Is this 16A PV disconnect a fire hazard?

[wpns]

over-current

Panels don’t produce overcurrent, Isc is pretty much it. The fuses are there to protect from other sources that might put too much current into the wires (more than one other parallel string, for instance).

 

[kolek]

Darn! Now you made me watch the video. Not sure what his thought process is for such, but makes no sense to me. Maybe that was the only DC breaker he had??? Or a sponsored video.

So now he built a system with no over-current or blocking in place. What now? Build another box with the correct size breakers or fuses?

Are you aware that you can buy these Chinese boxes off Amazon premade cheaper then he is building here.

Ok, I appreciate your input, but unless others on this forum are wrong too, it seems EXPLORIST is right, meaning they are in place for the purpose of being disconnects, not breakers, and therefore should be sized as disconnects, based on what I'm reading on this thread:

Reliable PV DC disconnect?

Hi all, I wired up 2x strings to a DC disconnect made by Dihool (Chinese)... https://www.amazon.co.uk/Isolator-Disconnect-pre-wired-connectors-Waterproof/dp/B0B8YRBHHZ/ However, I'm aware that the cheap brands of DC disconnect increase the risk of fire. Even if the fire risk is low I'd like to...

diysolarforum.com

Anyway, please don't take offense, I'm just passing along what I'm reading here on this forum. Thanks again for your input!

 

[MrThisIsME]

Panels don’t produce overcurrent, Isc is pretty much it. The fuses are there to protect from other sources that might put too much current into the wires (more than one other parallel string, for instance).

Agreed! But a blocking diode combined would be the best resort in my eyes.

Yes, in the past, I have turned solar panels into radiant heaters.

 

[MrThisIsME]

Ok, I appreciate your input, but unless others on this forum are wrong too, it seems EXPLORIST is right, meaning they are in place for the purpose of being disconnects, not breakers, and therefore should be sized as disconnects, based on what I'm reading on this thread:

Best of luck!

 

[kolek]

@Zwy

As you recommend I plugged my numbers into the Midnight Solar Calculator, here was the result:
Rated PV Array Power: 12740 Watts
Anticipated Array Power @ 40C: 12071 Watts
Rated PV Array Current: 43.68 Amps
Battery Charging Current @ 57.6 V: 221.2 Amps
VMP (Maximum Power Point Voltage) : 291.9 Volts
VOC (Open Circuit Voltage): 346.5 Volts
VMP @ -15 C°: 332.5 Volts
VOC @ -15 C°: 392 Volts

Seems like the IMO disconnects you're recommending are the safest option. Checking those now.

 

[Zwy]

@Zwy

As you recommend I plugged my numbers into the Midnight Solar Calculator, here was the result:
Rated PV Array Power: 12740 Watts
Anticipated Array Power @ 40C: 12071 Watts
Rated PV Array Current: 43.68 Amps

I think if you have 43A of PV current you won't find a charge controller that is rated for 43A unless you using a charge controller that has a low VOC rating like 150V. Common Victron charge controllers are the 150V and 250V versions and thus you will see users combine strings due to the lower max VOC rating.

My assumption is you are combining strings.

My rule is this, get VOC up with panels in series to the max without exceeding the charge controller VOC rating. String current can be as little as one string, which is the Isc of a panel or if combining 2 strings, it would be double the Isc of the panel. I prefer single strings without any combining. It will depend on the panels chosen, whether overpaneling is desired (which I don't do) and the charge controllers being used.

Take the array for my house as an example. 530W panels, VOC is around 48 to 49V, Isc is around 10 to 13A. I run 8 panels in series, that is around 400VOC and a single string is around 10 to 13A. With a 5000W rated charge controller, that comes in as a good fit. I've seen as high as 4.6Kw from a single string and I don't have any clipping. I run 2 charge controllers, an 8S string on each charge controller.

I don't what panels you are using or the charge controller but maybe you should list those so we can see what you are using. You can run multiple charge controllers on the same battery bank, each can pull the power from a string or a pair of combined strings. You can have 2, 3, 4, 5 or more. If you are using an AIO inverter that has multiple MPPT's, it is the same thing.

Battery Charging Current @ 57.6 V: 221.2 Amps

How big is the battery bank?

