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How close to failure is this MPPT+PV package and is there a way to protect against high voltage?

Checked! Panel max fuse rating is 25A.


Moving back to a 6S2P, combiner box output is >> Isc=27.70A & Imax=1.56*Isc=43.21A (NEC)

What do you call the expected current? Assuming it is the total Isc of 27.70A then
MCB=40A


I don't want it but if required I'll sort it out.
With only two strings, you don't need to protect each string. (Unless you just want to)
40a should be fine for the main output breaker.
SPD's aren't required. Just another layer of protection for the panels. I would recommend them at the charge controller.
 
With only two strings, you don't need to protect each string. (Unless you just want to)
Yes, 2 strings simplifies a lot. I guess I needed to go over the exercise to to better understand the science behind it. It has been a bit painful but worth it.

Here is what I have for the 2-string configuration:

250V Wiring.jpg



40a should be fine for the main output breaker.
Moving to a 2 string config I wouldnt have the combiner box but I think I would still need a DC disconnect switch. Imax=43A so 63A disconnect breaker?
 
Yes, this is for East-West orientations.


MPPT has only one set of input. So which/where to connect the two strings?

Can be MC4 Y cable, splice in a conduit box to THHN/THWN wire (I used to use wire nuts, now Ideal set-screw nuts), could be at inverter.
We aren't supposed to put two wires in a terminal, although it seems to work fine. I've seen crimp ferrules for 2 wires. I've used split-bolt (wrap in rubber tape, then vinyl.)

- At roof level, inside junction box, with a busbar? I think this would require an inline fuse between the two strings?

As was said, no fuses needed if only 2 strings in parallel.
(if 3 in parallel and one shorts, then 2 strings dump excessive current into it, which fuse could protect against.)

- Next to MPPT inside shed? This would also require a DC disconnect?

A DC disconnect is convenient.
DIN breakers are economical but require a box.
Some visible blade safety switches have DC voltage rating. Varying prices, and I try to buy on eBay for less.

How would you do this wiring for a 6S2P config?

Just needs to connect as a "Y" somewhere, as enumerated above. Almost anything works, just use UV resistant wire where exposed and keep connections dry.

Also run a ground wire from inverter/scc to panel frames. Various ways to make connections including lugs, WEEB washers, etc.


I don't want it but if required I'll sort it out.

(SPD)
If you have grid AC connection, definitely put something there. Power lines can carry surges from normal loads and switching, and can couple or be hit by lightning.

DC connection, I think it is for coupled current from lightning.

Midnight sells MOV based SPD for about $150. There are other brands.

The key component is a MOV about the size of a quarter that costs a few dollars. Three of those at PV input to SCC connecting PV+, PV-, Ground should protect (although I'm not sure if they burn up when they fail, I should try destructive tests some time.) What I bought were MOV with thermal protection so that doesn't happen. Midnight uses those, with LED to indicate "Protecting" or "Failed".
 
Moving to a 2 string config I wouldnt have the combiner box but I think I would still need a DC disconnect switch. Imax=43A so 63A disconnect breaker?

Pretty reasonable, but supposed to be 43A x 1.56 = 67A for thermal-magnetic breaker (or fuse) to avoid nuisance trip.
I think if no OCP (just a switch), or if magnetic-hydraulic breaker, then 43A x 1.25 = 54A would be sufficient. I'm not sure what NEC says about that.

There are some 60A switches available. Trick is finding one rated for the DC voltage you're using. Some safety switches are rated 600V AC/DC, some have a 250VDC rating.

I have some aged 63A AC breakers (which I was using for AC), and they were tripping well below rated current. Nuisance tripping is a real thing (wire and contact resistance contributes), and with age they get worse.

I don't know how magnetic hydraulic breakers age, but I think I like them.
 
Reality adjustment, for future reference: "Can afford a pre-made combiner but don't know how to build one?" Exactly, that's where I am.
The reality adjustment is some people go out and research certain subjects, educate themselves with available information and learn how to accomplish new things. Other people expect things to be handed to them on a silver platter while never expanding their mind and thought process. Anyone can do this, it just takes effort; both physically and mentally.


There are many photos and posts by members on how to build one. It's just a box, some DIN rails and breakers with SPD protection. If you want to combine strings, use a terminal block or strip.

Bad taste inn my mouth and not going back to EG4.

