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

[ColdEH]

Hi Maine Sail.

Just a quick thought , this top balancing process takes a long time, around one day for each 300 ah Sinolpoly cell , and I have 8 of them .
Is it ok to leave these things sitting at 3.75 v while I do the other ones ?


I will go back and top them all off quickly before I put them all in parallel.

Just a thought

Regards

[nimblemotors]

A short burst to 3.6v will not harm the cells, holding them at 3.6v or higher will wreck them

If they cells ARE BAD, then charging them will show them to be bad.
I recently finished testing over 300 cells, I must have wrecked all 300 of them at 3.85v...NOT. Some puffed up, indeed, BECAUSE THEY ARE BAD CELLS.
When you buy new cells, should you find out if they are bad so you can return them under warranty? I would. Bad cells still work, just relatively poorly.

In general Lithium should not be float charged.
Charging them at all does 'wreck' them, so if you want the battery to last, never charge one.

[T1 Terry]

Originally Posted by nimblemotors

If they cells ARE BAD, then charging them will show them to be bad.
I recently finished testing over 300 cells, I must have wrecked all 300 of them at 3.85v...NOT. Some puffed up, indeed, BECAUSE THEY ARE BAD CELLS.
When you buy new cells, should you find out if they are bad so you can return them under warranty? I would. Bad cells still work, just relatively poorly.

In general Lithium should not be float charged.
Charging them at all does 'wreck' them, so if you want the battery to last, never charge one.

No matter what I say, you have already decided you are right and I'(and many others) are wrong. so you just go ahead and do it your way, but please don't guide others to follow your path until you have at least 1,000 cycles on your cells to prove you really do know better

T1 Terry

[SV THIRD DAY]

The beauty of the different opinions on a chat room forum is that you start to get a good feeling of who's approach and in a way world view you want to follow. So even the bad advice can actually help in the learning process. The trick is that casual users of the forum have a hard time figuring out who knows what they are talking about vs just talking.

[T1 Terry]

Originally Posted by bill good

Terry, I am replacing my house batteries with LIFEPO4S. What is a "short burst" @ 3.6V? I note all the CV portions of the charge is approx 2hrs no matter on the capacity/brand & was going to use the overall voltage of 14.6V for manual top equilizing when/if needed. The 2 hr max charging time would always be active both with normal daily 14v max & the periodic 14.6V. Solar system max 30Amp 300 AmpHr CALB cells. Cell shunts from EV-POWER. Aim to operate 14-12.6V range. Any problem seen with this setup??

Regards Bill

A short burst means stop charging when the cell reaches 3.6v until the cell voltage drops below 3.4v, then resume charging and repeat the cycle as often as required to reach the 14v or 14.2v for faster charging max battery voltage. Once a mth manual equalising if you must to reset the 100%SOC, but stay under the 3.62v mark as your max. individual cell voltage, cell cycle life depends on it. If you want to gamble that I don't know what I'm talking about after over 1,000 cycles of house battery experience it's up to you, they are your $$ not mine.

T1 Terry

[roetter]

Problems with my 12V/1400Ah

Last december I installed 8x Balqon 700Ah cells in my boat as 2P4S.

I top balanced the cells with a bench top power supply to 3.8V until the current droped to less than 3A. I let them sit 24 hours and then pushed them to 3.8V again for one hour.

After the install I used them while living on the boat until end of March. My daily energy consumption is around 350Ah.

In March we stored the boat and I drained the cells to about 50%SOC. Left them completely disconnected. In July we returned to the boat for 2 weeks and all seemed well.

For storage in July I again drained the batteries to about 50% SOC.

The storage procedure is that the LiFePO batteries are completely disconnected by removing all cables. The starter batteries are connected to the house bank and maintained by 1800W solar reduced to max output of 20A at 14.5V/13.4V .

Upon return two days ago the two cells forming the second set were down to 2.6V while the other cells were at about 3.2V.

After changing the solar to charge the LFP's again, the lagging cells quickly caught up. Now, after just over 2 days, all cell-bundles are sitting at
C1-3.330V
C2-3.287V
C3-3.327V
C4-3.330V

I assume since this is pretty much on the flat slope, that could mean a 30%+ difference in SOC.

I have not run the battery above 13.4V yet, as we have run the water maker for 10 hours. Also, the fridges have been working hard as we filled them with groceries and drinks.

Tomorrow, I plan to take them to 13.8V and see what the diffrence in voltages is. If I have time I will take them higher, until the first set of cells reaches 3.5V.

I guess I will have a long time of top balancing the cells with the good old "short" cable.

What is a good way to easily check which of the cells is bad? I guess I would have to rearrange the cells into two 12V sets with the two questionable cells in one battery. Then top balance and run them down to see if one has reduces capacity. Hopefully that one would also be the one with the slow self discharge.

I "hope" I will be able to get the bad cell replaced by Balqon. Timing is a big thing as we will be in Ft. Lauderdale only for a few days in about 2 weeks. Right now we are in George Town, Exuma and will go to the Abacos after Ft. Lauderdale.

