Are My Batteries Shot?

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tavo2527
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Are My Batteries Shot?

Post by tavo2527 »

I recently installed four S6-460 AGMs on a 24V system. I referred to the install parameters and even posted here for other insights on which settings to update moving from an old FLA system to AGM.

In the first few days, everything seemed to be in perfect working order with the exception being that the batteries were seemingly being discharged to a SOC that was below recommended levels. So I made some modifications and looked into HBX use to buy when voltage dropped to a certain level.

Now it seems that even though the SOC is regularly 100%, 1) The system will not drop the grid unless I override and for the drop 2) more importantly, the voltage steadily diminishes past a LBCO point.

So my question is, could this be something related to how the Mate/FX is being programmed that I missed/screwed up, or are one or multiple batteries damaged causing the poor voltage.

Happy to provide some system readouts or figures to help troubleshoot. It just seems like these new Rolls shouldn't have run into an issue this quickly.
raysun
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Re: Are My Batteries Shot?

Post by raysun »

I'm strictly off grid, so can't really help with the grid stuff.

However, here's one thing to check:
The battery is rated at 24V @ 415AH. The 415 value should be the battery capacity programmed into the FNDC.

Doing the math, 24V x 415AH = 9960kWH, of which a maximum of 50% is usable, so the usable capacity is about 4.9kWH (kilowatt hours), or about 205AH (amp hours).

The FNDC should be able to track the input (charging) and output (discharging) accurately. Net AH consumed should be a good metric for battery health, and charging timing.

Battery voltage is a bit tricky, as for a given State of Charge, voltage varies with changes in load. If load, and discharge rate, is fairly steady, then a chart of voltage estimates can be created, but it will always be subject to variances as described above.

Hopefully someone with grid charging experience will chime in.
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Mike Curran
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- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

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

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Are My Batteries Shot?

Post by Mike Curran »

Tavo - What is your inverter set up to do? Better question, what do you want your system to do?

Regarding HBX, I would not be using it unless you are trying to avoid using the grid and have enough PV to power your loads most of the time and recharge your battery.

Tell us your desired operating mode and we can go from there.
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tavo2527
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Re: Are My Batteries Shot?

Post by tavo2527 »

Hi Mike - I think my goal is pretty simple. I want to maximize the usage of my small PV array (1.7kW) and use free energy as often as I can.

So during the day, using DC to power my home and store any surplus in the batteries. Sun goes down, battery consumption increases.

On good summer days I store everything I need to make it thru the night and then PV output picks up in the morning.

Our energy consumption is generally pretty low (we avg ~8 kWh/day) so we can surprisingly make it a good portion of the year in this process.

My concern about batteries being shot is even after 100% charged, when I drop the grid I can watch the DC voltage precipitously drop fairly quickly and I haven't even cracked 98%. So I'm open to any and all recommendations you can provide!
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Re: Are My Batteries Shot?

Post by raysun »

If consumption is around 8kWH/day, then of course, 8kWH needs to be put back every day + about 20% for losses and charging inefficiencies. Unless sited somewhere exceptionally sunny, the 1.7kW array is somewhat small for the task.

The FNDC will only track State of Charge accurately, if the capacity and charging parameters are accurate. The parameters in question are in the FNDC Battery Charging menu. Can you list each of the parameters, and their respective values?

A "precipitous" voltage drop on discharge is mentioned. What is the measured voltage? Also, while under discharge, what is the measured voltage of each of the four battery blocks (taken at their terminals. No need to disconnect them.)

Are all the battery cable connectors properly torqued? Are they all free of corrosion?
tavo2527
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Re: Are My Batteries Shot?

Post by tavo2527 »

Hi Ray,
Thanks for your note. I do realize the PV array sizing to consumption is not equal and that's definitely where the grid comes in to play. What I described was an ideal state and note that average does fluctuate significantly based on seasonality (AC in summer, boiler in winter for heat).

