New FNDC data mismatch with old equipment

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New FNDC data mismatch with old equipment

Postby Mike Curran on Thu May 12, 2016 9:52 am

Hello - I just installed an FNDC to help me keep on top of my 9 year old batteries, which I fear I've been neglecting. My problem is that the current and voltage readings I'm getting from it don't match those from my MX60 charge controller. I'm grid-tied (batteries used for backup only) so there's no other draws from my battery to affect the current reading.

Here's an example of the amperage discrepancy, (it varies with solar input): CC 33 amps, DC NOW 7 amps
The voltage discrepancy is fairly constant: CC 28.0 volts, DC NOW , 28.9 volts (almost always around 0.7 volts higher). I've verified the CC battery voltage with a DVM across the battery terminals, so I'm pretty sure it's right.

Btw, these same discrepancies exist on those occasions when I'm charging from the grid thru my inverter/chargers (I have to convert indicated 120 VAC watts to equivalent 24V DC amps to make the comparison).

I've seen a few posts regarding inconsistent meter readings (e.g., viewtopic.php?f=28&t=4133#p25245) and most seem to indicate a wiring problem around the shunt, but I've checked and rechecked my wiring and can't find anything wrong. I've attached a photo of the internal wiring of my PSDC, hoping it'll help someone else see what I'm missing:

2016-05-12 12.43.19-1.jpg


Thanks in advance!
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: New FNDC data mismatch with old equipment

Postby Mike Curran on Fri May 13, 2016 9:08 am

Here's a screenshot from my Winverter software that illustrates the problem. On the lower left is my MX60 data showing battery volts at 28.6 and charging at 39 amps (1115 watts). To the right of that is the FNDC data showing battery volts at 29.3 and charging at 4.3 (that's 4 POINT 3) amps (126 watts). This screenshot was taken when I had pretty good sunlight. What's interesting is at lower PV output, while the MX60 still shows it's charging the battery (and my inverter is in "pass-thru" grid-tied mode so no contribution from the battery), the FNDC charging amps goes negative. Always seems to be about a 20 amp difference.

I'm going to swap the shunt connection leads today to see If that makes a difference but don't see how it would affect the voltage discrepancy.

WNV screenshot.jpg
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: New FNDC data mismatch with old equipment

Postby larrywa on Fri May 13, 2016 9:44 am

Can you not just calibrate the FNDC voltage using the same meter?

I have calibrated my voltages in the Mate3, and usually show a slightly lower voltage at my common bars due to voltage drop between the CC's and the common bars. I increased my conductor sizes from #8 to #6 awg.cu. also, as the OB supplied conductors were too light to pass code going out of a panel through pipe.

Another thing, that may not apply to you is with two CC's and one split bus PV combiner the negative bus connections had to be split or the shunts shared currents and never read correctly.

I wasn't real impressed with the configuration of the FNDC.I mention this in case it jogs something there with your hookup.
The most important measurement is the battery currents, in and out. The battery current is just a summation of the other three shunts resulting in the net difference. This means the error is the sum of the shunts mismatch in currents,
The other measurements are real nice but why when the CCs all report individually would you meter them all again separately, but only meter the combined Inverter currents as one measurement. Then the battery current is mathematically derived from those three.

Perhaps your wiring doesn't agree with that configuration, above. Wiring it, from my experiences in life, it would not have been wired that way.
larrywa
Forum Guru
 
Posts: 351
Joined: Thu Jun 25, 2015 11:25 am
My RE system: FlexPower Two
2 x GVFX3648s,
2 x FM80s,
FNDC w/3 shunts,
Mate3 v3.015.005 (works excellent!)
Hub 10.3,
PV:1000W east@45, 600W west@45, 2400W south@19 deg.
Battery:48v @ 130Ahr Crown batteries, deep cycle <$380 for 6.25kWh

ISY994i HA, Insteon, X10, Philips Hue, MiLight bulbs & RGBW strips
WebControl 8 as weather station stuffing
ISY994 variables via REST interface

Raspberry Pi3 x 2, Pi1 B+

Re: New FNDC data mismatch with old equipment

Postby Mike Curran on Fri May 13, 2016 9:53 am

Larry - I'm using a Mate and far as I know, the FNDC voltage reading isn't adjustable. When I take a reading across the battery terminals with a digital voltmeter it exactly matches what the MX60 is telling me. Also, I only have one shunt and the way it's wired all battery current must pass through it.

One other thing I've just noticed (I just added the FNDC Winverter software module today so it's a lot easier to see everything at once) is that when my inverters are passing through the same watts (in = out) the MX60 charge amps pretty closely match the FNDC indication. But any other conditions (buying or selling) I get the mismatch.

Thanks for your comments about the voltage measurement not being critical. But I would've thought the FNDC would be the best source for this and so should be pretty accurate(?).
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: New FNDC data mismatch with old equipment

Postby larrywa on Fri May 13, 2016 10:15 am

LOL. I didn't make any comments about voltage not being critical. Current? yes. A single shunt application would not have the same problems as mine with three shunts.

