chrisski
Solar Boondocker
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Want to use this braided loom to make my ground mounted panel cables. Can you explain the hot glue in heat shrink?
Couple of cells in shade of AC unit on RV roof top
- Thread starter sunrise
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Want to use this braided loom to make my ground mounted panel cables. Can you explain the hot glue in heat shrink?
RCinFLA
Solar Wizard
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You really want to avoid shading as it is a lot more degrading then seems from shadow cast.
When a cell is shaded its illumination current drops off. It will get overwhelmed by other cells in series that are still getting sun. The non-shaded cells will drive the shaded cell(s) into reverse bias voltage condition. The reverse bias voltage will depend on how many cells are covered by each bypass diode. You can assume you will loose all the cells within the span of the cells covered by a single bypass diode. A 33 cell panel is an oddball panel and you will have to determine how the bypass diodes are configured.
Normally there is one bypass diode per one long row pair. It is done this way to put the bypass diodes at same end of panel usually in junction box on back of panel.
For example, take a 36 cell panel with four long rows of nine cells per row.
There will be two bypass diodes covering the two down and back row pairs (18 cells covered by each bypass diode). I am guessing for a 33 cell panel you have three rows of 11 cells with either two diodes, covering 22 and 11 cells or just one diode covering all 33 cells. There really should not be greater then about 20 cells for each bypass diode because it allows too much reverse bias on a single shaded cell. This is to protect against hot spots created by a spot shunt resistance defect on a shaded cell. The more reverse bias across the defect, the hotter the spot defect will get. It can melt a hole in plastic backcovering, crack the cell or even the front glass, or in extreme case start a fire.
In normal operation there will be Vmp of about 0.5v per cell for total panel Vmp of 36x 0.5v = 18 vdc. If one cell is shaded then one row pair will be taken out and replaced with forward biased bypass diode so voltage on that panel will be 18x 0.5v - 0.9v for bypass diode = 9v- 0.9v = 8.1vdc Vmp for that panel. That panel will put out a little less then half power due to a little shading in one corner of panel.
Imp will be the same if MPPT controller has enough total input voltage from remaining array to handle the 8.9v loss from normal Vmp of array. It doesn't matter if one cell or all the cells within the single bypass diode covered group is shaded. If another single cell in the other row pair is also shaded then the whole panel drops out and there will be almost -2vdc (two bypass diodes voltage drop) across panel taken away from what is left of the series panels array stack. So it really matters what direction the shadow is cast across the panel.
If panels are in parallel you lose all the power contribution from a partially shaded panel and any shunt leakage current of that panel will subtract some of the current from the other non-shaded panels.
Many 'cheap' panels use very weak bypass diodes. Under shaded condition a bypass diode has to pass up to Isc with a diode drop voltage across it. That can be 6 to 9 watts of heat that can make the diode very very hot causing it to be damaged in a short amount of time. If it blows open you may never know about it (unless you need its safety function), if it shorts out you lose all the output of the cells within its span.
When a cell is shaded its illumination current drops off. It will get overwhelmed by other cells in series that are still getting sun. The non-shaded cells will drive the shaded cell(s) into reverse bias voltage condition. The reverse bias voltage will depend on how many cells are covered by each bypass diode. You can assume you will loose all the cells within the span of the cells covered by a single bypass diode. A 33 cell panel is an oddball panel and you will have to determine how the bypass diodes are configured.
Normally there is one bypass diode per one long row pair. It is done this way to put the bypass diodes at same end of panel usually in junction box on back of panel.
For example, take a 36 cell panel with four long rows of nine cells per row.
There will be two bypass diodes covering the two down and back row pairs (18 cells covered by each bypass diode). I am guessing for a 33 cell panel you have three rows of 11 cells with either two diodes, covering 22 and 11 cells or just one diode covering all 33 cells. There really should not be greater then about 20 cells for each bypass diode because it allows too much reverse bias on a single shaded cell. This is to protect against hot spots created by a spot shunt resistance defect on a shaded cell. The more reverse bias across the defect, the hotter the spot defect will get. It can melt a hole in plastic backcovering, crack the cell or even the front glass, or in extreme case start a fire.
In normal operation there will be Vmp of about 0.5v per cell for total panel Vmp of 36x 0.5v = 18 vdc. If one cell is shaded then one row pair will be taken out and replaced with forward biased bypass diode so voltage on that panel will be 18x 0.5v - 0.9v for bypass diode = 9v- 0.9v = 8.1vdc Vmp for that panel. That panel will put out a little less then half power due to a little shading in one corner of panel.
Imp will be the same if MPPT controller has enough total input voltage from remaining array to handle the 8.9v loss from normal Vmp of array. It doesn't matter if one cell or all the cells within the single bypass diode covered group is shaded. If another single cell in the other row pair is also shaded then the whole panel drops out and there will be almost -2vdc (two bypass diodes voltage drop) across panel taken away from what is left of the series panels array stack. So it really matters what direction the shadow is cast across the panel.
