How to determine absorption charge time

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Manzinik
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How to determine absorption charge time

Post by Manzinik »

Hi Guys,
Please, I have these questions about my flexmax80 solar charger controller.
1. I have #4 VRLA 200AH battery connected in series parallel for 2 bank of 24volt.#8 PV Array (8x270 watt) = 2160watts
Now, what should I set my absorption charge time at? My absorbing volt set at 28.8v, floating volt at 27.2v
2. If I may what to used absorption end amps instead of absorption charge time. How do I determine the absorption end amp.

Please, I need help on this.

Thanks
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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: How to determine absorption charge time

Post by fcwlp »

Your battery manufacturer will typically specify what the end amps are for the absorption phase. For lead-acid batteries this can range from 0.5% to 3% of the C20 rate for the battery bank. A VRLA (Valve Regulated Lead Acid) battery is typically at the lower end of the range running from 0.5% to 2%.

IF the 200AH you state is the C20 rate, then for your two parallel strings you have 400AH. End amps of 1% would be 4 amps. If how ever you are also pulling substantial loads the CC is not the best way to terminate the charge. The better way is with a FNDC or similar which is measuring the current flow in and out of the battery bank and can thus accurately determine the end amps.
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Re: How to determine absorption charge time

Post by raysun »

What is the brand and model of the battery monoblocks?

The manufacturer usually gives specific specifications for Absorb Voltage, Time, and End Amp percentage.

VRLA batteries have two special considerations. Absorb is a controlled overcharge designed to force a full charge into the battery. VRLA suffer from two effects in an overcharge: grid corrosion, and permanent loss of electrolyte. Grid corrosion is mitigated to a degree by including calcium in the alloy. The water electrolysis during an overcharge can exceed the capacity of the recombination catalyst, resulting in gas venting and loss of electrolyte. This loss results in a permanent loss of battery capacity.

Properly charging a VRLA battery while minimizing the negative effects is a fine line. Quality VRLA battery cells charge rapidly for lead acid. Other VRLA batteries of similar capacity have 1 to 1.5H specified for Absorb Time.
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EA6LE-ONE
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Re: How to determine absorption charge time

Post by EA6LE-ONE »

fcwlp wrote: Fri Nov 27, 2020 1:25 pm Your battery manufacturer will typically specify what the end amps are for the absorption phase. For lead-acid batteries this can range from 0.5% to 3% of the C20 rate for the battery bank. A VRLA (Valve Regulated Lead Acid) battery is typically at the lower end of the range running from 0.5% to 2%.

IF the 200AH you state is the C20 rate, then for your two parallel strings you have 400AH. End amps of 1% would be 4 amps. If how ever you are also pulling substantial loads the CC is not the best way to terminate the charge. The better way is with a FNDC or similar which is measuring the current flow in and out of the battery bank and can thus accurately determine the end amps.
I am still a bit confused how to select the correct "Charged Return Amps" or end amps. Most manufacturers don't specify the amps and after researching on the web I find that most say that 2% of C20 is the number to use.

The only thing I can find in the manual of my batteries for full charge is this:

The sealed design of the VRLA batteries makes it impossible to measure specific gravity as a
state-of-charge indicator. The state-of-charge can be identified to some degree by the
amount of charging current going to the battery exceeding 2.35 volts per cell.

Determining the State-of-Charge
The following method can be used to determine the state-of-charge of the battery.
1. Place the battery on charge/recharge following a discharge.
Read the ammeter.
The charging current will be a combination of the load current plus the current
necessary to charge the battery.
2. The battery becomes fully charged when the current to the battery starts to
decrease and stabilize.
3. When the current level remains constant for three consecutive hours, the state-of charge is approximately 95 to 98%. Full charge can be assumed.

So the best I can do is to increase the absorb time and keep an eye FNDC until the charge current is stabilizing. adding few amps and using that value as end amps. the float will probably finish the rest of the charging that is left then.

Also the absorb charge advertised by outback is 55.6 which is smaller than the voltage advised by the manual from the manufacturer. which is 2.35V per cell and is 57.12V for the 24 cells. Is outback using the wrong voltage? the float is correct at 2.25V in the manual and outback brochure.

Raysun your opinion might shed some light here.
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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: How to determine absorption charge time

Post by fcwlp »

Every battery manufacturer is different. There is also the difference between AGM and FLA and those that use carbon in AGM and FLA. Trojan and Rolls Surrette have very detailed battery manuals. For VRLA AGMs, Trojan recommends end amps of 0.5% of C20 and Rolls recommends 3-4% of C20. Full River also has a good charging document and specifies for VRLA AGMs 1.2% - 2% of C20.

