Colleagues:
Lones, thanks for being in the hot-seat on this and many other Outback related issues. I need to remind myself that I do not know what engineers and product managers have to go through to get products listed and comply with all of the attendant regulations. So when some application does not make sense, it may be because of bureaucracy I am not familiar with. Also, if sometimes it seems like I am whining or nit-picking, please remember I consider Outback to be the best off-grid equipment on the market. I strive for excellence in my work and sometimes to get that I have to ask lots of questions. Let me stipulate that I am not going to start installing 300 volt rated inverter breakers on systems with FM100 charge controllers. I don’t think any other wrench is going to do that and it does not seem Lones is suggesting that. I am willing to install an FM100 in the same system with and FM60 or FM80. I will use external GFDI protection. However, in reviewing the Outback installation manuals, it is not clear how the GFDI breakers are installed and sized. Different manuals show different wiring diagrams and different breaker sizing specifications. Here is a breakdown of what I found and what I decided for my own projects: GFDI breaker placement: Various Outback manuals for the GFDI breakers and charge controllers show the GFDI being placed either before or after the charge controller. I checked the NEC and the requirement is this: either the current carrying conductors of the faulted circuit be disconnected or the inverter or charge controller cease supplying power. It is important to remember these GFDI circuits do not resolve a ground fault, they just let the system user know (somewhat vaguely, I might add) that something is wrong. The user only knows, eventually, that PV charging has stopped. I believe either NEC requirement is met with the GFDI either before or after the charge controller, so I will suit myself on a case-by-case basis. Combiner breakers will act as manual PV disconnecting means. Multiple GFDI breakers: What if you need more than 4 charge controllers, or you need GFDI breakers of different values? Either scenario requires more than one GFDI breaker assembly. If you install more than one GFDI and wire them each as indicated-- with one side of each 0.5 amp sense pole to the negative and the other to ground, you are paralleling the sense poles. Theoretically, this allows double the fault current (for two GFDI breakers, triple for three, etc.). Is this OK? This wiring does mean if one GFDI trips, all trip. You could wire the sense breakers in series and maintain the 0.5 amp trip level, but likely only one GFDI will trip in a fault. I have not decided which method I would recommend. Anyone have an opinion? Breaker sizing: Outback manuals give conflicting advice on breaker sizing. In the old days I had applied the 125% rule to the CC nameplate and put this sized breaker before and after the charge controller. After some thought, I conclude this is not correct. There are different criteria for input and output breaker sizing, as indicated: Input breakers: Proper design would have you calculate 125% the Isc of the connected PV array and pick a breaker the next standard size up from that value. That breaker must have a voltage rating greater than the highest Voc at the coldest possible temperature. Output breakers: CC output breakers will never be subjected to Isc currents. If there is a short circuit in the output side of a charge controller, the large ampacity of the battery bank will open the output breaker. I suggest that the proper sizing method is to use the nameplate wattage of the attached PV array and divide that by the lowest expected battery voltage. This gives the highest possible Imp. Multiply that by 125% and pick the next larger breaker. That breaker must be voltage rated greater than the highest battery voltage expected. Documents missing from the Outback web site: I looked all over and I cannot find these documents: A current version of the GFDI installation manual. Any listing of the GFDI breakers currently available from Outback. Am I not looking in the right place? I hope the above discussion helps you detail-oriented PV designers out there. I am hoping Lones can provide some input on these subjects. Lones has been very on top of his responsibilities and I am grateful to him. