Problems with default AGM settings (Low Voltage Cutoff)

[JoseAgustinV]

Recently I was experiencing issues with a 4 months old AGM battery, I've been using the default AGM Battery Type settings for my MPP solar 12v system and after 4 months it only activated the cut off voltage one time, after that the battery seems to be discharging way faster and the low voltage cutoff function activates again couple days after, at night even when I was using just my router, that never happens before, I could let the inverter on with the router until morning and still have 12.6V on the battery.

I figured out that adjusting the low voltage cut off won't take effect unless I change the Battery type settings to User-Defined, but it was too late until I figured out this. I contacted MppSolar support and asked them to provide me the information about default parameters for Battery Type AGM for float, bulk, and cutoff voltage, that was the answer:

• Float charging = 13.5V
• Bulk Charging = 14.1V
• Low Voltage Cut off = 10.5V

Everything seems ok but low voltage cutoff is very low, so I suppose I damaged the battery by reaching that voltage as its 100% DOD. I think that should not be the default settings for AGM as nobody recommends to discharge the battery to 10.5V, and I've seen that people are recommending to use the default battery type settings to AGM and change the low voltage cut off to 11.5-12V, and low voltage config won't take effect unless you change the Battery Type settings to User-Defined.

Also, I think I could set the bulk charging higher for the AGM battery. I wish to know what are the recommended settings for AGM batteries for float, bulk, and cutoff voltage since I can only find advice for lifepo4 ones.

Greetings to everyone!

 

[kernel]

First off it is best to check what the battery manufacturer states are the charge parameters for success with their product.

There are general agm type settings but it is good to know that you are charging to sufficient voltage and time or return amps termination point or just as the battery likely too deeply discharged, it might not get fully charged which can do two or more things to capacity.

First it cannot have full or reasonably near full capacity unless it is at proper voltage long enough to accept it.

Next it accelerates and causes loss of capacity by not driving electrolyte back to its reactive state and driving sulphates off the plates which can be permanent and to higher or loower degrees.

If you can get it back, it will be a full charge that does it.

I suggest using the user defined profile for your model battery if you can find its spec. If not use general guides from a swath of profiles for comparison from quality sources.

Example, morningstar solar fixed sealed battery settings arent known for killing batteries.....

 

[kernel]

Run it on the hot side after a moderate rate full charge cycle to determine if its going to have thermal trouble first.

If its going to work it will. Avoid off-gassing past the vent. Monitor this. It could piff a tiny bit but should generally not of its working well, or accepting the charge levels younare giving it.

Then a voltage reading at rest followed by a load test.

 

[kernel]

Lvd to 11.5 unless its a nuisance. If batttery rough soc is clearly fine, bump it down. Load compensated lvd varies in effectiveness or expectability of opeeration.

 

[kernel]

Is there an absorb time setting or end/return amps absorb termination set point? The manual should have this information.

14.1V is as high as you want to go unless the manufacture has a different number.

Very common to battery charging issues is insufficient absorb time. Either on the available source side or control. This is paramount. If it was deeply discharged being in absorb for a default 1 hour period could be too short a time.

Something to check while revising settings.

 

[JoseAgustinV]

Thx for your reply @kernel Unfortunately i dont have the tools to do these tests, ill attach the spec sheet to see if you can help mw with the settings, i dont know which settings should i have based on the specs.

 

[kernel]

If your inverter has a display of battery current, battery voltage, inverter power, and you have a stopwatchand notebook or other function of datalog in the machine, you can apply a load that matches the battery spec for so many minutes to a certain voltage and check voltage sag under heavy load.

Useless until fully charged.

 

[kernel]

Could you screen shot the page?

 

[JoseAgustinV]

Is there an absorb time setting or end/return amps absorb termination set point? The manual should have this information.

14.1V is as high as you want to go unless the manufacture has a different number.

Very common to battery charging issues is insufficient absorb time. Either on the available source side or control. This is paramount. If it was deeply discharged being in absorb for a default 1 hour period could be too short a time.

Something to check while revising settings.

I cant read anything about absortion voltage settings on the manual, only bulk voltage which is max charging voltage

 

[kernel]

Terminology varies.... part of the fun.

 

[kernel]

The battery spec is the important part.

 

[JoseAgustinV]

Could you screen shot the page?

For battery specs? Here

 

[kernel]

Looks like it requires 14.5V or bettter in absorb for cycle use.. as high as 14.9!
Float at 13.5-13.6

30A max rate. 15A-20A plenty. Id keep it below that max rate unless its occasional or to support heavy standby loads.

 

[kernel]

Try raising to 14.5 amd 1.5-2 hr. Minimum 1 hr. Note the current goinng to the battery and terminate before it accepts less than 2.5A. That outta do it for a full charge. If it still has low capacity go longer or higher voltage.

You will want temperature compensation operating proper.

 

[kernel]

No loads..... or compensate for them if the machine wont.

 

[JoseAgustinV]

Ok, i changed the bulk charging voltage to 14.5V, float to 13.6V and cutoff to 12.0V, i think the inverter will use the 12.0V as a base and will calc the to a lower voltage depending on inverter load, based on the inverter manual here:

 

[JoseAgustinV]

30A max rate. 15A-20A plenty. Id keep it below that max rate unless its occasional or to support heavy standby loads.

There are 3 settings for this:

1) Max charging current:



2) Max utility charging:



3) Charge source priority: this is set to utility first, and it wont charge the battery with both utlity and solar, just one at time.

How should i set this?

It was set to 40A max total and 20A max utility but i think 30max and 10max utility could be better, im not sure how many amps will i get with solar though, i think is max total amps - max utility amps im i right? I want to get more amps with solar since i only have loads on battery when using solar power (when there is no utility available).