I would agree that Enersys is weak on giving advice on how to maintain and charge their batteries. I searched the 70 page "EnergyCell RE High Capacity Battery, Installation Guide and Owner’s Manual" for the terms: bulk, absorb, "end amps", and amps. All queries returned no results or one result unrelated to charging the batteries.
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Re: How to determine absorption charge time

Post by raysun »

Rolls publishes an Absorb Time calculation that is fairly applicable to all AGM monoblocks:

We recommend a charge current of 20% of the 20 hr rate for both Bulk & Absorption charge phases on AGM & GEL VRLA models.

[10% min, 20% recommended, 30% max]

t = 0.38 x (C/I)

Where:
t = Absorption Charge Time (Hours)

C = 20 hr Rated Capacity (AH)
[ex: 2 strings x S6-460AGM-RE models (415 AH) = 830 AH rated capacity]

I = Charging Current (Amps)
[charger output min 10% up to max 30% of 20 hr rate]

EXAMPLE:

2 strings of S6-460AGM batteries

20 hr rate = 415 AH x (2 strings) = 830 AH

I =20% of 830 AH = 166 Amps OR If the charger output limit is 120 Amps max, then 120 is used

T = 0.38 x 830/166 = 1.9 hrs OR T = 0.38 x 830/120 = 2.63 hrs
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EA6LE-ONE
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My RE system: System 1:
MATE3s, 3 x Radian GS8048A,
4 x FLEXmax 100, HUB10,
2 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 4 x FLEXware ICS Plus,
54 x PANASONIC VBHN325SA17 325W

System 2:
MATE3s, Radian GS8048A,
2 x FLEXmax 100, HUB10
1 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 2 x FLEXware ICS
21 x PANASONIC VBHN325SA17 325W
Location: Providenciales, Turks & Caicos Isl.

Re: How to determine absorption charge time

Post by EA6LE-ONE »

Since I got the batteries I research everything I could find about them and I sent messages to enersys and outback asking about the best settings for charging in solar applications.
Only outback responded with the same specs they have on the brochure online. 55.6V absorb, 54V and 2 hours absorb and 2 hours float.
I set the end amps at 2% as that was the advertised on many forums. for the double battery that has a bigger array was finishing the absorb quicker and had longer float that probably helped to get the battery filled. and the SOC and voltage were matching every day level (only cloudy and rainy days that will not have much of float time will not match). on the single battery since the solar day got shorter I got lesser floating time and the SOC was not matching and I reduced the end amps to about 1.7% and then had enough float time and SOC and V were looking good again.
so if the manual advertise to keep the battery longer on absorb and see when the amps are stabilizing and add maybe 10 amps more for the single battery and 20 for the "Charged Return Amps" on FNDCs. Also I will watch the temperature on the batteries and try to corelate it to end amps.
I will keep the absorb at 55.6V as was working good for the last 6 months. the manual suggesting refreshing charge also using 2.35V per cell for 24 hours. I am wondering if I should use the 2.35V for absorb as well.

Any suggestions will be welcome. I want to get the most of their life. I can use them until they have 50% capacity left. maybe even 40%. By then the lithium might be lower cost and more proven.
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EA6LE-ONE
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Posts: 362
Joined: Tue May 05, 2020 7:51 am
My RE system: System 1:
MATE3s, 3 x Radian GS8048A,
4 x FLEXmax 100, HUB10,
2 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 4 x FLEXware ICS Plus,
54 x PANASONIC VBHN325SA17 325W

System 2:
MATE3s, Radian GS8048A,
2 x FLEXmax 100, HUB10
1 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 2 x FLEXware ICS
21 x PANASONIC VBHN325SA17 325W
Location: Providenciales, Turks & Caicos Isl.

Re: How to determine absorption charge time

Post by EA6LE-ONE »

raysun wrote: Sat Nov 28, 2020 9:53 am Rolls publishes an Absorb Time calculation that is fairly applicable to all AGM monoblocks:

We recommend a charge current of 20% of the 20 hr rate for both Bulk & Absorption charge phases on AGM & GEL VRLA models.

