My 200Ah AGM’s are kaput….got nothing to loose, I will try to desulphate them!

[Costa]

Hello Guys and Girls,

I am new to the forum…this is my second post. I gave a brief intro in my first post (Power Forum - Axpert King 5kW - Warning 32 )

 

In this writeup, I would like to share my experiences with trying to revive (desulphate) my otherwise kaput 200Ah AGMs!

 

 

Part 1: Background Info

 

My current system (V2.0) consists of a 5kW Axpert King & 4x 200Ah Allgrand AGMs. It’s purpose is to provide clean power and UPS to the essential stuff in my home. I installed it in Dec 2018 as an upgrade/replacement of my 1kW 24v Microcare & 2x 200Ah Deltec AGMs, which have served me since Dec 2014. The upgrade was triggered because after 4 years service, the Deltec’s had lost capacity and the backup runtime had become unaceptable!

My definition of “essential stuff” is all home lighting, alarm system, electric fence, gate motors, CCTV, computers, network, internet, TV and last but not least the fridge. My average load is approx. 400W-500W. It drops to minimum of 280W and climbs to a max of around 600W (ignoring the startup load of the fridge).

My required max runtime is between 9-12hours, ie to make it through the night. We have occasional power disruptions (once or twice a year) that last 24 hours and every other year we loose power for 2-4 consecutive days! This lovely reality is courtesy of City of Jhb and the aging infrastructure combined with cable theft and substation vandalisms!

I have a 9KVA generator that enables me to bulk charge my batteries for 4h in the morning and 4h hours at night and make it through the couple of days of ESKOM power disruption.

My upgraded system migrated to:

• 48v, in order to double up on the previous battery capacity (and hopefully improve the disappointing 4y service life of the Deltecs).
• The Axpert KING inverter, because of the 0ms transfer time as well as the healthy AC charging amps (for a good dose of 30A bulk charging during those 4hours of generator run-time). The built in MPPT is a nice to have for future upgrade/expansion.

Back to Reality

 

The 200Ah Allgrand AGMs barely lasted 2 years (disappointment is an understatement). They did not work hard during these two years. From my recollection and perception, they were not cycled many times either, unfortunately I do not have exact data to refer back to. They most definitely were not deep cycled “hundreds of times” as per the performance promises indicated on their datasheet!

I will discuss my speculations of the root cause of their failure in a later part of this writeup.

After experiencing a premature shutdown during load shedding, I started investigating and ran the following capacity load tests with a >2kW load (courtesy of a two element air heater):

 In summary, with a draw of 50A from the batteries I was getting less than 15min runtime!

These batteries are truly kaput! Specifically battery no 1 was collapsing prematurely and it's voltage was rapidly falling off below 10v!

 

Edited February 16, 2021 by Costa
OCD. To fix my errors.

[Costa]

Part 2 - My Desulphation efforts and the mixed results (to be continued tomorrow)

Teaser: The desluphation strategy that I applied resulted in the following improvements as achieved in the test results dated 20 Dec 2020

ie almost 9hours runtime while powering the normal loads connected to the inverter!

Details of the desulphation strategy and info on the DIY tools used will follow in Part 2.

 

[Costa]

Before delving into Part 2  (Desulphation stuff etc), I need to first fill you in on the following details;

Part 1.2 - Individual Battery Capacity Testing and the DIY Tools (V1.0) used.

I think everyone would agree, that the performance indicated by the tests dated 14 - 18 Nov 2020 are terrible. But what exactly is the theoretical “normal” performance that I should have seen?

According the datasheet for the Allgrand 200Ah AGM battery:

• This battery is rated as a 200Ah battery because it is able to deliver 10A continuously for 20hours (10A X 20h = 200Ah). It is considered 100% discharged at 10.5V (1.75V/cell).

Also note, that the 200Ah rating/capacity is valid only when you are draw 10A constant current!

• If you draw 34A you will only get 5h runtime down to 10.5V (ie 170 Ah capacity)
• If you draw 50A you will only get 3h runtime down to 10.5V (ie 150Ah capacity)
• If you draw 120A you will only get 1h runtime down to 10.2V (ie 120Ah capacity)

(Yes, this sucks, but this is an unavoidable reality of the Lead-Acid battery chemistry. This trend is known as Peukert’s Law.)

