Author Topic: LiFePO4 (LFP) bank - a work in progress  (Read 9035 times)

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Offline rossw

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LiFePO4 (LFP) bank - a work in progress
« on: April 25, 2014, 08:19:36 pm »
Some of you will have been following my trials and tribulations of batteries, and may remember my first ever bank.
These were a batch of basically freebie AGM cells. I had no way to monitor them, no way to really charge them properly, they were originally 300AH cells but by the time I got them, who knows...


They died a premature death when the contractors building the place drained them absolutely dead flat and left them that way while I was away. NOT IMPRESSED.

Unable to find replacements, I limped along on some flooded 220AH cells for a while, but they really were not up to the job asked of them.


Then I got onto some 500AH AGM cells - again, used but at a price I could afford (and I needed something that could hold up a bit better than the trojans were)


Almost 4 years on, several of the 500AH cells were getting a bit soft, and while trying to find some replacements, I was offered 50 (again, used and removed from service) for a price that was quite attractive. So I grabbed 'em


And after some time to tickle the old cells back, figured I may as well put them back into service


So now lets move on 4 more years. My love of AGMs has waned. Two broken shoulders (at different times) and I really don't enjoy lifting them (at 34kg / 75 lbs each), and with the extra power demands of more equipment, regular use of lathe, welder, grinders and other power tools, combined with poor monitoring of the banks and insufficient charge to regularly float them, they've been getting to be a problem. I'm over splurging $500 here and there to pick up some replacement cells and replace the dying ones. Worse, the rate of death has been increasing dramatically. I stopped buying cells and cannibalized the oldest bank, taking the best cells to prop up the other banks. When I ran out of them, I had to ditch the second bank to keep the primary bank operational. Of course, this reduced my capacity back to only 500AH (if the cells were all new and in good condition, and neither of those applied!). With a typical overnight demand of 150AH, that was hammering the cells pretty hard. They could manage it if I'd had a really good day, but introduce cloud and they were really struggling. The generator was running at least morning and evening, and more often than not once in the middle of the night.

It was way past time to take the plunge and get something different. Over the years I've looked at NiFe, and discarded them (too many reasons to go into here). I was sorely tempted to get a decent pack from a forklift, but they've got other problems.

So in the end it's come down to LFP (Lithium Iron Phosphate) as a cell with decent life, suitable voltage characteristics, manageable charging regime, reasonably resistant to abuse and "safe enough" to put inside the house.

So I decided initially on 300AH cells. They claim their 2000+ cycle life at 85% depth of discharge. I wanted to be able to handle 200AH overnight,  which is only 66% (so should lengthen the life). 200AH is equivalent to only discharging my old lead-acid cells 20% (for the 1000AH bank) or 40% (for 500AH bank). First pleasant surprise was when they turned up. It took me 6 trips from the delivery van, each time carrying less weight than one of the old 500AH cells. These suckers are SMALL and LIGHT compared to the AGMs!


Each cell is light enough to carry with one hand, and small enough to be "cute"!


There was a miscommunication about the cell interconnects, and they sent the wrong ones, so I had to wait on replacements. They duly arrived (they are about 2mm thick x 45mm wide - 90 sq mm CSA, or roughly equivalent to 000 wire). I quickly modified each with a couple of M5 bolts to attach the battery monitoring and cell equalizing equipment in a manner that would not require taking the bank out of service to do so.


So the whole new bank takes up half the height and half the depth as the AGMs that it replaces, yet has twice the usable capacity in 1/4 the space! It also only weighs 172Kg (380 lbs) compared to 816Kg (1800 lbs) for EACH BANK in AGMs!
This picture looks pretty messy, because the battery monitors are only temporarily connected, and the cell equalizing is just dropped in place, nothing has been tied up neatly yet... but here it is!


Before you ask - yes, there is a lot of space behind and in front of each cell. The plan is that when I save up my pennies, I can buy another 16 cells and put them cell-by-cell beside the existing bank to double the capacity.

So far, these are performing absolutely brilliantly! Better than I'd hoped.

Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #1 on: April 25, 2014, 08:54:59 pm »
Addendum: we had sun yesterday, but not enough to get the cells fully charged. Woke up to 100% overcast day today. The batteries were holding well, but we had a couple of loads of washing to do so I thought there was no point discharging the batteries unnecessarily and ran the genset. (Probably didn't need to as it turns out!) The generator explains the sudden jump in volts shortly after 8am until 10am.

