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Old 28-01-2014, 16:40   #3511
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

What is the difference in the Model CA & SE CALB cells ?

CA sells for $131 usd

SE sells for $129 usd

http://www.electriccarpartscompany.c...tock_c_12.html
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Old 28-01-2014, 16:54   #3512
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Steve,

These would be the best bang for the buck. 195 a-hr would have the same usable a-hr of 400 a-hr of lead and $740 for 4 ($185 for each cell).

Or with quantity price reduction you could go for over kill 585 a-hr @ $2145.96

195Ah 3.2V HiPower LiPo Li-Ion EV Battery LiFePo4 Lithium Prismatic 195Ah Battery
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Old 28-01-2014, 17:09   #3513

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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

cotemar-
Click on - CALB (USA Stock!) and then "View Details". There are a number of differences in max charge rate, self-discharge rate, overall battery weight, etc.
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Old 28-01-2014, 18:13   #3514
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I notice some configurations that suggest separating load and charging busses. This is a good idea BUT I would not recommend automatic recharging following an LVC event. If a LVC even occurs the cell voltages should be examined manually and a decision then taken to begin charging. Any cell with a lower then usual voltage may require pre-qualification charging.

Even better would be to have a warning LV limit, even though that's very hard to do in large C Li

Dave
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Old 28-01-2014, 18:24   #3515
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by goboatingnow View Post
I notice some configurations that suggest separating load and charging busses. This is a good idea BUT I would not recommend automatic recharging following an LVC event. If a LVC even occurs the cell voltages should be examined manually and a decision then taken to begin charging. Any cell with a lower then usual voltage may require pre-qualification charging.

Even better would be to have a warning LV limit, even though that's very hard to do in large C Li

Dave
The House Power BMS alarms at about 3.0 V and does not LVC until 2.9V. This is well above the 2.8V per cell you don't want to dip below and also in the safe range for recharging.
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Old 30-01-2014, 05:56   #3516
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post
Damn with that small bank you are going to pass me in no time. I just broke 231 cycles today...... With a 400Ah bank I can discharge to 80% DOD in about two hours but to charge takes me 5+ unless I want to lug my 100A charger into my office. So 1 per day max for me and if I am around then occasionally two.......

Your voltages match mine quite closely but I suspect those are not long rests.

My bank is currently sitting at 74.6% SOC (approx 21 hours) and is resting at:

#1 3.334V
#2 3.333V
#3 3.334V
#4 3.334V

The difference may be that I am drawing this cycle down at 11.5A - 12A which barely touches it...... I suspect I may get 500Ah at 11.5A - 12A out of this 400Ah bank.......
Update:

I finally completed my 0.03C test to simulate our own boats max avg loads. The results are in.

The bank puts up 441 Ah's at .03C.

The only real difference between a .25C load / 100A and a 11.5 - 12A / .03C load is that the .25C load hits 2.800V at -425Ah's and the .03C load hits 2.800V at -441 Ah's..

If I stop the .25C load at -425 and, let the voltage rebound, then turn on the .03C load I can get -440Ah's from the bank.

So a net difference of 1 Ah and well within the margin of error.....

I thought I could get 500Ah's at a low "C", never assume! 500Ah's was not the case but I am still performing better than the face value rating when drawing at below .5 "C" / 200A which is what the bank is rated at from Winston.

I think, for house bank use, we can take away that a .5C load would never be the load so we use on-board. If that is the case then we can expect slightly better Ah performance when drawing at well below .5C if the cells are within spec....

I suspect that a .5C load would yield 400Ah's +/- to 2.800V per cell but that if I turned it off, let the resting voltage rebound, then applied .03C I might still get the -440 +/- out of it... (this is another assumption and could easily be shown to be incorrect.)

Results of three complete capacity tests:

.25C = -425 Ah's to 2.800V
.25C to 2.800V / Rebound / Apply .03C = -440 Ah's
.03C = -441 Ah's to 2.800V

Initial capacity test 232 cycles ago: .25C = -425Ah's to 2.800V (I did not test for rebound with .03C)

In all cases I am charging CC/CV to a 13.8V pack voltage and allowing the current to drop to about 5A before terminating charge. This gives up a tad bit of performance on the very top end, perhaps 2% but allows for a head room safety margin...

