Need help calculating real world power - Frankenstien system

Discussion about the FM100, FM80, and FM60 Charge Controllers

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miahallen
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Need help calculating real world power - Frankenstien system

Post by miahallen » Fri Jun 03, 2016 5:20 am

I have a neighbor who has a huge (2000W+) 12V system which I have been trying to assist him with. The system was built piece by piece and it quite a monster at this point. I give you a brief breakdown:

6x Trojan L16RE-B 370AH + 2x Deka L16 370AH (eight 6V batteries total wired for 12V)
Outback Power
9x 100W 12V panels, each set of 3 running through identical Renology PWM CCs.
Flexmax80 Charge Controller with the following:
  • 3x 435W 18V nominal monocrystalline PV panels in series (54V nominal)
  • 2x 235W 30V nominal polycrystalline PV panels in series (60V nominal)
My question really then is, what voltage/current SHOULD I EXPECT to see on the input side of the Flexmax? Right now, I am seeing only 38-42V and up to about 23A. But it seems to me that it is a bit too low. I realize that ohms law is a PITA with two unequal power sources, and I'm asking for helps figuring out what I should expect because I don't know how the math works in this case. Thanks.

larrywa
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Re: Need help calculating real world power - Frankenstien sy

Post by larrywa » Fri Jun 03, 2016 6:02 pm

It's not really clear to me what the PV configuration is.

It sounds lie you have 9 x 100 W panels in series for a nominal 96 volts, in parallel with
3 x 18v panels for nominal of 54 v, in parallel with
2 x 30v panels for nominal of 60 v.

You will definitely waste power being that your MPP for each string would be at different voltages.


The FM80 can stand an input up to 150 vdc but with these mismatched strings you wouldn't be able to utilise that for less power loss in your wiring.

Usually PV panels are only either 30, 36, 60, or 72 cells making them nominally 12v or 24v for battery charging or direct inversion to grid-tie.

The idea would be to match the MPP voltage level for each panel style/string to get maximum power out of the group.
Your voltage found sounds reasonable, as a complete compromise, except the three banks of 100W 12v panels probably aren't carrying their capability as much as they should.

Current readings from each string would help you greatly to establish whether all panels are contributing properly.
I don't see the function of the three CC units unless they offer step up of voltage.

miahallen
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Re: Need help calculating real world power - Frankenstien sy

Post by miahallen » Fri Jun 03, 2016 9:22 pm

The 100W panels and their PWM CCs I belive are irrelevant to my question as they are totally independent from the 5 larger panels which are running off the Flexmax.

So there are two strings running in parallel off the Flexmax:
  • 3x 435W 18V nominal monocrystalline PV panels in series (54V nominal)
  • 2x 235W 30V nominal polycrystalline PV panels in series (60V nominal)

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Re: Need help calculating real world power - Frankenstien sy

Post by blackswan555 » Sat Jun 04, 2016 3:29 am

In an ideal world you would have 1000w of insolation hitting panels Square on @ 25c ( STC rating) charging a bank in early absorb ( bank wants as much current as you have) in that case I would expect to see 1775 w at around 50v giving about 35 amps in, This would translate to 147.7 amps at 12v,(1775w /12v) As the controller will only output 80amps no matter how much you put in, What you are seeing is it maxed out, 23A x 40v = 960w 960w / 12v = 80amps output @12v,

Tim

ps you are wasting half you panels,
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.

miahallen
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Re: Need help calculating real world power - Frankenstien sy

Post by miahallen » Tue Jun 07, 2016 11:08 am

Thanks Tim....and yes, I know he is wasting all kinds of power running this monster at 12V. I've been telling him for years, but he soldiers on unwilling to let go of the investment hes made in the outback inverter & 12V lights & fans.

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