Problems changing from AGM to Flooded

Ako · January 2022

For years my system has remained the same , panels feeding flooded batteries through a Morningstar TS60 PWM charge controller with a temperature sensor . Three weeks ago I changed from Flooded to Trojan AGM batteries and reduced my bank from 605 amp/hrs to 392 amp/hrs as I was struggling to maintain the 10% charge rate required and as my consumption at night was only between 60 and 100 amps my thinking was that I would still be well within the 50% DOD recommended .

The new AGM batteries are giving me concerns I didnt anticipate . My input and consumption is small but has always been consistent and predictable however for some reason the new batteries have changed everything . The flooded ones would not reach the set voltage around 29 volts until between 1pm and 2pm at which point I would have around 110 - 130 amps in rising through the absorption/Bulk to between 180-220 amp/hrs by the time charging ends .The new AGM reaches almost the same voltage by around 11am by which time I have only half what I would normally receive in Bulk . Because the Bulk charge allows all the available current into the batteries while the adsorption charge doesn't I am left with a decreasing input that insufficient to fully charge the batteries in the remaining time available which was never a problem with the flooded batteries . Previously I would see a total of 180-220 amps/hours input , now I get only between 115-130 . I have compared the Bulk charging amps and confirmed they are no different than they were with the Flooded batteries so the loss isn't there , its due to the change from Bulk to Adsorption far earlier with the AGMs . I know these batteries have a lower internal resistance which is promoted as a good thing but I cant see how .

The hours between 11-2 when I would receive the greatest input is lost , by 2pm i am getting only a third of what I would have with the Flooded batteries .

I have experimented a bit to try to understand more about the situation . This afternoon my incoming Amps were just under 10 so I turned on a 65 watt electric blanket and the incoming amps immediately went up to just over 12 amps . My system is 24 volts and the voltage at the time was 29 Volts as I was in Absorption . Am i being too simplistic and naïve to assume that the increase input was because the batteries were previously regulating the current coming is through resistance and my turning on the electric blanket lowered their resistance to allow the corresponding amps in or is it coincidental and wouldn't be as precise as it appears to be , ie: sudden 65 watts out and controller raises the input it allows in by approximately the same . Of course I could keep a larger load on the system all day and that would increase the amps coming in but they would be used during the day so counter productive .

The voltage shown just prior to charging while the batteries are at there lowest is around 24.45 which from the voltage/SOC guide in Trojans guide appears to indicate that I have cycled down to 50% . Unfortunately I cant get a completely at rest voltage as there is always 40 watts consumption for the Inverters self use , Internet and a 500va UPS . I dont think 40 watts load is going to have much effect on the voltage .

I found out that these batteries need to show 0.5% end amps to be 100% full , I cant get that low , again I don't know what effect the 40watt load makes to the end amps current either .

tabbycat · January 2022

I suspect that the larger bank took twice the amount of input to replace your consumption because it was operating in the absorption stage of the battery capacity. Topping off the last 20% of the bank is very inefficient.

The AGM's are doing the same job with far less energy.

Ako · January 2022

Thank you Tabbycat but i cant understand how a larger bank would take more input to replace whats been taken out hours before , surly if you use 80 amp hours you replace 80 amp/hours irrespective of the bank size .

Its the AGMs that are taking much longer to charge due to leaving Bulk early and being forced to charge in the Absorption stage .

Photowhit · January 2022

A few things...

Flooded lead acid are less efficient than AGM batteries, so greater charging is going on...

Also flooded batteries become less efficient as they age.

Ako said:

The flooded ones would not reach the set voltage around 29 volts until between 1pm and 2pm at which point I would have around 110 - 130 amps in rising through the absorption/Bulk to between 180-220 amp/hrs by the time charging ends .The new AGM reaches almost the same voltage by around 11am by which time I have only half what I would normally receive in Bulk . Because the Bulk charge allows all the available current into the batteries while the adsorption charge doesn't I am left with a decreasing input that insufficient to fully charge the batteries in the remaining time available which was never a problem with the flooded batteries . Previously I would see a total of 180-220 amps/hours input , now I get only between 115-130 . I have compared the Bulk charging amps and confirmed they are no different than they were with the Flooded batteries so the loss isn't there , its due to the change from Bulk to Adsorption far earlier with the AGMs . I know these batteries have a lower internal resistance which is promoted as a good thing but I cant see how

Have you changed your setting to AGM in the charge controller?