If panels are in parallel you lose all the power contribution from a partially shaded panel and any shunt leakage current of that panel will subtract some of the current from the other non-shaded panels.
Many 'cheap' panels use very weak bypass diodes. Under shaded condition a bypass diode has to pass up to Isc with a diode drop voltage across it. That can be 6 to 9 watts of heat that can make the diode very very hot causing it to be damaged in a short amount of time. If it blows open you may never know about it (unless you need its safety function), if it shorts out you lose all the output of the cells within its span.
Better quality heat shrink tubing has glue inside it. Cheaper options don't. The glue ensures that once the tubing has been shrunk onto the cable/lug it isn't going to slip. A downside is that it makes the cable/lug a bit stiffer, less flexible.
I bought all my heat shrink tubing from TEMCo and it's been bulletproof.
Hedges
I See Electromagnetic Fields!
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- Mar 28, 2020
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Several ways to make a harness bundling insulated wires together. I've seen some pulled through (silicone?) tubes inflated with air for an aerospace application. For CAT5 cable and the like they're probably molded on. split corrugated "convolex" tubing and spiral wrap can be used. Another I've seen is braided plastic tubing:
Clean Cut Heavy Duty Braided Sleeving
Clean Cut heavy duty is perfect for heavy duty applications where there is no access to a hot knife. Dual monofilament abrasion resistant braided sleeving.
It seems decent for cables that could get some wear in cabinets and racks.
To keep the ends from slipping I tried using cable ties and heat shrink (color coded wires and cables to keep track of 4 supplies x 4 outlets each, and polarity). But the heatshrink slips.
Later learned on this forum about heatshrink containing (hot melt) glue. It can seal a battery cable to the crimped terminal, so no place for water or acid to get in to reach the wires. Would have been good for my braid loom around cables.
"Ground mounted panel cables"
So you're putting PV panels on ground mounts, and want to manage cables? Need something UV resistant.
The MC cables already are. Before them I used UF cable (which does get some sunburn). Individual wires can be managed with cable ties or clips that slide on panel frames. Some systems have MC cables connected to inverter or combiner. I have pigtails coming out of electrical boxes and run conduit from there.
Not sure about you - exactly what do you want to assemble?
chrisski
Solar Boondocker
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By coincidence, the latest batch of heat shrink I have on order Has glue already, so I’ll save it To put over the braided sleeve.
The cables I’m making are two wires positive and negative, 10 gauge, with Anderson plugs for 400 watts of portable panels, so the cable will go across the ground And will be removed whenever I move the RV. Mostly Boondocking. I’ll probably make two, one 20 feet, and the other 5 feet.
The cables I’m making are two wires positive and negative, 10 gauge, with Anderson plugs for 400 watts of portable panels, so the cable will go across the ground And will be removed whenever I move the RV. Mostly Boondocking. I’ll probably make two, one 20 feet, and the other 5 feet.
My first "extension cord" was 25' using 10 awg PV wire. I used sections of heat shrink and a few cable ties to keep the cable pairs together. It's not as clean as it would be with split loom, but it's not as bulky either.
Hedges
I See Electromagnetic Fields!
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On the ground, they will get stepped on. Would be good to have a thick jacket to take the abuse and protect the insulation inside.
Was that two pairs positive and negative, for two strings of panels? A length of this 10/4 would be good.
Southwire 250 ft. 10/4 300-Volt CU Black Flexible Portable Power SJOOW Cord 55812644 - The Home Depot
The Southwire 250 ft. Black 10/4 SJOOW Cord is rated for up to 300 Volts and for temperatures ranging 40 - 194 degrees Fahrenheit (-40 - 90 degrees Celsius). Bare, flexible, stranded, class K copper conductors
www.homedepot.com
Otherwise, 10/2 would be easier to come by, and 12/2 is probably good enough unless you're pulling 35A.
Could just get an extension cord from HF and cut it:
25 ft. x 10/3 Gauge Triple Tap Extension Cord, Yellow
Amazing deals on this 25Ft X 10G Triple Tap Extension Cord at Harbor Freight. Quality tools & low prices.
www.harborfreight.com
Anderson? Could use MC3 for weather tight (no locks like MC4)
But I guess plugs could be off the ground to stay dry.
chrisski
Solar Boondocker
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The portable panels I bought were equipped with Anderson Plugs. At least with the original cable build, it will be Anderson Plugs. If those don't work out, I've got MC4s. I had not looked at the MC3 plugs. They do look like they can be connected easy enough. Another plus for the Anderson plugs is mounting them to the trailer wall for quick disconnect. The MC3 or MC4 don't seem to be built for that.
I've also got 100' of 10 gauge solar wire left over. The longer run would be all four panels in series, the shorter would be all four in parallel or 2S2P.
