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paulz
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# Posted: 20 Feb 2021 06:55pm
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Moved my CC in the cabin today. While doing so the cables from the arrays hit my arm. Yeeeow! Gave me a pretty good zap. Should have unplugged outside first but it gave me a good indication that there's a fair bit of juice. CC showed about 50-70v when I got it hooked back up.
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gcrank1
Member
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# Posted: 20 Feb 2021 07:14pm
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Tesla'ized!
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ICC
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# Posted: 20 Feb 2021 08:40pm
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Another reason to always install a breaker at the panels to make disconnect easy. Of course one has to use it as well.  You might have noticed I am "big" on installing breakers that are rated for DC switching use in many points in a solar system. The Midnite breakers are all rated for use as switches/ They mount to a DIN rail so are easy enough to custom fabricate, though that may not meet code.
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paulz
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# Posted: 21 Feb 2021 05:57pm
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Hey ICC, how about this? Came with a CC I bought. Wasn't sure where to use it. What about CC to batteries or battery to inverter?
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ICC
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# Posted: 21 Feb 2021 09:01pm
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Is it marked for voltage?
It appears to be a type of breaker sold by many Chinese sellers. Seems to me I have seen voltage ratings from 12 with a top of 48 or so. So, it may not be any good for PV panels in series. Also, note that many breakers are not meant to be used repeatedly as switches. Once in a while, like a few times a year may be okay. Unless it is marked SWD there is no way to know for certain without documentation.
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paulz
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# Posted: 22 Feb 2021 09:40am
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No markings, and it does look like the 12-48v ones I'm seeing online. Midnite does have higher DC breakers.
Thanks ICC.
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FishHog
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# Posted: 22 Feb 2021 02:32pm
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Paul that’s the breakers I’m using on my setups. Working just fine for me but I’m not switching them very often.
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gcrank1
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# Posted: 22 Feb 2021 04:49pm - Edited by: gcrank1
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I was thinking on getting a few of those to use when I would need to discon the array from the scc, not often as I am not disturbing the set up much but it sure would be a step up from the wire nuts 
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paulz
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# Posted: 24 Feb 2021 10:45am
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Thanks Fish. Yeah those Midnite breakers are about $100 a pop, not sure I'm in for those.
On another subject, I would like to add this array to my existing solar at the shop. What's the story on unmatched panels, can they go to the same CC? These are 75w wired in series, producing around 110v open, two strings. My existing panels are 260w and about 130v in series.
Can it be done with the same CC? Second CC hooked to the battery bank?
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gcrank1
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# Posted: 24 Feb 2021 01:04pm
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I think the arrays are too far apart in watts to combine on one scc but it is my understanding that you can hook up multiple arrays c/w their own scc, even mixed pwm and mppt, to the same battery bank; they will throw charge into the bank to what it can take if FLA.
Now LFP is another matter.
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ICC
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# Posted: 24 Feb 2021 02:49pm
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Quoting: paulz Thanks Fish. Yeah those Midnite breakers are about $100 a pop, not sure I'm in for those.
Midnite has probably got over a hundred breakers, in many amperage sizes with some designed for more demanding uses. The high voltage ones are pricey, the normal range like the MNEPV series are $18 or less a pop. Even those are good to a max of 150 VDC.
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ICC
Member
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# Posted: 24 Feb 2021 03:17pm
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Quoting: paulz What's the story on unmatched panels, can they go to the same CC?
Maybe they can be used if connected differently.
Here's the rule of thumb...
For series connection – the same current rating of the panels is more important than voltage
For parallel connection – the same voltage rating of the panels is more important than the current rating
Use a 10% difference in either voltage or amps as the Absolute Maximum difference between panel ratings.
In effect with a SERIES connection, the panel with the lowest Amperage determines the maximum power that can flow from that series string. A 6 amp panel will drag the output of a 10 amp panel down to 6 amps, no matter how bright the sun.
Connecting panels in PARALLEL is the opposite. A 19-volt panel will drag a 30-volt panel down to a maximum of 19 volts when they are connected in parallel.
EXAMPLE: Let's say we have 4 panels; three are 19 volts 8 amp (19x8=152 watts max each). One panel is 16 volts and the same 8 amps. (16x8=128 watts). That 16-volt panel will drag the other panels down to a maximum output of 128 watts. That is a loss of 24 watts per panel or a total loss of 75 watts of power from the three 19 volt panels.
Sometimes one can reconfigure the panels series/parallel mix to get closer. Sometimes it is simply best to get another charge controller. Several CC can feed the same battery bank, but their charge parameters should be set to the same values.
With three separate CC feeding our battery bank the three controllers switch from one mode to the next within a minute of each other. The variability comes from component tolerances and that is okay.
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paulz
Member
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# Posted: 24 Feb 2021 05:21pm
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Thanks ICC, I sorta understand. So what I have now is 4- vmp 31v imp 8.3a in series. What I want to add are vmpp 17v imp 4.4a panels. Is there a combination of these new panels that would come close enough to wire in parallel to the existing on same CC? Sounds like maybe not.
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ICC
Member
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# Posted: 24 Feb 2021 05:45pm
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How many Vmp 17v Imp 4.4a panels do you have in total, and how are the others configured?
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paulz
Member
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# Posted: 24 Feb 2021 07:04pm
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12 panels. The others are 4 in series, 4 sets in parallel, 16 panels, but I might steal 1 set for the cabin if I can hook up these other ones.
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gcrank1
Member
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# Posted: 24 Feb 2021 07:11pm
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Why not put the odd-balls on the cabin and leave the others alone?
