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://outbackpower.com/downloads/documents/appnotes/fm100_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 CA Lic. 773985
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