[Jd1]

Originally Posted by roetter

What is a good way to easily check which of the cells is bad? I guess I would have to rearrange the cells into two 12V sets with the two questionable cells in one battery. Then top balance and run them down to see if one has reduces capacity. Hopefully that one would also be the one with the slow self discharge.

I bought a cheap 3kw inverter from Canadian Tire the other day ($219.99, how could I go wrong at that sale price). I will use that to power my boats electrical heater and should be able to put a nice load on the batteries to test them. I will have the SOC meter hooked up and the BMS system will disconnect the load when a single cell hits 2.5V (I think). I will have to watch things as I get to the lower voltages with the one questionable cell I have but my SOC meter will tell me exactly how much power the lowest performing cell has just before everything shuts down.

I "hope" I will be able to get the bad cell replaced by Balqon. Timing is a big thing as we will be in Ft. Lauderdale only for a few days in about 2 weeks. Right now we are in George Town, Exuma and will go to the Abacos after Ft. Lauderdale.

You are missing all the gorgeous rainy and windy weather we are having out here in Victoria

[T1 Terry]

Originally Posted by roetter

Problems with my 12V/1400Ah

Last december I installed 8x Balqon 700Ah cells in my boat as 2P4S.

I top balanced the cells with a bench top power supply to 3.8V until the current droped to less than 3A. I let them sit 24 hours and then pushed them to 3.8V again for one hour.

After the install I used them while living on the boat until end of March. My daily energy consumption is around 350Ah.

In March we stored the boat and I drained the cells to about 50%SOC. Left them completely disconnected. In July we returned to the boat for 2 weeks and all seemed well.

For storage in July I again drained the batteries to about 50% SOC.

The storage procedure is that the LiFePO batteries are completely disconnected by removing all cables. The starter batteries are connected to the house bank and maintained by 1800W solar reduced to max output of 20A at 14.5V/13.4V .

Upon return two days ago the two cells forming the second set were down to 2.6V while the other cells were at about 3.2V.

After changing the solar to charge the LFP's again, the lagging cells quickly caught up. Now, after just over 2 days, all cell-bundles are sitting at
C1-3.330V
C2-3.287V
C3-3.327V
C4-3.330V

I assume since this is pretty much on the flat slope, that could mean a 30%+ difference in SOC.

I have not run the battery above 13.4V yet, as we have run the water maker for 10 hours. Also, the fridges have been working hard as we filled them with groceries and drinks.

Tomorrow, I plan to take them to 13.8V and see what the diffrence in voltages is. If I have time I will take them higher, until the first set of cells reaches 3.5V.

I guess I will have a long time of top balancing the cells with the good old "short" cable.

What is a good way to easily check which of the cells is bad? I guess I would have to rearrange the cells into two 12V sets with the two questionable cells in one battery. Then top balance and run them down to see if one has reduces capacity. Hopefully that one would also be the one with the slow self discharge.

I "hope" I will be able to get the bad cell replaced by Balqon. Timing is a big thing as we will be in Ft. Lauderdale only for a few days in about 2 weeks. Right now we are in George Town, Exuma and will go to the Abacos after Ft. Lauderdale.

Do you still have the bench top power supply available? If so you could separate the 2 suspect cells from the pack and charge each to 3.6v, then let them sit, the crook cell will drop lower than the good cell by a large margin over 12hrs or so.

T1 Terry

[ebaugh]

Hi everyone,

I've not been following the thread the last 12 mos or so. I hope everyone is well and having great success with their LFP installs. We have been marina bound, my wife and I essentially working full time to replenish the cruising kitty. But the boat has left the dock once in about 12 months.

Our LFP install is now a little over 2 years old. About a year ago we pulled 4 of 48 cells and ran a capacity test at about C/3. Just reran that exact same test a week or so ago. Year 1 the batteries were actively cruising. Year 2, the same 4 cells sat on a shelf waiting for me to reinstall them, but I never did. Not stored at 50%, as they should have been, probably more like 95%.

We don't have a baseline from the install, but assuming they met specification when new, we are seeing a capacity loss of 10-15% per year. The 100Ah cells are sitting at about 71-72Ah today. The loss appears to be more time dependent than number of cycles. These are GBS cells.

The 30A rate is roughly C/3 on new cells, but is approaching C/2, so that would tend to start skewing the results.

This difference while substantial, would not be readily apparent on the boat since I rarely went below 50% in normal operations.

Similar tests, one 12 months ago on new out of the box 100Ah cells and another this week, after one year of storage at 50% SOC showed a 5% reduction in capacity. These were Forzatec (Google is your friend) cells. Much better! But perhaps still significant.

The testing is with 4 cells in series after a fresh top balance. Outside of capacity, the cells behaved just like any other LFP cell. The 4 cells as samples in each group exhibiting almost identical capacity change.