[10% min, 20% recommended, 30% max]

t = 0.38 x (C/I)

Where:
t = Absorption Charge Time (Hours)

C = 20 hr Rated Capacity (AH)
[ex: 2 strings x S6-460AGM-RE models (415 AH) = 830 AH rated capacity]

I = Charging Current (Amps)
[charger output min 10% up to max 30% of 20 hr rate]

EXAMPLE:

2 strings of S6-460AGM batteries

20 hr rate = 415 AH x (2 strings) = 830 AH

I =20% of 830 AH = 166 Amps OR If the charger output limit is 120 Amps max, then 120 is used

T = 0.38 x 830/166 = 1.9 hrs OR T = 0.38 x 830/120 = 2.63 hrs
The problem with solar is that is hard to have charging amps kept constant, loads kicking in and clouds will reduce the charging amps. so the absorb time is useless. the best is the end amps.
raysun
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: How to determine absorption charge time

Post by raysun »

EA6LE-ONE wrote: Sat Nov 28, 2020 10:15 am Since I got the batteries I research everything I could find about them and I sent messages to enersys and outback asking about the best settings for charging in solar applications.
Only outback responded with the same specs they have on the brochure online. 55.6V absorb, 54V and 2 hours absorb and 2 hours float.
I set the end amps at 2% as that was the advertised on many forums. for the double battery that has a bigger array was finishing the absorb quicker and had longer float that probably helped to get the battery filled. and the SOC and voltage were matching every day level (only cloudy and rainy days that will not have much of float time will not match). on the single battery since the solar day got shorter I got lesser floating time and the SOC was not matching and I reduced the end amps to about 1.7% and then had enough float time and SOC and V were looking good again.
so if the manual advertise to keep the battery longer on absorb and see when the amps are stabilizing and add maybe 10 amps more for the single battery and 20 for the "Charged Return Amps" on FNDCs. Also I will watch the temperature on the batteries and try to corelate it to end amps.
I will keep the absorb at 55.6V as was working good for the last 6 months. the manual suggesting refreshing charge also using 2.35V per cell for 24 hours. I am wondering if I should use the 2.35V for absorb as well.

Any suggestions will be welcome. I want to get the most of their life. I can use them until they have 50% capacity left. maybe even 40%. By then the lithium might be lower cost and more proven.
The path you are on is exactly the path I took and seemed to yield fairly good results. Even though I did have two monoblocks fail in service, but I don't think it had anything to do with charging. Watching the charging numbers for alignment was confidence inspiring - until they lied. The system was happily chugging along at the original specifications until a "disturbance in the Force" prompted me to do a capacity test. My specified 350AH battery was now a 280AH battery. I think the capacity reduction was buried in the usage and charging data, but I couldn't back into them. I believed the capacity test, came to the conclusion the battery was EOL (for our purposes, after 4.5 years.) We upgraded our system, and the old system was sold intact as a piece. The battery was a "give away" with the caveat that its residual life is unknown. His daily consumption is far lower than ours, and so far the battery continues to perform without a hitch.

Moral of the story is: Charging AGM is half science, half art.

Periodic capacity tests are in order. Annually is probably a good interval. Check the battery manual warranty section for capacity testing guidelines.
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Re: How to determine absorption charge time

Post by Manzinik »

Thanks Guys for all your replies.
Here is the battery information:
Manufacturer: Rhino deep cycle battery
FCD12-200AH,C10
Standby use: 13.6v- 13.8v
Cyclic use: 14.4v - 14.9v
Initial current: 39.6A max.
My battery bank is 400AH, 24v system (2 strings of 12v, 200AH)
Total PV Array : 2000watt
My Flexmax80 controller settings are:
Charger current limit- 80Amps
Absorb voltage: 29v
Floating voltage 27.5v
Absorption time: 2hrs.

Please, do review my settings versus the listed requirements and advise.Especially, My absorb voltage, floating voltage, charger current limit and absorption time. Are my settings good and healthy for my battery bank?

Thanks in advance for your feedbacks
Manzinik
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Posts: 5
Joined: Thu Nov 26, 2020 5:12 pm
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Re: How to determine absorption charge time

Post by Manzinik »

raysun wrote: Fri Nov 27, 2020 3:05 pm What is the brand and model of the battery monoblocks?

The manufacturer usually gives specific specifications for Absorb Voltage, Time, and End Amp percentage.

VRLA batteries have two special considerations. Absorb is a controlled overcharge designed to force a full charge into the battery. VRLA suffer from two effects in an overcharge: grid corrosion, and permanent loss of electrolyte. Grid corrosion is mitigated to a degree by including calcium in the alloy. The water electrolysis during an overcharge can exceed the capacity of the recombination catalyst, resulting in gas venting and loss of electrolyte. This loss results in a permanent loss of battery capacity.

