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

[roetter]

Originally Posted by yamez4u

I love my Victron Quattro 5000 Inverter/Charger It has built in LiFePo charge profiles. I highly recommend Victron chargers.

With the USB interface to the Victron Multi and Quattro inverter/chargers, and I assume to the Phoenix chargers you can set any parameter for charging, inverting, relay use from your Windows computer.

[sv.antea]

Thanks Transmitter Dan and Roetter. The reason I was hoping for independent input and power on the Light Objects V-meter is because they have 5-6V DC (14Vac) power in terminals and separate measured voltage terminals. The specs don't give away what it means, even if they say it will read negative voltages.
I know about the Cell Logger. I have read the whole thread here. But someone mentioned way back how small the display is. That was when I thought about adding dedicated voltmeters to each cell. On Antea I have a Blue Sea analog V-meter eye level right next to the companionway and like the convenience of being made aware of the house battery voltage as I climb the steps.
Stan

[campr]

roetter, the BM16LF also seems to have the same features, but for 16 cells: chargery model power, Accessories is designed specially for big current application It's switching output has a greater capacity: 30V 1A. and it seems to be a little clearer on why it was tripped (it will tell you on the display). It also has a nice SOC graph.

I'm actually thinking of using 2 of these, one for the low-threshhold for switching off the loads (DC contactor, manual reset), and one to switch off the chargers (DC relay, automatic reset).

[roetter]

Originally Posted by campr

roetter, the BM16LF also seems to have the same features, but for 16 cells: chargery model power, Accessories is designed specially for big current application It's switching output has a greater capacity: 30V 1A. and it seems to be a little clearer on why it was tripped (it will tell you on the display). It also has a nice SOC graph. I'm actually thinking of using 2 of these, one for the low-threshhold for switching off the loads (DC contactor, manual reset), and one to switch off the chargers (DC relay, automatic reset).

Interesting item. Have you tried it?

The output of the Junsi can be connected to a small relay that drive bigger loads. I am using a 4-relay board I bought on Amazon on one boat. I use one relay to cut the 110V AC to the charger at 13.8. Another relay is driving an automotive relay to switch the alternator sensing from the battery to before the split diode, with that regulating the alternator right down. The third relay is switching the Blue Sea HVC solenoid. So the low current limit of the Junsi alarm port is not a problem.

The small display of the Junsi is not a problem for me, and I need glasses for reading in anything but very good lighting. I have not even hooked up my Junsi yet, as I am in No danger of an individual cell drifting out enough. I have a new boat and tons of other things to take care of. Since my Light Object cuts charge at 13.8V I would have to have a very serious imbalance to have a problem. Once the cells are 50% full and you are charging each voltage if upwards of 3.4V. If you have 3 cells at 3.4 V the highest cell would be at 3.6V when the HVC shut down occurs. That is well within the specs for the cells. At the moment I check my cells with a volt meter every 5 or so days when I am near 13.8V and charging. So far the drift, if any, is not noticeable.

I guess the trick is to install a larger bank and stay well away from the upper knee 95+% full and the lower knee 10% full. The nice thing about these batteries is, you not only have to fully charge them for a long life like FLA, AGM, and gel, but they will live longer if you do not fully charge them. I am running 1400 Ah and have been down to about SOC 35% after 5 rainy days, and always cut off at 13.8V at the upper end. Makes for a very relaxed living.

[deckofficer]

Staying away from upper and lower knees is the way to go. I just did a capacity test on one of my banks that now have 201 cycles to 82% DOD.

As we have all figured out, the a-hr ratings assigned to our cells is conservative. On this capacity test I went for 100% DOD based on the a-hr rating of the cell and was still above the discharge knee. My tests and cycles are performed at 0.41 C.

Percentage of discharge***Cell voltage under 0.41 C load**Cell voltage no load
***********LOAD*****************NO LOAD*****
10% DOD*3.25, 3.23, 3.23, 3.25**3.31, 3.30, 3.30, 3.31
20% DOD*3.24, 3.22, 3.22, 3.24**3.30, 3.29, 3.29, 3.29
30% DOD*3.22, 3.21, 3.20, 3.23**3.29, 3.28, 3.29, 3.29
40% DOD*3.21, 3.19, 3.19, 3.21**3.28, 3.27, 3.28, 3.28
50% DOD*3.20, 3.18, 3.17, 3.20**3.27, 3.26, 3.26, 3.27
60% DOD*3.19, 3.16, 3.14, 3.19**3.26, 3.25, 3.25, 3.26
70% DOD*3.17, 3.13, 3.10, 3.17**3.24, 3.23, 3.23, 3.24
80% DOD*3.14, 3.10, 3.06, 3.14**3.23, 3.21, 3.21, 3.23
90% DOD*3.11, 3.06, 3.01, 3.11**3.20, 3.18, 3.17, 3.21
100% DOD*3.07, 3.02, 2.93, 3.07*3.18, 3.16, 3.10, 3.19

As always, cell #3 is my weakest cell. For others that are testing, are my voltages under a 0.41 C load and no load match your cell voltages at the different states of discharge?

[Maine Sail]

Originally Posted by deckofficer

Staying away from upper and lower knees is the way to go. I just did a capacity test on one of my banks that now have 201 cycles to 82% DOD.

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.......

[deckofficer]

Originally Posted by Maine Sail

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.......

Yep, for testing, small banks are the way to go. I also discharge in 2 hours but charge in less than 2 hours, getting about 4 cycles per day. In the summer I'll have to find a load other than a space heater.

