular PV system architectures. The need for a positive ground only occurs when you have a module with the positive side of the cell facing up.
If my understanding of this is incorrect, I would be grateful for additional references to clarify the subject further.
Capt. Carter
www.shipofimagination.com
On Tuesday, June 10, 2014 11:05 PM, "James Sizemore james@deny.org [electricboats]" <electricboats@yahoogroups.com> wrote:
I see where you are missing what positive ground is. The ground comes from the frame and uses the green wire, the positive and negative cables on the panels act like they do on any panels. See the last two paragraphs on some random panel manuals I just googled:
On Jun 10, 2014, at 7:10 PM, "Carter Quillen twowheelinguy@yahoo.com [electricboats]" <electricboats@yahoogroups.com> wrote:
James,I'll admit that I'm still having some difficulty wrapping my mind around the concept of a "positive" ground and don't really completely understand this but I don't think your statement is completely correct.My understanding is that the reason this type of high efficient panel has a positive ground is because they are basically built backwards with the current carrying grid on the back of the cell instead of on the top. That's why you don't see any lines on them and they get more efficiency because they have more collection area since the grid lines on the typical solar cell covers a significant portion of the collection area, thus reducing the cells output per gross area. Without the grid lines in the sun, you have more collection area and get more electron flow.I'm petty sure you still have a negative ground even on high voltage strings using the cells that you can see the grid lines on. If you see the grid lines, then the cell is constructed with the negative side up, if you don't see the grid lines, then the cell is installed positive side up. I guess this results in the positive part of the photocell being in contact with frame, thus requiring a positive grounding system.This is how it was explained to me by a manufacturer's rep when I looked into using these cells on the Arc to get more power from my array. Unfortunately, it would also require the use of a different charge controller and inverter that was configured for a positive ground so I abandoned the idea. Not to mention the fear of promoting galvanic corrosion.The fact that these flexible panels have no metalic frame and thus are not grounded does make sense and I think they might work for my dinghy but they also mount this type of cell in rigid frames and that's a whole different animal that requires the positive grounding system.Capt. CarterOn Tuesday, June 10, 2014 7:25 PM, "James Sizemore james@deny.org [electricboats]" <electricboats@yahoogroups.com> wrote:
The comment about the positive ground is correct, in large high voltage strings SolarPower cells need to be positively grounded to bleed of a surface charge that will choke there output. These are very popular cells because of there industry leading power density. Most high voltage solar converters support positive ground because of this.But as I said in the last post, on a boat you will not have high enough voltage to worry about it. Plus the bendable panels are not grounded at all. So they should not be used in long high voltage strings regardless. If you did use them in high voltage strings with out positive grounding nothing bad would happen they would just not put out there full 19% efficiency.Though having something on your boat with a small positive surface charge might make you boat a more interesting lighting target. :-) But I doubt there would be enough of one to make a power boat more interesting then a sailboat with an aluminum mast!
On Jun 9, 2014, at 11:33 PM, "'Dan Hennis' dhennis@centurytel.net [electricboats]" <electricboats@yahoogroups.com> wrote:Quick comment I believe to be accurate.If memory serves, in about 1958-1960, all American companies stopped doing Positive ground. This I believe was a part of the NEC at the time. That is why you do not ever find any motor vehicles after that year with a positive ground. It is too confusing to us normal people to have to look up in a book for a direction. Also, it had to do with electrical engineering theory.Just sayin, ...Dan----- Original Message -----Sent: Monday, June 09, 2014 11:20 PMSubject: Re: [Electric Boats] Re: 1964 8 Metre Bobcat Catamaran Electric DriveDoes that Grape solar panel have a positive ground? and how does that work exactly?Looks just like the Renology panel, 100W Monocrystalline Bendable Solar Panel | Renogy Store, which I believe has a positive ground. Not sure exactly how to deal with that but would like to understand what difference it makes before I spend $2/watt for a couple of them for my dinhy. Only weights 3 pounds and looks like a good package but the positive ground thing has me concerned.Can anyone explain how this will affect a charging system? or does it matter?Captain CarterOn Monday, June 9, 2014 9:30 PM, "James Sizemore yamez4u@gmail.com [electricboats]" <electricboats@yahoogroups.com> wrote:
As long as the high and low cutoff can be user configured they would work. You would also want a contact relay so that the BMS could shut the charger down if a single cell went out of range. The 12 volt and 48 volt chargers are using the same feed in source so the limit is the watts used not the DC amps.120v 15a breaker can supply 1800 watts.1800 watts / 48 volt = 37.5 amps1800 watt / 12 volt = 150 ampsThe limit is almost always the source watts, just Ohm's law in action.The largest charger you can realistically buy is a forklift battery charger:You would need at least a 5000w generator to keep it feed.
On Jun 9, 2014, at 12:11 PM, "albert682@yahoo.com [electricboats]" <electricboats@yahoogroups.com> wrote:Hi Group,
I'm kicking myself for even shipping the 48v Lester chargers up to Canada but done is done. Can they even be used for charging Lithium Batteries? If not I'll use them for the coach RV batteries.
Otherwise I've been reviewing inverter/chargers and have found that 12v inverter/chargers output more amps than 48v inverter/chargers. Why is that? Also if that is the case should I be looking at a 12v high output charger?
Each of my motors produces 80amps for a combined output of 160amps full throttle. It would be nice to source out the components so that I can always return the same 160amps back to the bank. So if I'm thinking correctly then I get a large stand alone inverter and run multiple 48v chargers back into the system.
Everyone seems to go for the elcon 1500 charger but at the outset I don't know for sure if it charges at more than 20amps which would take forever to charge a large bank.
The safe limp home speed well it's more like the never going home speed I'm after. I do concurr though the DC generator is the way to go but prohibitively expensive. So AC generator(s) and a large output charger is what I'm after.
Arden
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Dan Hennis
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