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paulz
Member
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# Posted: 24 Feb 2021 07:42pm
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I could do that too. The cabin has the same 31v panels but only 3 in series because the CC has a 100v max. This other 12 panel setup has 6 in series so voltage is over 100 but I could rewire. It has solid wire in conduit instead of MP4 so it'd take a bit of work.
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ICC
Member
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# Posted: 24 Feb 2021 07:46pm
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paulz, before running numbers on those, there is a question about the capacity of the CC. Can your existing CC, at the battery bank voltage you use, handle all those watts? It doesn't matter what combination of series/parallel one uses if the total watts of the panels is higher than the rating.
I seem to recall that you might be over paneled anyhow because of lousy sun exposure.
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paulz
Member
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# Posted: 24 Feb 2021 08:39pm
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Yes, very over paneled. The renogy cc at the cabin is rated at 400w at 12v. I have 12 260w panels, 90% shaded. But it's working fine. Most charging amps I have ever seen on the cc was 5. It's supposed to shut itself down at panel over current, never has.
The Epever at the shop is higher but it too is way over spec.
I'm looking at 2 Xantrex 1800 pure sine wave inverters. almost new, for $900. They are 24v so I would be switching over from 12, but still over paneled.
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ICC
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# Posted: 24 Feb 2021 09:34pm - Edited by: ICC
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Well, my gut feeling was/is to simply take the 12 smaller panels and run them through an MPPT CC in some series/parallel strings to charge the batteries as an extra solar array.
Thoughts... two 17 v panels in series = 34V @ 4.4A
.... then two series strings of those in parallel (total of 4 panels) = 34 V @ 8.8A..... almost equal to one of the 31V panels.
One - 31 V panel @ 8.3 A = 257 watts
Four - 17 V panels @ 4.4 A = 75 watts x 4 panels = 300 watts
So one of the 31 V panels would drag four of the 17 V panels in a series/parallel string down by about 14%. That would be the power trade-off while requiring the more complicated S/P wiring of the twelve 17 V panels and the cost of all the wires and terminals. It could work.
Not worth the bother in my book. But others may disagree, especially if the PV panels in question were free or nearly so.
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ICC
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# Posted: 24 Feb 2021 09:36pm
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Quoting: paulz I'm looking at 2 Xantrex 1800 pure sine wave inverters. almost new, for $900. They are 24v so I would be switching over from 12, but still over paneled.
The graphic is confusing to me.... the chart seems more like the specs on a charge controller than an inverter? The "Nominal System Voltage = 12/24 Auto Recognition" line is what makes it sound like a CC to me. ???
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paulz
Member
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# Posted: 24 Feb 2021 09:59pm
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That chart is for the Renogy charge controller.
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paulz
Member
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# Posted: 25 Feb 2021 02:45pm
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On another subject, today I hooked up a couple of 100w panels the paver guy gave me a long time ago to a little 20 amp Renogy CC, to maintain my tractor batteries.
Now the dilemma. The CC is 12 or 24, so what's better, charge in series or parallel?
I think I may need to go to Solar Junkie Anonymous..
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paulz
Member
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# Posted: 28 Feb 2021 10:04am
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Was curious about how much dirty panels affect output. Some say almost nil, some say 35% or more. I get a lot of tree duff on my panels, washes right off in rain and I have noticed they seem to do batter after.
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ICC
Member
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# Posted: 28 Feb 2021 10:44am
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How does one measure how much dirt? Yes it does make a difference. Rain is nice.
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Steve_S
Member
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# Posted: 28 Feb 2021 10:59am
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When it is Pollen Season (and being in a coniferous forest that is heavy crap) I've found the panels get a yellow coating and performance drops. I'll go out early AM before the panels warm up too much and sprinkle them with the hose quickly and it does make a difference. Problem is, a slight breeze and they start turning yellow again...
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paulz
Member
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# Posted: 28 Feb 2021 11:54am
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Quoting: ICC How does one measure how much dirt?
Usually by my shower pan. 
Not easy for me to drag hose around. I have a large water filled fire extinguisher, might try that.
No rain in the forecast, way under 50% of normal. Going to be a rough summer.
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gcrank1
Member
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# Posted: 28 Feb 2021 01:56pm - Edited by: gcrank1
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One of those little 2gal? garden sprayer might be just the thing. Fill it and leave it sit by the panels, pump up and spray off as needed. Wonder if a dash of dish soap added would help 'break the surface tension'; ie, make it more effective as a rinse off.
As to 'parallel vs series'/12v vs 24v) as I understand it on p/12 with pwm (and on p even an mppt operates as a pwm) the charge output will always be no more than the Isc 'stacked' rating, but on s/24 it can go higher so you will always at least equal the performance of parallel and may get more.
My conclusion has been to go series if I have an mppt scc to use. But this issue of p vs s seems to be constant.....what do I know.
Of course you could do the real-deal test for us , I know Im interested in your results.
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paulz
Member
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# Posted: 1 Mar 2021 11:05am - Edited by: paulz
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Quoting: gcrank1 One of those little 2gal? garden sprayer might be just the thing.
Bought one yesterday, standby for testing..
On another subject, I have several of these little panels left over from LED lights that I hooked up to 5v cabin power. I put two in serial yesterday and got 14v open circuit. Put a little alarm battery on and it charged, then went down overnight. I suspect the panels drain in dark? Could I just put a diode in line and use these on dashboards?
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gcrank1
Member
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# Posted: 1 Mar 2021 11:18am
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Hmm...wonder if the device those normally plug into have the diode?
I cant seem to throw any solar stuff away either; do I need therapy?
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