Author Topic: LFP 1 year old  (Read 414 times)

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Offline lighthunter

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LFP 1 year old
« on: April 02, 2017, 03:23:12 PM »
Hi all, Its been 1 year since I put to use 8, 40AH GBS cells in a 24v series pack. They costed about $63
each for a total of $500. I put the recorder on the bank yesterday for a checkup and thought I would share the photos.  This is not the typical application for a battery as they get cycled hard every day. Their role is more like that of a capacitor. At 40AH 26V they only store 1kwh of power. They see charge and discharge rates of 40 amps on a regular basis and occasionally as high as 60.

I have no complaints with their performance after one year even though theyve been short cycled hard during this time and would guess the stress of 1 year has been equal to what a normal bank would get in 4 years. The graphs show a sample of what these batteries are exposed to. The internal resistance of each cell is more equal now than when they were new. The cells are top balanced and run daily from 50%to 100% level. They are connected to a 24v pj inverter modified to 4kw.  There are a couple of fairly new 1300A starter batteries that can help with surges but normally they just float beside while the LFPs do the work. The inverter is connected to 4kw of solar that sheds to 2kw when not needed and the whole house is fed from inverter with load shedding. It took a month or two to get phase matched switching to work correctly but you dont notice loads switching anymore.

LH

Offline lighthunter

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Re: LFP 1 year old
« Reply #1 on: April 02, 2017, 04:19:07 PM »
The cell max and min statistics are over 1 full solar day and night and part of next day at 1 sec intervals. Sorry about the poor quality photos. Best i could do for now. They are pretty small batteries for all that work, about the same physical size as 2 car batteries.
LH

Offline rossw

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Re: LFP 1 year old
« Reply #2 on: April 03, 2017, 06:26:26 AM »
Nice stuff.
I just went to the big smoke last thursday to collect my new cells.
52 * 200AH LFP.
I've connected them in parallel blocks of 3 cells, then 16 in series for 48V/600AH (a bit over 31kWh).
Brought them online on sunday mid-afternoon and I'm chuffed.
(The other 4 are to make a small, easily-portable yet decent sized boost-pack for around the farm)

Offline lighthunter

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Re: LFP 1 year old
« Reply #3 on: April 07, 2017, 04:55:43 PM »

52 * 200AH LFP.
I've connected them in parallel blocks of 3 cells, then 16 in series for 48V/600AH (a bit over 31kWh).

If this tiny bank can source 70 amps (1800w) with little voltage drop, can you imagine how much current you could pull from that bank without heat?  500A 26kw surge wouldnt even dip voltage. Your setup is far stronger than any grid supply.

GBS is a good battery but there are several to choose from how did you decide which brand to go
with?

 These are rated for 2000 cycles (im probably nearing that now) and i know of another review of these cells that shows degradation at 3 years. Yet some are claiming 20+ years. How many years are you expecting to get out of yours?

Defenitely a good battery technology, the price justification is in the performance and longevity calculations.
LH

Offline rossw

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Re: LFP 1 year old
« Reply #4 on: April 07, 2017, 05:09:59 PM »
If this tiny bank can source 70 amps (1800w) with little voltage drop, can you imagine how much current you could pull from that bank without heat?  500A 26kw surge wouldnt even dip voltage. Your setup is far stronger than any grid supply.

I have 200A fuses on it (actually, 200A fuse on the 600AH pack, and another 200A fuse on the 300AH pack) - they tend to share current pretty nicely so far, about 2/3 of the amps to/from the 600AH pack and the rest from the old 300AH pack.
So I dare say I could easily pull 300A with it as it stands, but that's far more than I ever need or use.

And yes, it doesn't sag or drop so far I'm absolutely wrapped with them all.

Quote
GBS is a good battery but there are several to choose from how did you decide which brand to go
with?

In the end, when I simply could not get the same as my original bank, I went with a combination of:
 * who had cells of the right physical dimensions to suit the space I had
 * who was most responsive to my emails
 * who seemed most technically competent, able to converse in english and sounded like they had some clue
 * who offered the best price (consistent with all the above)

Quote
These are rated for 2000 cycles (im probably nearing that now) and i know of another review of these cells that shows degradation at 3 years. Yet some are claiming 20+ years. How many years are you expecting to get out of yours?

Most of the LFP cells seem to quote around that 2000-3000 cycles "useful life" (they don't die then, they're just down to 70% to 80% of original capacity). I was hitting my old bank pretty hard and I'd say I've probably taken something close to the equivalent of 800 cycles from them. By adding a decent chunk of extra capacity, and expecting only a modest increase in demand, I fully expect to get 15+ years out of this lot now, and won't be surprised if I get a lot more.

Quote
Defenitely a good battery technology, the price justification is in the performance and longevity calculations.

And the space savings, and the weight savings, and the elimination of potentially explosive gas and corrosive fumes, and the inevitable liability of "toxic waste" of all that lead in years to come. (I'm going to go out on a limb here, and say that right now, today, you can sell your old batteries and get 50-60c/Kg for them - in years to come, you'll be paying several dollars/Kg in "safe disposal" fees to dispose of them... factor THAT into your lead-acid storage equation!)

LFP are basically "completely maintenance free". Put decent continuous balancers on them, and some sort of monitoring so you can spot a problem early (I haven't had any on any of mine, but it's still comforting to know), and never have to touch them again.