Considered cycling them a few times to see if the numbers changed, but don't really have the time now. The charge following the discharge shows the usual almost even one amp out equals one amp in to recharge, so if there was a change it would be very gradual.

I am looking forward to other reports, but it looks like 5-10% capacity loss per year might be unavoidable. If you can get your 2000-3000 cycles in 5 years there is a much stronger case than if it's going to take you 10 years or more to get there.

Best Bob


Sent from my iPad using Cruisers Sailing Forum

[roetter]

Originally Posted by Jd1

...
You are missing all the gorgeous rainy and windy weather we are having out here in Victoria

We are glad we left on the first really bad day. Before that it would have felt strange to go to The Bahamas.

[roetter]

Originally Posted by T1 Terry

Do you still have the bench top power supply available? If so you could separate the 2 suspect cells from the pack and charge each to 3.6v, then let them sit, the crook cell will drop lower than the good cell by a large margin over 12hrs or so.

T1 Terry

No, the benchtop power supply is at home, 3000 miles away. I emaild Balqon 10 minutes ago. Let's see what happens.

[goboatingnow]

We don't have a baseline from the install, but assuming they met specification when new, we are seeing a capacity loss of 10-15% per year. The 100Ah cells are sitting at about 71-72Ah today. The loss appears to be more time dependent than number of cycles. These are GBS cells.

Interesting , I wonder if the rate is linear over time.

[Jd1]

I finally was (sort of) able to do a capacity test today.
I tested down to 2.6V from about 3.5V per cell using an inverter and a heater. For most of the test I was pulling around 170A which of course dropped towards the end. I was also running into issues with low voltage for the inverter and had to substantially reduce power draw (down to 600W) at the end to keep the inverter from shutting down. I measured 630 Ahr capacity but I encountered an error in the beginning of the test that reset my A hr counter. I would guess that I am pretty close to 700 A hr total capacity but will not be able to verify this for at least another week or two until everything is hooked up. The charger that I am currently using can only do 20A and it will take forever to charge the batteries at that rate.
One nice little twist of irony - the cell that I was all worried about because it kept dropping from 3.6V to 3.4V while sitting actually had the highest voltage when the test stopped. I was very pleased to see that I was worried for nothing.

[T1 Terry]

Originally Posted by Jd1

I finally was (sort of) able to do a capacity test today.
I tested down to 2.6V from about 3.5V per cell using an inverter and a heater. For most of the test I was pulling around 170A which of course dropped towards the end. I was also running into issues with low voltage for the inverter and had to substantially reduce power draw (down to 600W) at the end to keep the inverter from shutting down. I measured 630 Ahr capacity but I encountered an error in the beginning of the test that reset my A hr counter. I would guess that I am pretty close to 700 A hr total capacity but will not be able to verify this for at least another week or two until everything is hooked up. The charger that I am currently using can only do 20A and it will take forever to charge the batteries at that rate.
One nice little twist of irony - the cell that I was all worried about because it kept dropping from 3.6V to 3.4V while sitting actually had the highest voltage when the test stopped. I was very pleased to see that I was worried for nothing.

A good result, so the cell was still filling up, not actually loosing capacity, just distributing it throughout the cell. That first conditioning charge can be quite nerve-wracking the first time as you always expect the worst. This recharge cycle will get then full so be prepared for a bit of top balancing when you get that far.

T1 Terry

[Maine Sail]

Originally Posted by Jd1

I finally was (sort of) able to do a capacity test today.
I tested down to 2.6V from about 3.5V per cell using an inverter and a heater. For most of the test I was pulling around 170A which of course dropped towards the end. I was also running into issues with low voltage for the inverter and had to substantially reduce power draw (down to 600W) at the end to keep the inverter from shutting down. I measured 630 Ahr capacity but I encountered an error in the beginning of the test that reset my A hr counter. I would guess that I am pretty close to 700 A hr total capacity but will not be able to verify this for at least another week or two until everything is hooked up. The charger that I am currently using can only do 20A and it will take forever to charge the batteries at that rate.
One nice little twist of irony - the cell that I was all worried about because it kept dropping from 3.6V to 3.4V while sitting actually had the highest voltage when the test stopped. I was very pleased to see that I was worried for nothing.

Why did you go to 2.6V? Was that just the lowest cell? Winston told me not to go below 2.8V even though the manual says 2.7V. For an accurate bottom balance 2.65V is okay in order to achieve a 2.75V resting voltage but this is carefully monitored and done with low "C" rate loads.

All my capacity tests have been cut off with the lowest cell reading 2.8V and no inverter shut down because this is 11.2V or better.....

Current should have actually gone up as the voltage dropped unless it was your inverters losing efficiency. I prefer to run the inverter at less than full bore so my current stays steady, though it will rise slightly as the voltage drops....

My capacity tests from 550 cycles forward will be done with a lab grade DC load device for better accuracy. I will establish a new baseline...

A full Winston cell will rest at about 3.38V - 3.40V. They won't stay at 3.6V for very long...