Flexnet DC not reading correct current draw/charge

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coolness
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Flexnet DC not reading correct current draw/charge

Post by coolness » Sun Mar 17, 2019 10:37 pm

Is there a way to calibrate the shunt amp readings as they seem to be way off spec they don't even agree with my charge controllers output current and when i'm drawing lots of power from my system about 4 Kw the inaccuracy increases

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Re: Flexnet DC not reading correct current draw/charge

Post by raysun » Sun Mar 17, 2019 10:52 pm

You might want to start with a mechanical calibration and confirm all the connections are torqued to specification (not too loose, nor too tight.) Look for any corrosion, even minor dulling of the terminals, washers, nut faces, etc. Clean and dress as needed.

The shunts are 1000:1 ratio. After confirming all connections are of proper integrity, measure with an accurate digital volt meter at all the test points to make sure the voltage drops are within secification.

coolness
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Re: Flexnet DC not reading correct current draw/charge

Post by coolness » Sun Mar 31, 2019 10:56 am

So yet another faulty flexnet dc I wonder if Outback power even calibrates them anymore and what's the best way to calibrate the shunts

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Re: Flexnet DC not reading correct current draw/charge

Post by raysun » Sun Mar 31, 2019 11:23 am

What leads to the conclusion of a faulty FNDC?

The install and operators manuals have a defined set of test points. Have measurements been made and recorded at the TPs? What were the results?

The shunts themselves are pretty monolithic, and calibrated at the factory. They have better tools for that than we do, so it's best to assume the shunts do not need calibration. A simple sanity check is to take voltage (in the very low mV range, so be sure the test meter is very accurate +- 0.0001 at worst), and current (again, measurement accuracy and linearity is critical), to observe how the two correlate.

If you suspect a shunt, the most practical approach is to replace it.

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Re: Flexnet DC not reading correct current draw/charge

Post by Kurt Lundquist » Mon Apr 01, 2019 8:23 am

1. It is important to wire the shunt sense wires to the little screws on the side of the shunt. If you connect the sense wires to the big bolts on the top you will not get a proper reading.

2. Shunts are ~80% duty cycle rated devices. If you are exceeding 400A on a 500A rated shunt the reading can be off. If you exceed 500A for long enough the shunt can get out of calibration.

3. Shunt sense wires need to be twisted pair and should be kept away from other power conductors.

-Kurt
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Re: Flexnet DC not reading correct current draw/charge

Post by JRHill » Mon Apr 01, 2019 6:53 pm

Kurt Lundquist wrote:Shunt sense wires need to be twisted pair and should be kept away from other power conductors.
I believe this is a really important point. With all the emphasis people sometimes put into dressing things for a super clean install, these sense lines at 1000:1 should get special care and be away from other conductors carrying amperage and other potential interference and not be in a conduit with other wiring. Always maintain the twist rate and hopefully the sense lines to the shunts are as short as possible.

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Re: Flexnet DC not reading correct current draw/charge

Post by Mike Curran » Tue Apr 02, 2019 9:05 am

I agree but it's kinda hard to get this perfect considering the sense wires are located in direct proximity to the high current wires. (My FNDC seems to work okay, btw.)
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Re: Flexnet DC not reading correct current draw/charge

Post by raysun » Tue Apr 02, 2019 9:13 am

Sensitive circuits can be protected from errors caused by induced voltages/currents by shielding or cancellation. Twisted pair conductors help with the latter.

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Re: Flexnet DC not reading correct current draw/charge

Post by Kurt Lundquist » Tue Apr 02, 2019 9:17 am

Mike,

I don't want to hijack this thread but it looks like you have a green/white wire on one side of the shunt and a black/white on the other side. That solid green looks like it might be double lugged with the black/white wire. Solid black appears to go off towards the positive bus plate. What is going on there?

-Kurt

Back on topic:

Your right the shunt sense wires connect right next to the DC power conductors. My point was more that if you have a shunt 15' away at the battery bank you shouldn't run the shunt sense wires via the battery conductor conduit. Also if you have AC wires running through ungrounded conduit you wouldn't want your wires inside or tied to the outside of the conduit.
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Mike Curran
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Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback:
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- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Flexnet DC not reading correct current draw/charge

Post by Mike Curran » Tue Apr 02, 2019 9:32 am

Kurt Lundquist wrote:I don't want to hijack this thread but it looks like you have a green/white wire on one side of the shunt and a black/white on the other side. That solid green looks like it might be double lugged with the black/white wire. Solid black appears to go off towards the positive bus plate. What is going on there?
Kurt - The black wire is going to my main battery breakers to sense positive battery voltage. The black/white wire is the negative voltage sense wire. I wired it this way because my battery is split into 2 battery boxes with the negative lead coming from one and the positive lead from the other, thus no possibility of running a twisted pair for voltage sensing. And yes, that black wire is double-lugged with the green current sensing wire. Is that a cause for concern?
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Re: Flexnet DC not reading correct current draw/charge

Post by JRHill » Tue Apr 02, 2019 11:25 am

To reiterate, "as short as possible." You have some slack twisted pair in which the extra is twisted again. If it was me dressing it in*, I'd use the extra wire to cross other conductors at a right angle with as much space as possible. And you could keep the twist tighter right up to the junction.

