Project Journals > RossW
LiFePO4 (LFP) bank - a work in progress
rossw:
--- Quote from: MadScientist267 on April 27, 2014, 05:44:22 am ---Didn't know about the Trojans, thought you had run AGM all the way through for the house... Sucks about the contractors and the original AGM set, what they do, burn them up thru the inverter with tools and such?
--- End quote ---
The original set needed to be handled with kid gloves to bring them back. Unfortunately, I had to go out of town for a week or so. "The contractors" (collectively) toasted them. Anecdotally, I found that they'd run them until the inverter shut down, but then found that if they turned the inverter off and back on, they could get a bit more out of them. They'd do this repeatedly until it simply wouldn't start. THEN they either didn't bother turning up, or ran on generator.
Of course, each trade blamed the other, so I couldn't nail any one particular lot to the wall. Bloody pissed off I was!!
dochubert:
Hi Rossw,
It's been over a year now since you put in your LFP battery bank. I'd be very interested in an update of how they are doing. I'm not off grid yet but hope to be before this time next year, and trying to learn all I can about inverters and batteries in the meantime. (That's why I'm here! You guys either already know this stuff or are actively trying to figure it out if you don't - My kinda guys)
Did you add the second string?
Any cell balance issues?
How much charging amperage do you get from your solar? Is it enough for your needs or do you run the gen alot?
Just checked ebay for a price range reference and Whew! Pricey! But the old "You get what you pay for" usually applies, and I'm figuring to have to lay out serious cash when its time to buy my off grid bank.
Hope I'm not being too nosy
rossw:
--- Quote from: dochubert on February 19, 2016, 09:19:58 pm ---It's been over a year now since you put in your LFP battery bank. I'd be very interested in an update of how they are doing.
--- End quote ---
Going great. Really. Wish I'd done it earlier, wish even more that I'd got the full 600AH at the outset.
--- Quote ---Did you add the second string?
--- End quote ---
Spent the last 12 months trying to get more of the same cells. The manufacturer seems to have disappeared, so I'm back to the same problem of finding something in the price/capacity/size that suits me, all over again.
--- Quote ---Any cell balance issues?
--- End quote ---
None. Although, I do have cell balancers (active charge shuffling devices, not merely top or bottom balancing.
--- Quote ---How much charging amperage do you get from your solar?
--- End quote ---
I have 3.4kW of PV in the air now, and usually see around 60A peak charging current.
--- Quote ---Is it enough for your needs or do you run the gen alot?
--- End quote ---
With an adult daughter moved back home, and additional power-using devices added in the last year, they are managing fine during these months of longer sun, with the generator rarely being needed. As the days get shorter, it won't be long before generator will need a brief run either in the morning or at night.
I have an additional 42 x 180W panels ready to put up, which should help a lot with poor-solar days, and may get the batteries charging earlier in the morning, but I am still going to need more capacity for overnight.
--- Quote ---Just checked ebay for a price range reference and Whew! Pricey! But the old "You get what you pay for" usually applies, and I'm figuring to have to lay out serious cash when its time to buy my off grid bank.
--- End quote ---
I don't think ebay would be my "go-to" place for batteries!
I imported my own direct from the manufacturer. It was a bit of mucking about, but I think I still ended up with good quality cells, landed at my door for about 50% of the "domestic retail" price.
Now that we all know LFP is a real contender, and really DOES work as well as it looked like it might, please don't skimp on whatever you get. Work out how much you actually need, add 50% or so, and buy it in one hit. Yes, it might hurt, but the pain of the cost will fade quickly - compared to the on-going pain of doing it wrong!
dochubert:
Hi and thanks for the reply and info!
Glad they're working well. I love the idea of lighter, as well as much better quality batteries. I do like my agm batts, but had planned tentatively on looking for a forklift set for off grid. Now I've got a new plan!
I wouldn't buy from ebay (batteries, anyway) but often reference there for pricing. Glad to hear you found a much better deal. Hope I can too when its time.
