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

[deckofficer]

Cotemar, you should start a new thread on that wheel. It sounds perfect for ground transportation for a cruiser.

[Cotemar]

Originally Posted by deckofficer

Cotemar, you should start a new thread on that wheel. It sounds perfect for ground transportation for a cruiser.

OK, I will make a new thread.
I do agree that it would be a great addition to any boat.

Just wanted to show this to the LifePO4 team. This type of transportation would not be possible with older battery technology. LifePO4 batteries make it possible.

[deckofficer]

That is true. I'm also into general aviation and we now have a few all electric planes on the market. Of course they use the more energy dense lithium chemistry that can get hot and also have 1/3 the cycle life of LiFePO4. For our needs, LiFePO4 is by far the best all around.

[Opie91]

Originally Posted by deckofficer

That is true. I'm also into general aviation and we now have a few all electric planes on the market. Of course they use the more energy dense lithium chemistry that can get hot and also have 1/3 the cycle life of LiFePO4. For our needs, LiFePO4 is by far the best all around.

So what are you not into? That's probably a shorter list.

[deckofficer]

Originally Posted by Opie91

So what are you not into? That's probably a shorter list.

I don't skydive.

My sister has always told me I've been able to do everything I want. She raised a family of 4 kids and now has 8 grandkids, so will be enjoying a family gathering tomorrow. I on the other hand never married, didn't raise a family, and all my decisions in life was only taking me in consideration. Tomorrow is just another day for me while my sister will be enjoying the family she created.

More answer than you wanted, right?

[deckofficer]

Back on topic. Cycling is going like clockwork, these cells are robust. At first I powered the space heater on high, 1500 watts. By the end of the 5th cycle the low battery alarm came in at 62 minutes, the first cycle was 57 minutes, so I conclude after sitting unused for a year, capacity increases with repeated deep cycles.

T1 Terry mentioned that cycle tests above 0.5 C wouldn't fairly represent cycle life. I can't get down to 0.5C because the two settings on the space heater is 1500 and 1100 watts, so 129 amps on high to 94 amps. This works better because the cables, Anderson connectors and terminals don't get as hot.

T1 Terry also mentioned to stop charging before the knee. When the charger dropped to 20 amps (from 50 amps) I stopped charging but discovered the run time at 1100 watts went from 84 minutes to 78 minutes. Knowing this I just let the charger do its thing all the way to voltage shut off.

Cell voltage after full charge (14.16)
3.56
3.51
3.55
3.54

Cell voltage after 42 minutes @ 1100 watts (approx 40% DOD)(13.05)
3.26
3.26
3.27
3.26

Cell voltage after low alarm (11.48)
2.94
2.84
2.64
3.06

At full charge and through most all the discharge the cell voltages stay tight. The discharge knee is where the cells spread out a bit.

[ColdEH]

This is great info Deckofficer. Thanks for all the hard work , you are taking a lot of the guess work out of how to properly take care of these batteries .

I may have missed it , but how many amp hours is that small bank you are using?

Regards

[senormechanico]

During a phone conversation with the CEO of Balqon, I asked him about charging voltages they recommended.
He said for a 24 volt system, they use 27.4 Absorb, 26.8 float.

[deckofficer]

Originally Posted by typhoon

This is great info Deckofficer. Thanks for all the hard work , you are taking a lot of the guess work out of how to properly take care of these batteries .

I may have missed it , but how many amp hours is that small bank you are using?

Regards

I think I have the smallest of this group, (2) 12 volt 100 a-hr banks. They are for my electric propulsion kayak. 60 lbs of LA gave me an 18 nm range, same weight of LiFePO4 gives 80 nm range.

I'm only running the one bank on these cycles. I figure after 2000 cycles it could be down to holding 80% of advertised capacity so for kayak use it will be the outbound battery so I have the confidence the other battery will always return me to where I launched.

Cells sat at Balqon for 3 years before I got them and cycled about 5 times then sat for another year.

Cycles since 11-24-13

@ 1500 watts run time
6) 57 min
7) 59 min
8) 60 min
9) 62 min
10) 62 min

@1100 watts run time
11) 84 min (then charged as per T1 Terry to a lower celll voltage)
12) 78 min (6 minutes less so returned to letting the charger turn off)
13) 83 min
14) 84 min


...and still going, hoping to be the 1st to pass 2000 documented cycles. Got a ways to catch up to Maine Sail @ 200+ to date or T1 Terry @ 850+.

I have 14 cycles (5 a year ago, 9 in the last 3 days). At this rate it will take 2 years, lol

[Maine Sail]

Originally Posted by deckofficer

I have 14 cycles (5 a year ago, 9 in the last 3 days). At this rate it will take 2 years, lol

200 was a lot of work to do in slightly under one year but exceeds the cycles most boaters do before their lead acid batts are toast.........

I don't know why you would stop at 20A of acceptance? What voltage was that at? The taper is still short but for on-the-boat use I stop at 5A acceptance and 13.8V. If I push it to 14.0V the taper is slightly shorter but I still stop at 5A acceptance. Either way I still get over 400Ah's on a 400Ah bank at these charging vltages so I have no need to push to a higher voltage.

I find it interesting that Balquon stated 13.7V absorption and 13.4V float to SM in the above post..... I was told last year that 13.8V to 14.0V was fine for absorption, I don't float them. I then spent all winter testing charging voltages and settled right back where Balquon had originally told me 13.8V to 14.0V....