Instruments:

*Cell Voltage Monitored Using Cell Log 8S (Calibrated to Fluke)
*Cell Voltage Manually Checked With Fluke 179 (Calibrated)
*Pack Voltage Measured Using Fluke 179
*Ampere Hours Recorded Using Victron BMV-602
*.25C Loads Applied Using 2000W Inverter and Ceramic Disc Heater
*.03C Loads Applied With Light Bulb


Hope this data helps....
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Old 30-01-2014, 07:11   #3517
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

All,

It looks like the CALB 100Ah cells would be the best for me, they can stay upright in the existing two battery boxes. With 12 cells, 6 in each box, configured as 3P4S, that would be 300Ah max or 240Ah usable at 80% DOD which is almost equivalent to 500Ah of LA at 50%DOD. With 6 cells in each box there is still plenty of room for BMS modules, wiring, and connectors. A nice neat install should be possible.
For the shore power charger I have an older Mastervolt 30A, while the settings are not adjustable it does have a float only mode of 13.8V. Assuming that it will provide up to 30A at 13.8V does anyone see a problem using this charger on a BMS protected bank? Once this weather warms up a bit I'll get down to the boat and pull the charger so I can test it on the bench and verify my assumptions.

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Old 30-01-2014, 08:51   #3518
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I don't think I'd want to "float" a bank at 13.8v. I float at 13.2v which basically shuts down the charger entirely. If you try to use your current charger, I'd stand next to it and continually monitor it, don't rely on the BMS to control charge cycles!
For what your spending on the cells get something like the Sterling Procharge 30-40 or 60. It's probably one of the cheaper chargers (and a nice unit) that can be fully programed to a custom charge profile.
Dwain
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Old 30-01-2014, 08:52   #3519
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Would someone mind going into the details of the Low and High voltage cutoff wiring and what relays they are using? I know it will probably be based on the individual charger used but a general layout would be nice to see.

Steve in Solomons MD
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Old 30-01-2014, 11:53   #3520
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Quote:
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I don't think I'd want to "float" a bank at 13.8v. I float at 13.2v which basically shuts down the charger entirely. If you try to use your current charger, I'd stand next to it and continually monitor it, don't rely on the BMS to control charge cycles!
For what your spending on the cells get something like the Sterling Procharge 30-40 or 60. It's probably one of the cheaper chargers (and a nice unit) that can be fully programed to a custom charge profile.
Dwain
Try if possible not to float charge Li. Better the charge cycle stops and disconnects then reconnects at a lower voltage

Dave
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Old 30-01-2014, 14:03   #3521
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by goboatingnow View Post
Try if possible not to float charge Li. Better the charge cycle stops and disconnects then reconnects at a lower voltage

Dave
Great idea in a utopian world. In real life a bit more difficult, although admittedly doable. I still haven't seen any "real life" evidence that floating at a very low voltage on a large prismatic pack does any harm. At 13.2v with pack voltage at 13.3-13.4 there is no current and no voltage applied to the pack so please explain how damage can be done and please quantify it! If damaging a pack by .1% or something, it's only an academic argument, as are many on here!
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Old 30-01-2014, 14:31   #3522
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
I still haven't seen any "real life" evidence that floating at a very low voltage on a large prismatic pack does any harm.
how would you know if you saw or didn't see they damage


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Old 30-01-2014, 14:57   #3523
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by goboatingnow View Post
how would you know if you saw or didn't see they damage


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I was asking you to show me where it's documented, I wasn't touting my merger endeavors, you seem to have all of the answers!
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Old 30-01-2014, 15:07   #3524
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I was asking you to show me, you have all of the answers!
Dwain
The research indicates that what typically happens is, the slow plating , is only partially removed during discharge. Hence the indications are that a percentage of capacity is lost.

But capacity is very different to profile accurately in Li, especially in high c banks. so while Ive seen some loss in 18650 cells, I have no figures for large prismatics.

WHat I do know, is that the research indicates that that floating causes loss of capacity and if one examines the various Li charger designs , they all disconnect and reconnect.

Dave
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Old 30-01-2014, 15:11   #3525
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Why does a float voltage (OK 13.8V might be high) harm a LiFe pack? If the float voltage stays well below the HVC level and the cells stay balanced there should be no current flow once the pack terminal voltage reaches the float voltage.

What I want to avoid is discharging my bank by even 10% because the fridge is running on a sunny day but the BMS says it's above the LVC so don't charge, that's what the solar panels are for, pick up the load when it can. I think most of the info I have seen from sites like House Power are geared to the EV folks where the vehicle batteries are either loaded while running or sitting at a charger station, not having loads and charging at the same time.

So what is the best way to use a resource like solar or wind which might not be available when the bank runs down to a charge now or else level?

Steve
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