I posted the above results in hopes that you, T1 Terry, or others could confirm that as the cell size is scaled up, the cell voltages remain the same at different DOD's. This would be handy for determining remaining charge at a glance of voltages. i.e at 3.265 volts no load 50% DOD.

[Maine Sail]

Originally Posted by deckofficer

I posted the above results in hopes that you, T1 Terry, or others could confirm that as the cell size is scaled up, the cell voltages remain the same at different DOD's. This would be handy for determining remaining charge at a glance of voltages. i.e at 3.265 volts no load 50% DOD.

It is odd and I don't quite know what to make of it but when drawn down at low loads the voltage barely budges.. I am 25% down on my bank now and the resting voltages are 3.334.....

It is funny that in my last test I drew the bank to 2.800V for the lowest cell at a .25C load and was at 425Ah' the SAME EXACT spot I was at 200 cycles earlier using the same exact test, instruments etc. meaning in 200 cycles to 80% DOD I had ZERO capacity loss.

I then shut the .25C load off and voltage rebounded so I hit it again with a 15A load and got another 15Ah out of the bank before once again hitting 2.800V for the lowest cell. In that test .25C to 2.8V then 15A to 2.8V I got 440 Ah's out of a 400Ah bank, BUT I am only charging to a max of 13.8V for a 12V nominal pack....

You can even go slightly below 2.8V but I don't... This is what spawned my current capacity test of 11.5 -12A / .03 "C" ...... Unfortunately I am looking at 35-40 hours of monitoring the bank so I am doing it in spurts....

[deckofficer]

Originally Posted by Maine Sail

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

No rests, just removed the load so I could see voltage sag at different DODs. Many years ago I did a test similar with lead acid, talk about big sag and huge voltage swings over the range of discharge. Our cells are sure robust in the no sag department.

For my next project I've been gleaming the Internet for high energy density cells, and it appears Envia (backed by GM) will soon be producing batteries in the 400 w-hr per kg range. I'm not sure our heavy Winstons are breaking 100 w-hr per kg. I'm going to wait for the Envia cells to come out and grab some to test, then hopefully fly (literately) with them.

[noelex 77]

Originally Posted by deckofficer

There is no reason cruisers who have switched to LiFePO4 cells couldn't go to a fully electric galley with induction cook tops and get rid of the propane.

Getting rid of propane is very worthwhile, but LiFePO4 batteries are only part of the answer.
The bigger problem is how you replace the energy. It requires a large solar array (only practical on a cat, or large monohull). Frequent visits to a marina, or running of a generator.
In the later case (if it is installed primarily for cooking) the reliability/convenience will be less than propane.

[Maine Sail]

Originally Posted by Maine Sail

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.......

After this post I turned the 11.5A load on again and drew the bank to exactly 200Ah's removed (400Ah rated bank)

Based on Ah consumption (not figuring for Peukert) the bank is sitting at 50% SOC and has been resting now for approx 10 hours at 69F.


My bank is currently sitting at 50.0% SOC (approx 10 hours rest) and is resting at 13.24V or :


-200Ah - 10 hour rest 13.24V:
#1 3.310V
#2 3.309V
#3 3.310V
#4 3.310V

[Maine Sail]

Originally Posted by Maine Sail

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.......

After this post I turned the 11.5A load on again and drew the bank to exactly 200Ah's removed (400Ah rated bank)

Based on Ah consumption (not figuring for Peukert) the bank is sitting at 50% SOC and has been resting now for approx 10 hours at 69F.


My 400Ah bank is currently sitting at -200Ah with approx 10 hours rest and sitting at 13.24V.


-200Ah - 10 hour rest 13.24V:
#1 3.310V
#2 3.309V
#3 3.310V
#4 3.310V

*Based on Ah removed NOT Peukert Calculated

75% SOC 21 Hour Rest = 13.335V
50% SOC 10 Hours Rest = 13 .239V

Voltage Difference for 25% of capacity = 0.096V

I won't be home to see it hit 21 hours so that difference could be even smaller.

[deckofficer]

Well Maine Sail your voltages at different DOD's are higher than mine. Maybe size does matter.

14.56 volts. This was pack voltage as the charger had tapered down to 1 amp, so it is the highest the pack will ever be.

13.52 volts. This is the fully charged pack at rest.

Resting voltages at X DOD

10% DOD 13.22 volts
20% DOD 13.17
30% DOD 13.15
40% DOD 13.11
50% DOD 13.06
60% DOD 13.02
70% DOD 12.94
80% DOD 12.88
90% DOD 12.76
100%DOD 12.63

[Maine Sail]

Originally Posted by deckofficer

Well Maine Sail your voltages at different DOD's are higher than mine. Maybe size does matter.

14.56 volts. This was pack voltage as the charger had tapered down to 1 amp, so it is the highest the pack will ever be.

13.52 volts. This is the fully charged pack at rest.

Resting voltages at X DOD

10% DOD 13.22 volts
20% DOD 13.17
30% DOD 13.15
40% DOD 13.11
50% DOD 13.06
60% DOD 13.02
70% DOD 12.94
80% DOD 12.88
90% DOD 12.76
100%DOD 12.63

I think our friend Peukert is the reason. Your load is .41 "C" mine is .03 "C"..... Could be some meter error too. My Fluke is NIST calibrated so I tend to think it is pretty tight...

[deckofficer]

Originally Posted by Maine Sail

I think our friend Peukert is the reason. Your load is .41 "C" mine is .03 "C"..... Could be some meter error too. My Fluke is NIST calibrated so I tend to think it is pretty tight...

What your saying is if I would have given the cells a rest before taking the no-load voltage, the readings would be higher? As mentioned, those voltages came right after the 0.41 C load was removed.