ADV/DC/BAT parameters are as follows:
Capacity- 420amp hours

ADV/FC/CHARGER parameters are as follows:
Charger limit: 18.0 aac
absorb setpoint: 27.8 vdc
absorb time limit: 2.0 hrs
float setpoint: 26.2 vdc
float time period: 1.0 hours
refloat setpoint: 25.0 vdc
equalize setpoint: 30.4 vdc
equalize time period: 1.0 hrs

9:25pm EST
Voltage reported at Mate pre "drop": 26.4V SOC 99%
Voltage reported at Mate 5 minutes post "drop": 24.6V SOC 99%

I'll need to measure voltage at the terminals. I had them installed by an electrician while doing some other work so my assumption is the proper torque was applied. And they are corrosion free, stored in a vented box in a dry basement.
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Re: Are My Batteries Shot?

Post by raysun »

Measuring the blocks after the voltage drops might tell one of two stories:

• If the blocks have uneven voltages, the lower voltage unit(s) may be damaged. Look to have them tested and replaced under warranty. Without thorough testing, however, its hard to assess cell damage.

The first step would be to read on.

• If the blocks have equal voltages it may be the battery is being undercharged.

Looking over the Rolls User Manual, there's a couple of things to consider.

Absorb Voltage setting.
If using Temperature Compensated Charging (you should be), the set point for 25°C is 28.56V.

Absorb Time.
Rolls gives a formula for computing Absorb Time. T = 0.38 x (c/i) + 5% where c is the C20 discharge capacity (415AH), and i is the Bulk charge current. (5% is added for losses)
18AAC is about 70ADC charging current. The result is 2.5H roughly.

Since charge current varies on solar, the formula may not be as useful as Outback's Auto Charge Termination control. A Charged Return Amps of roughly 3% (12A) might be a good target.

If measuring the blocks shows equal voltage on each, then its possible the battery is being undercharged. The high voltage just after charging may be a "surface charge" reading, which would drain off quickly under load. The lower voltage representing the actual charge put into the battery. Adjusting the Absorb phase parameters may be in order.

EQ settings. DON'T EQ this battery. It will result in permanent capacity loss.
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Re: Are My Batteries Shot?

Post by Shadow_Storm56 »

tavo2527 wrote: Wed Dec 29, 2021 12:03 pm I recently installed four S6-460 AGMs on a 24V system. I referred to the install parameters and even posted here for other insights on which settings to update moving from an old FLA system to AGM.

In the first few days, everything seemed to be in perfect working order with the exception being that the batteries were seemingly being discharged to a SOC that was below recommended levels. So I made some modifications and looked into HBX use to buy when voltage dropped to a certain level.

Now it seems that even though the SOC is regularly 100%, 1) The system will not drop the grid unless I override and for the drop 2) more importantly, the voltage steadily diminishes past a LBCO point.

So my question is, could this be something related to how the Mate/FX is being programmed that I missed/screwed up, or are one or multiple batteries damaged causing the poor voltage.

Happy to provide some system readouts or figures to help troubleshoot. It just seems like these new Rolls shouldn't have run into an issue this quickly.

Some interesting things to check, absorb voltage and time is super critical.... apparently years ago the tech told me wrong and what's stamped on the battery is not what to go by it's not that simple. Rolls has good support so asking them the best settings for your situation would be a good idea.

Also rolls batteries have a chemistry that they take a few cycles to come up to full capacity, they say 50 ish but it was 20 or less for me. Also over discharging them is definitely not advisable....

Definitely wouldn't eq thoes style of battery unless you really need to, there is no way to test and monitor it so would risk damage more than anything. Important question, did you individually charge all the batteries before putting the bank together as this is super important.

Lastly what's your instantaneous load like? A smaller bank will lose charge very fast when it has high current draw.

There are so many things but you need to be careful not to overdo it, the batteries are likely fine and if you start doing things to try and fix it you may create a problem that wasn't there.
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Re: Are My Batteries Shot?

Post by raysun »

Some interesting things to check, absorb voltage and time is super critical.... apparently years ago the tech told me wrong and what's stamped on the battery is not what to go by it's not that simple. Rolls has good support so asking them the best settings for your situation would be a good idea
Rolls support is about the best out there.

