Will be installing 6 - 400 watt solar panels in 2 strings of 3 with each string outputting 124V and 10A, then paralleled to be 124V and 20A. This is based on Voc and Isc of the panels and no temperature correction. It will be about 200 feet from the panels to the Victron Energy 250/100 MPPT SCC. Currently installed wire for existing panels is #4 AWG Aluminum rated at 600V. I believe this is sufficient from what I have found. Will this wire work for the proposed new panels?
Right Wire Size
- Thread starter TommyD
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
If you don't have shading issues, would it be possible to go to 248V (All panels in series)? This would cut your current in half and your line-loss would be divided by 4 with the same wires.
BTW: For safety calculations, you should definitely use Isc. For efficiency calculations Imp is a more appropriate number. Imp is lower so the calculations are not quite as bad.
I would use 4 gauge copper. If you want to stay with aluminum, you should be looking at 2 Gauge.
BTW: For safety calculations, you should definitely use Isc. For efficiency calculations Imp is a more appropriate number. Imp is lower so the calculations are not quite as bad.
I would use 4 gauge copper. If you want to stay with aluminum, you should be looking at 2 Gauge.
No shading issues. MPPT is rated for 250v, but as I understand it, as it gets cooler, voltage rises which could overload the SCC, so reason I went with the two strings mentioned.
so, 4 gauge copper it is??
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Actually, I forgot to use round trip when I looked it up so 4 Gauge is the absolute smallest wire I would use. Larger would be better.
Since you have 400 ft round trip, there is going to be a very substantial voltage drop even with 4 gauge...
Take a look at the last slide in this slide deck:
https://docs.google.com/presentation/d/1720u-tB3Ey3bvsO4Itk3pmpdhtBdpd14ViiNGqX4U1o/edit?usp=sharing
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jasonhc73
Cat herder, and dog toy tosser.
The MPPT adjusts the amps to match the voltage to the highest available, the end result is the most watts possible for any situation. It's an always adjusting device. Yes, when it is colder the Volts are significantly higher, but the amps are much less also.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
The problem is that if the batteries are full the MPPT stops all current. This looks like an open circuit to the panels so the voltage goes to Voc. If the Voc exceeds the capability of the MPPT it can damage it.
@upnorthandpersonal built a nice little calculator that will help you figure out the temp adjusted voltage:
https://diysolarforum.com/threads/maximum-open-circuit-voltage-calculator.4500/
jasonhc73
Cat herder, and dog toy tosser.
It cannot damage anything when there is no amps.
His loss as is was 2.5% under nec guidelines.
Ampacity is absolutely safe.
Copper (#4) would pass more current with less voltage loss and that would be 1.6% well under the 2% standard of the industry for loss in a pv line.
The question is, is it in your interest to replace it? Versus cost?
If you plan on adding pv, you could up the voltage, do not exceed max voc.
Or another line.
Or beef up the existing by replacing it so it can handle upsize even with bumping voltage by a module or as many as work in your case.
Ampacity is absolutely safe.
Copper (#4) would pass more current with less voltage loss and that would be 1.6% well under the 2% standard of the industry for loss in a pv line.
The question is, is it in your interest to replace it? Versus cost?
If you plan on adding pv, you could up the voltage, do not exceed max voc.
Or another line.
Or beef up the existing by replacing it so it can handle upsize even with bumping voltage by a module or as many as work in your case.
When calculating loss, do be sure of actual distance especially if you are at or nearing the max acceptable loss. If the line is buried, it has 5 to 6 feet of stub up to an enclosure or connection point generally, i hqve seen this flop calculations.
Wire is cheap. Effort sometimes not so cheap. Everything un-needed is more expensive.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yes it can. The Mosfets in the MPPT are 'stopping' the current. They are designed to handle a certain voltage while doing this. When you exceed that voltage, they break down, current will start flowing and they are no longer functional mosfets.
Appreciate the assistance and thought a "very rough Diagram" may help you.
Specifics of the two PV Arrays, the Old and the New are set out above.
Plan is to install the New Array and remove and sell the Old Array
A represents the existing wire from the Old Array
B is the idea of "adding on" a wire from the New Array
C is the idea of a whole new Wire
Appreciate your thoughts on way to go
Specifics of the two PV Arrays, the Old and the New are set out above.
Plan is to install the New Array and remove and sell the Old Array
A represents the existing wire from the Old Array
B is the idea of "adding on" a wire from the New Array
C is the idea of a whole new Wire
Appreciate your thoughts on way to go
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Will you be keeping the old array or is the new array replacing it?
I believe I am going to be replacing it as I don't know of a way to wire the 9 panels effectively to the MPPT; it is a Victron Energy 250/100 and I believe I would exceed the specifications if I were to hook up the 9 panels, especially when temperature coefficient is applied. If I could use the 9, then I would move the existing 3 old panels onto the roof of the house, which then be a distance of say 40 feet to the MPPT for those 3 and 200 for the 6 new ones.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Have you considered buying another MPPT?
The VE MPPT is brand new and not yet installed.
The exising SCC is an old Trace C40. I understand that I could leave this SCC with the existing panels and use the new VE MPPT for the new panels, but I understood that having two different charge controllers going into one Battery Bank may cause them not to place nice with each other?? Am I wrong here?
The exising SCC is an old Trace C40. I understand that I could leave this SCC with the existing panels and use the new VE MPPT for the new panels, but I understood that having two different charge controllers going into one Battery Bank may cause them not to place nice with each other?? Am I wrong here?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
There is a lot of debate about that, but I am in the camp that says it is fine to put multiple controllers on one bank. (@Will Prowse does it in his videos as well)
If you decide to add a new wire line, then why not try it? Set the charge profiles as close to the same as the controllers will let you and it should work fine.
Does the new information I have provided help you answer these questions?
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