fm80 and fm60, one battery, two part question

zozomike · March 2014

Hi, I am upsizing my pv and my online FM80 is already fed by 1980 watts, ( read 2.2 kw today for a while) I need to add at least 1000 watts to the system, I have the physical space to add up to 1500 watts, This would be a separate array and separate cable feeding a FM 60 I have in storage now. By my calculations even adding 1500 watts would be too much amperage ( 1500 w /24v system = 62.5 amps ? nominal + overage factor 25% ) for the FM 60 except I am confused that the FM manual recommends 1600 watt array for the FM 60, whats the deal there? How much wattage can I really add?
I Hoped to use the stored FM60 to save money rather than buying a larger controller and having two excess controllers plus the mate in storage. So how do I wire the second controller to the battery, Just run two more cables to the battery or what? And what sort of conflicts will I see with the two controllers going to the same battery? I can find no info in the manuals about using two controllers.

Cariboocoot · March 2014

Re: fm80 and fm60, one battery, two part question

No worries because a 1500 Watt array isn't going to put out 1500 Watts most of the time. More like:

1500 Watts * 0.77 derating / 24 Volts = 48 Amps

You can "over panel" FM controllers without any problem; they will simply 'clip' and surplus power available. You could in fact put (60 Amps * 24 Volts / 0.77 derating

1870 Watts on it.

As for wiring it up, there's no problem there either. Just give it its own wires to the battery (with fuse/breaker) and let it go. There will be no conflict, even though the two might have a slight difference of opinion on battery Voltage. Each should have its own RTS too, otherwise you'd need to add a HUB and MATE so they can communicate and share data.

zozomike · March 2014

Re: fm80 and fm60, one battery, two part question

Thanks, that's gratifying info as I can spend more on watts than controllers and combiners. I had been thinking to buy the MNPV6 Disconnecting Combiner to replace my existing combiner, but the combiner will be 100' from where the pv power enters the equipment area. SO, as I read some of the NEC stuff a disconnect needs to be at point of entry. ( already have one there of course) And unless I am misunderstanding, I will need separate disconnects for the two arrays? Don't I need to keep the two feeds separate till they reach the Batt? Does this mean two disconnects? Or what is the most simple means?
Don't know what I would do out here in the woods without you guys, but I am sure there would be exciting sparking and blackened things involved, thanks

Cariboocoot · March 2014

Re: fm80 and fm60, one battery, two part question

Yes; you do not want to couple the arrays or inputs to the two controllers.
Unfortunately this means on a system that requires a disconnect you must have one each. Hopefully no overly officious bureaucrat will demand both be shut down with the same switch.

That's the beauty of the forum: many talented people here who have already done the sparks, blackened things, and magic smoke experiments so you don't have to!

zozomike · March 2014

Re: fm80 and fm60, one battery, two part question

I guess you guys never sleep. As a thought, could I go ahead and get the MNPV6 Disconnecting Combiner, put it at the point of entry with two higher amp breakers, use the existing combiner at the arrays ? Would that not give me the single switch disconnect at the point of entry and keep the feeds separate? I can't see the insides of that thing but it seems to be just an arm that throws breakers mounted inside? An added DC disconnect would cost the same and be more wiring and throws????

Cariboocoot · March 2014

Re: fm80 and fm60, one battery, two part question

No, because that unit combines the input from multiple breakers. Such is the nature of a "combiner".

Before you go out and spend money, explain to the AHJ what you are planning to do and find out if individual disconnects (side by side) are acceptable. If they are not and one switch for both arrays is required maybe they'd like to tell you what equipment meets the need.

zozomike · March 2014

Re: fm80 and fm60, one battery, two part question

Thanks, another witty idea shot down, hehe. ok, two disconnects face identified with my favorite marksalot! Still only two throws and I think NEC says 6 max. And there has never been an inspector here, I dread the day!

vtmaps · March 2014

Re: fm80 and fm60, one battery, two part question

zozomike wrote: »

And there has never been an inspector here, I dread the day!

Are you saying that there is no requirement to pass inspection, or are you saying that the inspector hasn't come yet (but will come)?

--vtMaps

zozomike · March 2014

Re: fm80 and fm60, one battery, two part question

vtmaps wrote: »

Are you saying that there is no requirement to pass inspection, or are you saying that the inspector hasn't come yet (but will come)?

--vtMaps

We are in a remote area, and decided as have many in the outer areas of the county to trust our own understandings. I suppose some day a state inspector could have too much time on his hands and drive up. That could be a bad day.

solar_dave · March 2014

Re: fm80 and fm60, one battery, two part question

zozomike wrote: »

We are in a remote area, and decided as have many in the outer areas of the county to trust our own understandings. I suppose some day a state inspector could have too much time on his hands and drive up. That could be a bad day.

Of course the down side to all that is if you have homeowners insurance and any thing happens you are giving the insurance company a real way out of paying.

zozomike · March 2014

Re: fm80 and fm60, one battery, two part question

Thanks for that solar Dave, there is a downside to everything.
BTW I work as an on call catastrophe insurance adjuster, have worked disasters all over US for 16 years with the better companies, and have never asked such a question of an insured, nor am I aware of any other property adjusters in the field bothering with checking permits. That kind of slipperyness is usually resorted to by health,causualty and auto adjusters. Typically if a property underwriter takes a risk, they do so by pre risk inspection or by blind faith in the odds. If they agree to the risk, the contract rules both parties. I have seen burned down and blown down things which should have fallen under their own weight paid for, ( I have done it) The only issues I have seen raise flags are flagrant lack of maintenance ( ie rotten roofs) or fraudluent intent.

fm80 and fm60, one battery, two part question

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