Should I buy a FLEXnet DC?

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pioneerMan
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Should I buy a FLEXnet DC?

Post by pioneerMan »

What is your opinion of this device? Does it really help provide life changing information about the battery bank that isn't already provided on the screens of the Mate3s? How much does one roughly cost?

Thank you!
raysun
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Re: Should I buy a FLEXnet DC?

Post by raysun »

Yes, the FlexNet DC enables valuable battery monitoring that the Mate3s cannot provide. It is a highly integrated component in the Outback ecosystem that tracks current flow into and out of the battery, dynamically calculates and displays battery state of charge, and with the Mate, supports advanced charger control for Outback inverters and charge controllers.

Deriving battery state of charge from voltage alone is a tricky proposition with lead acid batteries, and borderline impossible with lithium. A "current counting" monitor is the only practical tool for either. The FNDC is such a device. It, and the Victron BMV-7xx/SmartShunt series, are the two top devices for this purpose.

The FNDC requires a Mate. In order to monitor and control OB inverters and chargers, a Hub is needed (not listed in your profile.) If Mate and Hub are part of the system, then the FNDC is worth its relatively high cost, IMO. About $400 from a reputable dealer: https://www.solar-electric.com/oupoflsymo.html

The Victron BMV-712 is another consideration. While it doesn't integrate into the Outback ecosystem, it does provide high quality battery monitoring. As a stand-alone unit, it can be used with any battery and equipment combination. It's about $200 from a reputable dealer: https://www.solar-electric.com/victron- ... nitor.html

The BMV -7xx series is also highly imitated by the Chinese clone manufacturers. Cheap copies of the basic BMV-700 is available for under $100 on Amazon. I don't recommend any of them, but if it's a choice between nothing, and a clone, they are better than nothing.
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Re: Should I buy a FLEXnet DC?

Post by fcwlp »

raysun wrote: Fri Oct 21, 2022 2:04 pm The FNDC requires a Mate. In order to monitor and control OB inverters and chargers, a Hub is needed (not listed in your profile.)
You will also need at least one shunt connected to the battery lead and preferably a second one for the CC(s) input. If you add the second shunt you will need some additional hardware as shown in the attached PDF. One of my very remote ranches recently changed ownership and the new owner wanted monitoring capability as his cowboys will not be there full time. The design shown below is what I built and installed along with a Hub10, FNDC, Mate3s and a Victron positive bus bar. Mate3s is connected to OpticsRE through a TP-Link range extender and Starlink. Original plan was to put in a Radian with GSLC, to replace 20-year-old Xantrex, which would not have required the custom setup but that has been deferred for a couple of years.
Shunt Design.pdf
(44.86 KiB) Downloaded 22 times
raysun
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Re: Should I buy a FLEXnet DC?

Post by raysun »

fcwlp wrote: Sat Oct 22, 2022 8:21 am
You will also need at least one shunt connected to the battery lead and preferably a second one for the CC(s) input.
Good point. The FNDC doesn't come with the needed shunt(s).
The Victron BMV-7xx does come with a shunt.
pioneerMan
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Trimetric 2030A battery monitor
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Re: Should I buy a FLEXnet DC?

Post by pioneerMan »

fcwlp wrote: Sat Oct 22, 2022 8:21 am If you add the second shunt you will need some additional hardware as shown in the attached PDF.
Is this extra hardware you're referring to a "battery negative plate"?
raysun
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Re: Should I buy a FLEXnet DC?

Post by raysun »

pioneerMan wrote: Sat Nov 12, 2022 7:22 pm
fcwlp wrote: Sat Oct 22, 2022 8:21 am If you add the second shunt you will need some additional hardware as shown in the attached PDF.
Is this extra hardware you're referring to a "battery negative plate"?
A bus plate like the one illustrated gives a solid "landing point" for the Battery Negative cable, and the "Battery" end of the shunts.
20221111_115626.jpg
Battery Bus Plate with three shunts attached.
Lower middle Shunt A: Inverters
Upper left Shunt B: Charge Controllers
Upper Right Shunt C: External AC Battery Charger
Note: The "Battery" end of Shunt C has the Battery Negative cable attached via the 5/8" bolt.
pioneerMan
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My RE system: 12 volt system
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Trimetric 2030A battery monitor
Mate 3s
Dual fuel 4500 watt AC generator
Location: Northern Utah

Re: Should I buy a FLEXnet DC?

