Ok, I have watched the fusing video - this still feels wrong

[TheCoachStone]

Ok, I am looking at 10 310w panels. I can wire them in series for 100v and 40.25a. The panels have a series fuse of 15 and a short circuit current of 9.93.

If I am understanding correctly because my Isc is below my series fuse amperage I do not need to fuse? Or, am I missing something?

Controller is a LV6048 -

PV INPUT / Solar Charging

• Max PV Input Power: 8000W (4000W each input)
• Max PV Input Volt: 145VDC (open circuit Voc)
• MPPT Range: 60 - 110VDC
• Number of PV Input: 2
• Max Charging Current: 160A (80A x 2)

 

[Rocketman]

We need a little more info to get at the correct answer.
On the back of the solar panels what is the:
Voc-
Vmp-
Imp-
Does it give a temperature coefficient?

Where are you located (nearest big city- and what is the coldest it EVER gets there?

Also can you move up to 12 panels? - if it is better/easier to do?

 

[TheCoachStone]

Voc- 40.25
Vmp- 33.05
Imp-9.38
Does it give a temperature coefficient? Temperature Coefficient Isc %/K 0.03
Temperature Coefficient Voc %/K -0.30
Temperature Coefficient Pmax %/K -0.38

Birmingham, AL

 

[Rocketman]

Ok you can put three panels is series. That will give @3s:
Voc -121v
Vmp- 99v (running voltage)
Imp- 9.38a (running amps per string).

That gives you a size of three or four strings- 9 or 12 panels. (Sorry 10 does not work well).

Even four strings will go into a single input (that about maxes it out).

If you go 3s4p - you will need a fuse on every string. If you have 3+ strings - you need to fuse each string. This also maxes one input and leaves the other empty for future expansion.

You could also go 3s2p into each input- then you don’t need to fuse each string- but there will be more to change up if you ever decide to expand.

Or with 3s3p go into one input - don’t forget to fuse the strings.

If you must have 10 panels -
Input1 6panels 3s2p
Input2 4panels 2s2p

The second input will be running at 66.1v - with the lower range cutoff of 60v

I am not confident enough to verify that the Voc of 121v will not go over the max of 145v - when it gets cold. I keep messing that calculation up - I think you are fine with a 16% margin- but it is close enough to get someone else to verify that calculation.

 

[upnorthandpersonal]

To clarify some aspects regarding the reason you need fuses once you have more than two strings:

- If you have one string, and you short it, you have Isc flowing, which a panel/string of panels can handle
- If you have two strings, and one goes wrong and shorts, you still have a max of Isc flowing which is fine
- Once you have three or more strings: if one goes wrong (i.e. shorts) you now have the two or more other strings dumping their Isc in the short, that's 2 x Isc (or n x Isc for n good strings) which the faulty string won't be able to handle so you need the fuse on that string to break that current.

 

[LakeHouse]

I am not confident enough to verify that the Voc of 121v will not go over the max of 145v - when it gets cold. I keep messing that calculation up - I think you are fine with a 16% margin- but it is close enough to get someone else to verify that calculation.

This would be fine all the way down to -40C (-40F). The calculation is: Voltage increase = Voc * Temperature Coefficient Voc * (Min Temp - 25C) = 40.25 * -0.3% * (-40 - 25) = 7.85V
So the max a single panel puts out is 40.25V + 7.85V = 48.1V
3 in series = 48.1V * 3 = 144.3V
144.3 < 145, so this is ok.

 

[zanydroid]

This would be fine all the way down to -40C (-40F). The calculation is: Voltage increase = Voc * Temperature Coefficient Voc * (Min Temp - 25C) = 40.25 * -0.3% * (-40 - 25) = 7.85V
So the max a single panel puts out is 40.25V + 7.85V = 48.1V
3 in series = 48.1V * 3 = 144.3V
144.3 < 145, so this is ok.

How much buffer is there for sample variation between solar panels?

There is a variation on electrical specs listed in the spec sheet.

 

[LakeHouse]

How much buffer is there for sample variation between solar panels?

