5 years of CALB LiFePO4 battery operation

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Re: 5 years of CALB LiFePO4 battery operation

Postby karrak » Thu Jan 25, 2018 8:31 am

australsolarier wrote:karrak,
the link you added is totally unsuited to lifepo4 batteries. i mean totally useless.
for one thing it has a 50A limit. and the balance function starts way over the lifepo4's.

If you read the description you will see it says it is suitable for LiFePO4 batteries. It is fully programmable. Might be worth confirming this with the supplier. I have 2 12S 30A units that are similar to this one that I use on our electric bikes.
BMSsettings.jpg


In this case I was suggesting it as a cheap means to view and log the individual cell voltages.

You do not have to use the battery disconnect capability if you don't want to. They do have some units with much higher current capacities, up to 150A I think but they cost allot more.

If you did want to use the balancing function I disagree that 50mA is not enough if you start with a well balanced battery. I manually balance my battery. Last year I had to remove 1.5Ah of charge from two cells to keep it balanced. That equates to ~4mAh/day.

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller
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Re: 5 years of CALB LiFePO4 battery operation

Postby Gordon-Loomberah » Thu Jan 25, 2018 12:22 pm

Thaks Simon :)

karrak wrote:I was wondering if your battery impedance had changed much over the five years?


I haven't done any calcs on impedance, but I suspect it has increased a bit, although the battery gets hit with much larger loads in recent years cf when new, so I'd have to search through my data for some useful comparative data.

One thing I have noticed is that the max current the battery will accept at various SOC levels does vary over time. I'll see if I can find a couple of recent graphs to demonstrate.

... reasonably priced 16S BMSs from China


Looks ok for cell voltage monitoring, but the cell voltage high and low cut-offs are a bit of a worry, definitely not suitable for my battery.

I've thought about putting a big cap across my battery to reduce the 50hz ripple, but haven't done anything about it yet.


australsolarier wrote:if i remember correctly Gordon has the ev-power bms installed.


I did start off with one when operating 8S2P, which was totally inadequate and was close to starting a fire before I modified it, but haven't run a BMS for over 3 1/2 years now. I do have a couple of 48V 200A contactors sitting in boxes though ;)
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Re: 5 years of CALB LiFePO4 battery operation

Postby karrak » Thu Jan 25, 2018 3:45 pm

Gordon-Loomberah wrote:I haven't done any calcs on impedance, but I suspect it has increased a bit, although the battery gets hit with much larger loads in recent years cf when new, so I'd have to search through my data for some useful comparative data.

The reason I asked was that there was a paper written on storage at various SOC of different lithium ion batteries and the effects on capacity and impedance. The impedance of LFP batteries didn't change over the test while the others did. Implies that LFP batteries will age better than the others.
LiIonstorage.Small.jpg


Looks ok for cell voltage monitoring, but the cell voltage high and low cut-offs are a bit of a worry, definitely not suitable for my battery.

I thought I would try and reprogram my 12S BMS for LFP rather than the current Lipo settings. Worked just fine.
lfp.jpg


If you ever did want to drive the contactors from the OVP and UVP signals that should be possible.

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller
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Re: 5 years of CALB LiFePO4 battery operation

Postby Gordon-Loomberah » Thu Jan 25, 2018 4:02 pm

karrak wrote:The reason I asked was that there was a paper written on storage at various SOC of different lithium ion batteries and the effects on capacity and impedance. The impedance of LFP batteries didn't change over the test while the others did.


I think I might have seen that study at some time, or a similar one, but I don't know how relevant storage for 9 or 10 months at a particular SOC is to a working off-grid system that isn't really stored at any SOC, as SOC varies continuously. At least mine does ;)

If you ever did want to drive the contactors from the OVP and UVP signals that should be possible.


I was planning to use my Morningstar RD1 relay driver, just set a high and low limits with a (say) 1 min delay to cover big load starts - my water chiller can hit 15kWDC when starting.
For HVD I was going to turn on a fairly large resistive load, or disconnect a charge controller if the condition persisted (4 channels available).
For low voltage disconnects, my inverter has handled that well a few times so far, and I am inclined to rely on it. If one cell goes low, chances are 1 or 2 others will be getting low too, and the inverter LVD will catch it. I had it modified by Latronics at purchase time, to my spec.

Lots of house shaking due to close lightning here, time to unplug!
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Re: 5 years of CALB LiFePO4 battery operation

Postby australsolarier » Fri Jan 26, 2018 2:57 pm

just an observance about the impedance of my battery (lifepo4 /48V / 400Ah):
as i have 3 midnite classics now with each around 6kwp panels , it is possible the charge current exceeding 200A. (the blue ev-power box is supposed to disengage when 200A is reached after a certain short time , each midnite is capable of 86A = 258A total.)
so i programmed the midnite classic with the battery shunt to limit charge current into the battery to 200A. next day i tried to see if it worked. i discharged the battery to 65% SOC and then threw everything at it. the current ramped up to 180A, V absorb was reached, i raised V absorb another 0.6V on all chargers, but still only 190A. (the battery spec says max charge is 400A). i terminated the experiment then.
so it looks to me the chemistry cannot keep up well with high charge current. i suppose it is sort of another redundancy.
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Re: 5 years of CALB LiFePO4 battery operation

Postby Gordon-Loomberah » Fri Jan 26, 2018 3:33 pm

I've only briefly seen much over 100A net charging lately, and need to be fairly deeply discharged for that to happen. Even when new, 400A was never going to happen!
Referring to what I mentioned earlier, there was a recent period when the battery would only accept <50A at ~50%SOC, but that seems to have sorted itself out and it once again will go higher. It's a mystery as to how the impedance can increase and then decrease again.
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Re: 5 years of CALB LiFePO4 battery operation

Postby Warpspeed » Sat Jan 27, 2018 11:47 am

One quick question, at what voltage do you terminate charging your Winstons ?
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Re: 5 years of CALB LiFePO4 battery operation

Postby Monkeytom » Thu Feb 08, 2018 3:51 pm

Hi Gordon, I also would like to thank you and others on this forum, as you helped me take the big step into the unknown. Abit longer than two years ago I started asking hard questions, and with help from you and others, I purchased two sets of six year old EV batteries that I bought right and have repurposed.
45 Blue CALB 100Ah cells and 45 Yellow Thundersky 90Ah cells and I run them 100Ah+90AhP x 15S X 3P these are now 8 years old and still working really well these give me about 25Kwh storage, they are charged with 6kw of panels into two PIP4048's 3Kw into each, The system with a few changes along the way is going great and has paid for itself ($7K) in the last two years with the FIT and saved energy costs. So we couldn't be happier.
And the Virtual tracking on my Grid tie system has nearly doubled its output too. Thanks a bunch.
Best regards Tom
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Re: 5 years of CALB LiFePO4 battery operation

Postby Gordon-Loomberah » Thu Feb 08, 2018 4:02 pm

Thanks Tom, glad to be of assistance :)
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