 

Looking back at the test data from 15 Nov 2020:

• The current draw started at 40A, stabilised at ±45A and then briefly climbed to 50A. For the sake of simplicity for this example, lets agree to call it 50A continuous.
• According to the table above, we would have expected a runtime of approx. 3hours while drawing 50A. ie 3h x 50A = 150Ah total
• Yet, the actual runtime was less than ¼ hour (it was 13min to be exact). ie (13min / 60) x 50A = 10.8 Ah actual capacity!

The battery was only able to deliver (10.8/150) = 7.2% of its rated capacity! Battery = Kaput!

In reality, it takes just one battery to be Kaput for the whole battery bank to have dismal performance. Next, I needed to test each battery separately.

 

Test Setup V1.0

For continuity and for comparison purposes, I wanted to continue testing with the approximately 50A constant current discharge. I needed to build a 600W array of 12V 50W dichroic lamps. 12 lamps would allow me to achieve the desired 50A magic number.

The funny thing is, these 50W lamps have become as scarce as hen’s teeth, no one wants them anymore! At least two different salespeople looked at me like I must be mad after offering me the best of the best 7W LEDs and I just shook my head mumbling “too complicated to explain, those won’t work, they are too efficient!”. So I eventually hunted down the only place that still stocked 12V 50W dichroic bulbs.

 

Armed with a pencil, paper, stopwatch, multimeter & 600W light emitting heater … I proceeded to discharge one battery at a time and record the voltage vs time:

 

The tests confirmed that Battery #1 was Kaput...arguably the rest are Kaput aswell!

But battery #1 is causing the whole bank of batteries to “collapse” within 15 minutes; What if I could improve and somewhat recover some of the capacity of Battery #1? ... time to read-up about Lead-Acid battery sulphation and desulphation...

 

[Costa]

Part 1.3 – What Exactly is Sulphation and De-Sulphation?

 

In summary:

1) What is Sulfation?

            According to the Battery University (BU-804b: Sulfation and How to Prevent it

“During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the battery’s active material, which is responsible for the performance.

 

There are two types of sulfation: reversible (or soft sulfation), and permanent (or hard sulfation). If a battery is serviced early, reversible sulfation can often be corrected by applying an overcharge to an already fully charged battery in the form of a regulated current of about 200mA. The battery terminal voltage is allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on a 12V mono block) for about 24 hours. Increasing the battery temperature to 50–60°C (122–140°F) during the corrective service further helps in dissolving the crystals.

 

Permanent sulfation sets in when the battery has been in a low state-of-charge for weeks or months. At this stage, no form of restoration seems possible; however, the recovery yield is not fully understood. To everyone’s amazement, new lead acid batteries can often be fully restored after dwelling in a low-voltage condition for many weeks. Other factors may play a role.”

 

 

2) De-Sulfation refers to any process that aims to reverse sulfation.

 

3) What is an Equalizing Charge?

            According to the Battery University (BU-404: What is Equalizing Charge?

 

“An equalizing charge is nothing more than a deliberate overcharge to remove sulfate crystals that build up on the plates over time. Left unchecked, sulfation can reduce the overall capacity of the battery and render the battery unserviceable in extreme cases. An equalizing charge also reverses acid stratification, a condition where acid concentration is greater at the bottom of the battery than at the top.”

 

4) Conditioning Charge (extract from Lifeline Batteries Technical Manual, page 21)

 

 

 

5) References and Literature Study (for whoever is interested in additional info)

• https://batteryuniversity.com/learn/article/equalizing_charge

• https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

• https://batteryuniversity.com/learn/article/water_loss_acid_stratification_and_surface_charge

• https://batteryuniversity.com/index.php/learn/article/charging_the_lead_acid_battery

• https://batteryuniversity.com/index.php/learn/article/sulfation_and_how_to_prevent_it

 

• https://lifelinebatteries.com/2015/10/can-i-equalize-agm-batteries/

• https://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

 

 

Reading the theory helped, but I was still sceptical....until I came across the following YouTube video:

 

YouTube - Battery Desulfation Demonstration Start to Finish - Part 2/2

This video convinced me to take my "brave pills", and proceeded to order an adjustable bench type power supply

The PSU I found (locally) allows control between 0-30V & 0-10A

 

[Costa]

Part 2 – My Desulfation efforts and mixed results

Armed with the following desulfation tools:

• Adjustable PSU
• CTEK charger MXS5
• Multimeter

And a desulfation strategy summarised as follows:

     Step 1 – Bulk, absorb and float charge the battery (with either the PSU or CTEK)

     Step 2 – Use PSU re-check float charge and confirm that battery has absorbed (float charge current should drop to less than 0.2A)

     Step 3 – Pre-Set the PSU to an open circuit voltage of 15.89V (check with multimeter)

     Step 4 – Connect the PSU to the battery to start the desulfation.