Charge controllers are basically regular run-away voltage. They just keep the voltage from running too high and ruining the battery.

The battery it's self allows only so much current to flow into it. Once the voltage reaches the set point the charge controller limit's the voltage. at this point the you have switch from Bulk to absorb stage of charging. You may be able to adjust the time it's in absorb or use end amps, if available, to regulate this (Which I think you have alluded to, but it should stay in absorb until it reaches the limited flow)

Ako said:

Unfortunately I cant get a completely at rest voltage as there is always 40 watts consumption for the Inverters self use , Internet and a 500va UPS . I dont think 40 watts load is going to have much effect on the voltage .

I found out that these batteries need to show 0.5% end amps to be 100% full , I cant get that low , again I don't know what effect the 40watt load makes to the end amps current either .

That is a huge load for a relatively small inverter. I think my Prosine 1800watt was spec'd at <20 and measured around 15 watts. My Exeltech was listed as 20 watts and they thought that was high enough that they made a low wattage version.

Photowhit · January 2022

Also the self discharge of your older battery back was likely much higher!

Ako · January 2022

Thanks Photowhit , i get the points your making . I did adjust my charge controller to the new AGM specks from the Trojan Data sheet , Voltage only needed slight adjustment and temperature compensation was identical but float needed larger adjustment .

Did another experiment today , only had about 120 amps after years of around 160-180 at that point in the day so i decided to turn off the inverters and leave the input to just charge the batteries with no draw under Absorption .Trojan quote 1.85 amps as being 1/200 of C20 .watched for an hour as the amps jumped up and down through about half an amp but were gradually decreasing , they got down to 2.40 then i ran out of daylight and went into bulk , im sure given more time it would have gone down to the required input , think the input i did get meant the batteries are getting towards a full state so i feel a bit more confident . Compared the total daily input i did get and it was just 5 amps more then my consumption since end of charge yesterday .

My 1500 watt pure sine wave Solener inverter shows 25 watts passing through it with no load so i presume thats its self consumption . Looking at specks it says power consumption <70 ma and an efficiency under load of 85 - 97% but efficiency with nominal load 85% .

tabbycat · January 2022

The Sandia National Lab report on flooded batteries concluded that at a high SOC nearly half the available energy is serving losses rather than charging the battery.

Ako · January 2022

Not sure if i have done any long term damage to my battery . AGM batteries i read should never be overcharged but tonight i was within 0.6 amps of end Amps before they went into Bulk but for some idiotic reasoning i thought i would finish it off with the batterie charger .

Normally i would use my charger when the weathers not been very good and batteries are below 24.5 prior to starting the evening and the 20 amp charger after running for a few hours would raise the batterie voltage to around 26.5 - 27 volts while the charger would typically start off showing an output of 17 amps reducing to around 11 or 12 amps .

Tonight when i started the charger it showed a 5 or 6 amps output but within 3 mins raised the batterie voltage from 27 to 35 volts according to the charge controller read out . As soon as i heard the Inverter alarm and turn off i turned of the charger also but by then i don't know what damage i could have done . Checked each of the 6 volt batteries several times and al the voltages are the same and they have charged and acted no differently that they have for the 2 weeks that i have had them . Does the term overcharging refer to Voltage or Amps or either ?

From al the replies with explanations to my original post im more accepting now that the charging profile i have become used to seeing now is correct and to be expected while being very different than the flooded battery charging i have always been use to for a combination of the reasons provided .

tabbycat · January 2022

Don't use a charger that will continue to charge past the recommended voltage set point. That will damage an AGM. Flooded batteries are more forgiving.

Problems changing from AGM to Flooded

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