Have you heard about Aqeon (spelling?) batteries? Some sort of salt water cells, I think. Supposed to be equivalent to lithium in usage specs, but of course without the lithium, no fire hazard. Probably back to heavy, though. Probably more expensive too since fairly new stuff. I started looking into them recently when I first heard about them, then got distracted. Supposed to be available in large ah 48v packs for off grid use. I like the 'no fire hazard' part, as stories of exploding or burning up lithium cells had me a bit leary.
What do you use for your cell balancing/monitoring? I saw in your pics the little boxes connected to each cell. How does that work? Do they actually do something or just tell you there's a problem? When I get to off grid I will definitely want to do something like that to hopefully catch a problem before it progresses too far, especially if I go lithium. Oh, speaking of burning cells, any battery heating issues with yours? I have a friend who works for Tesla motors, and he seems to spend a lot of time on battery packs. The Tesla car uses a lot of power just keeping the batteries cooled. Of course, they are run pretty hard, but seems like diminishing returns from all the needed cooling would get you eventually, in that application. For our purpose I would think, oversize the bank and run it lightly?
I hope you don't mind all my questions and ramblings. I appreciate your indulgence. I have truly learned more in the short time i've been on your excellent site than since I got my first powerjack almost two years ago. Thanks again
dochubert
rossw:
--- Quote from: dochubert on February 20, 2016, 07:52:22 pm --- Have you heard about Aqeon (spelling?) batteries? Some sort of salt water cells, I think.
--- End quote ---
A friend pointed me to them a week back.
All I can say is... if it looks like snakeoil, and smells like snakeoil, and reads like snakeoil, I think it's just a bunch of people got together to sell... well, seawater in boxes.
Almost infinite lifetime.... hah, you're kidding right? <70% capacity after 3000 cycles?
Price? National secret... but once you swallow all their "good for the environment and almost infinite life" line, then the "amortized cost" justification says "expensive".
They're also heavy as sin, and bloody huge.
They're also hideously inefficient (claims up up to 90% cycle efficiency seem exaggerated, and under best possible test conditions - real life seems more like 80-85%, which sucks big time if you ever need to burn fuel to charge them).
--- Quote ---I like the 'no fire hazard' part, as stories of exploding or burning up lithium cells had me a bit leary.
--- End quote ---
LFP (as opposed to lithium ion) seems pretty safe.
--- Quote ---What do you use for your cell balancing
--- End quote ---
Commercial single-cell balancers. They all connect to a common, isolated bus. The cells with highest voltage contribute most, those with lowest take most, so they balance during charge, discharge and simply standing.
--- Quote ---monitoring?
--- End quote ---
I built my own monitors. They're a tiny little board that monitors up to three cells (volts and temperature for each), that daisychain to monitor virtually any voltage string (component isolation would limit the string to 1500 volts). They output a constant (RS232) status of each cell in the string.
--- Quote ---I saw in your pics the little boxes connected to each cell. How does that work? Do they actually do something or just tell you there's a problem?
--- End quote ---
If they were the balancers, they do something. If they were the monitoring system, they let me see what's going on so I can do something before I'm forced into doing something because something's broken!
--- Quote ---When I get to off grid I will definitely want to do something like that to hopefully catch a problem before it progresses too far, especially if I go lithium.
--- End quote ---
Prevention beats cure every time.
--- Quote ---Oh, speaking of burning cells, any battery heating issues with yours?
--- End quote ---
Never seen any of them get more than a couple of degrees rise above ambient.
--- Quote ---The Tesla car uses a lot of power just keeping the batteries cooled. Of course, they are run pretty hard, but seems like diminishing returns from all the needed cooling would get you eventually, in that application. For our purpose I would think, oversize the bank and run it lightly?
--- End quote ---
Telsa isn't using LFP. Different chemistry, different behaviour.
I hope you don't mind all my questions and ramblings. I appreciate your indulgence. I have truly learned more in the short time i've been on your excellent site than since I got my first powerjack almost two years ago. Thanks again
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