Here's the individual cells:


And to put it in context, here's the whole string:


By comparison, the old AGM cells, taken in arguably their "peak" operating conditions - summer, within a week of the summer solstace (ie, the longest sun day), with minimal loads on, no lights etc, behaved like this!


Offline bj

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #2 on: April 26, 2014, 06:52:43 am »
   Very nice Ross.  I have often thought (dreamed) of them for various projects, but never gotten
serious about it.
    With your reduced depth of discharge, a predicted life of 6+ years?
    Much drool on my keyboard.
    Very nice indeed.
    Edit----just did a bit of dirty math on life curves,  probably more like 10 years?
"Even a blind squirrel will find an acorn once in a while"
bj

Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #3 on: April 26, 2014, 04:52:08 pm »
    Edit----just did a bit of dirty math on life curves,  probably more like 10 years?

That's around the numbers I came up with too. But then factor in the "real life" conditions. I don't always draw that much overnight - generally only winter with long nights and pumps etc running. In summer it can be as low as 60-70AH overnight.

And if I do save up and get an additional set in parallel, I could be looking at 25 years.

Remember also, that their "life" figure is where the cells retain only 80% of their original capacity. So by "end of life" they'll act like they're only 240AH cells, not 300...

Offline MadScientist267

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #4 on: April 27, 2014, 05:44:22 am »
Worked out well Ross, congrats. ;)

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?

Steve
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Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #5 on: April 27, 2014, 05:49:48 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?

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!!

Offline dochubert

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #6 on: February 19, 2016, 09:19:58 pm »

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

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Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #7 on: February 20, 2016, 03:39:10 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. 

Going great. Really. Wish I'd done it earlier, wish even more that I'd got the full 600AH at the outset.

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Did you add the second string?

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.

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Any cell balance issues?

None. Although, I do have cell balancers (active charge shuffling devices, not merely top or bottom balancing.

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How much charging amperage do you get from your solar?

I have 3.4kW of PV in the air now, and usually see around 60A peak charging current.

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Is it enough for your needs or do you run the gen alot?

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.

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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.

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!

Offline dochubert

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #8 on: February 20, 2016, 07:52:22 pm »
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
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Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #9 on: February 20, 2016, 08:25:07 pm »
  Have you heard about Aqeon (spelling?) batteries?  Some sort of salt water cells, I think.

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).

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I like the 'no fire hazard' part, as stories of exploding or burning up lithium cells had me a bit leary. 

LFP (as opposed to lithium ion) seems pretty safe.

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What do you use for your cell balancing

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.

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monitoring?

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.

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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?

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!

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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.

Prevention beats cure every time.

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Oh, speaking of burning cells, any battery heating issues with yours?

Never seen any of them get more than a couple of degrees rise above ambient.


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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?

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

Offline dochubert

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #10 on: February 20, 2016, 09:29:27 pm »
Well, my ignorance is showing once again.  I thought the lfp and lithium ion were essentially the same thing.  Thanks for clearing that up.

And yeah, I was leary of the seemingly amazing specs for a salt water battery.  Figured that was something I would wait and see what someone who actually tried one had to say.  Be nice if it worked....
Probably right about the pricing too.  I couldn't find any pricing online,  only a couple locations one could call.  Not interested in a sales pitch, so then I got distracted by something else and forgot about them until I was writing my earlier reply

I also didn't realize you were using a different gadget for balancing than the one for monitoring.  Figured it was the same little box for both. No experience at all with them.  I haven't had a large battery bank to work with yet, but would balancers work with my current setup so I could get familiar with them before I do have a large bank?  If so, can you recommend one to try?  I currently just have four 180ah agm 12v telecom batteries in series for my 48v bank.  They stay fairly even, although the pos end batt is always a little higher and the neg end batt is always a little lower voltage. Shouldn't be enough to matter, but I even them up or swap them around when the system is down for other reasons.  Highest charge I get at peak sun with current solar setup is about 22 amps when the inverter is powering the house.  At this point 60a of charging is only wishful thinking here.  Soon hopefully
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Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #11 on: February 20, 2016, 10:49:28 pm »
Well, my ignorance is showing once again.  I thought the lfp and lithium ion were essentially the same thing.  Thanks for clearing that up.

Similar in many regards, quite different in others. As usual, the devil is in the detail.

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I also didn't realize you were using a different gadget for balancing than the one for monitoring.  Figured it was the same little box for both.

