Expanding an FP1 3648

[Chrisunderground53]

Good day All,
I currently have a functioning Outback FP1-3648, utilizing ten 415 watt Mission panels and 16 Battleborn 100 ah batteries. Everything seems to be functioning correctly, and has been for about two years. However, even in west TN, I rarely am able to keep the batteries full, nor run all the electric I would like.
I have a spare Outback 3648 inverter and a spare FM80 charge controller. I also have 8 extra batteries and am picking up another dozen panels (unknown which but possibly Piemar 450watt Perc)
Purchasing an FP2 or 3 is not feasible currently.
I would like assistance with wiring considerations to create a homegrown FP2. Are there other mounting or chassis components I need? I would be stacking the inverters as 120 volt. What extra breakers and control might be needed? I understand it's quite confined inside, but there must be a way, if Outback can do it.
I appreciate any comment, positive or negative. But, I really need to expand my system to be completely self sufficient and run what's needed and limit reliance on a generator.
This forum has been quite helpful in the past and I appreciate y'all sharing the vast knowledge base.
Thanks to Everyone

[raysun]

I had an FP1 and thought it would be nice to add another FM80. I talked with the OB engineers and their reply was "it will be tight". They weren't kidding. I managed to modify the DC panel, but when I was done, I swore I'd never touch it again.
When it came time to step up to FP2 capabilities, I took the modified FP1 off the wall, gave it to a disabled Army vet, and bought an FP2 with FXR -A01 inverters.
No good dead goes unpunished. The old FX class stacked reliably. The FXR -A01 were a nightmare that lasted 4 years. Even with input from the Outback engineers, the system was never stable. I've since replaced the whole stack and am much better served.
The DC panel has one Battery/Inverter disconnect. A second should be added. The single GFDI disconnect used in the FM80 - Battery circuit should be replaced with a dual GFDI assembly. They are getting hard to find. A second 80A array disconnect is required. The mod I did had all the parts above added except the 2nd Battery/Inverter disconnect. It took some creative use of the unused panel mount slots in the "back side" of the DC panel. I don't think there is room for the 2nd Battery/Inverter disconnect. If I had to do this again, I'd use a separate DC panel and move all the disconnects to it.
Modifying the AC panel for a second inverter will be challenging. The inverter bypass assembly will no longer work properly as it's designed for a single inverter. The bypass lockout plate must be removed and the inverted Bypass circuit breaker remounted and rewired for AC Output from the 2nd inverter.
The AC panel wiring will only allow parallel inverter stacking at best. Even with that, the AC Input and AC Output wiring for each inverter must be electrically identical or inverter imbalances are all but guaranteed. A 2nd AC Input disconnect will need to be added.
If a "full fledged" FP2 was to be implemented, here's the schematic: north_american_fp2_off-grid.pdf https://share.google/fYKdx8jgfUgs6lsGB
That is for off grid. The autotransformer can be ignored.

[Chrisunderground53]

Hi Raysun. Thanks for the reply, and link.
When I purchased all this equipment several years ago I had the youthful naivety to think , since an FP2 existed, I should be able to create my own when needed. Unfortunately, I don't have the means to go out and purchase the upgrade at this point.
Do you have any photos of your modified system to share?
My goal is obvious. Add more panels, more battery and therefore have more available AC power.
Is there a different avenue? Could I stack the FM80s to charge the one battery bank but run the inverters individually to two AC panels? Or would that require another Mate3 and Hub?
Despite being neck deep in this solar equipment and running our homestead off it for a couple years, the reality is I haven't much understanding of the works. Definitely Not an engineer! I appreciate the assistance as I have appreciated your help on other steps on this road.

[Chrisunderground53]

Also, in reviewing the Outback quick start guide for the FP2, the schematic shows two, considerably larger enclosures for both AC and DC wiring and breakers. I would definitely follow suit with that concept.
I don't know if those chassis parts are readily available or if I would have to fabricate.
Are there complications in setting the Master/slave synchronization via the Mate3? That question is probably too far down the line for concern....

[raysun]

Also, in reviewing the Outback quick start guide for the FP2, the schematic shows two, considerably larger enclosures for both AC and DC wiring and breakers. I would definitely follow suit with that concept.
I don't know if those chassis parts are readily available or if I would have to fabricate.
Are there complications in setting the Master/slave synchronization via the Mate3? That question is probably too far down the line for concern....

That's a possibility. The two panels are FW-500 AC and FW-500 DC. Like all the "legacy" OB gear, availability depends on what distributors have gathering dust in the back corner of their warehouse. I see a couple of the AC versions on eBay, but not the DC.

I'll think on this a bit more.

[raysun]

Candidate for the dual FM80-Battery circuit. This unit is rated 100A where the Outback is rated 80A. Feed wires between FM80s and the battery bus would need to be 4AWG. The FM80 itself is rated to 113A.

https://www.solar-electric.com/midnite- ... HirQp0hnbA

[raysun]

Possible schematic for adding FXR and FM80 to an FP1.

NOTE* The AC side is ghetto AF, but should work. It disconnects both inverters as a single unit, but preserves the AC circuit breakers as-is. That is with the exception of the Inverter AC Output swapped for an 80A unit.

The DC side will need a 2nd Inverter Main 175A disconnect and a dual GFCI (100A shown). Those will not fit into the FW250, so some sort of external panel will be required.

[attachment=0]PXL_20260518_020111743~3.jpg[/attachment

*EDIT*
If using the ePanel (below) this schematic is invalid. It will require some small changes to the wiring scheme.

