voltage drop

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

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

Google 12volt side of life. great read

12.7 is full charge.

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.

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.

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

good read there. thanks

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.

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.

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