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Axpert Solar Panel Strings


Arandoza
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Hello All,

I wonder if you can give us some advice?

Recently one of my two Solar arrays has started tripping the 63a 220v Circuit breaker on the PV array input on my second Axpert inverter. And the PV cabling  (6mm)  to and from the breaker box's and arrray's is really hot to the touch :( (Maybe 40-45deg?)  I take it this not a good thing :( (one can see the power dip on PVoutput below when the one array trips out.)

image.png.acd3602d65807586501806fe427c191a.png

This appears to only happen when I am pushing the teamed (2) inverters to max capacity, and they are running at 4600-4800W PV input for about 30-45 mins, then the breaker trips, on the 2nd inverter with the 5 string array and the breakers are hot, as are all the cables, for both arrays.

 

What is the normal operating temperature of the PV cables typically? What do installers see in the field?

 

My configuration is

  • 2 X Axpert 5kva inverters paired on a single phase.
  • 8 x 245ah TE35  Trojan battery bank.
  • 1  array x 12  panels of 250W panels   3 Per string, 4 strings for the original inverter.
  • 1 array x 15 panels of mostly 260W panels, So 3 per string, 5 strings for the array, 1 string maybe a set of 3 250w Panels.
  • Each array runs its own set of cables and its own breaker box, to each inverter via a dual 63A (220v) trip switch box, on both negative and positive, on each array.

 

Also on AICC I noticed that the second array and inverter seems to be running at 80 volts and around 46 amps,  and the first inverter is also running around very similar Volts and Amps on the first array, when the PV trip occurs.

 

I having been thinking of upgrading the safety protection for the PV side, and have been looking at things like combiner box's but would really like to build my own.

And I don't seem to find good reading material on how to spec the fuses, and or trip switches, and lighting protection for such a combiner box. Any tips here would be appreciated.

 

 

 

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34 minutes ago, Arandoza said:

 

Recently one of my two Solar arrays has started tripping the 63a 220v Circuit breaker on the PV array input on my second Axpert inverter. And the PV cabling  (6mm)  to and from the breaker box's and arrray's is really hot to the touch :( (Maybe 40-45deg?)  I take it this not a good thing :( (one can see the power dip on PVoutput below when the one array trips out.)

Ooooh I think the PV side of your inverter needs a big overhaul.

34 minutes ago, Arandoza said:

This appears to only happen when I am pushing the teamed (2) inverters to max capacity, and they are running at 4600-4800W PV input for about 30-45 mins, then the breaker trips, on the 2nd inverter with the 5 string array and the breakers are hot, as are all the cables, for both arrays.

I think that is a classic sign of undersized cabling. How are the individual strings combined in each array? If one guesses  that each string will be about 9A we looking at 36A for the one and correctly as you have observed 45A for the other.

Using http://www.solar-wind.co.uk/cable-sizing-DC-cables.html we can see that for home runs of 4m or more and 36A  you should be at least 10mm2 and  it could as high as 25mm2 for a 10m home run. The second array is much the same only a little worse.

41 minutes ago, Arandoza said:

I having been thinking of upgrading the safety protection for the PV side, and have been looking at things like combiner box's but would really like to build my own.

And I don't seem to find good reading material on how to spec the fuses, and or trip switches, and lighting protection for such a combiner box. Any tips here would be appreciated.

Building your own combiner box would be a good idea they seem to demand a king's ransom for them nowadays. Fusing should be a 12A  ceramic PV fuse (Isc *1.25 = 11.25A). One derates the fuse by 25% due to the higher temperatures in South Africa. Lighting protection Type 2 from Citel. (probably a DS50PV-600/51) but ask the supplier. Finally your circuit breakers. The one you have is AC rated I would recommend NoArk  500V DC breakers 40A for the smaller array and 50A for the bigger one. The circuit breaker must be mounted within 1 m of the inverter and then it doubles as a PV disconnect.

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Evening Chris thanks for the Reply.

The 4 (3000w -250wp)  (or 5 (Mixed 260&250wp 3780 total - Not all facing the same direction so unlikely to get to Max - 3 North - 1east - 1 west) ) strings are connected together (parallel-using MC4 Branch Connectors)  on the roof and single 6mm set of PV solar cables  (Pos+Neg) come down into the garage. For each array. So two sets of 6mm Solar PV Cables. And the 9 amps is about right per string.

Originally I was concerned that the MC4 connectors are only rated to about 30 amps  from the research i found on the web. Also the Panels only come with 4mm pigtails off the panels. And I had thought the MPPT would keep the voltage higher and lower the amps so this may not have been a concern?

Hence the 6mm Solar PV Cabling was used for less resistance, heat etc.  And the MC4 Connectors amp rating made me look into combiners but they too only seem to use 6mm PV cable in the box for each string and then from the combiner to inverter? Which did not seem to address the amp rating concern.

 

Will definitely take up your advice on the combiner box and investigate thicker PV Cable sizes, I estimate the runs to be around 30m at max (Array1) and 20m (Array2) across the roof(s) down to the garage.

 

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Hi @Arandoza

The 63a breaker that you are using is most likely of the "Thermal/Magnetic" variety so it will trip for excessive heat and excessive current. You are not exceeding the current rating of your breaker, but the 6mm cables at 45amps are running at their maximum rating and will definitely heat up - this heat is probably being transferred to the breaker and causing a thermal trip. You could test this theory by setting up a powerful fan and blowing a bit of a gale onto your breaker and see if the tripping is reduced.

I would recommend upgrading to at least 10mm from the combiner box of your larger array to your CB, and also replacing the AC rated breaker with a corrrectly rated DC breaker as mentioned by @Chris Hobson above.

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12 hours ago, Arandoza said:

.