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Tuss, Lones *Sent:* Friday, January 21, 2022 9:39 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Mixing Outback FM100 CC with Fm80 or 60. Ahh the can of worms get opened. In our conversation Willian brought up the same points. All true, but the white paper was required by legal (CYA). I think getting the new unit listed also came into play. *From:* RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> *On Behalf Of *Maverick Brown *Sent:* Friday, January 21, 2022 9:29 AM *To:* RE-wrenches <re-wrenches@lists.re-wrenches.org> *Subject:* Re: [RE-wrenches] Mixing Outback FM100 CC with Fm80 or 60. *CAUTION:* This email originated from outside of the Company. Do not click links or open attachments unless you recognize the sender and know the content is safe. Using that logic, wouldn’t the inverters and batteries also be exposed to 300Vdc? And the MX60 would also be at risk for exposing the inverters and batteries to 150Vdc under similar failures? If that’s the only limiting factor, I’d like to take back a couple AC Coupling arrangements I have made for past Radian expansions. ;-) Maverick Brown Off-Grid Solar Commander since 2006 *Maverick Solar Enterprises, Inc.* * • Solar Commander Remote Power* * • SunFlow Systems Cathodic Protection *maver...@mavericksolar.com 512-460-9825 On Jan 21, 2022, at 11:15 AM, Tuss, Lones <lones.t...@enersys.com> wrote: Hi William Thank you for taking my call. I believe the reason we do not recommend mixing the FM100 and the fM60/80 is. If the FM100 were to short out pv input to output you could expose the 150 volt rated dc breakers on the FM60/80 to 300 vdc. *From:* RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> *On Behalf Of *William Miller *Sent:* Thursday, January 20, 2022 10:54 PM *To:* RE-wrenches <re-wrenches@lists.re-wrenches.org> *Subject:* [RE-wrenches] Mixing Outback FM100 CC with Fm80 or 60. *CAUTION:* This email originated from outside of the Company. Do not click links or open attachments unless you recognize the sender and know the content is safe. Friends: I am sure many of you are familiar with the somewhat new Outback FM100 charge controller. It allows PV input at up to 300 volts and battery feed at up to 100 amps. It has a built in GFDI fuse, much like the old XW--now branded I think Conextant-- charge controller. Outback recommends against installing an FM 100 in an installation with FM60s or FM 80s. Here is the tech note <https://protect2.fireeye.com/v1/url?k=31323334-501d2dca-31313abf-454455534531-4df62a772b14c6eb&q=1&e=d5f26548-4212-48c3-91e9-e4b3dde4c8e7&u=https%3A%2F%2Foutbackpower.com%2Fdownloads%2Fdocuments%2Fappnotes%2Ffm100_fm80_app_note.pdf> that gives that recommendation. Below is one paragraph from that tech note. *There is little benefit to mixing an FM100 with an FM60/80. If circumstances require it, this application* *note will explore an option.* Note the language is pretty dang squirrely. Let’s parse the above paragraph: Sentence 1: I submit there may be many scenarios where there is significant benefit: Like if you already have an FM60/80 and you want to add more PV and you want to enjoy the benefits of an FM100, such as higher input voltage or higher output amperage, and not have to fork out an extra $1000 to replace a working FM60/80. Or you installing more than one PV array, one array nearby and/or smaller and one further away or larger, and you don’t want to spend close to $1,000 to charge control the nearer array. Sentence 2: They are offering “an option,” not the only option. I believe there are multiple options. In a mixed installation, the FM100 can rely on its internal GFDI fuse and the FM60 or 80 can rely on the old familiar GFDI breaker with the 1 or 0.5 amp pole connected between the negative and equipment grounding system. Alternatively, Midnite sells a 300 volt rated, multi-pole GFDI breaker that could be shared by an FM100 and an F60/80. It says right in the FM100 manual that you can use external GFDI devices (page 14). I am not at all clear as to what problem there is to mixing the two generations of charge controllers. I reviewed the NEC. There is no indication that thou shall not mix GFDI styles. If anyone has a definitive reason why or why not to mix these models of Outback charge controllers, I would be most interested. Most Sincerely, William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com <https://protect2.fireeye.com/v1/url?k=31323334-501d2dca-31313abf-454455534531-18562c478088e59c&q=1&e=d5f26548-4212-48c3-91e9-e4b3dde4c8e7&u=http%3A%2F%2Fwww.millersolar.com%2F> CA Lic. 773985 This email and any attachments may contain confidential information that is intended only for the recipient(s). If you have received this email in error, please notify the sender and delete it from your system. 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