The manual has details for charging as well:
https://rollsbattery.com/wp-content/upl ... Manual.pdf
charge all the batteries before putting the bank together
I don't see this stated in any of Rolls' commissioning documents. It wouldn't hurt, but it wouldn't be worth the cost of a quality programmable 6V charger to pre-charge the blocks either. (An auto supply store 6V/12V charger is definitely going to do more harm than good.) The self-equalizing nature of new lead acid AGM cells should be sufficient.
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Re: Are My Batteries Shot?

Post by Shadow_Storm56 »

raysun wrote: Wed Dec 29, 2021 8:54 pm
Some interesting things to check, absorb voltage and time is super critical.... apparently years ago the tech told me wrong and what's stamped on the battery is not what to go by it's not that simple. Rolls has good support so asking them the best settings for your situation would be a good idea
Rolls support is about the best out there.

The manual has details for charging as well:
https://rollsbattery.com/wp-content/upl ... Manual.pdf
charge all the batteries before putting the bank together
I don't see this stated in any of Rolls' commissioning documents. It wouldn't hurt, but it wouldn't be worth the cost of a quality programmable 6V charger to pre-charge the blocks either. (An auto supply store 6V/12V charger is definitely going to do more harm than good.) The self-equalizing nature of new lead acid AGM cells should be sufficient.
Generally rolls sends out all the batteries pre charged all the same, but it's not a bad idea to make them equal before hand so you don't have batteries out of sync.
raysun
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Re: Are My Batteries Shot?

Post by raysun »

Generally rolls sends out all the batteries pre charged all the same, but it's not a bad idea to make them equal before hand so you don't have batteries out of sync.
*Peering down yet another rabbit hole*

What would be the evidence these monoblocs aren't delivered to Rolls specifications? Did they suddenly decide quality control is not important?

Charging each 6V monobloc separately doesn't accomish what's being implied at any rate, as each one consists of 3 cells in series. There will be no more assurance that charging 3 series cells will "sync" them any better than charging 12 series cells.

Its far better to use the high quality charger in the inverter to get the battery (all 4 monoblocs in series) properly charged. A subsequent voltage measurement test will answer any questions about the need, if any, for remedial charging.

Enough on notions, and back to standard practice.

Good advice:

• Contact Rolls support and get their input on proper charge voltages and times.
Ask them about a commissioning charge, if any, they might recommend.

• Run a charge cycle and take voltage measurements for the battery, and each block, immediately after charging, and again after 1% and 2% Depth of Discharge.
tavo2527
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Re: Are My Batteries Shot?

Post by tavo2527 »

Any reason why I'm getting "Full Conditions Met" but the grid is not being dropped thereafter? As a grid-tied setup, my assumption was this would then drop the grid but that never happens.

Getting back around to all of this and am contacting Rolls as well. Sorry for the hiatus.
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- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

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

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Are My Batteries Shot?

Post by Mike Curran »

I don't think the VFX inverters automatically drop the grid once charge parameters are met. Rather, in normal grid-tied operation with a PV source and charge controller, at that point the inverter is allowed to sell excess solar while maintaining your battery at float (actually, sell) voltage.

With your intention to use grid as little as possible and with the limited functionality your VFX offers in this respect, you might consider using the griduse function, which allows you to specify the time periods you want your system to use and drop the grid. If your battery reaches the low battery cutoff setpoint while grid is dropped, your inverter will reconnect to grid, disregarding the preset time for reconnection.

A description of this function is in the Mate2 manual starting on page 69. https://documentcloud.adobe.com/link/re ... 6ec1185a5a
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
tavo2527
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Re: Are My Batteries Shot?

Post by tavo2527 »

Thanks Mike!

Update here:

I've setup griduse but it seems when the LBCO is reached there is no further grid dropping once enabled, even within the specified griduse window. Is my read on that correct?