* But really, if things were this tight I'd find some 18-20ga Beldin cable, foil wrapped with a grounded drain line. It may seem anal.... But when people say they are getting divergence from what is expected then the easiest stuff to fix is first on the list. I always wear my foil hat while pondering this stuff. Joking aside, my shunts are spot on. I have a Fluke AC/DC clamp on and I think the shunts are more accurate than the tool. But ya have to take a clamp on with a grain of salt anyway.

coolness
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Re: Flexnet DC not reading correct current draw/charge

Post by coolness » Wed Sep 11, 2019 8:58 pm

I'm a bit late on the reply as it turns out shunt B was incorrectly calibrated and now it reads the correct values and it also corrected the SOC decreasing during float also

raysun
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Hyundai 355 watt panels (6 - 3 strings @ 2 series)

Re: Flexnet DC not reading correct current draw/charge

Post by raysun » Wed Sep 11, 2019 9:04 pm

coolness wrote:
Wed Sep 11, 2019 8:58 pm
I'm a bit late on the reply as it turns out shunt B was incorrectly calibrated and now it reads the correct values and it also corrected the SOC decreasing during float also
How was calibration corrected?

JRHill
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My RE system: -House: FM 80, VFX 3648, FlexnetDC, FlexWare xformer, Mate 3 / Hub, WattPlot/, 2925w SunTech 195, Trojan L16RE-B Batteries. Backup 1: Honda EU7000is w/2 wire auto start via FM80 aux, backup 2: 11kw Miller Bobcat;
-Well: Grundfos 11-SQF-2 pump, controller & AC switch (CU200, IO101), Tristar 45 Controller, 780w SunTech 195, Trojan golf cart batteries.
-All running since July '11 with various upgrades and workarounds.
Location: South central WA
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Re: Flexnet DC not reading correct current draw/charge

Post by JRHill » Thu Sep 12, 2019 11:05 am

raysun wrote:
Wed Sep 11, 2019 9:04 pm
coolness wrote:
Wed Sep 11, 2019 8:58 pm
I'm a bit late on the reply as it turns out shunt B was incorrectly calibrated and now it reads the correct values and it also corrected the SOC decreasing during float also
How was calibration corrected?
If the shunt reads low I take my pocket knife and carve off some material on the struts between the lugs. If high, I use increasing sizes of number bits bridging the lugs until its spot on.

JUST KIDDING. Sorry, I couldn't help it...

Seriously, I don't think there is a way to easily calibrate the shunts to actual in the field. I think Kurt's earlier caution about amperage flow and the effects of heat are more realistic. But my gosh, 400 amps? A spike wouldn't do that - it would have to be a continuous, very heavy load to heat the struts between the lugs. I can't imagine that but I don't doubt it happens some place, somewhere. And I would hope that the manufacturers QC is more precise and verified than the average multimeter. Even those multimeters on the high end unless verified to a standard are suspect. If not verified, who is to say which measuring device is off true? The earlier post was noticing a BIG divergence and to me, more than something other than an outside contributor.

coolness
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My RE system: Midnite classic 200 thermodyne 500 Watt wind turbine Flexmax 80 X 3 Mate 3 flexnet DC 1 Kw fixed solar array and 2X 2.6 KW sun tracking SOLAR arrays controlled with 2X darkstar V2 blutooth tracking systems coupled with Firgelli optic pulse feedback actuators powerd by 15 ah deep cycke AGM battery and Victron 75/15 MPPT bluetooth charge controller 450 AH 24V Trojan T105 Battery bank 3X 500 A shunts Victron Quattro 8KVA inverter/charger 4KW inverter Generator
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Re: Flexnet DC not reading correct current draw/charge

Post by coolness » Fri Sep 13, 2019 10:49 am

I used my FM 80's as a reference and and my maths skills and finally getting a clear sunny day helped too.
In my earlier post I stated a 4 Kw draw not 400 Amps my inverter can do 340 A continuous and 670 A for 30 ms 16,000 W 24V system

JRHill
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My RE system: -House: FM 80, VFX 3648, FlexnetDC, FlexWare xformer, Mate 3 / Hub, WattPlot/, 2925w SunTech 195, Trojan L16RE-B Batteries. Backup 1: Honda EU7000is w/2 wire auto start via FM80 aux, backup 2: 11kw Miller Bobcat;
-Well: Grundfos 11-SQF-2 pump, controller & AC switch (CU200, IO101), Tristar 45 Controller, 780w SunTech 195, Trojan golf cart batteries.
-All running since July '11 with various upgrades and workarounds.
Location: South central WA
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Re: Flexnet DC not reading correct current draw/charge

Post by JRHill » Sat Sep 14, 2019 11:58 am

Dang, I can't find it to forward. It was a shunt and module that gave a bunch on info, wireless/remote or USB from the batteries. It didn't tie into OB but gave everything you need to know for calculations. I've used it for years 'cause my well system is separate. But I don't have to access the pit to see stats. The devices are out there.... Chinese of course. Regardless of the weather it works. The kit was so cheap I bought a spare. The original has been working for years.

coolness
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My RE system: Midnite classic 200 thermodyne 500 Watt wind turbine Flexmax 80 X 3 Mate 3 flexnet DC 1 Kw fixed solar array and 2X 2.6 KW sun tracking SOLAR arrays controlled with 2X darkstar V2 blutooth tracking systems coupled with Firgelli optic pulse feedback actuators powerd by 15 ah deep cycke AGM battery and Victron 75/15 MPPT bluetooth charge controller 450 AH 24V Trojan T105 Battery bank 3X 500 A shunts Victron Quattro 8KVA inverter/charger 4KW inverter Generator
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Re: Flexnet DC not reading correct current draw/charge

Post by coolness » Sat Sep 14, 2019 1:33 pm

I actually have a separate shunt and display or a master shunt i should call it it's how i discovered something was off on my system

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