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Old 16-11-2014, 02:27   #16
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Re: Some more lithium thoughts and questions

I have been watching this whole LFP thing for a while now. I wish I could afford a LFP system but just to damn expensive atm. Waiting for the bloody alternators and regulators to go down in price :O.
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Old 16-11-2014, 03:48   #17
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Re: Some more lithium thoughts and questions

Maine Sail, when you mention the different percentages of SOC, are you determining that by AH remaining as determined by your battery monitor?


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Old 16-11-2014, 14:06   #18
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Re: Some more lithium thoughts and questions

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[T]he common thinking is the battery does not get damaged by 3.6V cell voltages.
...
My second question is in regard to charge voltage. I am currently set up to charge at 14.4 V with my Balmar alternator and MC614 external regulator. This is fine for the lead acid batteries still in the system (but isolated from the lithiums via a FET isolator) but it cramps my style for charge current for the lithiums. My goal is to charge the lithiums at around 160A to almost full charge so I am thinking of upping the charge voltage a bit.
I hesitate to agree with the idea that 3.6V is a safe charging voltage for LiFePO4 cells. For a relatively short time (avoiding heat build-up), it will not damage the cells, but regularly charging LiFePO4 at excessive voltages (i.e. over 3.5V per cell) may eventually push them out of balance. 3.5V per cell is sufficient to achieve a full charge. I suspect but have not confirmed that 3.45V per cell is probably sufficient to achieve a full charge. I would never ever program any charge to source to apply more than 3.5V to a LiFePO4 cell.
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Old 16-11-2014, 16:30   #19
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Re: Some more lithium thoughts and questions

I finally got around to doing a proper (sort of) capacity test. The results are disappointing
The bank is 700 Ah at 12V, I started my discharge at 2000W load, about 175A or 0.25C. Due to voltage drop, by the time the first phase was done the load was down to 1870W.
At 610 AH, the lowest cell was at 2.81V (at 1870W draw)
Dropping the load to 1000W gave me an additional 30 AH for 640 AH total. This is to 2.8V which is when the protection relay kicks in.
Now I mentioned 'disappointing' above .... this is only in relation to capacity. In all other respects I have literally oooodles of power available.
I would rate the cells at 600 AHr, well short of the 700 AHr they are spec'd at. I can't shake the thought that they are seconds or used cells. Fortunately I only paid $600 per cell (these are from Balqon) instead of the regular price of $700 so I am not going to jump up and down wanting replacements but I reserve that option if they loose significant capacity from here on in.
I have all the power I need (and then some) so they will do the job but it just wasn't quite as good a deal as I had originally thought.
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Old 16-11-2014, 17:18   #20
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Re: Some more lithium thoughts and questions

My charging setting on the 700Ah cells started out last year with 14.0V.

I have since dropped it to 13.8V as I have ample power with 1400Ah capacity- maybe .

I don't like my cells to go above 3.5V. I do start to recharge with sunrise with 1800W of solar. I do not wait until the SOC goes down to a specific value. So every day they are up to ~90% full, then go down to about 70% overnight.

Last January during a very long spell of bad weather I took them down to about 25% SOC.

I did not change anything on my alternators. A relay will diconnect them from the LFPs when at 13.8V and they will continue charging the LA stater batteries up to 14.4V.
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Old 16-11-2014, 17:26   #21
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Re: Some more lithium thoughts and questions

TESLA cars charge to 80% full unless you do a specific range mode override. The higher than 80% setting will go back to 80% after 24 hours.

You can set the regular daily charge SOC to 50-80% on a TESLA.

At low temperatures the batteries do not charge until they have been heated to a higher temperature. At high temperatures charge current is mimited until the temperture control system has cooled thenm to the safe temperature.

The cells are liquid colled and heated. TESLA uses small cylindrical 18650 cells so they can be cooled or heated quickly.

If you want to charge LFP cells at low temperatures, I would look at puting them in an isolated box and have a heater kick in before the charge is allowed to reach the cells.
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Old 16-11-2014, 17:33   #22
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Re: Some more lithium thoughts and questions

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Why stop at 50%??? 20% SOC to 90% is fine...

Our bank is close to 550 cycles, most to 80% DOD with no loss of capacity. Even the best lead acid banks would have been dead long ago doing this..