[deckofficer]

Originally Posted by Maine Sail

200 was a lot of work..... I don't know wy you would stop at 20A of acceptance? What voltage was that at? The taper is still short but for on-the-boat use I stop at 5A acceptance and 13.8V. I still get over 400Ah's on a 400Ah bank at these numbers so I have no need to push to a higher voltage. I find it interesting that Balquon stated 13.7V absorption and 13.4V float.... I was told last year that 13.8V to 14.0V was fine for absorption, I don't float them.

I misread what T1 Terry told me and turned off the charger at 3.4 volts per cell. 14 volts is what this so called "lithium profile" charger does for absorption, I'm pleased with the charger, it stays at 49.8 amps for around 110 minutes then tapers for 15 minutes.

On the 3rd cycle today I'll try your 5 amp acceptance for ending the charge and see what I get. That would save some time.

I just finished a cycle while typing, only 78 minutes @ 1100 watts, so I must also conclude the higher surface voltage from right after a charge is giving me a few extra minutes of run time. This was the first cycle today so the battery sat at full charge for 9 hours before this cycle. I'll see if it goes back to 84 minutes on the next cycle.

[deckofficer]

Maine Sail, how much over 400 a-hr are you getting on what load? On a 1100 watt load (94 amps) it appears I'm getting 132 a-hr from a 100 a-hr bank when battery voltage drops to 11.48 volts. What is the DOD at this voltage? I think it is deeper than 80% DOD, maybe even over 90% DOD.

122 a-hr for the 100 a-hr battery on a 9 hour resting from the charger.

Any input on this from the pros?

[Maine Sail]

Originally Posted by deckofficer

Maine Sail, how much over 400 a-hr are you getting on what load? On a 1100 watt load (94 amps) it appears I'm getting 132 a-hr from a 100 a-hr bank when battery voltage drops to 11.48 volts. What is the DOD at this voltage? I think it is deeper than 80% DOD, maybe even over 90% DOD.

122 a-hr for the 100 a-hr battery on a 9 hour resting from the charger.

Any input on this from the pros?

I am manually cutting my test off at 425Ah (with voltage still above lower knee) and it is running a .25C load or 100 - 105A load. I am sticking with that load because that is what I started with. I should do .5C load but my inverter can't handle 200A....

These manufacturers claim almost zero Peukert so a .25C load should produce similar results to a .5C load, in theory....

[deckofficer]

I've decided to change the cycling a bit. By pulling the battery all the way down to the inverter's low voltage alarm, I think that represents a DOD of over 90% and not a fair way to determine cycle life. 84 minutes at 94 amp draw already is more than the manufacturer's rating of 100 a-hr by 32 a-hr. Maine Sail is pulling 425 a-hr on his cycles from his 400 a-hr bank, so I'll reduce to that for my bank. He is pulling 6% more than the rating so I'll reduce to 106 a-hr from the 132 a-hr it has been giving me. At 94 amp draw each cycle will be 67 minutes instead of 84 minutes. After 200 cycles I'll see if it can still go the 84 minutes, but these cells are so conservative rated, who would have thought how hard it is to determine what 80% DOD is? It would be easy if the cells could only do their rating, thus 80 a-hr draw down on a 100 a-hr cell, but since a 100 a-hr cell has no problem delivering 132 a-hr with bank voltage at 11.48 volts, it is guess work for 80% DOD.

I will go with Maine Sail's recommendation of stop charging a 5 amp acceptance as that will save time and keep the cells from their charged knee and I'll be curious of the cell voltage after 67 minutes discharge instead the the 84 minute discharge, that should keep me from the low knee. I think we are all in agreement that if you avoid both knees they will have a longer cycle life.

Too bad I don't have a new 100 a-hr (@ 20 hour rate) lead acid battery for comparison, but I'll speculate that it wouldn't even make it to 25 minutes and die in 100 cycles.

15) 78 minutes
16) 82 minutes, all future cycles will end at 67 minutes at 0.94 C

[Maine Sail]

Originally Posted by deckofficer

I've decided to change the cycling a bit. By pulling the battery all the way down to the inverter's low voltage alarm, I think that represents a DOD of over 90% and not a fair way to determine cycle life. 84 minutes at 94 amp draw already is more than the manufacturer's rating of 100 a-hr by 32 a-hr. Maine Sail is pulling 425 a-hr on his cycles from his 400 a-hr bank, so I'll reduce to that for my bank. He is pulling 6% more than the rating so I'll reduce to 106 a-hr from the 132 a-hr it has been giving me. At 94 amp draw each cycle will be 67 minutes instead of 84 minutes. After 200 cycles I'll see if it can still go the 84 minutes, but these cells are so conservative rated, who would have thought how hard it is to determine what 80% DOD is? It would be easy if the cells could only do their rating, thus 80 a-hr draw down on a 100 a-hr cell, but since a 100 a-hr cell has no problem delivering 132 a-hr with bank voltage at 11.48 volts, it is guess work for 80% DOD.

I will go with Maine Sail's recommendation of stop charging a 5 amp acceptance as that will save time and keep the cells from their charged knee and I'll be curious of the cell voltage after 67 minutes discharge instead the the 84 minute discharge, that should keep me from the low knee. I think we are all in agreement that if you avoid both knees they will have a longer cycle life.

Too bad I don't have a new 100 a-hr (@ 20 hour rate) lead acid battery for comparison, but I'll speculate that it wouldn't even make it to 25 minutes and die in 100 cycles.

15) 78 minutes
16) 82 minutes, all future cycles will end at 67 minutes at 0.94 C

If you want to go to 80% DOD just get a Victron BMV 600 battery monitor. You can set it to alarm at 80% DOD or to make or break a relay and stop discharging.. They are well under $200.0 and have many uses...