So...is 2000w max just a suggestion?

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BoulevardBricks
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So...is 2000w max just a suggestion?

Post by BoulevardBricks »

Hi, folks!

I've got a Flexmax 80 and a 24v system. Specs we know and love say 80A out, 150VDC max in, and solar array max 2000w. I may have an opportunity to pick up 12 good condition used panels for more power. Panels are 265w, 9.11A, and 38.3V. If I wired series/parallel, I'd have 3 panels in 4 strings; each string would be 114.9v at 9.11A. With the combiner there would be 114.9V at 36.44A going to the Flexmax 80. So, I'd be under the 150VDC input max. Is there an unpublished amperage max limit? Or would the Flexmax handle the Amps? Total panel watts would be 3180W...well over the published 2000w limit for a 24v system.

Where I see this as an advantage is on peak days I will lose power as the controller shuns the extra amps, but on less-optimal days I'd be maximizing my energy capture.

Is my math wrong? Any thoughts out there? And THANKS in advance!
raysun
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Re: So...is 2000w max just a suggestion?

Post by raysun »

The FM80 is rated at 80A maximum output current. If driven to higher current, damage to the unit may occur. A common failure is overheating and burnout of the power FETs.

There is no way for the controller to ignore the excessive drive current, it must be handled by the control circuitry.

Hopefully a properly installed 80A disconnect is in place to protect the controller and the battery.

"Overpaneling" can be "gotten away with" under certain circumstances, but in general is a bad idea.

If the extra 1200W of panels are desired, get a 2nd charge controller to go with them.
BoulevardBricks
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Re: So...is 2000w max just a suggestion?

Post by BoulevardBricks »

Thanks for the reply, and fair enough. I am now rethinking my power needs and how to split up the power.

Thanks again!
Mike
:grin:
raysun
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Re: So...is 2000w max just a suggestion?

Post by raysun »

BoulevardBricks wrote: Thu Apr 08, 2021 10:32 am Thanks for the reply, and fair enough. I am now rethinking my power needs and how to split up the power.

Thanks again!
Mike
:grin:
The battery specs are not mentioned, but in general, charge controllers can be connected to the battery in parallel, each contributing a portion of the total charge. The maximum battery charging rate (in Amps) must be taken into consideration when figuring the total PV array/charge controller layout.

For example, a battery that can accept 120A of charging current maximum could be connected to two charge controllers: one generating 80A maximum (2000W PV @ 24V) and one generating 40A maximum (1000W @ 24V). If both charge controllers are FM80s, there is built in redundancy should one need to be taken out of service for any reason.

With enough PV, (4000W in two arrays) a pair of FM80s can deliver 160A @ 24V.
SandyP
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Re: So...is 2000w max just a suggestion?

Post by SandyP »

BoulevardBricks wrote: Wed Apr 07, 2021 6:38 pm ../..Any thoughts out there? And THANKS in advance!
As @raysun said overpanelling with an array set up for maximum output at noon and no upper limit set on the Flexmax will lead to the FMs failure.
Of course not everyone's solar array is set up optimally and rarely runs at STC therefore you may only see rated output for very short periods of time.
If you have more "less optimal days" than optimal ones you could consider an alternate array layout (virtual tracker array or "flat" array layout.

That being said, if you have the cash for another FM charge controller then that is the best way to go.
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raysun
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Re: So...is 2000w max just a suggestion?

Post by raysun »

SandyP wrote: Fri Apr 09, 2021 12:20 am
BoulevardBricks wrote: Wed Apr 07, 2021 6:38 pm ../..Any thoughts out there? And THANKS in advance!
As @raysun said overpanelling with an array set up for maximum output at noon and no upper limit set on the Flexmax will lead to the FMs failure.
Of course not everyone's solar array is set up optimally and rarely runs at STC therefore you may only see rated output for very short periods of time.
If you have more "less optimal days" than optimal ones you could consider an alternate array layout (virtual tracker array or "flat" array layout.

That being said, if you have the cash for another FM charge controller then that is the best way to go.
I live at 19°N and have my panels virtually flat. It seems to work well for our perpetually cloudy afternoon's. In the mornings, its not the most efficient layout, but I don't need that. In fact, I really can't deploy a PV array at the theoretical maximum (STC) for my FM80s because we regularly see events that cause solar irradiance exceed the STC 1kW/square meter. My arrays are 3.5kW, but I have seen peaks of 4.3kW during events that lasted long enough to make me nervous.

Every site's situation is different, but being conservative with ratings is universally applicable.
706jim
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Re: So...is 2000w max just a suggestion?