Will definitely take up your advice on the combiner box and investigate thicker PV Cable sizes, I estimate the runs to be around 30m at max (Array1) and 20m (Array2) across the roof(s) down to the garage.

 

Using  www.solar-wind.co.uk  at 3% losses  they reckon 25mm for Array 1 and  16mm. The shorter distance makes a big difference. This coast guard table yields similar results.

  1. Measure your distances accurately. and put in combiner boxes.
  2. Perhaps move your inverter closer to your strings if possible. I have a 17m home run from combiner box to inverter consisting of 25mm2 (the last metre is 16mm2 as the terminals on an Axpert cannot handle 25mm2). Perhaps consider installing an inverter(s) capable of accepting higher voltages.

 

DC_wire_selection_chartlg.thumb.jpg.6f548bfce561dca87423751d368d9df5.jpg

 

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  • 3 weeks later...

When upgrading the PV side by 6x 260W JA Solar panels I decided to experiment on the strings. Effectively the upgrade and North-facing wall-mount has 3 strings of 2x each and "combined" through a customised termination box. The inverter is in the kitchen some 20m or so away. I also opted to have the combiner box near the inverter. Initially I had 3x for 2 strings but this didn't seem to work well so I resorted to 2x. So the entire array is fed to the combiner via a single string.

I did check the 6mm2 PV cable specs and it has an amperage tolerance of upto 70A (see attached) for open air and about 57A if two cables I believe. Given the 3 strings I am effectively pushing 27A. I am wondering why that 6mm cable is heating up in @Arandoza case though I have noted what you good people have indicated.

I think that anyone with atleast 6x panels they must include a combiner box. I am thinking of replacing my current one with a Besco one (it includes a DC isolater switch which my current 5-string doesn't include).

5-stringCB.jpg

PV Cable.pdf

NorthPV.jpg

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On 04/09/2017 at 3:18 PM, Arandoza said:

Hello All,

I wonder if you can give us some advice?

Recently one of my two Solar arrays has started tripping the 63a 220v Circuit breaker on the PV array input on my second Axpert inverter. And the PV cabling  (6mm)  to and from the breaker box's and arrray's is really hot to the touch :( (Maybe 40-45deg?)  I take it this not a good thing :( (one can see the power dip on PVoutput below when the one array trips out.)

image.png.acd3602d65807586501806fe427c191a.png

@Arandoza out of interest, how is your Axpert connected to the net to output this data. I would like to signup and do the same. Great stuff

 

 

 

 

 

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On 9/4/2017 at 9:41 PM, pilotfish said:

Hi @Arandoza

The 63a breaker that you are using is most likely of the "Thermal/Magnetic" variety so it will trip for excessive heat and excessive current. You are not exceeding the current rating of your breaker, but the 6mm cables at 45amps are running at their maximum rating and will definitely heat up - this heat is probably being transferred to the breaker and causing a thermal trip. You could test this theory by setting up a powerful fan and blowing a bit of a gale onto your breaker and see if the tripping is reduced.

I would recommend upgrading to at least 10mm from the combiner box of your larger array to your CB, and also replacing the AC rated breaker with a corrrectly rated DC breaker as mentioned by @Chris Hobson above.

Yup. @Arandoza you are looking for trouble with that AC breaker. At some stage the contacts will weld together, leaving you without protection and possibly start a fire. 

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  • 2 weeks later...

Hi @Kalito

This is the software http://iccsoftware.co.za/ it all started here on the forum, A few folks on the forum got the idea going and I think @Manie is developing and updating etc. And it was built for the axpert / infini inverters, and they may add support for more inverters over time, if not mistaken.

 

it works really well and I like the pi version, but am still using an older pc version presently.

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Hi All,

 

Just a bit of feedback, on my original problem. The hot wires :( 

 

I upgraded my cabling from the second array to the 10mm2 cable and also found that the positive PV cable  breaker - the cable clamp on the breaker, despite being tightly screwed in did not appear to grip the cable with much force, so I suspect I was also getting a loose connection where the cable entered the breaker? Also adding to the problem.

Since replacing the 2nd array cable and the breaker, the new cable definitely runs cooler, around 25 deg c, when compared with the first arrays cable, about a 10 deg c difference. Also bought a IR temperature thermometer, the point and shoot type, and find a big difference under load of the cable and breakers compared to the first array.

 

I still need to replace the first arrays cable, to 10mm2 and also replace all the breakers as @SilverNodashi recommended, on the D.C. Array side. Also I would like put together a 5 or 6 string type combiner box, but the costs are slowing me down, and I will need two of them ;)  any suggestions on where to buy the well priced components for a diy combiner or already built version will be welcome.

 

Thanks to everyone for their input, it's always appreciated.

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21 hours ago, Arandoza said:

Hi All,

 

Just a bit of feedback, on my original problem. The hot wires :( 

 

I upgraded my cabling from the second array to the 10mm2 cable and also found that the positive PV cable  breaker - the cable clamp on the breaker, despite being tightly screwed in did not appear to grip the cable with much force, so I suspect I was also getting a loose connection where the cable entered the breaker? Also adding to the problem.

Since replacing the 2nd array cable and the breaker, the new cable definitely runs cooler, around 25 deg c, when compared with the first arrays cable, about a 10 deg c difference. Also bought a IR temperature thermometer, the point and shoot type, and find a big difference under load of the cable and breakers compared to the first array.

 

I still need to replace the first arrays cable, to 10mm2 and also replace all the breakers as @SilverNodashi recommended, on the D.C. Array side. Also I would like put together a 5 or 6 string type combiner box, but the costs are slowing me down, and I will need two of them ;)  any suggestions on where to buy the well priced components for a diy combiner or already built version will be welcome.

 

Thanks to everyone for their input, it's always appreciated.

 

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  • 3 months later...

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