Second, I have reached out to Rolls Support but we're working on week 3 of no response so I'm missing some important input on their end.

Finally, I still can't seem to get around why the SOC read is 99% in many cases but when running on just batteries, the voltage very quickly dispenses below 24. There seems to be a calculation or setting missing because reaching a state for Full Conditions Met should give me several hours of battery use before any grid buying should occur.
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Mike Curran
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My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

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

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Are My Batteries Shot?

Post by Mike Curran »

tavo2527 wrote: Mon Feb 28, 2022 6:15 am I've setup griduse but it seems when the LBCO is reached there is no further grid dropping once enabled, even within the specified griduse window. Is my read on that correct?
Yes, when you reach LBCO it forces grid use to prevent discharging your battery any further.
tavo2527 wrote: Mon Feb 28, 2022 6:15 amFinally, I still can't seem to get around why the SOC read is 99% in many cases but when running on just batteries, the voltage very quickly dispenses below 24. There seems to be a calculation or setting missing because reaching a state for Full Conditions Met should give me several hours of battery use before any grid buying should occur.
Your FNDC may need to be reset, looks like it's not giving you a true SOC reading. You need to fully charge your battery using specific gravity or your battery manufacturer's instructions, then unplug/replug your FNDC LAN cable from your Hub. That'll reset SOC to true 100%. Per app note:
Screenshot_20220228-112520_Adobe Acrobat.jpg
Link to app note: https://outbackpower.com/downloads/docu ... p_note.pdf
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
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Re: Are My Batteries Shot?

Post by raysun »

Finally, I still can't seem to get around why the SOC read is 99% in many cases but when running on just batteries, the voltage very quickly dispenses below 24. There seems to be a calculation or setting missing because reaching a state for Full Conditions Met should give me several hours of battery use before any grid buying should occur.
Once the FNDC is properly synced (see Mike's post above) the State of Charge should be an accurate indicator.

Some things to check:

• The FNDC Battery Charging parameters are properly set. In the Mate/Setup/FNDC/Battery Charging menu, confirm the Battery AH is set to the C20 Amp Hour capacity of the battery.

• The FNDC shunts are wired properly and enabled.

Once both of the above are confirmed, and the FNDC synced at 100% SoC, the discharge current reading (and SoC) should be accurate.
tavo2527
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1.8 kW array

Re: Are My Batteries Shot?

Post by tavo2527 »

OK so I followed Mike's steps on resetting the FNDC but based on both your comments I'm confused about the initial charge.

Ray - you commented "Its far better to use the high quality charger in the inverter to get the battery (all 4 monoblocs in series) properly charged. A subsequent voltage measurement test will answer any questions about the need, if any, for remedial charging." However Mike states to "fully charge your battery using specific gravity or your battery manufacturer's instructions".

Can I just use the inverter to charge the bank? If so, is there a particular charge cycle I need to run through the inverter? Today the system is dumping any excess solar energy that the house is not drawing, I believe because it assumes its at 100% battery capacity, even when it is not.

I'd prefer to rely on the inverter to do any charging vs any other source if I can.

Also what would be considered a high load on this size bank? Like 85 amps?

Sorry for my lack of understanding here...
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REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Are My Batteries Shot?

Post by raysun »

tavo2527 wrote: Mon Apr 18, 2022 2:12 pm OK so I followed Mike's steps on resetting the FNDC but based on both your comments I'm confused about the initial charge.

Ray - you commented "Its far better to use the high quality charger in the inverter to get the battery (all 4 monoblocs in series) properly charged. A subsequent voltage measurement test will answer any questions about the need, if any, for remedial charging." However Mike states to "fully charge your battery using specific gravity or your battery manufacturer's instructions".
Of the two measurement techniques, Specific Gravity is the better indicator of state of charge. If the battery is flooded lead acid, use this.

