Battery configuration for AGM batteries in series/parallel

[off.the.grid]

Have I got my figures right for ny setup?
I'm setting up my controller now.
I have 4x 12v 270Ah batteries (2 pairs in series then in parallel) providing 24 volts.
Charge current specs say don't exceed 50A.
I guess I'll set the controller to 49A each battery to be on the safe side.
AFAIK, batteries in series have the charge current the same, but in parallel, it's double the current?
So am I right to set it as 98A @29.2V for all 4 batteries?
The charge specs say 14.6V per battery, so this would be 29.2V in total.

Datasheet for batteries is here.

12V 270AH NOMAD E2 DEEPCYCLE BATTERY 5Yr WARRANTY | Waveinverter

waveinverter.co.nz

Am using an epever controller that I cam program via the smartphone app.

 

[rmaddy]

In series you add the voltage. In parallel you add the amperage.

So you are correct. If one battery is 14.6V with a charge current of 50A then 4 batteries in 2S2P means double the voltage and double the amperage. So charging the bank at 29.2V and 100A is correct. You will have a 24V 540Ah battery bank.

Disclaimer: I know little about AGM batteries and I didn't look at the specs. I'm just confirming that your general thoughts and math are correct based on the numbers you provided. I don't actually know if charging AGM at 29.2V and 100A is considered ideal.

 

[BentleyJ]

I'm not an AGM battery user but I did look at the specification sheets at the link you provided. Two things caught my attention.
1) 50A is the MAX charging current not the recommended current. I would go with 25 to 40Amps depending on how long of a charging cycle you require. Lower current is better for the life of the battery.
2) The supplemental battery charging page specifies that the voltage should never ever exceed 2.45V per cell yet they are calling for charging voltages of 29.2 which is 2.43V per cell. This makes absolutely no sense, there is no room for error. On the other hand, curiosity was with me so I did more searching and found other brands of Deep Cycle AGM batteries that recommend charging up to 30V. Not sure what to conclude but its probably worth more research to determine the best parameters to extend the life of the batteries and get the most of your investment.

 

[off.the.grid]

Well I guess I can tweak in future if necessary. My supplier says 14.6v is the recommended voltage, so I'm not sure what to go for.

 

[off.the.grid]

Anyone familiar with these epever controllers?
I can't see anywhere under basic or advanced battery settings to set charge current.
There is a bunch more parameters I'm unsure about here too.

There are also preset settings available.
Not sure if AGM comes under the "sealed" or "gel"

 

[mikefitz]

Having used AGM this is my comment.
The battery is 220Ah at the 20 hour rate, and this Ah capacity is the normal for calculations based on C, battery capacity.
AGM batteries suffer reduced service life due to,
Under charging, low charge current, and high temperature . The service life halves for every 10 degCent above 25 degCent

An ideal charge rate is between 0.2 and 0.25 C, that's 44 to 55 amps, the cycle graph indicated tests were made at 0.25C.

Typical charge volts , temperature compensated, will be 14.4 to 14.8 volts.

Float volts, 13.4 to 13.8 volts, for standby use use the lower value.

An ideal charger would charge in bulk to , say 14.6 volts, hold this voltage constant for the absorbtion period, until the charge current falls to 0.5% of capacity, 2.7 amps for the battery pack under discussion.

Solar charging AGM with an Epever is a compromise as termination of absorbtion is time based .
Use 14.6 for boost volts , and 13.8 float, the high float will 'top up'. ( times 2 for a 24 volt system)

Mike

 

[off.the.grid]

Ok

Having used AGM this is my comment.
The battery is 220Ah at the 20 hour rate, and this Ah capacity is the normal for calculations based on C, battery capacity.
AGM batteries suffer reduced service life due to,
Under charging, low charge current, and high temperature . The service life halves for every 10 degCent above 25 degCent

An ideal charge rate is between 0.2 and 0.25 C, that's 44 to 55 amps, the cycle graph indicated tests were made at 0.25C.

Typical charge volts , temperature compensated, will be 14.4 to 14.8 volts.

Float volts, 13.4 to 13.8 volts, for standby use use the lower value.

An ideal charger would charge in bulk to , say 14.6 volts, hold this voltage constant for the absorbtion period, until the charge current falls to 0.5% of capacity, 1.1 amps for the battery under discussion.

Solar charging AGM with an Epever is a compromise as termination of absorbtion is time based .
Use 14.6 for boost volts , and 13.8 float, the high float will 'top up'. ( times 2 for a 24 volt system)

Mike

Ok thats helpful, I had set the charging limit voltage to 14.6 (29.2)
I'll set boost to that tomorrow along with the floating voltage.

