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4x285W Trina solar panels tripping 50A DC Breaker


Kalito
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Here is a lockdown challenge to keep your grey matter firing!

Solar Panel details:

Pmax: 285W+-2.5%

Vmp: 31.5V

Imp: 9.05A

Voc: 38.8V+-3%

Isc: 9.53+-4%

Max series fuse: 20A

Power selection: 0~5W

Synerji 3KVA PWM Inverter Solar Charger details:

Rated current: 50A

System voltage: 24VDC

VOC: 70VDC

Max Charge Current: 80A

The PV array is connected in parallel using a Y-Connector and about 12m x 6mm2 Exhellent PV cable (Rating of 70A/km at 60 degrees celcius open air and resistance of 3.4 ohms/km) through a 50A DC breaker to the Inverter.

At certain times of the day (noticed from 11am) with no change in load, the breaker is tripping. I checked for any cable issues and loose MC4s, they are all perfectly intact. Earlier a 0.5HP submersible pump and load totalling 1.3kW were running on solar/batt for 45min with no issue. This intermittent tripping has been observed in the last week. Weather has been clear skies. I am left with no option but to think over-STC performance of the panels?

I measured the VOC of each panel it came to about 33V at midday and the combined VOC was generally the same. at the DC breaker it was about 28V.

Questions:

  1. Is the 50A breaker undersized for peak? I thought the panels will not exceed 40A normally as peropen circuit worst case scenario rating?
  2. I noticed the Inverter rating is 80A, so could it be the inverter is pulling as much solar as it can pusing the panel beyond its limit given the great weather? (what is the 50A rating?)
  3. What is the 30-32V operating voltage range of the inverter?

Synerji3kva.jpg

Trina.JPG

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On 2020/04/13 at 3:41 PM, Kalito said:

Is the 50A breaker undersized for peak? I thought the panels will not exceed 40A

This is an interesting question, I would also think the 40A should be suffice, so tripping a 50 A and you mention it happens after 11am this is probably when pv input is at it’s peak. I would like to know what factors could cause a 50A breaker to trip when the actual pv output cannot exceed the 9.53A x 4 = +-40A max, there must be some explanation of the relevance of voltage drop and watts drawn from pv to make this happen. It seems like the pv dc breaker has to be overrated to prevent tripping.

I had a similar experience wit a 32A dc breaker tripping where the current could not actually exceed 27A and it still puzzles me.🤔🧐

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On 2020/04/16 at 3:40 PM, Gerrie said:

This is an interesting question, I would also think the 40A should be suffice, so tripping a 50 A and you mention it happens after 11am this is probably when pv input is at it’s peak. I would like to know what factors could cause a 50A breaker to trip when the actual pv output cannot exceed the 9.53A x 4 = +-40A max, there must be some explanation of the relevance of voltage drop and watts drawn from pv to make this happen. It seems like the pv dc breaker has to be overrated to prevent tripping.

I had a similar experience wit a 32A dc breaker tripping where the current could not actually exceed 27A and it still puzzles me.🤔🧐

It is interesting. But there is one even more interesting aspect. The panel specs are based on 1,000W/sqm irradiance. So if this value in the field is higher the panel will inevitably over perform. So to resolve this dilemma I used the US Code of 1.56 factor. 9.53A X 4 X 1.56 = 60A problem solved. No more nuisance tripping - lol.

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On 2020/04/13 at 6:29 PM, Hannes Bester said:

Hi Kalito, you have 4 panels right..... Now are they all connected in parallel or do u have a series parallel configuration? 

This install is at a friend's and they are all in parallel as the inverter only has a VOC of 70V

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OK just a thought I'm no solar expert but I am a industrial electrician. Is it maybe possible that due to the parallel connection u have low voltage but high amps which which will generate some heat. It is possible that the breaker specs are for ac which will have a over current protection of 50A but at higher voltage which means less heat. Some breakers make use of a bimetal plate that triggers the trip mechanism of the breaker. So in simple DC amps and ac ams can't be assumed to be the same which is why you will always find much thicker and stranded wires in a DC system. 

Correct me if I'm wrong please I'm a solar newbie. 

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8 hours ago, Hannes Bester said:

OK just a thought I'm no solar expert but I am a industrial electrician. Is it maybe possible that due to the parallel connection u have low voltage but high amps which which will generate some heat. It is possible that the breaker specs are for ac which will have a over current protection of 50A but at higher voltage which means less heat. Some breakers make use of a bimetal plate that triggers the trip mechanism of the breaker. So in simple DC amps and ac ams can't be assumed to be the same which is why you will always find much thicker and stranded wires in a DC system. 

Correct me if I'm wrong please I'm a solar newbie. 

Hi, your explanation is electrically sound but not applicable. I have seen a Youtube video of an AC breaker used on DC and it trips at higher amperage for the reasons you have given.

You might have missed this statement:

"The PV array is connected in parallel using a Y-Connector and about 12m x 6mm2 Exhellent PV cable (Rating of 70A/km at 60 degrees celcius open air and resistance of 3.4 ohms/km) through a 50A DC breaker to the Inverter."

The Inverter has a PWM Solar Charger (these require max amps as they match the voltage to the battery voltage unlike MPPT which will take excess voltage and use it.).

Further, the panel specs which are on paper not expected to be exceeded are at irradiance of 1000W/sqm. If the field irradiance is higher than this certainly the panel will perform higher than the specs.

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On 2020/04/13 at 3:41 PM, Kalito said:

I am left with no option but to think over-STC performance of the panels?

I just saw my own solar drawing more from pv panels than it should. I have 6 x 330W panels they drew 2.1KW and I checked Amps with tong tester as well as on Inverter display was at 34A. Panels are 2S & 3P. I did not expect this as panels Isc=9.3A/each, It should be max 27.9A & 1980W. I have a main breaker on solar pv of 32A that have tripped before now I can understand why.

B5C61F02-B799-462C-A253-9957D6B73306.jpeg

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20 hours ago, Gerrie said:

I just saw my own solar drawing more from pv panels than it should. I have 6 x 330W panels they drew 2.1KW and I checked Amps with tong tester as well as on Inverter display was at 34A. Panels are 2S & 3P. I did not expect this as panels Isc=9.3A/each, It should be max 27.9A & 1980W. I have a main breaker on solar pv of 32A that have tripped before now I can understand why.

B5C61F02-B799-462C-A253-9957D6B73306.jpeg

Indeed. One thing we forget is that the panel ratings are at STC which is 25 degrees and 1,000W/msq. When the irradiance is more as would be in this part of the world and the temp is right boom overperformance beyond STC. At 9.3A x 3 and a factor of 1.5 your PV breaker should be 40A to prevent the nuisance tripping.

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