Can I just use the inverter to charge the bank? If so, is there a particular charge cycle I need to run through the inverter?
The inverter charger should be programmed in accordance with the manufacturer's specifications for charge rate during Bulk, Absorb Voltage and Time.
Today the system is dumping any excess solar energy that the house is not drawing, I believe because it assumes its at 100% battery capacity, even when it is not.
Is the charge controller set in accordance with the manufacturer's charging specifications?

Is Automatic Charge Termination enabled? If so, disable for now.
I'd prefer to rely on the inverter to do any charging vs any other source if I can.
Program it properly and it should charge the battery as needed. If a regular charge cycle does not get every battery cell fully charged, an Equalization charge should help remedy the imbalance if the battery type supports Equalizatiin charging.
Also what would be considered a high load on this size bank? Like 85 amps?
85A @ 24V is roughly 2kW load.
tavo2527
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1.8 kW array

Re: Are My Batteries Shot?

Post by tavo2527 »

1. These are Sealed Lead Acid
2. I have followed manufacturer spec:

ADV/FC/CHARGER parameters are as follows:
Charger limit: 18.0 aac
absorb setpoint: 27.8 vdc
absorb time limit: 2.0 hrs
float setpoint: 26.2 vdc
float time period: 1.0 hours
refloat setpoint: 25.0 vdc
equalize setpoint: 30.4 vdc
equalize time period: 1.0 hrs

3. I'll need to check on Automatic Charge Termination
4. I couldve sworn that an equalization charge was not recommended earlier in this thread
5. Are you saying a 2kW load is a lot?
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Are My Batteries Shot?

Post by raysun »

Generally speaking, Equalization is not used on sealed batteries. Some manufacturers may recommend a "freshening" charge, essentially Absorb voltage for an additional time period.

2kW isn't necessarily an overly large load. Refer to the manufacturer's specs for maximum continuous discharge current.
Last edited by raysun on Wed Apr 20, 2022 9:35 am, edited 1 time in total.
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Mike Curran
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My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

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

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Are My Batteries Shot?

Post by Mike Curran »

Here's the specs
20220420_120613.jpg
They don't list a max discharge current, but a 2Kw load is about 80A, close to the listed max charging amps. But his battery is only good for 2.5 hours at that rate assuming max 50% DOD (someone check my numbers please! :grin: ).

Edited - for 24 volt battery
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
tavo2527
Forum Member
Posts: 14
Joined: Sun Nov 12, 2017 5:58 pm
My RE system: Inverter: Outback Power VFX3524
Solar Charge Controller: Outback Power FM80-150VDC
Battery Monitor: Outback Power Flexnet-DC
System Controller: Outback Power Mate-B Flush
1.8 kW array

Re: Are My Batteries Shot?

Post by tavo2527 »

I've turned off the Automatic Charge Termination and still no dice.

Doubling back to the manufacturer's instructions, I see the following:
VRLA AGM ABSORPTION CHARGE TIME
Where : T = 0.38 x C /I
T = ABSORPTION CHARGE TIME
C = 20 hr RATED CAPACITY (total battery bank)
I = Charging Current (Amps) (recommended 20% of C/20 discharge rate)
0.38 = ( 20%/50%) + 5% (5% is added due to losses)

EXAMPLE:
2 strings of 6 Volt S6-460AGM models
20 hr AH rate = 415 AH x (2 strings) = 830 AH
I = 20% of 830 AH = 166 Amps
T = 0.38 x 830/166 = 1.9 hrs

Based on this example, is that assuming 2 strings in parallel? I'm confused by the 830AH Calculation.

My goal is to just run a full charge cycle to get back to a "real" 100% SoC and I just can't seem to get there...
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SandyP
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My RE system: 8 x 190W 24V Suntech panels (4 strings of 2) July 2011
4 x 325W 24V Suntech panels (2 strings of 2) added Sept2018
Mate2
Outback FM60 MPPT (max output lowered to 55amps)
12 x 2V Hoppecke GEL 612 Ah C24 - 24V System (June 2011)
Outback VFX3024 Inverter/Charger
Victron BMV-602s
Honda 5.5kW Genset
Location: Victoria, Australia

Re: Are My Batteries Shot?