                    At this point, the battery would accept all 10A but I set the PSU to CURRENT LIMIT @ 4A (roughly based on the Lifeline battery guidelines)

     Step 5 – Monitor the desulfation process and stop/abort:

                    a)       If there is excessive venting/gassing (subjective). The Allgrand batteries make a whistling sound when they vent.

                    b)      If the battery becomes abnormally warm/hot (subjective)

                    c)       If the battery voltage drops below 15v (desulfation only effective above 15v)

                    d)      After 8 hours (based on the guidelines from Lifeline)

 

The following voltage and current curves indicate the principle behaviour observed when my Allgrand batteries were being desulfated:

[Costa]

So after desulfating the batteries one by one, I repeated the individual battery capacity tests. The following graphs show the performance:

Before desulfation:    29-30 Nov 2020

After desulfation:       01-06 Dec 2020

All 4 batteries achieved a runtime of more than 2.5hours with the same 50A continuous current draw!

Taking a closer look at Battery #1   Before & After:

29 Nov 2020 - Runtime         14m30s - 12Ah (8% capacity relative to the datasheet 150Ah)

01 Dec 2020 - Runtime     2h36m10s - 130Ah (86.6% capacity relative to the datasheet 150Ah)

 

Needless to say, I was really chuffed with these results!

I couldnt wait to power up the inverter and repeat the system test.

I was also exhausted from the old-school "paper, pencil & stopwatch" method of data capturing. This required urgent action to automate the testing and also to add datalogging (I was planning to run more tests...more on that in the next part)

 

[Speedster]

Really fun project to read. Thanks for sharing!

I bought one of these a while back, the pulse repair function helped save some of my small (7Ah) lead-acids. 

[Costa]

Part 2.2 – Actions taken BEFORE proceeding to evaluate the desulfated batteries

 

“Insanity:         Doing the same thing over and over again and expecting different results!”

 

So, before proceeding to reconnect the freshly rejuvenated batteries, I was still concerned with understanding “why” my AGM batteries failed prematurely (failed to achieved 2 full years service) in the first place!

·         The inverter is always on/standby (AC power from the grid). Therefore the batteries are always fully charged and maintained/floated by the multi-stage charger built into the Axpert King. I have no reason to doubt or fault the Axpert King as being the root cause of the premature battery failure.

·         The battery bank has not worked hard and has not been cycled frequently during the past two years. Therefore, it is unlikely that the degradation was caused by regular deep cycling.

 

So what caused the premature degradation?

 

Theory No 1:   Applying the equalization charge improved their capacity. This indicates that a certain amount of sulfation had been reversed and some capacity was restored.

But according to the literature for Lead-Acid batteries, irreversible sulfation only occurs when the battery is allowed to sit, for extended time, in a partial state of charge! These batteries are being monitored continuously and charge is topped up by the multi-stage charger.

How then, did my batteries become sulfated due to “partial state of charge”?

 

Theory No 2:   Perhaps batteries do not like sitting in standby mode for pro-longed periods of time? Maybe “some or other amount of cycling” is actually healthy for them and keeps them in good condition?

This is pure speculation because I have not found any literature that supports or disproves anything along these lines.

 

This thinking and questioning was continuously going on, while I was conducting the various capacity tests and tinkering with recharging the whole bank vs recharging each battery individually…until I observed something vitally important!

Applying an overall charging voltage across a bank of 4 batteries in series, DOES NOT automatically guarantee that each battery is receiving an equal share of voltage!

During my initial back-to-back capacity tests of the Inverter + Battery Bank (tests done between 14 Nov through to 18 Nov), I actually tried to equalize & desulphate the battery bank by applying the battery equalizition feature available in the Axpert King. Here are some of my observations:

The above table illustrates how the individual battery voltages were deviating (relative to each other) while being charged as a bank.

