Cut off for 24 v system

[Szabie]

Hi guys was seeking advice for my batteries ...I have 2 12v 12fft100 batteries in a 24v set up what I have been doing is recharging it at 24.8v ( at night) as I'm led to believe that is between 50 and 75% Soc left in battery.... was just wondering if that is the right way to go

[Mike90250]

you are killing your batteries and need to get them properly charged as soon as possible, if they are not dead already..

If they are flooded cells (take caps off and add distilled water type of battery) They should be charged at almost 30v (for 24V battery bank) You have to use higher voltage to "push" charge back into the batteries. Even pulling the batteries out and using a automotive 12V charger for 24 hours is better than what you have done to them,

[Szabie]

Ok now I'm really confused ...I just looked at the other page which you posted to look up sealed lead batteries and it to shows there is 70% left in battery so that is wrong you say and I'm now killing batteries or am I just reading it wrong

[littleharbor]

A fully charged 24 volt battery at rest with no loads will be at 25.6 volts. As Moderator Mike 90250 mentioned you need higher voltage to push the amperage. into the battery. Where did you get the idea to charge at 24.8 volts? You want to FULLY charge the battery. Voltage is a poor guide to state of charge if the battery has recently been charged or discharged. You want to charge at no less than 29.6 volts and up to and beyond 30 volts for some batterys.

[Szabie]

Ok have batteries with no load at the moment resting with no charge or load they are reading 28v ...I am running a tristar 60 pwm which I had set at 29.6 but was advised that was too high and to drop it to 28.4 ...I have a magna-sine inverter charger by enerdrive and on cloudy days some nights etc have it set for 24.8v to start the charge ...the batteries themselves have a float of 13.62 as I'm a novice I hope you can see how it looks from my point of view all getting confusing very fast ...I will change voltage setting back 29.6 as you said and appreciate the advice

[Mike90250]

.... what I have been doing is recharging it at 24.8v ....

Looks like you made a typo, which caused us to go into full alarm mode, because charging at 24.8 is bad. 29.6 is much closer to the "About 30v" I mentioned. 28.4v is also good if you are floating them for long periods.

Are they flooded batteries, or sealed batteries ? Do you use them daily or just weekends ? How much PV do you have?

[NEOH]

Szabie is the following information true ?

The 12fft100 battery is made by FIAMM, a Vietnamese company, they make FAT, FIT & FFT type batteries
They appear to be AGM.
Mainly for Telecom STANDBY - long term FLOAT ?

FAT = Front Access Telecom
FIT = ?
FFT = ?

http://www.weiku.com/products/13413480/12_FFT_100_Fiamm_battery.html

http://www.btc.nu/batinfo/AGM_Engineering_Manual.pdf

[NEOH]

Szabie is this true ?
It is a FIAMM 12FTT100 battery
This battery is manufactured by FIAMM, a Vietnamese company.
This is an AGM "SEALED" battery.
FIAMM makes batteries mainly for the telecom industry
Is this a Long Term Float battery or a Deep Cycle battery?

Users manual ?

http://www.btc.nu/batinfo/AGM_Engineering_Manual.pdf

Float Charge "FFT" type at 27.24 Volts = 12 cells x 2.27 volts per cell @ 20 Degrees C
Constant Voltage with Charge Current LIMITED to 0.25 of ( C/10 to C/20 )

http://www.weiku.com/products/134134...m_battery.html

Modified Constant Voltage Charging
============================
The IU recharge method, also known as modified constant potential, has been used for many years and in a variety of applications, as it combines the need of having the battery quickly recharged while ensuring maximum battery life. With this method, recharge starts at a constant current rate. The voltage increases up to a pre-set value. The pre-set voltage is maintained and the current then decreases to a minimum defined value. Finally, the recharge is completed at a final constant voltage value equal to or less than that defined for float charge with the current decreasing to the value used in float.