There are Battery Management Systems out there that do monitoring, but at the time (and perhaps still), they were very expensive, and you got one that did a particular bank. If you went then from 24V to 48V, you threw it out and bought a new one. I didn't want to go that way.

My Battery Monitoring System is here.

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would balancers work with my current setup so I could get familiar with them before I do have a large bank?

The ones I used are available in 2V nominal, and 3V nominal versions. I suspect they are identical but perhaps with small tweeks. I used the ones I got for my lithiums on my AGMs for a while first just to see how they worked. They did ok, even though they were supposed to be for 3V systems not 2V.

I haven't found anyone selling them recently, but then I haven't looked too far or too hard. They were moderately expensive at around $50 each. That didn't sound so bad when they seem to do almost any sized bank up to about 1000AH.

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I currently just have four 180ah agm 12v telecom batteries in series for my 48v bank.

That's going to be a problem for you. I'm not aware of any system that'll balance 12V blocks properly, and I wouldn't consider monitoring in 12V chunks to be adequate to see what's going on with the system, or to pick up a failing cell.


Offline dochubert

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #12 on: February 21, 2016, 04:27:45 pm »
Thanks for the info.  Guess I'll just have to wait on balancers until I have a suitable system. 

Interestingly, when I was searching for LiFePO4 batteries, the largest capacity I could find was 180ah.  This morning, while looking at battery maintenance systems, I stumbled across this 300ah.  Seller claims 100s in stock.  Not the same brand as yours and chinese made to boot, but thought I would pass it on in case you want to check into them;

http://www.ebay.com/itm/Lithium-Battery-300Ah-/291683712784?hash=item43e9b43f10:g:XMIAAOSwT~9WluSJ
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Offline lighthunter

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #13 on: April 14, 2016, 09:17:21 pm »
Ross, Hi, I really have appreciated your information and opinions/data regarding
Your LFP bank. As you know, mine can hardly be called a bank, more of a buffer.
really, yet I am incredibly impressed with performance and has solved all issues i.
had with load regulation and stability for zero grid tie faults. I doubt mine will last
5+ years as they see over 1C charge/discharge levels for short stints many times/day.
Maybe equivalent of 5-10 complete cycles/day.

I mainly am posting because i remember you mentioning that you could use a bit
more battery for long nights/winter etc. Rather than larger bank why not add wind.
power to offset solar downtime instead. Maybe your location wouldnt work for that
but it just seems like everyone has solar but i dont see wind mentioned much and
im puzzled as to why. Isnt it cheaper /watt than solar? Just curious. I am getting around
11-12kw daily now and i honestly am finding it challenging to use it all up. During the day.
we just dont use that much. If i added more solar it would just go to waste xceptfor
cloudy days. Any amount of wind that is added though would have better chance
of decreasing utility bill.  I guess i dont understand why it isnt more popular.

Cheers, LH
Health Warning: May contain traces of nut!
LH

Offline rossw

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Re: LiFePO4 (LFP) bank - a work in progress
« Reply #14 on: April 14, 2016, 09:31:20 pm »
Rather than larger bank why not add wind.

I have a 2.5kW wind turbine, but we are in a very poor wind environment. Perhaps 1 in 10 nights, there would be any "useful" wind. The odd puff just doesn't count!

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it just seems like everyone has solar but i dont see wind mentioned much and
im puzzled as to why. Isnt it cheaper /watt than solar? Just curious.

Wind turbines have for years, been cheaper per watt *OF CAPACITY* - that is, a 2kW turbine was around a thousand bucks, but a 2kW PV install would be around five times that (including controllers, etc).

Since then, PV has gotten way cheaper and is probably about the same price of "capacity" as wind... but solar doesn't require much maintenance, doesn't have all the regulatory problems, and produces significant amounts of power all day, most days.


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I guess i dont understand why it isnt more popular.

In many places, you now need all sorts of permits to erect a turbine of any non-trivial size, and many places that permission simply is not forthcoming. Also far higher insurance (in some cases, uninsurable) with a wind turbine. Also complaints from ignorant neighbours who don't like the look of it, or are scared it'll fall on them, or that it'll kill all the birds, or make them sick.

Private wind is basically dead in my view.

I was just inspecting my turbine blades yesterday and it needs to come down for maintenance. Significant erosion of the leading edge. I'm not sure I'll even bother putting it back up to be honest.