Post by 706jim »

You could try doing what I have set up. One bank of panels facing southeast and the other southwest. This will mitigate the overpanelling somewhat.
sbrownian
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Re: So...is 2000w max just a suggestion?

Post by sbrownian »

So, the FM80s aren't 'smart enough' to limit their current output to levels below component failure?
raysun
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Re: So...is 2000w max just a suggestion?

Post by raysun »

sbrownian wrote: Fri Apr 09, 2021 11:24 am So, the FM80s aren't 'smart enough' to limit their current output to levels below component failure?
It assumes "intelligent design" exists upstream.
sbrownian
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Re: So...is 2000w max just a suggestion?

Post by sbrownian »

Har.

Good one! :mrgreen:
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Smarter-Than.jpg
raysun
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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
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Re: So...is 2000w max just a suggestion?

Post by raysun »

I didn't say it was a good assumption necessarily.
SandyP
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Outback FM60 MPPT (max output lowered to 55amps)
12 x 2V Hoppecke GEL 612 Ah C24 - 24V System
Outback VFX3024 Inverter/Charger
Victron BMV-602s
Honda 5.5kW Genset
Location: Victoria, Australia

Re: So...is 2000w max just a suggestion?

Post by SandyP »

sbrownian wrote: Fri Apr 09, 2021 11:24 am So, the FM80s aren't 'smart enough' to limit their current output to levels below component failure?
Only if you leave the current limit set at the default.
Otherwise set it at say 70A and, other than brief excursions over this value, it will usually stick to this limit.
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sbrownian
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Posts: 503
Joined: Mon Nov 30, 2020 9:23 am
My RE system: GS8048 FM80 FNDC Mate3
4kw solar
7kw Kubota propane gen
Had 1200 Ahr FLA Locomotive batts
Just replaced with
2 x 300 Ah ReLion Lithium packs
MUCH more efficient!!
Location: Central Washington State

Re: So...is 2000w max just a suggestion?

Post by sbrownian »

SandyP wrote: Sat Apr 10, 2021 1:20 am
sbrownian wrote: Fri Apr 09, 2021 11:24 am So, the FM80s aren't 'smart enough' to limit their current output to levels below component failure?
Only if you leave the current limit set at the default.
Otherwise set it at say 70A and, other than brief excursions over this value, it will usually stick to this limit.
That behavior seems to be the norm with certain aspects of Outback technology.

The setpoints of certain parameters seem to be more of a 'suggestion' rather than a precision value.

Like the rectifier on the GS8048..

There is a spot to enter max DC current output, but it actually limits by means of setting the limit on the INPUT AC current, and some of the voltage set points don't always work as expected, either.
raysun
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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: So...is 2000w max just a suggestion?

Post by raysun »

sbrownian wrote: Sat Apr 10, 2021 10:11 am
SandyP wrote: Sat Apr 10, 2021 1:20 am
sbrownian wrote: Fri Apr 09, 2021 11:24 am So, the FM80s aren't 'smart enough' to limit their current output to levels below component failure?
Only if you leave the current limit set at the default.
Otherwise set it at say 70A and, other than brief excursions over this value, it will usually stick to this limit.
That behavior seems to be the norm with certain aspects of Outback technology.

The setpoints of certain parameters seem to be more of a 'suggestion' rather than a precision value.

Like the rectifier on the GS8048..

There is a spot to enter max DC current output, but it actually limits by means of setting the limit on the INPUT AC current, and some of the voltage set points don't always work as expected, either.
I always like to leave a sensible "operating margin" with any equipment. We rarely run our vehicle engines at "red line", why would we think its practical to do so for power electronics?

I like leaving a 20% margin below maximum ratings and it might come as absolutely no suprise that I never see operational or failure issues.
sbrownian
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Posts: 503
Joined: Mon Nov 30, 2020 9:23 am
My RE system: GS8048 FM80 FNDC Mate3
4kw solar
7kw Kubota propane gen
Had 1200 Ahr FLA Locomotive batts
Just replaced with
2 x 300 Ah ReLion Lithium packs
MUCH more efficient!!
Location: Central Washington State

Re: So...is 2000w max just a suggestion?

Post by sbrownian »

Agreed.

We usually size the UPS systems such that they are carrying about 50% to 60% of full load, max.

Interestingly, the ten alternators at one project were rated for 40 years at 70 megawatts. The hydro turbines on each could output 90 MW of energy, so the management decided to run them at about 105 to 110% of the rated 70.. The English engineers who designed the whole banana, showed them the lifetime deration curve, and it predicted about 17.5 years before things might go "bang."

Yep, they were right. Hit it within a MONTH...
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