Is there anything else I need to worry about on the other voltage settings? There are quite a few parameters, but I assume boost and float are the most critical.

So are you saying that these controllers automatically adjust current accordingly over time?

I guess the temperature sensor could be useful, im assuming it slows charging down if the batteries get too hot from what I can tell.

 

[pollenface]

Solar charging AGM with an Epever is a compromise as termination of absorbtion is time based .

Absorption times I found in a Victron manual.

12.6v or higher = 1hr
12.2 - 12.6v = 2hrs
11.9 - 12.2v = 4hrs
11.9v or lower = 6hrs

 

[off.the.grid]

There is quite a bit more to charging these things than you realize, I just thought it was setting the volts per cell and away you go. I don't think car battery chargers do anything like this.
I guess it's just a way to maximize life more than anything.

 

[off.the.grid]

The supplier of the batteries just told me to leave on the "sealed" settings with my epever controller. Does this sound right?
Any harm in tweaking it to the recommended float and boost voltages?
Does it vary much between brands of batteries?

 

[mikefitz]

The sealed battery default setting is within the range suggested by the battery manufacturer, I would perhaps increase the boost volts a little. See how get on, solar and AGM is not an ideal combination if you have variable solar conditions.

Mike

 

[pollenface]

The supplier of the batteries just told me to leave on the "sealed" settings with my epever controller. Does this sound right?
Any harm in tweaking it to the recommended float and boost voltages?
Does it vary much between brands of batteries?

SEL = Equalize 14.6v 180min, Boost 14.4v 180min, Float 13.8v.

I would use GEL if unsure (No equalize and Boost 14.2v 180min) until you come up with a better idea of your charging requirements and make your own charging profile.

 

[off.the.grid]

The sealed battery default setting is within the range suggested by the battery manufacturer, I would perhaps increase the boost volts a little. See how get on, solar and AGM is not an ideal combination if you have variable solar conditions.

Mike

I was thinking I would do that and set boost volts to 29.2v
I expect that there default values won't be far off.
Never realized that AGM was so problematic on solar. Is it because when there is little sun, you cant get enough current to properly charge the batteries?

 

[off.the.grid]

SEL = Equalize 14.6v 180min, Boost 14.4v 180min, Float 13.8v.

I would use GEL if unsure (No equalize and Boost 14.2v 180min) until you come up with a better idea of your charging requirements and make your own charging profile.

Ok do it will really just come down to energy use vs sunlight?
I thought battery equalize was only for flooded cells to desulfate the plates?
I will probably use more energy over summer when it's hotter and the freezer will use more power, along with the swimming pool pump.
Upside is we get more sun to make up.

 

[mikefitz]

Equalise is only for flooded batteries but the default is only 14.6 so will not harm an AGM. The GEL setting boost volts is too low for AGM.

 

[pollenface]

Equalise is only for flooded batteries but the default is only 14.6 so will not harm an AGM. The GEL setting boost volts is too low for AGM.

I think it varies a from one battery to another. I have a bunch of AGMs which specify 14.1 to 14.4 for cycling.

There seemed to be a strong consensus on this forum a while ago about using the GEL setting with Epever and AGM and never exceeding 14.4v.

Who's right? I have no idea, I'll just try to pick a happy medium somewhere and hope for the best

 

[off.the.grid]

Well from what I can gather, if I keep equalize between 14.4 and 14.6 I should be safe?
I also see some brands of AGM claim to be designed to take equalizing.

 

[mikefitz]

The Nomad battery data suggests charge between14.4 and 14.6.
Equalise at 14.6 every 28 days for 2 hours won't be an issue.
Mike

 

[off.the.grid]

Here are my current voltages, look ok to you?
Battery appears to be charging well on a cloudy day

 

[off.the.grid]

Just to add, it appeared my batteries charged full after about 2-3 hours and then dropped back to similar levels where it was to begin with.
See screenshot below.
This was after around 2-3 hours.
It says 100% full.
Now when i took the screenshot, I could hear the battery bank bubbling. Im used to hearing this with the old wet cells, but read that this is bad for AGM batteries.
The voltages all look ok from what I can tell.


What's odd is after about another hour, it dropped back in charge, down to 96%. This was after the sun started to drop away.


Then it dropped back even more.
I have no load or inverter connected to the batteries yet.

Any ideas? Should I be lowering my charge voltage perhaps?