This sounds like you may have your shunt wired backwards.

If you feed the CC current into the shunt from the side not connected to the FDNC common then your voltage measurement will include the voltage drop across the shunt making it higher or lower by a small amount determined by the current flowing through it.
The current may read reversed polarity and I don't know what the metering circuit will show.

IIRC the FNDC shares a common voltage wire and shunts. Without research I am not sure how it is configured anymore.

My understanding is that the FDNC metering resolution is very low and attempting to use it at only a few percent of it's FS rating only gets lower resolution.

I suggest a stand back approach and making a schematic diagram of what you have installed, marking +/- across every component. By the time you are done, usually something clicks and it become clear, if you have made some logical wiring error.
larrywa
Forum Guru
 
Posts: 351
Joined: Thu Jun 25, 2015 11:25 am
My RE system: FlexPower Two
2 x GVFX3648s,
2 x FM80s,
FNDC w/3 shunts,
Mate3 v3.015.005 (works excellent!)
Hub 10.3,
PV:1000W east@45, 600W west@45, 2400W south@19 deg.
Battery:48v @ 130Ahr Crown batteries, deep cycle <$380 for 6.25kWh

ISY994i HA, Insteon, X10, Philips Hue, MiLight bulbs & RGBW strips
WebControl 8 as weather station stuffing
ISY994 variables via REST interface

Raspberry Pi3 x 2, Pi1 B+

Re: New FNDC data mismatch with old equipment

Postby Mike Curran on Fri May 13, 2016 11:44 am

Thanks for your responses. I was interpreting your comment "The most important measurement is the battery currents, in and out" to mean the voltage measurement wasn't critical. Sorry if that's not what you meant to imply.

Yeah, I sorta thought I had the shunt sensing wires backwards until I saw the CC and FNDC current readings matched under certain conditions (when the inverter/chargers are in "pass-thru" mode, no sell, no buy, no support). Now I'm not so sure. I'm sure there's a clue in there somewhere... I do have a schematic but I haven't added the sensing wires for the FNDC yet. Your suggestion is appreciated, if I keep staring at this stuff something's gonna pop out at me.
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: New FNDC data mismatch with old equipment

Postby Mike Curran on Fri May 13, 2016 1:49 pm

Well I think everything is wired right (without changing anything) because amps through the shunt match MX60 indicated amps when there's no buying, selling or "support". I guess I underestimated the effect selling and support have - e.g., the DC current required to sell 120 watts AC is a lot more than 5 amps DC (120 watts divided my battery voltage, 24VDC). And so all this time I thought my battery was charging (high PV watts and amps, indicated by MX60), when I was selling the watts sold were taking a lot more DC current than my estimates from the AC/inverter side of the equation.

I know, if you're reading this, you may be thinking "blah, blah, blah". But I hope my experience may help someone else. And if you're reading this and you think I've missed the boat entirely, please respond.
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: New FNDC data mismatch with old equipment

Postby larrywa on Fri May 13, 2016 5:38 pm

We never think "blah, blah, blah". ...:) Sorry just a quote from a kids movie. :lol:

But that's the way it happpens. You throw it out there and kick it around. Half the time on forums, I find just organising my thoughts, to type it, gives me the brainstorm answer.

Just as a rough figures my system eats about 200-300 Watts of power when running medium load...say 1000 Watts PV. So about 700 Watt ac output.
...and about 400-500 Watts of power when outputting it's max at about 2800 Watts PV. About 2300-2400 Watts ac output.

CC units seem fairly efficient. Batteries waste about 20-40% (58 volts charge = 48 volts discharge), and inverters run about 75 - 85% effiicient.
They want you beleive that inverters are better efficiency before you buy, but feel the heat out of the side once, and compare it with a small fan heater....300-500 Watts? It keeps my utility room dry though. :grin:
larrywa
Forum Guru
 
Posts: 351
Joined: Thu Jun 25, 2015 11:25 am
My RE system: FlexPower Two
2 x GVFX3648s,
2 x FM80s,
FNDC w/3 shunts,
Mate3 v3.015.005 (works excellent!)
Hub 10.3,
PV:1000W east@45, 600W west@45, 2400W south@19 deg.
Battery:48v @ 130Ahr Crown batteries, deep cycle <$380 for 6.25kWh

ISY994i HA, Insteon, X10, Philips Hue, MiLight bulbs & RGBW strips
WebControl 8 as weather station stuffing
ISY994 variables via REST interface

Raspberry Pi3 x 2, Pi1 B+

Re: New FNDC data mismatch with old equipment

Postby Mike Curran on Fri May 13, 2016 6:06 pm

Thanks!!!
Mike Curran
Forum Guru
 
Posts: 470
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.


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