My hypothesis for the root cause of the failure is that, the weak battery (within a bank of batteries) will keep getting undercharged and will progressively sulfate and get weaker and weaker. This will eventually spiral out of control and lead to the destruction of the whole bank of batteries!

This is why:

• You need to replace all batteries in a bank (do not mix new batteries with old batteries)

• You need to install a separate device that will ensure the bank of batteries remain in sync/balance with each other!

Based on my hypothesis, to avoid a recurrence of this problem, I needed to install a battery balancer. I decided to go with the HA02 battery balancer and hopefully salvage a little more life out of these batteries.

 

Confusingly, the manufacturer of the HA02 actually calls it a battery equalizer (ie. it’s purpose is to ensure the individual batteries have equal voltage)…which should not be confused with equalization charging for the purpose of desulfation!

 

 

 

 

 

Part 2.3 – Installation of the HA02 Battery Balancer

This device monitors the individual voltage of the 4x batteries. If the voltages deviate more than 10mV, it discharges the higher voltage battery to charge the lower voltage battery until all battery voltages are equal. It is able to balance the batteries with a maximum of 10A current.

10mV is a very small voltage difference. Ideally, you need to install the provided cables directly to the batteries without extending (or cutting) the provided cables. Unequal length cables (or frankly any difference in cable type or cable cross section) can very easily cause voltage drop differences of more than 50mV (especially when the current could be as much as 10A).

With my battery rack layout, it was impossible to connect the existing leads directly to the batteries (leads were too short). So I devised the following setup which also provided test points for easily measuring the individual battery voltages :

 

[Speedster]

13 hours ago, Speedster said:

Really fun project to read. Thanks for sharing!

I bought one of these a while back, the pulse repair function helped save some of my small (7Ah) lead-acids. 

Lol. I see my link failed. This is the one I bought

https://banggood.app.link/RNqckiQSYdb

[Costa]

13 hours ago, Speedster said:

Lol. I see my link failed. This is the one I bought

https://banggood.app.link/RNqckiQSYdb

Hi Speedster.

 

Thank you for sharing the link to the charger. Despite the cryptic details and specs, you’ve got me pondering to get one too. The price is pretty good too at the moment.

 

You say you have had good success with it on the 7Ah batteries? If you’ve been able to extend the life of two-three batteries then it’s basically paid itself off!

[Speedster]

5 hours ago, Costa said:

Hi Speedster.

 

Thank you for sharing the link to the charger. Despite the cryptic details and specs, you’ve got me pondering to get one too. The price is pretty good too at the moment.

 

You say you have had good success with it on the 7Ah batteries? If you’ve been able to extend the life of two-three batteries then it’s basically paid itself off!

I needed a 12v/24v charger anyway, so the repair functionality is a bonus

[Costa]

Part 2.4 – Summary and status of what has been done so far

• My 48v inverter + 4x200Ah batteries were installed in Dec 2018 (without a battery balancer)
• My average load on the inverter is ± 500W – therefore the average current draw on the battery bank is ±10A
• According to the battery datasheet, these batteries are able to provide 10A continuously for 20hours (100% DOD - depth of discharge)
• Based on my required runtime of 9-12 hours @ ±10A, we can roughly expect a 45% - 60% DOD
• Less than 2 years after installation, the battery capacity is unable to sustain ±10A for 4 hours load shedding & the inverter shut down at the 42.0V low voltage cut-off! (I do not have detailed data & graphs @ 10A draw)
• I conducted capacity tests with the inverter + battery bank @
  ±50A draw and confirmed that the runtime was less than 15min (these batteries should be able to deliver 50A continuously for 3h)
• I then proceeded to conduct individual battery capacity tests @ ±50A draw and identified that battery 1 was definitely kaput.
• I then attempted to desulfate all four batteries, as per the strategy discussed above.
• I again repeated the individual battery capacity tests @ ±50A draw and the results are summarised in the following graphs:

 

[Costa]