My interpretation of their "Modifed IU Recharge Method" is ...
a) I mode = Constant Current charge at 25% of C/20 Rating ( 25 amps ? ) until 27.24 Volts then ...
b) U mode = Constant Voltage charge at 27.24 volts ( forever )
Discharge, then repeat above

12FTT100 Battery -> Open Circuit Volts should be 12.78 Volts = 100% SOC !


Typical AGM batteries can be BULK Charged until 28.4 Volts to 28.8 Volts, then Absorb Mode, then Float Mode.
Above 28.8 volts an AGM battery will generate gas.
I don't know if your batteries can be treated like a TYPICAL AGM or not.
I think, 29.6 Volts is too high for an AGM battery!

[Szabie]

Ok I have 6 210w 47.7v 5.25amp panels which are in parellel so they running around 30 amp to the charge controller which is Morningstar tristar 60 the batteries are monolite 12FFT100 sealed batteries ...i use it on a daily basis and it runs a fridge which is a 24v fridge/freezer which is wired straight to the batteries and a small tv sattelite set up radio anything big that draws like toaster ill start generator for ...I honestly thought that I was doing it right so when should if cloudy etc you put them back on generator charge or should I always have them on charge for instance at night should they still be on float ....I know they only have small amp hours but at $100 for the pair in aussie they have paid for themselves 5 times over...I think the reason I have so wrong is the fact that the charts show 70% is still in the green ...I hope other beginners read this so that they can get it right the first time

[Szabie]

Yes they agm I'm unsure wether deep cycle or long term float

[Sunking]

If they are Telecom batteries, they will not last long if cycled. At best 100 to 300 cycles. Less than one year.

[Szabie]

Oh well I can get more and for the price I can't complain it's now official auzzies pay the most for power in the world with the average punter paying $1000 a quarter

[NEOH]

Yes they agm I'm unsure wether deep cycle or long term float

Typical AGM batteries ( Lifeline, Trojan ) ...
a) BULK Charge ( Constant Current ) until 28.4 Volts to 28.8 Volts
b) Then ABSORB Mode ( Constant Voltage ) at 28.4 Volts to 28.8 Volts until the AMPS drop down.
c) Then FLOAT Mode ( Constant Voltage ) at 27.24 Volts at 20 Degrees C (see URL to users manual posted earlier )

FIAMM does not specify any voltage for BULK Mode.
So, keep the Bulk Voltage low enough to prevent excessive gassing.
If you hear your batteries "hissing", then they are losing water and that is a bad thing.

12FTT100 Battery -> Open Circuit Volts should be 12.78 Volts = 100% SOC

How deeply are you discharging the AGM batteries? 50% Max?
With 30 Amps from PV Panels you should be able to Bulk, Absorb and Float between sunrise & sunset - depends upon your daytime loads.

[Szabie]

Well I thought I was discharging them about 30% ie down to what I thought was right 24.8v at the lowest ....why do the charts that I have viewed show that to be in the green when by all accounts what I've been told today I'm destroying them keep in mind I'm no electrician

[littleharbor]

OK, I think something got lost in the translation, so to speak.

Are you saying that you are initiating a charge cycle on your batteries when they reach 24.8, or charging them at a set 24.8 max charging rate? It seemed you were saying you were charging at 24.8 volts , not starting the charge cycle when your batteries dropped to 24.8. Maybe only my misunderstanding. You also mentioned you were charging at night. Obviously you cant use solar to charge at night.

Quote, "Hi guys was seeking advice for my batteries ...I have 2 12v 12fft100 batteries in a 24v set up what I have been doing is recharging it at 24.8v ( at night) as I'm led to believe that is between 50 and 75% SOC left in battery.... was just wondering if that is the right way to go"


There is nothing wrong with starting a charge cycle at 70%SOC Voltage isn't the best way of determining SOC You can get a better idea of SOC with a properly set up shunt based meter like a Bogart Tri Metric or other similar meter. These meters keep track of the amps in, and out of your battery bank. They need to be set up with proper amp hour capacity of your battery to know what the state of charge is. As your battery ages and loses capacity the meter will give misleading SOC numbers unless re set with a lesser Ah capacity. As to your charging and float setpoints, you should find and follow the Mfg. recommendations.