voltage drop

[tlaffourtit]

how much voltage drop is normal for a agm 12v battery or any battery if it is fully charged and connected to nothing?

[tlaffourtit]

thanks smkettner for the info. I copied a page from my inverter/charger manual about charging. will this type of charger charge my batteries correctly and not shorten their life?

There are 3 charging stages:
Bulk Charging: This is the initial stage of charging. While Bulk Charging, the charger supplies the battery with controlled constant current. The charger will remain in Bulk charge until the Absorption charge voltage (determined by the Battery Type selection) is achieved.
A software timer will measure the time from A/C start until the battery charger reaches 0.3V below the boost voltage, then take this time asT0 and T0×10 = T1.
Absorb Charging: This is the second charging stage and begins after the absorb voltage has been reached. Absorb Charging provides the batteries with a constant voltage and reduces the DC charging current in order to maintain the absorb voltage setting.
In this period, the inverter will start a T1 timer; the charger will keep the boost voltage in Boost CV mode until the T1 timer has run out. Then drop the voltage down to the float voltage. The timer has a minimum time of 1 hour and a maximum time of 12 hours.
Float Charging: The third charging stage occurs at the end of the Absorb Charging time. While Float charging, the charge voltage is reduced to the float charge voltage (determined by the Battery Type selection*). In this stage, the batteries are kept fully charged and ready if needed by the inverter.
If the A/C is reconnected or the battery voltage drops below 12Vdc/24Vdc, the charger will restart the above cycle.
If the charge maintains the float state for 10 days, the charger will deliberately reset the cycle to protect the battery.

[time2roll]

12.8 or higher is the DEKA AGM 100% charged resting voltage.

http://www.dekabatteries.com/assets/base/0139.pdf see pg 13

[Gau_8]

As mentioned, the higher voltage reading from a freshly charged battery that has had no drain applied is know as "Surface Charge." It will quickly drop to the 12.6v range once a load is applied.

[Gau_8]

pianotuna wrote:
Hi,

Do you mean agm battery?

Self discharge can be as little as 1% per month or as great as 1% per day. It depends on the chemistry that the battery maker is using.

How does the chemistry vary? They are all lead/acid batteries.

[tenbear]

This higher voltage that leaks off when the charger is disconnected is a phenomenon called surface charge. It is perfectly normal.

[pianotuna]

Hi,

As Land pointed out AGM batteries initially need to be used. I'd do about 5 cycles to 50% followed by rapid (compared to flooded) recharges. The less you pay for the agm the more likely this is going to be needed.

I'm lusting after a pair of 8D agms, since LI is not going to be affordable in the near future.

I wonder if I got twin 8Ds, and four Group 31's from the same company if I'd keep my charging profiles the same for all batteries.

[tlaffourtit]

landyacht318 wrote:
AGM fully charged resting Open Circuit Voltage varies widely. My Northstar AGM is 13.06v

12.7v rested OCV would be about 70% charged on my battery.

Your voltages seem fine for Deka/East penn AGM, but I would try and see if you can get a fully charged rested voltage from them, and post their answer.

FWIW, when I first got my AGM, I could not get the rested voltage above 12.7v until I did a ~ 50% discharge and a 25 amp+ recharge, and the battery has been doing tarzan yells and thumping its chest like a meth addled gorilla since.

message sent. will post reply when sent.

[tlaffourtit]

Crazy Ray wrote:
Google 12volt side of life. great read

good read there. thanks

[landyacht318]

AGM fully charged resting Open Circuit Voltage varies widely. My Northstar AGM is 13.06v

12.7v rested OCV would be about 70% charged on my battery.

Your voltages seem fine for Deka/East penn AGM, but I would try and see if you can get a fully charged rested voltage from them, and post their answer.

FWIW, when I first got my AGM, I could not get the rested voltage above 12.7v until I did a ~ 50% discharge and a 25 amp+ recharge, and the battery has been doing tarzan yells and thumping its chest like a meth addled gorilla since.

[old_guy]

it also depends on the condition of the top of the battery. if it has dirt on it, it will discharge at a faster rate. my friend owns a battery store and he showed me the difference one day on a clean top and a dirty top.

[Mandalay_Parr]

12.7 is full charge.

[Crazy_Ray]

Google 12volt side of life. great read

[tlaffourtit]

found this online. mostly the same info from before.

SPECIFICATIONS
Nominal Voltage: 12-Volt/145 ampere-hours
@ 8 hr. rate to 1.75 final v.p.c.
Positive Plate: Pure lead, low-calcium, high-tin alloy
Negative Plate: Lead calcium alloy
Post Seal: Epoxy-sealed
Terminal: Front access, 1/4" - 20 threaded insert
Container: Flame-retardant, polypropylene -
UL 94 V-0/>28% L.O.I.
Safety Vent: Low positive pressure, self-sealing
w/ flame arrestor
Float Voltage: 2.25 v.p.c. ± 0.01 v.p.c.@ 77ºF (25ºC)
(Range: 13.44 to 13.56 volts per 6-cell battery)
Battery Life: 10 years in float
applications at 77°F (25°C)
Dimensions: 17.58" (446.6 mm) L
x 6.89" (174.9 mm) W
x 10.10" (256.5 mm) H
Weight: 105 lbs. (47.7 kg)


http://www.eastpennmanufacturing.com/wp-content/uploads/0737-Unigy-I-Ohmic-Values.pdf

[Dakota98]

tlaffourtit wrote:
the batteries I have i float at 13.5v. once I disconnect them from the charger; I am guessing they shouldn't stay at 13.5v but drop down into the 12v range? example I had the batteries floating at 13.5 volts for a couple of hours. then I disconnected the charger and took a reading of 12.96v across the 8 battery string. this morning the reading was 12.84v. my question is; it this normal? you responded it depends on the make up of the battery. is there any other information I could get from the battery label to help?

I would say that is quite normal. If you were reading the voltage at 13.5 volts while the charger was still plugged in & connected to the battery bank, that reading was from the charger, not the batteries. A 12.6 + volt reading taken directly from the string or individual battery indicates a fully charged battery. Unfortunately you can't check them with a temperature compensating hydrometer, since they are sealed AGM's

[tlaffourtit]

pianotuna wrote:
Hi tlaffourtit,

What make and size of batteries?

deka is the brand name
part No.: 12avr145ET
nominal voltage: 12v
capacity 145 ah @ 8 hr rate to 1.75 vpc
float rate: 13.50 +/- .06 vpb @ 25*c
weight: 105 lbs, 47.7 kg
torque value: 100 in. lbs, 11.3 Nm
non-spillable