VMP (Maximum Power Point Voltage) : 291.9 Volts
VOC (Open Circuit Voltage): 346.5 Volts
VMP @ -15 C°: 332.5 Volts
VOC @ -15 C°: 392 Volts

Seems like the IMO disconnects you're recommending are the safest option. Checking those now.

IMO is rated for PV disconnect under load. It was designed for this purpose. Read this entire thread. I mount the IMO just like Johnny does with a chase nipple and Myers hub. Inside the Vevor box it looks like this.




I run a breaker on each string and an SPD. There is also the green EGC that is from the panel frames. I showed this in one of my videos.

 

[rancher5]

Darn! Now you made me watch the video. Not sure what his thought process is for such, but makes no sense to me. Maybe that was the only DC breaker he had??? Or a sponsored video.

So now he built a system with no over-current or blocking in place. What now? Build another box with the correct size breakers or fuses?

Are you aware that you can buy these Chinese boxes off Amazon premade cheaper then he is building here.

By regulation you need a PV disconnect as the video showed. just to shutdown the PV array from inverter. Has nothing to do with over current.

 

[kolek]

I think if you have 43A of PV current you won't find a charge controller that is rated for 43A

I'm using the Deye model SUN-8K-SG01LP1-US, spec sheet says:
PV Input Current (A) = 26 + 26
Max. PV I (A) = 44 + 44

I'm still reviewing the rest of your last msg just wanted to post this.

 

[Zwy]

I'm using the Deye model SUN-8K-SG01LP1-US, spec sheet says:
PV Input Current (A) = 26 + 26
Max. PV I (A) = 44 + 44

I'm still reviewing the rest of your last msg just wanted to post this.

A few things, one is the most you will ever see this output for battery charging amps is 190A. The 221A you listed will not happen.

I'm not familiar with the MPPT's for this unit but from what I guess, this unit will clip current to 26A per MPPT. Someone more knowledgeable about Deye might be able to help you. The 26A for combined strings makes sense if the total PV capacity is 10Kw with a pair of MPPT's each at 5Kw. But like I said, I'm not familiar with it.

 

[AmpD]

op the clarification in the video to your post for me was at 7:50 mark.

Also helpful to me was the reasoning behind using a double pole or single pole mcb. Another riddle solved.

Is it wrong to use mcbs as disconnects? i’ve seen more than one user doing this. With the required fusing to protect wires or wires rated for amps of breaker being met.

Finally Nate was one of my gurus for learning. I did wonder about a few things here and there but mostly found his channel informative and helpful. Further proof you need to go over the details with multiple sources before jumping off the cliff.

 

[rhino]

Just use an IMO disconnect which is designed precisely for what you are trying to do and has no issues even disconnecting under load.

 

[meetyg]

No i think the example I linked to should take you to the middle of the video, that shows a case where the input amperage is 4X the rating of the breaker and it burns up even tho its polarity is set correctly.

No, look at it again. First they show it opens at 4x the amperage, but no fire, cause it's wired correctly. Then they do the same test but wired in reverse: immediate fire!

 

[Hedges]

Right but it makes sense that you'd want 30-50% or more extra ampacity of your disconnects to your panel ISC when connecting in series. Logically, and that's unrelated to the youtube video. No? Feel free to correct me, I'm no expert.

Yes. You don't want fuses or breakers to trip due to Isc, or higher Isc from cloud edge effects.

Per NEC, size fuses or (thermal) breakers 1.56x Isc. Size wire at least that large.

if using magnetic-hydraulic breakers, which don't get pushed toward tripping by hot weather or hot wires/connections, then 1.25x Isc is sufficient.

Wire ampacity must be at least as high as breaker rating. Ought to use 1.56x Isc as a minimum regardless of breaker type.

I want to interrupt both PV+ and PV- somewhere between array and equipment before working on the wires, so 2-pole disconnect.