• The improvement in battery capacity indicates that, to some degree, sulfation had been reversed.
• My hypothesis for the root cause of the pre-mature battery failure is that, in the absence of a battery balancer within a bank of batteries, the weak battery will keep getting undercharged and will progressively sulfate and get weaker and weaker. This will eventually spiral out of control and lead to the destruction of the whole bank of batteries!
• I added the HA02 battery balancer, then reconnected and powered-up the inverter.
• I repeated the capacity tests with the inverter + battery bank at an average inverter load of 450W (the current draw from the batteries was on average around 10A). The runtime had improved to 8h 40min! Not too shabby! (refer to the graph below for moredetails):

 

 

• 8hours 40min runtime @ 10A vs a theoretical maximum 20h @ 10A indicates a battery bank health/capacity of 43%

 

• I also installed a shunt and an energy meter (ill share closeup photos in a future post) and recorded that the batteries had in fact delivered 3896Wh during the above test.
• A crude estimate of the (theoretical) maximum stored energy in a 48v 200Ah battery bank = 48*200 = 9600Wh.
• Interestingly, the measured capacity vs theoretical capacity also indicate a battery bank health/capacity of 40%!

Not a bad improvement for batteries that are technically kaput!

 

I wouldn't trust them to carry me through the night, but they should be fine for 2h or 4h of load shedding!

[Richard Mackay]

In the bad old days when you could add water to these batteries when applying an equalization charge. So the battery electrolyte could be topped up.

These days with most batteries being sealed or semi sealed you can't do that. (Good for battery sales I guess!)

Edited February 20, 2021 by Richard Mackay

[Costa]

3 hours ago, Richard Mackay said:

In the bad old days when you could add water to these batteries when applying an equalization charge. So the battery electrolyte could be topped up.

These days with most batteries being sealed or semi sealed you can't do that. (Good for battery sales I guess!)

Richard, I think you are correct.

The classic "wet cell" lead-acid batteries probably deliver a decently long life (assuming you put in the required effort to rigorously maintain them).

Since the average consumer neglects the batteries (due to the laborious effort required to maintain them) it is understandable that the emergence of “maintenance free” sealed type lead-acid batteries have been very well received.

In effect, the design of sealed batteries have struck a different balance of compromises between user convenience vs “ultimate long life”!

Yup...good for battery sales. Probably not too great for the environment...

 

ps. I have come across YouTube videos, whereby nutty people experiment with reviving dead AGMs by adding acid and various other stuff!

[Chris Louw]

47 minutes ago, Costa said:

Richard, I think you are correct.

The classic "wet cell" lead-acid batteries probably deliver a decently long life (assuming you put in the required effort to rigorously maintain them).

Since the average consumer neglects the batteries (due to the laborious effort required to maintain them) it is understandable that the emergence of “maintenance free” sealed type lead-acid batteries have been very well received.

In effect, the design of sealed batteries have struck a different balance of compromises between user convenience vs “ultimate long life”!

Yup...good for battery sales. Probably not too great for the environment...

 

ps. I have come across YouTube videos, whereby nutty people experiment with reviving dead AGMs by adding acid and various other stuff!

Removed the sealing tape of a 30 month old LDV battery. The top of the lead plates was not covered by electrolyte. Top this battery up a few times and still going. 

[paulus]

On 2021/02/19 at 10:56 PM, Costa said:

• The improvement in battery capacity indicates that, to some degree, sulfation had been reversed.
• My hypothesis for the root cause of the pre-mature battery failure is that, in the absence of a battery balancer within a bank of batteries, the weak battery will keep getting undercharged and will progressively sulfate and get weaker and weaker. This will eventually spiral out of control and lead to the destruction of the whole bank of batteries!
• I added the HA02 battery balancer, then reconnected and powered-up the inverter.
• I repeated the capacity tests with the inverter + battery bank at an average inverter load of 450W (the current draw from the batteries was on average around 10A). The runtime had improved to 8h 40min! Not too shabby! (refer to the graph below for moredetails):

 

 

• 8hours 40min runtime @ 10A vs a theoretical maximum 20h @ 10A indicates a battery bank health/capacity of 43%

 

• I also installed a shunt and an energy meter (ill share closeup photos in a future post) and recorded that the batteries had in fact delivered 3896Wh during the above test.
• A crude estimate of the (theoretical) maximum stored energy in a 48v 200Ah battery bank = 48*200 = 9600Wh.
• Interestingly, the measured capacity vs theoretical capacity also indicate a battery bank health/capacity of 40%!

Not a bad improvement for batteries that are technically kaput!