Did they refund your money? I lost track of your story. In my case, they did issue a full refund. Was the problem entirely their fault? No, I think the problem was the manufacturer changed the product without going thru a certification process. I think it caught SS completely unaware and they certainly tried to make things right.

I had said I wouldn't buy their products again after my experience but realized it really was a manufacturer issue and they did refund my money, so I decided to try these SCC's. I will say the one I have working has been working great. The other is 80% installed, just need a few items to finish.

Chopping your head off to spite someone doesn't accomplish anything.

In one post you say you have a budget crisis, yet want to spend money on what some consider Tier 1 products. It is definitely a Tier 1 price because there are products that surpass the functionality at a better pricing point for that or more functionality.


Also, at 25W idle consumption does not work with my off grid situation.
If you are worried about 25W when the unit is actually working charging the batteries and supplying power to the DC bus, then you have some serious issues.

The EG4 SCC shuts down when no PV is available. The 25W is mainly for lighting the display. Victron doesn't have a display so they can claim it doesn't have a draw. Victron instead wants you to use other items for monitoring/displaying production and settings. Those items draw power, just not thru the SCC or inverter but the power to display it comes from somewhere. Ever notice Victron claims low idle consumption but never has any display on the product?

When the sun goes down, the EG4 SCC goes to sleep. There isn't any draw. When the sun comes up and there is PV voltage, the SCC wakes up and the display is lit. I had slightly overpaneled my array to the EG4 6500EX's. The most I could yield at peak sun was 3.9Kw per MPPT. With the EG4 SCC, I have seen actual yield more than the 4240W of panels at 4300Kw.

So what was that you were saying about 25W?
 
The reality adjustment is some people go out and research certain subjects, educate themselves with available information and learn how to accomplish new things. Other people expect things to be handed to them on a silver platter while never expanding their mind and thought process. Anyone can do this, it just takes effort; both physically and mentally.


There are many photos and posts by members on how to build one. It's just a box, some DIN rails and breakers with SPD protection. If you want to combine strings, use a terminal block or strip.



Did they refund your money? I lost track of your story. In my case, they did issue a full refund. Was the problem entirely their fault? No, I think the problem was the manufacturer changed the product without going thru a certification process. I think it caught SS completely unaware and they certainly tried to make things right.

I had said I wouldn't buy their products again after my experience but realized it really was a manufacturer issue and they did refund my money, so I decided to try these SCC's. I will say the one I have working has been working great. The other is 80% installed, just need a few items to finish.

Chopping your head off to spite someone doesn't accomplish anything.

In one post you say you have a budget crisis, yet want to spend money on what some consider Tier 1 products. It is definitely a Tier 1 price because there are products that surpass the functionality at a better pricing point for that or more functionality.



If you are worried about 25W when the unit is actually working charging the batteries and supplying power to the DC bus, then you have some serious issues.

The EG4 SCC shuts down when no PV is available. The 25W is mainly for lighting the display. Victron doesn't have a display so they can claim it doesn't have a draw. Victron instead wants you to use other items for monitoring/displaying production and settings. Those items draw power, just not thru the SCC or inverter but the power to display it comes from somewhere. Ever notice Victron claims low idle consumption but never has any display on the product?

When the sun goes down, the EG4 SCC goes to sleep. There isn't any draw. When the sun comes up and there is PV voltage, the SCC wakes up and the display is lit. I had slightly overpaneled my array to the EG4 6500EX's. The most I could yield at peak sun was 3.9Kw per MPPT. With the EG4 SCC, I have seen actual yield more than the 4240W of panels at 4300Kw.

So what was that you were saying about 25W?
My friend, I'm more interested in learning and discussing the technical stuff versus the preaching and pointless discussions.

I know you are able to do both but I'm asking that you stick to the technical help and questions that i am trying to answer. If your technical help only comes with the persistent preaching and the side distractions then, unfortunately to me, I'll have to pass.
It is just exhausting trying to figure this science out and on top of that dealing with these excessive judgements and distractions.

I really hope you can make this exception and stick to electrical science when addressing my posts because I have learned from you before. If you can't, then thank you for the help so far but let's stop here.
 
My friend, I'm more interested in learning and discussing the technical stuff versus the preaching and pointless discussions.

