Batteries Won't Charge Up

[ChrisOlson]

Well, we over-did it a bit this time. Our battery bank has not been charged to 100% yet this month - actually hasn't been above 85% SOC. We been running A/C and that takes all the power all the RE equipment can make, plus some prime generator power to keep it lit. We got a nice cool breeze off the lake today so we shut the A/C down. The solar panels absorbed the battery for 8.7 hours today and finally got 'em down to 30 amps. They need to get to 23 amps for full charge. I check the SG's on some random cells and they were only at 1.240

When the batteries are that close and haven't been charged for that long, I do something I normally don't do. I enabled the charger in the XW and started up the genset to finish absorbing them with Power Charging. Three hours of that Power Charging now and I finally got 'em down to 25A:



I checked SG's again and now I got 1.250-1.255. It's gonna take at least another 3 hours to get 'em to 23A and 1.265 and they're up to 40C so they're pretty warm. I'm thinking I might stop this process tonight and let the solar panels finish it tomorrow. And even then it'll take two more full days of absorbing to get 'em back to 100%.

That freakin' air-conditioning is hard on batteries

[inetdog]

That freakin' air-conditioning is hard on batteries

But so much easier on people.
Conventional wisdom says that instead of finishing the absorb on the generator, the first thing to do is use the generator to speed up the bulk charging, letting the PV take care of as much of the absorb time as possible. The higher the current you get while on generator the more effective use you are making of its run time.

[ChrisOlson]

But so much easier on people.
Conventional wisdom says that instead of finishing the absorb on the generator, the first thing to do is use the generator to speed up the bulk charging, letting the PV take care of as much of the absorb time as possible. The higher the current you get while on generator the more effective use you are making of its run time.

Only problem with that is that the amps will hit 200-250 on charging with both the genset and solar on bulk. Ideal bulk charge rate is 120A. The bulk charging wasn't the problem - it was absorb. You get a bank full of these Surrettes sulfated and it takes 16-18 hours to absorb 'em at 2.55VPC. If you split it up and do some mini cycles above 85% SOC then it takes 30-40 hours of actual absorb time instead of 16-18 hours. The solar never would get the job done unless we turned a bunch of stuff off to reduce the load on the power system so they'd get to absorbing by 10:00AM for the next 3-4 days.

So that's when I break out Old Reliable - the generator. We got plenty of other stuff to keep a genset busy when it's running - like water heaters. Our hot water supply was down to like 65% so I use the balance of the power that's not needed for charging for water heating to keep the generator loaded up.

I stopped the thing for tonight because the batteries are continuing to climb on temp and they went up one more degree to 41C. I got the fan running in the battery case to try to drop them on temp a little overnight. They're caught up enough now that the solar can get them to end amps tomorrow - forecast is for cooler and bright and sunny. After a long cycle like this, there's always a few "lagger" cells that will be around 1.250-1.1255 and it takes 2-3 more days getting them to end amps every day to get those "laggers" up to 1.265.

[inetdog]

Only problem with that is that the amps will hit 200-250 on charging with both the genset and solar on bulk.

Which just means that you do the generator bulking before the panel production gets too high. Like first thing in the morning, maybe.

[ChrisOlson]

Which just means that you do the generator bulking before the panel production gets too high. Like first thing in the morning, maybe.

OK yeah, I see what you're saying. That would definitely work too. This is not something we normally do here. I had thought we were keeping the batteries at high enough SOC, cycling 38-85% SOC for over 3 weeks so hard sulfation would not be an issue. But sulfate hardens faster when the batteries are warm than it does when they're cooler. So while we can get away with it in winter and get back to true 100% SOC fairly easily, in the summer when the batteries are warmer it can't go that long.

Batteries are a never ending source of learning new things.

[russ]

Batteries are a never ending source of learning new things.

For all the newbies reading this thread - Chris is an old hand with batteries and he makes a very true statement.

[inetdog]

OK yeah, I see what you're saying. That would definitely work too.
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Batteries are a never ending source of learning new things.

For all the newbies reading this thread - Chris is an old hand with batteries and he makes a very true statement.

Sometimes even an old dog can learn new tricks.

One of my favorite quotes from "M" (Mother Margolies) in the Israel Bond (Oy-Oy-Seven) parody books:
"You can't teach an old dog new tricks, but you can teach an old dog to teach a new dog old tricks."

[ChrisOlson]

Pretty happy overall - we got a full absorb today and it took 6 hours 13 minutes in absorb and the batteries finally got down to 23A. Checked SG's on a couple random cells and they were at 1.265, which is good for Surrettes. I'm sure if I checked them all I'd find some "laggers" at 1.250 but a couple more absorbs without discharging them too deeply usually "fixes" those cells. Weather is supposed to hold nice and sunny for the next couple days so might get these batteries back to 100% yet. They're only 7 years old and they still take a lickin' and keep on tickin' - and they still put out rated amp-hours on a full discharge according to my battery monitors.

No, I'm not really new to batteries since we live with 'em every day here. And I've seen a lot of people wreck the same batteries we got in 6 years. But the main problem is that these people don't have any sort of way to keep track of the health of the battery by monitoring its capacity with a good battery meter, and they don't use the hydrometer. They wait until it becomes dead obvious that they got a serious problem and then they're doing corrective EQ's trying to save 'em. That's sort of like treating the patient after he's been declared dead. Taking care of off-grid batteries is a full time job. They have to be monitored and prevent problems before they become real problems, and they'll serve you long and well.

[paulcheung]

HI Chris,

I see you said your battery bank finally gone down to 23 amps on absorb charge. That is a little bit less than 3% of the 820AH capacity. Does a healthy battery bank always go down to about 3% charging rate of the 20 hours capacity when it fully charged? Is there any exceptions? what voltage do you set your charger when you do this absorbing charge?
Thanks

[ChrisOlson]

I use 2% of the 20hr rate for absorb end amps @ 2.58VPC Absorb V because that's pretty representative of our charge rate. I use 100hr rate for discharge because that's more representative of our discharge rate when on pure battery power. During the day our loads are MUCH higher, but they are powered by solar and the rest goes to battery charging.

After this whole ordeal I still ended up with a "lazy" cell after the air-conditioning season. I finally got around to fixing that today. Took another 3 1/2 hours of genset time.