Post by pioneerMan »

raysun wrote: Sat Nov 12, 2022 8:25 pm A bus plate like the one illustrated gives a solid "landing point" for the Battery Negative cable, and the "Battery" end of the shunts.
Solar-Electric.com, which is the site Outback suggested I buy the flexNET DC from, apparently does not sell bus plates. Where do you recommend I buy one from? Because I think I'll be buying 3 shunts as well:

1. Inverter
2. Charge controllers
3. Wind generator (if I can eventually get that thing repaired)
raysun
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
2 Midnite Solar MNPV6 combiners w/20A DC disconnects.
Honda EU7000is gas fuel generator
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Re: Should I buy a FLEXnet DC?

Post by raysun »

fcwlp
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I install and maintain grid-tied and off-grid systems in my area and consult on solar system design/operation.
Location: 80 miles NE of Phoenix at 5500'

Re: Should I buy a FLEXnet DC?

Post by fcwlp »

raysun wrote: Sat Nov 12, 2022 8:25 pm Battery Bus Plate with three shunts attached.
Lower middle Shunt A: Inverters
Upper left Shunt B: Charge Controllers
Upper Right Shunt C: External AC Battery Charger
Note: The "Battery" end of Shunt C has the Battery Negative cable attached via the 5/8" bolt.
Thanks raysun for picking up the thread, the benefits of multiple time zones for the forum. That should be a 3/8" bolt which takes a 9/16" socket/wrench.
raysun
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2 Midnite Solar MNPV6 combiners w/20A DC disconnects.
Honda EU7000is gas fuel generator
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Re: Should I buy a FLEXnet DC?

Post by raysun »

fcwlp wrote: Sun Nov 13, 2022 8:01 am
raysun wrote: Sat Nov 12, 2022 8:25 pm Battery Bus Plate with three shunts attached.
Lower middle Shunt A: Inverters
Upper left Shunt B: Charge Controllers
Upper Right Shunt C: External AC Battery Charger
Note: The "Battery" end of Shunt C has the Battery Negative cable attached via the 5/8" bolt.
Thanks raysun for picking up the thread, the benefits of multiple time zones for the forum. That should be a 3/8" bolt which takes a 9/16" socket/wrench.
Yes, correct on the bolt spec.
pioneerMan
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My RE system: 12 volt system
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Outback VFX2812 inverter and two FLEXmax 60 inverters
Trimetric 2030A battery monitor
Mate 3s
Dual fuel 4500 watt AC generator
Location: Northern Utah

Re: Should I buy a FLEXnet DC?

Post by pioneerMan »

raysun wrote: Sat Nov 12, 2022 8:25 pm A bus plate like the one illustrated gives a solid "landing point" for the Battery Negative cable, and the "Battery" end of the shunts.
I assume that all 3 shuts that I buy will fit onto this plate AND mount inside the FW250 (DC side of inverter)?
raysun
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Honda EU7000is gas fuel generator
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Re: Should I buy a FLEXnet DC?

Post by raysun »

pioneerMan wrote: Sun Nov 27, 2022 8:16 pm
raysun wrote: Sat Nov 12, 2022 8:25 pm A bus plate like the one illustrated gives a solid "landing point" for the Battery Negative cable, and the "Battery" end of the shunts.
I assume that all 3 shuts that I buy will fit onto this plate AND mount inside the FW250 (DC side of inverter)?
That's exactly what's depicted in the photo above.
pioneerMan
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Trimetric 2030A battery monitor
Mate 3s
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Location: Northern Utah

Re: Should I buy a FLEXnet DC?

Post by pioneerMan »

raysun wrote: Sun Nov 27, 2022 8:26 pm That's exactly what's depicted in the photo above.
This is good news, because my current system has a black negative wire coming out of the inverter, going to a shunt used by the Tri-Metric, and then making it's way to the battery bank. Now that I know all 3 shunts can go into the FW250, that means I just need to purchase equal length cables going to from the inverter to the battery.

Thanks!
raysun
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Re: Should I buy a FLEXnet DC?