Post by SandyP »

tavo2527 wrote: Wed May 11, 2022 8:20 pm .../..
EXAMPLE:
2 strings of 6 Volt S6-460AGM models
20 hr AH rate = 415 AH x (2 strings) = 830 AH
I = 20% of 830 AH = 166 Amps
T = 0.38 x 830/166 = 1.9 hrs

Based on this example, is that assuming 2 strings in parallel? I'm confused by the 830AH Calculation.

My goal is to just run a full charge cycle to get back to a "real" 100% SoC and I just can't seem to get there...
As you have a 1.8kW array the max current you will get is 75Amps, so the formula becomes :
T=0.38 x 830/75 = 4.2 hrs
Of course the solar array never puts out the max for the whole day and if you are using AC power whilst charging then not all of the amps from the charge controller will be going to charge the battery bank.
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My RE system: Flexpower Two: (2) FXR3048A-01, (2) FM80, MATE3s, FlexNetDC
6 SimpliPhi 3.8-48 (48v @ 75AH. 450AH total)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Are My Batteries Shot?

Post by raysun »

If the battery consists of a single string, then 415 would be used in the equation where 830 is in the example.

I've always had issues with the formula because it assumes the constant current (Bulk) stage is just that - constant: I = 20% of 415AH (C20 discharge rate). For solar charging, I is almost never constant. What's being implied is that with constant rate I, the battery will reach Absorb voltage at a specific state of charge (typically 80% SoC) and the calculated Absorb Time is sufficient to reach 100% SoC at constant voltage (the Absorb voltage.) To be precise, Absorb Time would need to be calculated every charge cycle from an integral of the charge current leading to the Absorb Voltage. Not practical in the least, so a one-time calculation must assume a charge rate, and make a ball-park estimate of Absorb Time. Not ideal, but the best there is to charge by a fixed time for Absorb.

Thats where End Amps (Charged Return Amps in OB parlance) becomes valuable for terminating Absorb charging. It doesn't rely strictly on time, rather uses an event in the battery's chemistry. Essentially maintain constant voltage (Absorb Voltage) until the charge current declines to a fixed value, usually 2 - 5% of the battery C20 capacity. The battery manufacturer should be able to provide the value. Plugging it into the Battery Charge - Charged Return Amps parameter in the FNDC and enabling Automatic Charge Termination Control provides Absorb cycle termination at the optimum duration. *Note* Absorb Time still needs to be set on all chargers with sufficient time such that they do not time out before being commanded by the Mate to terminate.

Since disabling Auto Charge Termination Control didn't help the situation, we can assume it wasn't interfering with charging. If the battery was still not getting fully charged, then the Absorb Time is likely too.short.

I'd try this:
Set Absorb Time on all chargers to 3 hours. (This should be long enough to fully charge the battery.)

Set the FNDC Battery Charge Parameters:
Battery Capacity = 415
Charged Return Amps = 22.5A
Charged Voltage = 29.0V
Charged Time = 1 minute

Set the Inverter Charger - Battery Charge
Absorb Voltage = 29.4V
Absorb Time = 3.0H

Set the FlexMax - Battery Charge
Absorb Voltage = 29.2V
Absorb Time = 3.0H

Set the Mate - Global Charge
Automatic Charge Termination Control = Enabled

Run the Inverter Charger and monitor charging. Sometime within the Absorb Phase, the charge current should decline to the target, and charging will stop. If 3 hours elapses and Absorb times out, the Absorb time needs to be increased (add 30 minutes) and repeat the charge cycle. (It will run fast the 2nd time.)

Once a "Charged Parameters Met" record is written in the event log, charging will be complete.

Note* During charging, ignore State of Charge readings on the Mate/Optics. The State of Charge reading will be correct when the battery is properly fully charged.

From that point, you can test discharge. If still seeing a rapid drop in voltage, then there's likely a dead cell in one of the battery blocks. Measure each 6V block with a volt meter. Likely one of them will read low, or even negative. If you find that, the block needs replacing.
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