Properly charging a VRLA battery while minimizing the negative effects is a fine line. Quality VRLA battery cells charge rapidly for lead acid. Other VRLA batteries of similar capacity have 1 to 1.5H specified for Absorb Time.
Thanks Guys for all your replies.
Here is the battery information:
Manufacturer: Rhino deep cycle battery
FCD12-200AH,C10
Standby use: 13.6v- 13.8v
Cyclic use: 14.4v - 14.9v
Initial current: 39.6A max.
My battery bank is 400AH, 24v system (2 strings of 12v, 200AH)
Total PV Array : 2000watt
My Flexmax80 controller settings are:
Charger current limit- 80Amps
Absorb voltage: 29v
Floating voltage 27.5v
Absorption time: 2hrs.

Please, do review my settings versus the listed requirements and advise.Especially, My absorb voltage, floating voltage, charger current limit and absorption time. Are my settings good and healthy for my battery bank?

Thanks in advance for your feedbacks
raysun
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Posts: 3829
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
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: How to determine absorption charge time

Post by raysun »

I've found that VRLA batteries tend to charge quite easily for lead acid, and needn't be "pushed" as hard as flooded lead acid.

The balance in charging is to charge at high enough rate to complete in a timely manner, but not so high a rate that there is electrolyte loss due to incomplete recombination of oxygen and hydrogen. Electrolyte loss represents permanent capacity loss. In my experience, its preferable to slightly undercharge VRLA batteries than it is to overcharge them.

I might suggest starting with slightly lower charging parameters for Absorb and Float:
Absorb Voltage - 28.8
Absorb Time - 90 minutes
Float Voltage - 27.0

Does thevsystem have a battery monitor?

Does the system have a Outback Remote Temperature Sensor (RTS) for temperature compensated charging?
Manzinik
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Re: How to determine absorption charge time

Post by Manzinik »

raysun wrote: Mon Nov 30, 2020 5:03 pm I've found that VRLA batteries tend to charge quite easily for lead acid, and needn't be "pushed" as hard as flooded lead acid.

The balance in charging is to charge at high enough rate to complete in a timely manner, but not so high a rate that there is electrolyte loss due to incomplete recombination of oxygen and hydrogen. Electrolyte loss represents permanent capacity loss. In my experience, its preferable to slightly undercharge VRLA batteries than it is to overcharge them.

I might suggest starting with slightly lower charging parameters for Absorb and Float:
Absorb Voltage - 28.8
Absorb Time - 90 minutes
Float Voltage - 27.0

Does thevsystem have a battery monitor?

Does the system have a Outback Remote Temperature Sensor (RTS) for temperature compensated charging?
Thanks,
My system doesn’t have battery monitor other than the Charger controller.
The Flexmax80 has RTS. Mine is on wide
Manzinik
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Posts: 5
Joined: Thu Nov 26, 2020 5:12 pm
My RE system: Flexmax80 charge controller, 1.5kva shieneder electric hybrid inverter, 200Ah x 4, 24v system

Re: How to determine absorption charge time

Post by Manzinik »

Image
Rhino battery datasheet pg2
Rhino battery datasheet pg2
Rhino battery data sheet pg1
Rhino battery data sheet pg1
Above is attached data sheets of my battery.
Please, can you advise me on my
* Absorption voltage setting ?
* floating voltage?
* Absorption time settings?

Present settings are;
Absorption voltage 29v
Floating voltage 27.3v
Absorption time- 2hrs
Charger controller set at 80amp limit
Battery bank 2 strings of 200AH, C10 = 400AH
PV Array = 2000watt

Thanks
raysun
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Posts: 3829
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
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: How to determine absorption charge time

Post by raysun »

Manzinik wrote: Tue Dec 01, 2020 12:38 pm ImageFE2B6F84-9B8E-49E3-B704-D4410F212DC2.jpegDEC270CD-B070-405F-B179-9706DD01936A.jpeg

Above is attached data sheets of my battery.
Please, can you advise me on my
* Absorption voltage setting ?
* floating voltage?
* Absorption time settings?

Present settings are;
Absorption voltage 29v
Floating voltage 27.3v
Absorption time- 2hrs
Charger controller set at 80amp limit
Battery bank 2 strings of 200AH, C10 = 400AH
PV Array = 2000watt

Thanks
Yes, I found these docs on line. The charging recommendations I made above were derived from them.
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