New red light coming on - Battery Low

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stevetull
Forum Virtuoso
Posts: 91
Joined: Tue Feb 24, 2015 6:40 am
My RE system: FlexPower Two:
2 VFX3648, X240, 2 FM80, Mate 3s, FnDC, Hub 10
One array facing south at 30 degree tilt
One array facing southwest at 10 degree tilt
Total of 8kW
16 Fullriver AGM DC400-6 = 830Ah @ 48v
OpticRE: Paige cabin
Location: Near Bastrop Texas
Contact:

New red light coming on - Battery Low

Post by stevetull »

Below the AC wiring block on each of my two VFX3648s there is a series of LEDs that are supposed to indicate the SOC of the battery. I'm now getting the red LED staying on, the manual says that means our battery bank SOC is 46 volts or less, however my FNDC is telling my mate that my state of charge is 98%. 46 volts divided by 4 on my 48 volt system is 11.5 volts which is 0% SOC. That would be bad.

I know that the FNDC will only tell me what I told it to be true when I installed it, so now I am second guessing myself. I wouldn't want to screw around and damage our new battery bank.

I'm tempted to disconnect the battery bank from the system, let the batteries rest a while and then throw a volt meter on it and see where we are. Is this the proper procedure to get an accurate reading? As they are Full River sealed AGMs I cannot check the specific gravity.

The way I initially set the system up, I tested the 16 batteries when they were delivered right before I installed them. Eight of them read 6.34v, three read 6.35v and five read 6.36v. I was told that there was no need to charge them further as AGMs have a long shelf life and to consider them at 100% SOC.

Edit:
So I couldn't wait. I disconnected the battery bank and tested each string of batteries with the voltmeter. I get 6.01 volts. I've hooked them back up and started a bulk charge through the inverters. Tomorrow after a good charge and a resting period I'll check them with the voltmeter again.

Here's where I think I went wrong. When programming the system, I told the FNDC that the batteries were 100% SOC, when in reality they were more like 75%. So for the 10 weeks since we started using them we've never given them a proper charge, since I told the system they're full at 75%.

We've been running in HBX mode everyday, we'd set the grid disconnect threshold at 92% SOC and the connect at 90%. That means that most sunny or partly sunny days we'll drop grid use by 10:30am and remain off-grid into the evening, connecting automatically to the grid around 7pm or so. During the daylight hours we run all we want, including 120v loads in the cabinet shop. All the while the plan was the spare our shiny new battery bank by only drawing it down to 90% SOC. Oh well...

Thank you for any insight please.

-Steve

Thank you!

-Steve
raysun
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Posts: 4624
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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

I may be wrong on this, the FNDC monitors the state of charge, but does not control it. The charge controllers work independently from the FNDC.

The widely used practice with a misreading FNDC is to fully charge the battery, then unplug the FNDC from the hub, wait a moment, then plug it back in. It will wake up and assume the battery is at 100% SOC.

How to tell if the battery is fully charged. AGMs make it a bit more difficult, but monitoring the charge cycle is helpful. During the Absorb phase, the charge current will drop to something between 1% - 3% of the rated amp hour capacity, and that should indicate 100% SOC.

Voltage measurement after the battery has reached 100% SOC, and rested for 24 hours can give a additional sanity check, but don't rely on voltage alone.
stevetull
Forum Virtuoso
Posts: 91
Joined: Tue Feb 24, 2015 6:40 am
My RE system: FlexPower Two:
2 VFX3648, X240, 2 FM80, Mate 3s, FnDC, Hub 10
One array facing south at 30 degree tilt
One array facing southwest at 10 degree tilt
Total of 8kW
16 Fullriver AGM DC400-6 = 830Ah @ 48v
OpticRE: Paige cabin
Location: Near Bastrop Texas
Contact:

Re: New red light coming on - Battery Low

Post by stevetull »

Thank you raysun. I've given the batteries a good charge and reset the FNDC. Today I disconnected charging from the charge controllers so that I could draw the battery bank down to what I believe is about 75%. Tomorrow morning I'll use the inverters to give a good bulk charge and then an absorption charge and monitor the current to see how long it takes. I now have it set for 4 hours, up from the 1 hour absorption phase I had previously. I've already noticed an increase in performance due to the batteries actually receiving closer to a full charge. That's encouraging!
I have so many questions I'm still seeking answers for around this subject I don't even know where to start. I'll ask the most (seemingly) simple.
Can you check open-circuit voltage on the battery bank without disconnecting battery cables? Provided my system is off and I have no loads?

Thank you raysun.

-Steve
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

Do you have a battery disconnect between your bank and the inverter? If so, throw the breaker and you will be sure there is no load. Then you can measure the no-load voltage on the entire bank. You can measure across each battery within the bank as well, without disconnecting the connections between them. At-rest voltage measurements will be most meaningful if the batteries at left idle for 24 hours.
stevetull
Forum Virtuoso
Posts: 91
Joined: Tue Feb 24, 2015 6:40 am
My RE system: FlexPower Two:
2 VFX3648, X240, 2 FM80, Mate 3s, FnDC, Hub 10
One array facing south at 30 degree tilt
One array facing southwest at 10 degree tilt
Total of 8kW
16 Fullriver AGM DC400-6 = 830Ah @ 48v
OpticRE: Paige cabin
Location: Near Bastrop Texas
Contact:

Re: New red light coming on - Battery Low

Post by stevetull »

I have the two 175 amp DC breakers, each feed an inverter. The positive battery bank cable feed these. However I don't have another external battery bank disconnect or fuse. Would this be sufficient?

