Soc verses battery temperature chart.

[UpNorthMan]

Hello everyone,
I've been searching for a chart that references battery voltage for specific temperature and soc. Does anyone have a reference document? I have some AGM batteries at my cabin and would like to use it for a reference. It isn't uncommon for me to show up in the winter and the batteries are below freezing. And they never fully warm up on our weekend visits. I don't have a Whiz Bang installed yet. Hopefully later this year I'll finish my install. I am waiting for the new inverter to be released. I have a 48v system, but I can convert if the chart is 12v/24v.
Thanks in advance,
Ed

[ClassicCrazy]

I think I have seen charts in the past but really they aren't too accurate trying to determine capacity based on voltage.
The only real way is to know is using the Whizbang which monitors everything coming in and out . The Soc calculation in the Classic will also be compensated for temperature . So if the batteries are cold it will show less capacity available than if they were warm.
If you have the temperature compensation set up on your system  according to battery manufacturer guide then at least you know your batteries are filling up when the sun is out even if the batteries are cold.

Larry

[mike90045]

The battery mfg should supply the chart for THEIR batteries, here's some generic stuff

(As it gets colder, the battery wants more voltage to charge, IIRC )

[UpNorthMan]

I agree that the Whizbang is the best way to go. Once tweaked in, it should give a accurate soc. The batteries I bought are new / but were on the shelve to long to sell as new. I got a very good deal on them and so far I haven't had any problems with them. The shop I bought them from sells to large systems like cell towers. He then also buys them back for recycling and if they haven't been abused, to the general public as used. I wasn't able to get a in depth spec sheet for them. But for a weekend cabin/first set, I am very satisfied with them. They were at 30% the original cost. I was willing to take the risk. My batteries are AGM and can't check specific gravity.

I do have the temp sensor set up on my Kid as well. I also set the max charge voltage for the batteries.

I read somewhere that a fully charged battery will have different voltages when it was warm compared to cold. Such as 77f (25c) compared to - 10f (-17c). These ranges are not uncommon for my cabin. I was just looking for a quick reference chart. Right now my loads are light so I don't get much battery heat from internal resistance. In the winter, they don't really warm up.

Does anyone have any insight on battery voltage /temperature for a fully charged battery?

Ed

[ClassicCrazy]

it really depends on how cold the batteries are. AGM in my experience act a lot differently when very cold and the voltage  under charge will jump way up soon. But they will fill up over time on float . For your use you probably have a good choice on those bargain batteries. The other thing I have noticed about AGM is that even when older they might not make their high capacity discharge ratings but seem to do fine at low amp outputs. There are of course lots of different manufacturers and qualities of AGM .
I have seen some small AGM that were old but showed a good voltage - until a load was put on them and then it would take a dive. I also had a smaller AGM that I had outside connected to two old Arco panels - it had one job to run a small 12v bilge pump once in awhile. I couldn't believe how long that battery did it's job considering it was used when I got it.

Larry

[Westbranch]

Did you get the adjustment factor from your Manufacturer?  If you get them, I believe you will need  you will need a Classic to be able to get a good sold weather charge.
Like Larry said a cold AGM is good at low Amp draw, but can look like it is failing when you need a lot of amps at on time, like the fridge and water pump kick in together.

[UpNorthMan]

I was able to get a comp factor. The AGM batteries are in the cabin and warm up some on a weekend visit. Generally, my loads will be small. The 250w inverter hasn't overload in the year and a half that we've used it. This year, I'm hoping to use the small fridge we bought and vacuum.

We are hand building the cabin and insulated it very well. R21 walls and R60 in the ceiling. This keeps the inside around freezing for several days after we leave. In the heart of the winter, it can easily get well below - 30F outside temperature. This is usually more than enough time to replenish the batteries before they get real cold.

I will keep my eyes on the batteries once I get a bigger inverter and have larger loads.  Our current loads are led lights, a radio, and a very large high efficiency ceiling fan. The fan is amazing, 68" and on speed 3 of 9, it only uses about 6 watts and moves around 3000 cubic ft. No TV in the plans. It's a place to get away from the rest of the world!