Most coastal cruisers won't do this many cycles even in 5 years.. At 80% DOD you should expect to see 1500 - 2000+ cycles.. Course with a 700Ah bank that is going to take some serious time to recharge especially at a .22C charge rate. If you are hitting absorption voltage, even at 13.8V to 14.0V, before the high 90's, there is something wrong.

50% is lead acid mentality there really is no need for this mentality with LFP.

Discharge to 20% SOC recharge to 13.8V - 14.0V and about 20-30A net accepted current and your bank will likely outlast you...

Be very careful relying on an Ah counter for continual cycle monitoring. You will still want to do manual synching every time the bank meets your chosen "full" parameters... Even on LFP they drift if not kept on top of..

Just this afternoon I was finally getting around to removing the bank from the boat for the winter. It hit 18F last night so no charging today.......

In the next week or so I will have it reassembled in the shop and will do another capacity test..

Today's removal procedure:

I also would want to start charging with solar at 50% soc. My reasoning is that I have a power hungry boat. My current 12 v 800amp golf cart bank is enough but not excessive. If my LiFe 400amp bank ( theoretical at this point) reached 80% soc before noon on one day and didn't get down to a 30% soc trigger point before sundown the next day I would be getting really short of amps by the next morning. And if the next day was gloomy, rainy type day I may need to start the genset. This would be less of an issue if there was a way to utilize the solar panels during the first day for refrigerator loads. ( The "don't float issue " I would sure like to see a way utilize the solar power while the batteries were above 50%.) Of course if I went with 700amp cells I should have no issue. Is there a way to use the solar panels without the batteries seeing it as float?
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Old 16-11-2014, 17:52   #23
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Re: Some more lithium thoughts and questions

"Something to remember about Li "shelf life", is that it's not like they suddenly stop working" Are the prismatic cells really any different from the LiOn cylindrical cells that way? Because I have seen multiple brand name cylindrical cells, used in computer battery packs, that literally went from 100% charge to totally dead as they hit four years age. Kept as spares, rotated in use, and all of a sudden one that was perfectly good 2-3 months before, was totally dead.


As to how far they can be discharged and cycled...What, anyone would doubt the veracity of manufacturers' claims when they indicate ~5~8000 cycles at deep (~ 70~80%) discharge depths?


Although I seem to recall a mention on the Panbo site that at least one user thinks they will lose 10% capacity every year, no matter "it was the best of butter" how well they are treated?
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Old 16-11-2014, 18:32   #24
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Re: Some more lithium thoughts and questions

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I finally got around to doing a proper (sort of) capacity test. The results are disappointing
The bank is 700 Ah at 12V, I started my discharge at 2000W load, about 175A or 0.25C. Due to voltage drop, by the time the first phase was done the load was down to 1870W.
At 610 AH, the lowest cell was at 2.81V (at 1870W draw)
Dropping the load to 1000W gave me an additional 30 AH for 640 AH total. This is to 2.8V which is when the protection relay kicks in.
Thank you for sharing your data. I had suspected that this might be the case for the Winston 700AH cells because they weigh significantly less per AH than any other Winston cell. Now it seems clear why.
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Old 16-11-2014, 20:11   #25
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Re: Some more lithium thoughts and questions

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Thank you for sharing your data. I had suspected that this might be the case for the Winston 700AH cells because they weigh significantly less per AH than any other Winston cell. Now it seems clear why.
The cells that Balqon delivered are Thundersky cells which may or may not be the same as Winston (lost track of who stole who's design). If I take the weight of the 700 Ah cells and adjust to 400 Ah I get 26.8 lbs. The 400 Ah cells are spec'd at 30 lb so the difference is about 10%. I am not sure if this alone explains the difference but it sure is an interesting theory.
The 700 Ah cells also have 4 power posts compared to two posts on the 400 Ah cells so that might bring the difference in active cell compound up a bit - possibly sufficient to explain the capacity shortfall.
Interesting though, if you look at the 1000Ah cells they are way heavier per Ah then even the 400 Ah cells .... I guess I am saying that I am not sure if this weight theory holds true.
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Old 16-11-2014, 20:35   #26
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Re: Some more lithium thoughts and questions

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Interesting though, if you look at the 1000Ah cells they are way heavier per Ah then even the 400 Ah cells .... I guess I am saying that I am not sure if this weight theory holds true.
If my theory that the weight explains the capacity holds true, then the nominally 1000AH cells should have an actual capacity exceeding 1000AH by an even greater factor than the 425AH which MaineSail gets from his 400AH cells. Has anyone tested the 1000AH cells?
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Old 16-11-2014, 20:54   #27
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Re: Some more lithium thoughts and questions

Sinopoly, ThunderSky and Winston - DIY Electric Car Forums


Two year old posting elsewhere seems to indicate that if Winston sold you a "Thundersky" branded battery, it would have been made no later than 2012?