 

I wouldn't trust them to carry me through the night, but they should be fine for 2h or 4h of load shedding!

 

[paulus]

Thanks for this, very useful and informative. Pictures also useful.

Did you come across any cheap data logging solutions? You could try an Arduino (which has built in voltage ADCs), and maybe add a  current sensor (around R100-200) which converts current to voltage using a hall effect sensor.

Your hypothesis about the lack of a battery balancer leading to the imbalance sounds pretty plausible.

[Costa]

On 2021/02/21 at 9:21 AM, paulus said:

Thanks for this, very useful and informative. Pictures also useful.

Did you come across any cheap data logging solutions? You could try an Arduino (which has built in voltage ADCs), and maybe add a  current sensor (around R100-200) which converts current to voltage using a hall effect sensor.

Your hypothesis about the lack of a battery balancer leading to the imbalance sounds pretty plausible.

Hi Paulus,

Funny you should mention this

Yes, I eventually ended up looking at the Arduino ecosystem…I actually started playing with them for the first time a few weeks ago…more about this in a moment;

The tests that I conducted between Nov – Dec 2020 were crazy time consuming! Not a sustainable nor practical way to do it….but I didn’t want to spend the next few weeks-months figuring out the Arduino stuff…so I opted for a different interim solution:

Battery Capacity Testing Tools v2.0

Step 1: I upgraded my 600W “light emitting heater” with a 100A shunt and LCD display that provided Voltage, Current, Power & Energy. Also upgraded to 10sq mm power cables and seperate 4sq mm cables for voltage sensing.

 

Step 2: Manual data capturing was replaced by a USB “pen type” voltage datalogger.

Step 3: I added a low voltage cutoff (KEMO M148A). This allows me to adjust and set the low voltage cutoff (for example to 10.7v). This can drive a second high power relay that will disconnect the 50A lights to automatically stop the test.

Step 4: I added an audible buzzer, to alert me that the KEMO switched over at the pre-set cutoff voltage

This allows the battery capacity tests to proceed unmanned (ie I don’t need to stand over it and watch the proverbial paint dry). The datalogger handles all the data capturing of the battery voltage. The KEMO switch will stop the test at the pre-set cut-off voltage. Finally, the buzzer also goes off to alert me to go and inspect and ensure that the test has stopped and the battery does not get discharged past the cut-off voltage.

Note 1: My 1^st attempt with a “claimed” 80A high power automotive relay failed miserably within the first 10 min of operation. Turns out, I should have trusted my instinct…just because the Chinese factory printed 80A on the casing does not mean they have miraculously achieved it!

 

 

[Costa]

Note 2: My subsequent (hasty) attempt to replace the automotive relay with a high power solenoid/contactor used on a motorbike starter motor ... also failed miserably. In my haste, I completely overlooked the duty-cycle! The starter solenoid is designed to deliver 300-400 amps for 4 seconds and then cools down till the next time. The starter solenoid will effectively cook itself to destruction, just from being energised continuously – even with ZERO amps current draw from the battery! I wasted way too much time and money on this dead end...but I did have lots of fun!

 

[Costa]

In summary: with Battery Capacity Test Tool V2.0,  have been turning the 600W light ON-OFF manually by hand. Start the test, the datalogger records the battery voltage vs time. Listen out for the buzzer, then go and witness the last few minutes of discharge till the cut-off voltage and finally switch off the lights (manually).

 

Spoiler alert 1: I have used this setup to revive and evaluate my old Deltec 200Ah batterieis and another set of Allgrand 200Ah that are installed at my father-in-law (more about those results in a future post).

Spoiler alert 2: I am busy playing with an ESP8266 (similar to Arduino) + OLED screen + INA219 current & voltage sensing board + microSD card, to build a comprehensive datalogger setup (V3.0). Im already sitting at over 900 lines of Arduino code. The baby shunt on the INA219 will eventualy be replaced with my 100A shunt. This is intended to also switch the 50A load via a software controlled cut-off voltage.

[dave1]

Hi Guys,

I have 2  Allgrand 12 V 200 Ah batteries connected to my inverted. These batteries only provide me with 15 minutes of life during a load shed. I must admit that we are currently experiencing extreme levels of load shedding. I'm wondering if a desulphur exercise would revive these batteries.

Thanks,

DaveG