-Steve
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

Yes. The 175 amp breakers do the job of disconnecting the battery from the load(s).
stevetull
Forum Virtuoso
Posts: 91
Joined: Tue Feb 24, 2015 6:40 am
My RE system: FlexPower Two:
2 VFX3648, X240, 2 FM80, Mate 3s, FnDC, Hub 10
One array facing south at 30 degree tilt
One array facing southwest at 10 degree tilt
Total of 8kW
16 Fullriver AGM DC400-6 = 830Ah @ 48v
OpticRE: Paige cabin
Location: Near Bastrop Texas
Contact:

Re: New red light coming on - Battery Low

Post by stevetull »

So I started a bulk 4 hour charge at 4:30 this morning and by 8:30 I'm at 100%. It's only taken less than 60 minutes of absorb charge to reach the recommended 1% of the battery bank amp hour rating. I'm assuming I total my battery bank at sixteen 415 ah batteries equals 830ah total. That means I watch the amps until it reaches about 8.3 amps going in, does that sound correct? Full River actually recommends less than the 1%, at .7%.

Or do I calculate using the amp hour rating of one string of batteries, which is 415ah?

I attribute the short absorption phase to very new batteries.

-Steve
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

Sounds about right. You may want to contact Fullriver about their recommendation on a commissioning sequence for the batteries. They may have you discharge them fully, then recharge, or some sort of extended absorb/float cycle. In any event, it will do no harm at this point to disconnect the battery bank, let them rest for 24 hours, and take voltage readings on each battery.

It will be very helpful to maintain a log of the voltages as you go for future reference.
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

Your Fullriver AGM DC400-6 are rated 6 volts / 415 amp hours.

Assuming, as you have here, that all the batteries are the same specification, they can be combined in series and parallel to make a larger battery.

When batteries are connected in series, the voltages add, so 8 of them in series makes a 48 volt 415 amp hour battery.

When batteries are connected in parallel, amp hour capacity adds, so 2 series strings of 8 batteries each makes a 48 volt 830 amp hour battery.
stevetull
Forum Virtuoso
Posts: 91
Joined: Tue Feb 24, 2015 6:40 am
My RE system: FlexPower Two:
2 VFX3648, X240, 2 FM80, Mate 3s, FnDC, Hub 10
One array facing south at 30 degree tilt
One array facing southwest at 10 degree tilt
Total of 8kW
16 Fullriver AGM DC400-6 = 830Ah @ 48v
OpticRE: Paige cabin
Location: Near Bastrop Texas
Contact:

Re: New red light coming on - Battery Low

Post by stevetull »

Yes, my bank is 830 ah. And the lowest I've seen going into the battery bank is 6.3 amps. That's pretty close to the .7% that Full River suggests I shoot for.
In order to accurately set up my FNDC, right now I'm trying to figure out what to enter as the Return Amps value and the Battery End of Charge Voltage. I look on my Mate 3s and have a hard time seeing what the FNDC manual says to use. They suggest doing another Bulk and absorb charge and keep monitoring during absorb to get those values. We'll see....


-Steve
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

I'm sure you've read through Fullriver's installation and charging documents. A quick scan brings up a few interesting points.

Fullriver takes a fairly "plug and play" approach to commissioning - almost "strap 'em in and let 'er rip". They must be very confident in the construction of their batteries.

They recommend a pretty high bulk/absorb voltage. They must have a very robust catalyst assembly in the batteries to recombine the gasseous charging byproducts (hydrogen and oxygen.) You are using temperature compensation when charging, yes?

They recommend cross-wiring the individual batteries between the parallel strings in order to help maintain cell balance. Not all manufacturers recommend this, but I have learned (by bitter first-hand experience) that unbalanced AGM batteries in a series/parallel scheme leads to premature battery death. I'd strongly consider taking their advice here, if you haven't done so already. (Ref.: 2.7 of installation guide.)
raysun
Forum Emperor
Posts: 4624
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: New red light coming on - Battery Low

Post by raysun »

stevetull wrote:Yes, my bank is 830 ah. And the lowest I've seen going into the battery bank is 6.3 amps. That's pretty close to the .7% that Full River suggests I shoot for.
In order to accurately set up my FNDC, right now I'm trying to figure out what to enter as the Return Amps value and the Battery End of Charge Voltage. I look on my Mate 3s and have a hard time seeing what the FNDC manual says to use. They suggest doing another Bulk and absorb charge and keep monitoring during absorb to get those values. We'll see....


-Steve
I have learned to "trust but verify" what the FNDC is telling you. (A very expensive lesson.)

You'll want to verify this with Fullriver, but I'd think the Return Amps value would be the 6.3A you are seeing, rounded up to 7A, as you can only enter a whole number in the MATE if I recall correctly.

By Battery End of Charge Voltage, do you mean the Absorb voltage? That's in their Installation and Operation guide in section 4.4.2 and is listed as 48.8V.
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