There is going to be some variation in a production run of panels, but I think that mostly gets sorted out when they group panels. Normally spec sheets show a range of panel Power output (like 340W to 375W), but you only buy a set of (e.g.) 355W panels. So the panes you get should already all be very similar.
Regardless, I think I’d be pretty comfortable with using those panels down to -40C; an extra volt isn’t likely to fry an SCC. Plus, I doubt Alabama gets down to -40C very often.

 

[zanydroid]

There is going to be some variation in a production run of panels, but I think that mostly gets sorted out when they group panels. Normally spec sheets show a range of panel Power output (like 340W to 375W), but you only buy a set of (e.g.) 355W panels. So the panes you get should already all be very similar.
Regardless, I think I’d be pretty comfortable with using those panels down to -40C; an extra volt isn’t likely to fry an SCC. Plus, I doubt Alabama gets down to -40C very often.

They do bin it but they also often provide error bars in the spec sheet per bin

I think the way to go is to claim a higher minimum safe temperature. There’s less than 1% buffer in the calculations you provided for -40C.

Whereas if we discussed -30C you get 3% buffer back.

 

[TheCoachStone]

Ok you can put three panels is series. That will give @3s:
Voc -121v
Vmp- 99v (running voltage)
Imp- 9.38a (running amps per string).

That gives you a size of three or four strings- 9 or 12 panels. (Sorry 10 does not work well).

Even four strings will go into a single input (that about maxes it out).

If you go 3s4p - you will need a fuse on every string. If you have 3+ strings - you need to fuse each string. This also maxes one input and leaves the other empty for future expansion.

You could also go 3s2p into each input- then you don’t need to fuse each string- but there will be more to change up if you ever decide to expand.

Or with 3s3p go into one input - don’t forget to fuse the strings.

If you must have 10 panels -
Input1 6panels 3s2p
Input2 4panels 2s2p

The second input will be running at 66.1v - with the lower range cutoff of 60v

I am not confident enough to verify that the Voc of 121v will not go over the max of 145v - when it gets cold. I keep messing that calculation up - I think you are fine with a 16% margin- but it is close enough to get someone else to verify that calculation.

Ok, so to do 12 I would need 4 strings of 3 panels in series? Then all 4 wire pairs into a combiner box?

 

[Danke]

Ok, so to do 12 I would need 4 strings of 3 panels in series? Then all 4 wire pairs into a combiner box?

4 strings, but 2 string per MPPT/PV Input.

 

[TheCoachStone]

Ok you can put three panels is series. That will give @3s:
Voc -121v
Vmp- 99v (running voltage)
Imp- 9.38a (running amps per string).

That gives you a size of three or four strings- 9 or 12 panels. (Sorry 10 does not work well).

Even four strings will go into a single input (that about maxes it out).

If you go 3s4p - you will need a fuse on every string. If you have 3+ strings - you need to fuse each string. This also maxes one input and leaves the other empty for future expansion.

You could also go 3s2p into each input- then you don’t need to fuse each string- but there will be more to change up if you ever decide to expand.

Or with 3s3p go into one input - don’t forget to fuse the strings.

If you must have 10 panels -
Input1 6panels 3s2p
Input2 4panels 2s2p

The second input will be running at 66.1v - with the lower range cutoff of 60v

I am not confident enough to verify that the Voc of 121v will not go over the max of 145v - when it gets cold. I keep messing that calculation up - I think you are fine with a 16% margin- but it is close enough to get someone else to verify that calculation.

This is how this would work? How big should each fuse be?

 

[upnorthandpersonal]

This is how this would work? How big should each fuse be?

I don't see the panel fuses in your diagram?
Each fuse should be between Isc and 2 x Isc.
So if you have a 10A Isc, put 15A or so.

 

[TheCoachStone]

I don't see the panel fuses in your diagram?
Each fuse should be between Isc and 2 x Isc.
So if you have a 10A Isc, put 15A or so.

I found that online.

 

[zanydroid]

This is how this would work? How big should each fuse be?

Where are the combiner fuses?

Combiner fuses should match the max fuse rating of the panels

 

[zanydroid]

I found that online.

Feels like a bad source for diagrams then. Since it only listed 1 out of 5 fuses you need. So objectively 80% garbage /s