 

[kolek]

@Zwy or anyone else familiar with IMO disconnects
Maybe I misunderstood but wasn't the purpose of using the Midnight Solar calculator to determine which IMO disconnect to use?
I will have 4 strings of 7 panels in series, total of 28 panels. I am not combining them (nothing is parallel). There are inputs for 4 strings on my Deye inverter. Here again was the result of the Midnight Solar calculation, after inputting the data on my panels:

Rated PV Array Power: 12740 Watts
Anticipated Array Power @ 40C: 12071 Watts
Rated PV Array Current: 43.68 Amps
Battery Charging Current @ 57.6 V: 221.2 Amps
VMP (Maximum Power Point Voltage) : 291.9 Volts
VOC (Open Circuit Voltage): 346.5 Volts
VMP @ -15 C°: 332.5 Volts
VOC @ -15 C°: 392 Volts

Anyone have IMO disconnect recommendations based on this?

 

[Zwy]

@Zwy or anyone else familiar with IMO disconnects
Maybe I misunderstood but wasn't the purpose of using the Midnight Solar calculator to determine which IMO disconnect to use?
I will have 4 strings of 7 panels in series, total of 28 panels. I am not combining them (nothing is parallel). There are inputs for 4 strings on my Deye inverter. Here again was the result of the Midnight Solar calculation, after inputting the data on my panels:

What are the panel specs? 12Kw divided by 4 strings comes to 3Kw per string. With a Vmp of around 300V, that is 10A. The 43.68A is the total amps for all the panels, not a string. The Midnite calculator is used to determine string VOC for the coldest temp in your area.

4 strings would require either two 4 pole or one 8 pole IMO.

Rated PV Array Power: 12740 Watts
Anticipated Array Power @ 40C: 12071 Watts
Rated PV Array Current: 43.68 Amps
Battery Charging Current @ 57.6 V: 221.2 Amps
VMP (Maximum Power Point Voltage) : 291.9 Volts
VOC (Open Circuit Voltage): 346.5 Volts
VMP @ -15 C°: 332.5 Volts
VOC @ -15 C°: 392 Volts

Anyone have IMO disconnect recommendations based on this?

 

[labeeman]

Panels don’t produce overcurrent, Isc is pretty much it. The fuses are there to protect from other sources that might put too much current into the wires (more than one other parallel string, for instance).

On a partly cloudy day I have seen 15% more current than on a clear day due to cloud reflections.

 

[wpns]

On a partly cloudy day I have seen 15% more current than on a clear day due to cloud reflections.

Sure, you should have some margin, but 8.43A fuses are hard to find, and no one is going to try to make 22 gauge wire work when 20 gauge is technically just fine, so you’re gonna have some margin anyway.

 

[kolek]

@Zwy
>What are the panel specs

Thanks for responding, here's the info:

LONGI SOLAR HALF-CUT LR4-72HPH-455M, (455W) MODULES

• STC Power Rating 455W
• PTC Power Rating 424.77W 1
• STC Power per unit of area 209.3W/m2 (19.4W/ft2)
• Peak Efficiency 20.93%
• Power Tolerances 0%/+5%
• Number of Cells 72
• Nominal Voltage not applicable
• Imp 10.92A
• Vmp 41.7V
• Isc 11.66A
• Voc 49.5V
• NOCT 45°C
• Temp. Coefficient of Isc 0.05%/K
• Temp. Coefficient of Power -0.35%/K
• Temp. Coefficient of Voltage -0.134V/K
• Series Fuse Rating 20A
• Maximum System Voltage 1500V

 

[Zwy]

@Zwy
>What are the panel specs

Thanks for responding, here's the info:

LONGI SOLAR HALF-CUT LR4-72HPH-455M, (455W) MODULES

• STC Power Rating 455W
• PTC Power Rating 424.77W 1
• STC Power per unit of area 209.3W/m2 (19.4W/ft2)
• Peak Efficiency 20.93%
• Power Tolerances 0%/+5%
• Number of Cells 72
• Nominal Voltage not applicable
• Imp 10.92A
• Vmp 41.7V
• Isc 11.66A

This is the max amperage any series string will be.

Use either a pair of 4 pole IMO's or an 8 pole IMO.

• Voc 49.5V
• NOCT 45°C
• Temp. Coefficient of Isc 0.05%/K
• Temp. Coefficient of Power -0.35%/K
• Temp. Coefficient of Voltage -0.134V/K
• Series Fuse Rating 20A
• Maximum System Voltage 1500V