But you bought them when?
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Old 16-11-2014, 21:02   #28
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Re: Some more lithium thoughts and questions

They were bought a couple of month (or so) ago.
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Old 17-11-2014, 08:01   #29
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Re: Some more lithium thoughts and questions

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The cells that Balqon delivered are Thundersky cells which may or may not be the same as Winston (lost track of who stole who's design). If I take the weight of the 700 Ah cells and adjust to 400 Ah I get 26.8 lbs. The 400 Ah cells are spec'd at 30 lb so the difference is about 10%. I am not sure if this alone explains the difference but it sure is an interesting theory.
The 700 Ah cells also have 4 power posts compared to two posts on the 400 Ah cells so that might bring the difference in active cell compound up a bit - possibly sufficient to explain the capacity shortfall.
Interesting though, if you look at the 1000Ah cells they are way heavier per Ah then even the 400 Ah cells .... I guess I am saying that I am not sure if this weight theory holds true.
Jd1,

What were the cells charged to voltage wise?

Was this voltage measured at the battery terminals or at the charge source?

What was the tail current at that voltage when you stopped charging?

What was the voltage of the cells that were not at 2.81V?

What were the voltages of the cells when you DC'd charging?

What were the temps of the cells during discharge?

How was the Ah counter set up?

When capacity testing it is important that you set it up in a scientific manner and that you can repeat this in the same manner the next time. In other words tests done in an A to B manner will yield different results test to test, while tests conducted in an A to A manner can be directly comparable.

These cells are impacted by cell temperature and folks tend to forget that. The lower the cell temp the less capacity to LV you get out of them. While not impacted as badly as lead acid by discharge temps, they are impacted by cell temp changes.

I try to do all my capacity tests at 75-80F cell temps. Terminal voltages and tail current are always cut off at the same point so that each discharge capacity test is done as close to an A to A manner as possible.

Also your cells are old-stock, may have been used, and may need to be cycled a few times to come up to capacity. You bough used old stock cells, I did too, and I feel I got lucky with mine. You seem to be on the opposite end of where I ended up, but I would not consider it bad, especially for what you paid.......

Even if you are 60Ah's shy, which I would want to confirm more than once, you still have a 640Ah LFP bank for not a lot of dosh....

If you really want to confirm your usable capacity do a discharge test at your vessels average load... While capacity can vary slightly between high current discharge and low current it is nowhere near the difference you see in lead. These have a low Peukerts constant but not zero Peukert effect....

As I have said many times I would not again buy cells from Winston/Balquon. I think they are horrible to deal with and the variability of the Winston cells seems to be worse than with CALB. Lucky for me mine are doing fine. If I had to buy again, for my own boat, it would be CALB CA's.....

640 Ah's, for what you paid, seems pretty good... Run some more tests and see if it is repeatable or if it changes..
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Old 17-11-2014, 09:08   #30
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Re: Some more lithium thoughts and questions

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Jd1,

Also your cells are old-stock, may have been used, and may need to be cycled a few times to come up to capacity. You bough used old stock cells, I did too, and I feel I got lucky with mine. You seem to be on the opposite end of where I ended up, but I would not consider it bad, especially for what you paid.......
Agreed, the price was right as long as the cells perform properly (although reduced) from here on in. BTW, the cells were represented as new and current (not old) stock.
I did not consider temperature in my testing - they were probably in the neighbourhood of 5 degrees C so that would account for some reduced capacity.
I would not consider the capacity to be 640 Ah as I had to reduce current draw substantially - like I said, I would call it at most 600 Ah and even that was at less than spec'd current draw (not taking temperature into account as I do not know how much temperature affects things).

Anyway, time will tell all The next capacity test will happen next summer.
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