Post by raysun »

I just need to purchase equal length cables going to from the inverter to the battery.
Actually there is one, and only one, black cable from the battery bus bar, to the shunt bus plate. The gauge should be 0000 (4/0AWG).
Each shunts "Battery" end attaches directly to the bus plate.
(Study the picture above.)
The battery blocks to the battery bus bar must be equal length. They should be 4AWG.
That's it for the negative side of the battery circuit.
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Re: Should I buy a FLEXnet DC?

Post by pss »

I don't think I would invest in a Flexnet DC if I were using Li ion batteries and had a battery management system.
pioneerMan
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Trimetric 2030A battery monitor
Mate 3s
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Re: Should I buy a FLEXnet DC?

Post by pioneerMan »

pss wrote: Mon Nov 28, 2022 12:16 am I don't think I would invest in a Flexnet DC if I were using Li ion batteries and had a battery management system.
The Tri-Metric does not "talk" to the Outback system like the Flexnet DC does. And I need the ability to charge the batteries with the generator, using state of charge, instead of just voltage. Correct me if I'm wrong.
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Re: Should I buy a FLEXnet DC?

Post by provo »

pioneerMan wrote: Mon Nov 28, 2022 8:50 am
The Tri-Metric does not "talk" to the Outback system like the Flexnet DC does. And I need the ability to charge the batteries with the generator, using state of charge, instead of just voltage. Correct me if I'm wrong.
You're not wrong, and the FNDC would be a big help even with Li-ion batteries that had a BMS and a display of their own.
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Re: Should I buy a FLEXnet DC?

Post by raysun »

I find the FNDC quite useful. Relying on voltage alone for State of Charge in any battery under load is a tricky proposition. Relative to lead acid, interpolating SoC from voltage on a lithium battery is orders of magnitude trickier. Like lead acid, lithium terminal voltage varies with load (rate of discharge). Unlike lead acid, lithium terminal voltage varies much less with SoC (for a given load). TBH, I scarcely look at voltage.
Counting current, on the other hand, while not perfect, is much more rational for tracking SoC. That's what the FNDC does. Unfortunately, it's Peukert's Constant is fixed to lead acid, but at modest rates of discharge typical with most home systems, lines up pretty well. I use both the FNDC and a Victron BMV700 on my battery, the Victron being configured with Peukert's Constant for LiFePo4, and the two SoC readings agree closely. The FNDC typically reads low by 1%, but that's workable.

I don't use AGS, so don't know how well it works with SoC, but the typical charge profile for LiFePo4 is "Bulk until full". Voltage Start AGS seems to require a full Absorb cycle, which in the "Bulk until full" profile is essentially a termination voltage. Being able to cut off charging at some at some lower capacity while using AGS would be beneficial, IMO. Charging a battery to 80% SoC, for example, could be a fuel savings, as well as a battery cycle-life savings.

My battery gets fully charged via solar most days. The FNDC plays another role here. As LiFePo4 cells reach full capacity, their impedance rises dramatically, and current acceptance falls precipitously. If left to charge at the termination voltage, the charge current will drop to near zero, and the voltage across the battery cells will contribute to heating them. High heat is not healthy for the battery, so it's best to terminate charge ASAP after reaching full capacity. The method for charge termination with the OB gear is to set the Absorb Voltage to the termination voltage, and Absorb Time to 0.1H (6 minutes, the shortest possible. 0H cannot be used.) Without the FNDC, the battery will be held at the termination voltage for 6 minutes, not the end of the world, but we can do better. Using the Mate Auto Charge Termination Control, charging can be terminated at the target voltage (Absorb Voltage) in combination with a target charge current (FNDC Charged Return Amps) to give a more precise cutoff.

All commercial lithium batteries have a battery management system (BMS), but in most cases, they aren't useful for managing the battery. (Its a bit hyperbolic, but I liken relying on a BMS as being similar to relying on the air bag to tell you when to stop your car.) In most Chinese batteries, the BMS is a $5 part. It may cut off the battery at some low voltage, but generally doesn't do any true capacity control. Shutting down the battery is the "air bag" approach in any event. In some U.S. batteries, (I'm talking SimpliPhi), absolutely zero limiting, other than maximum current via a circuit breaker, is built into the BMS. All operating limits must be managed externally. I prefer this approach, because I know what I'm doing, but it could be a rude awakening for someone who doesn't. The FNDC becomes another tool in the operations management kit.
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