[raysun]

MidNite Solar MNDC175PLUS Mini DC Disconnect PC Plus. https://share.google/KtVrOjvFkoIlx9k75

Though a bit clumsy and pricey, the panel above comes with the 175A main disconnect for the 2nd inverter.
It also accomodates DIN rail mounted PV circuit breakers (5 slots), and panel mount circuit breakers (3 slots). Install two of the DIN 80A version for the two PV Array - FM80 circuits.
https://www.midnitesolar.com/productPho ... er=1&act=p
or install the existing panel mount PV Disconnect from the FP1 along with an identical circuit breaker for the 2nd FM80 into two panel mount slots.
https://www.midnitesolar.com/productPho ... r=13&act=p

The single GFCI 80 in the FP1 can be removed to open 4 panel mount slots. Mount the Dual GFCI 100 in that opening.

The 2nd array will need a combiner panel that will depend on the PV panel specs.

[raysun]

I've looked this over about 50 times (or so it seems), and that's an indicator I don't like my proposed solution. Since nobody has waded in to critique this, I'll do it myself.
• The design is functional on paper, but employs non-standard implementation of the FP1. Someone looking at it is right to ask: "What the h*** was he smoking?"
• "Piggybacking" the two inverters on the AC disconnects removes the critical ability to disconnect a single inverter independent of the other.
• Modifying the FP1 voids it's UL/ETL listings. If this came up in an insurance matter it could be grounds for denying a claim.
• The wiring mods, while simple, are difficult to accomplish in the tight spaces within the FW-250 panels. The work-around adds an additional wiring panel and disconnects, but ends up a compromised solution especially on the AC side.
• IME, the FXR inverters are "twitchy" when stacked. Changes made to evolve the FX to FXR firmware seem to have "upset the applecart" somewhat. My own 4 years of research into it never found a solution, including my FP2 FXR, nor definitive cause. I've seen a half dozen cases like mine, and none were resolved. Putting the two FXRs together in an optimal design carry the risk. Using an inproven design adds to the risk.

There's got to be a better way to do this.

[raysun]

The Midnite Solar ePanel makes deploying the FXR/FM about as easy as it gets:
https://www.stellavolta.com/midnite-sol ... back-175a/

My main system is installed on one of these ePanels.

The two inverters can be connected to the Hub, and managed with the Mate. Each will be independent. Both can connect to the common battery. Both FM80 will charge the battery. Both FXR can be configured to charge via generator/grid as well.

Nothing needs be done to the FP1 except run some wires from the ePanel.

Another nice thing about this approach is once the second inverter is installed, they can be easily configured for parallel operation. If that works, job done. If it acts wonky (and I can give you some quick tests) then proceed to splitting the loads and inverters.

This approach has the benefit of not breaking what is working, gives a great deal of flexibility in testing and deploying the 2nd inverter and solar charger, acts as built-in redundancy, and maintains UL listing throughout.

[Chrisunderground53]

Hey Raysun.
Goodness me! You put some brain cells to work there. I have to review that drawing several more times to understand fully how it comes together. Fuzzy still. Lots of effort though. Thank you.
Although UL listing isn't really a big concern, I had been searching for external boxes that might replace the FW-500s and associated conduit boxes. I could make some if it really came to it. Essentially trying to mimic the traditional layout of the FP2.
there are many complications to this non-standard approach. Opening vulnerability to improper function of both FXRs. And lots of parts, pieces and costs associated.
You're final post showing the e panel seems optimum. It's actually quite an elegant solution. If I'm getting this correct, this panel creates a stand alone platform that will function in tandem with my existing FP1, and be capable of separating the two for diagnostics, repairs, or even dividing/combining power output.
Most importantly, as you mentioned, it leaves the original unit in functional order before, during and after the alterations. That is a highly critical element of the whole process. I would be devastated if I inadvertently damaged or destroyed my source of energy independence.
In retrospect, it seems that ePanel should be a default solution for expanding any OB FP system. " Oh, you need to add more power? Try this epanel!"
I will look into this Midnite ePanel option further, but it certainly seems the best answer I could hope for. As far as equipment goes, it doesn't seem overly expensive either.
I have an additional Midnite PV6 combiner box and breakers coming. I had already purchased a 175v inverter breaker but might not need it with the ePanel. Spare inventory I guess.
Raysun, thanks very much for your insight, effort and direction. Again.

[raysun]

I just helped a friend with an FX on an ePanel that was installed 20 years ago. Not bad track record.

Having both inverters functioning "stand alone" will be a solid first step. The ePanel will provide that without any changes to the FP1.
One step to pay attention to is the battery to ePanel wiring. The DC cables feeding the ePanel should be electrically identical to the cables feeding the FP1 (equal gauge and length.) I use

Once the "new" FXR is up, tested and running, integration wiring can be added. I use Battery Cables USA for all my cable fabrications. https://www.batterycablesusa.com/?gad_s ... 5lEALw_wcB
If using the stock Outback battery cables for the FP1 and they are still in good shape, note their wire gauge and lengths, and have another set built. If that doesn't allow the ePanel to be conveniently sites, it wouldn't hurt anything (except your budget) to have new, identical cables built for both panels.

Whether used separately or in tandem, the two inverters can share AC IN sources (generator / grid). If using generator, then it must have enough capacity to satisfy AC load + charging demands of both units.

AC OUT will be the "grand experiment". Parallel stacking of the inverters will make the integration testing fairly straight forward. It can start with both inverters connected to the battery, and the AC OUT of the ePanel connected to nothing. Run a RJ45 (ethernet) cable from the new inverter's Hub/Mate port to the Hub. (FP1 imverter must be in port 1.) Configure the stacking for Master/Slave parallel and adjust AC IN current limits for the generator (each inverter will take ½ total continuous generator output current). Next fire up the generator and start a battery charge session. Both inverters should participate through the entire charge cycle. If they do with good stability then the AC OUT will be the next test

That's a big spoonful of the ingration testing. There's more details but those can be fleshed out when the ePanel route is settled on.