I know you are able to do both but I'm asking that you stick to the technical help and questions that i am trying to answer. If your technical help only comes with the persistent preaching and the side distractions then, unfortunately to me, I'll have to pass.
It is just exhausting trying to figure this science out and on top of that dealing with these excessive judgements and distractions.

I really hope you can make this exception and stick to electrical science when addressing my posts because I have learned from you before. If you can't, then thank you for the help so far but let's stop here.
I've offered my opinion on what I would do in your situation and offered the alternatives such as the EG4 SCC.

Once you get to a certain array size, it makes more sense to use higher PV voltages, especially if any distance from array to MPPT. The problem with 250V VOC ratings is it limits the number of panels in series and requires strings in parallel. This may require larger PV wire size, combiner boxes and much higher amperage to move the same number of watts. This increases the complexity and failure points. Higher amperage leads to more power loss simply due to resistance of the wire. Power loss due to higher amperage is exponential, Current squared x resistance = power loss.

With a lower string voltage, voltage drop will be more pronounced. Take the calculator here: https://www.southwire.com/calculator-vdrop Input DC and 200 feet distance round trip, conductor size 10AWG. Compare 400V and 200V for 4000W which is 10A for 400V and 20A for 200V. The voltage drop for 200V is 4 times the voltage drop for 400V.
 
Everyone likes to spend OPM (other peoples money). For two strings it is not needed. Save your money till you have more strings. That could be expanded but a lot of work.
 
He is spending his own money.
I'm trying to discourage him. lol
It doesn't matter anyway, he has certain ideas that won't change. I say let him spend it.

That combiner looks to be 2 to 1. It actually will hurt yield compared to higher voltage single strings. I sometimes think it would be better to combine strings at the SCC, less yield loss. But if the wire is being run anyway, might as well leave the strings single and add another SCC.
 
It doesn't matter anyway, he has certain ideas that won't change. I say let him spend it.

Thank you for your royal authorization. I am glad you are allowing me to spend my money they way I choose to. I was waiting for you to authorize it before pulling the trigger and now I am ready.
 
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For two strings it is not needed. Save your money till you have more strings. That could be expanded but a lot of work.

Needed? Like everything else in life, it depends: for an electrician or someone doing this for a while? Maybe not. But for someone going over this the very first time? Maybe yes.

If you have the patience and the desire to read 4 pages of technical jargon I personally don't fully understand, sprinkled with arrogant subtleties disguised as help from some key Trolls, you'll realize that $100 is an excellent price for me to move on. I actually feel like it is a bargain!
 
He is spending his own money.
I'm trying to discourage him. lol

(y) (y) (y)

You are good, bro. I hear you.

But I suspect all of this comes so easy and natural for you that you loose touch with how hard it is for someone new in the field to learn the science. And the learning curve comes with a component that costs a lot more than money, IMHO: time.

What am I really saving (or wasting) trying to reduce a final combiner box price of $84 ($100-$16 for Y splitters) when I don't master the science behind to build my own? It has taken 401 posts to get to this Combiner Box. How many more posts (and time) would take to build my own box and save $30?
 
Solar arrays having higher current availability (parallel strings of solar panels) than the maximum overcurrent protective device rating specified for the panel shall be protected from overcurrent. EXCEPT when the short circuit currents from all sources do not exceed the ampacity of the wires and maximum overcurrent protective device size rating specified on the PV module nameplate.
 
Solar arrays having higher current availability (parallel strings of solar panels) than the maximum overcurrent protective device rating specified for the panel shall be protected from overcurrent. EXCEPT when the short circuit currents from all sources do not exceed the ampacity of the wires and maximum overcurrent protective device size rating specified on the PV module nameplate.
What does the above mean to you, in plain english, for a 2P config with the following panel specs:
Panel Isc=13.85A
Panel Max Fuse Rating=25A
 
(y) (y) (y)

You are good, bro. I hear you.

But I suspect all of this comes so easy and natural for you that you loose touch with how hard it is for someone new in the field to learn the science. And the learning curve comes with a component that costs a lot more than money, IMHO: time.

What am I really saving (or wasting) trying to reduce a final combiner box price of $84 ($100-$16 for Y splitters) when I don't master the science behind to build my own? It has taken 401 posts to get to this Combiner Box. How many more posts (and time) would take to build my own box and save $30?
What I was saying was that with only two strings, you don't need any box. But I agree that it is your money. And if $100 gives you piece of mind. Then it is probably worth every penny.
 
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