Alternator Size with LiFePo4

[tanglewood]

Originally Posted by Maine Sail

The OPE-Li3 line was co-developed by Bruce and Lithionics. Lithionics makes it but it is specific to Bruce's design goals.

Cool, thanks.

[john61ct]

Originally Posted by rgleason

John, what is the C-rates used for the CC profiles?

In all those examples ~60A made available.

[john61ct]

About Al Thomason's SAR project

open source Very Smart Regulator / "Smart Alternator Regulator" *
http://www.cruisersforum.com/forums/...ps-181318.html
Others, sorry not clickable


* Yes been telling him he needs a more trademark-able, google-able name 8-)

[Maine Sail]

Originally Posted by rgleason

Newhull in answer to your question I think John has Winston or Thundersky.

I don't know that John has purchased any LFP cells yet?

[tanglewood]

Originally Posted by john61ct

Easy for anyone to see who wants to observe for themselves.
Just need:
an adjustable power supply
a DMM / ammeter and AH counter
the gear and patience to do load tests, the only way to measure and compare Actual differences in ending SoC between pairs of charge profiles

Measuring AH going **in** will be relatively accurate only at relatively low stop-charge points.

Given the bank is 360AH nameplate rated, PSU can deliver 60A, temp is 77°C

Profiles:
#1 is 3.65Vpc Absorb, taper held until current stops, 0A flowing 100%
#2 is CC only, To 3.65V and Stop, no Absorb 99.1
#3 is 3.45V held to 0A as with #1 99.84
#4 is 3.45V held to .03C 99.23 (defined 100%)
#5 is CC only, To 3.45V and Stop, no Absorb 97.9

Actual AH stored, using 2.99Vpc as 0%, after a 4-hour isolated rest
#1 386AH, 100.7%
#2 381AH, 99.5%
#3 384AH, 100.3%
#4 383AH, 100.0%, for BM calibration
#5 378AH, 98.7%, normal cycling

Now, if you use an AH counter to record the energy returned after each load test discharge cycle, you will see the incremental AH differences, measuring what has **apparently** been "accepted" by the bank while charging, is much larger than the incremental differences between the **actual** resting SoC load test results, the higher up into the shoulder you go, the higher % of current is being absorbed as heat, and likely other destructive chemical forces.

For example, about 15A between #4 and #1, which would seem to be a SoC difference of over 3%.

Of course these are just example numbers, each bank will be different, and varies with wear, and with CC-only charging, the higher the charge current the greater the discrepancy.

Are this illustrative numbers, or actual test results?

[rgleason]

Originally Posted by Maine Sail

I don't know that John has purchased any LFP cells yet?

John is a bit of an enigma sometimes, and very helpful and full of information, and the detail in these particular posts does not look "made up", but I don't know what the C-rate is for the CC profiles.


PS: And I really appreciate all his knowledge, time and patient responses.

[newhaul]

Originally Posted by rgleason

John is a bit of an enigma sometimes. The detail in these particular posts does not look "made up".

I'm sure the numbers are legit however I would love links to the discussions where they come from . I'm sure there is a lot more data in the discussions the numbers come from . Likely on some diy off grid or ev site. Or blog

[Delfin]

Originally Posted by tanglewood

Are this illustrative numbers, or actual test results?

<Sound of crickets...>

Real or illustrative, I am probably missing something, but I am not sure that posting numbers that show a 3% differential between actual Ah stored when charge voltage is high vs. low substantiates John's statement that "Since getting up that high (note: voltage, presumably) only a small fraction of AH measured at the post is actually increasing SoC". As a side note, I seem to recall seeing this data from somewhere, but I can't recall. Maine Sail perhaps?

On the main point, am I missing something TT?

[Q Xopa]

Originally Posted by CatNewBee

Oh, sorry, I have an engineering background, for me this numbers have a different meaning and I know how tests like this are planned, set up and performed in controlled environments.

Yes well, I guess Im embarrassed to say I am an Engineer.
Do you have a link or something where that test info came from?

[kmacdonald]

OK, some real numbers to chew on. I'm charging a 12V deep cycle LA battery, as I type. It was put in service on 5/2016, so two seasons use. In 7 hours it has gone from 3.1 Amp to 2.9 Amp acceptance @ 14.8 volts. I'll let you know what it is in the morning. It's a 90 Ah battery so that's 0.0322C or about 3% C. I said in another thread that a lot of batteries won't get to 0.5% C (magic tail number according to some) no matter how long they charge at 14.8 volts. We'll see.

Ambient temp is 75 degrees F and the battery is 85 degrees F.

[rgleason]

Attached are two graphs showing Charge, Cell Voltage, SOC for LiFePo4 and a proposed charge profile by John.

[newhaul]

Originally Posted by rgleason

Attached are two graphs showing Charge, Cell Voltage, SOC for LiFePo4 and a proposed charge profile by John.

so he is recommending using 62% of the banks capacity to get 7,000 cycles?

For with my use cycle that's about 30 years

Vs the typical 5,000 cycles at 75%
For my use that's about 27 years
I can live with that

[CatNewBee]

Originally Posted by Q Xopa

Yes well, I guess Im embarrassed to say I am an Engineer.
Do you have a link or something where that test info came from?

I dont know how exactly Winston or other manufacturers do their quality management and how they come to this figures (what are of course are statistical things). I assume, they run long time tests with a batch of few cells, but also extrapolate life expectancy derived from the results with harsh parameters, like high or low temp and high currents to do an artificial quick ageing and speed up test results from years to weeks or days.


If I would run a lab to test the quality of a battery life, that would be the way to do it, taking advantage of the published specs and sticking to them, so the manufacturer cannot claim the test was performed outside of the parameters.

Anyway, real world usage is much more dynamic, there are partial cycles, high currents, low currents, temp variations and stress by motion. There is no way to do a standard test or predict cycles, nor count cycles at all - especially as often suggested - because cells are not charged to full.

The battery will age and one day the performance will be below your expectations or your energy demand may be different and you will replace it.

There are also user faults that wreck batteries, especially with people who think balancing can be done manually to extend life and a BMS is not needed, on the other side, BMS and cell modules have also a MTBF and can fail with consequences to the battery.

I am here more pragmatic, I chose the battery based on the required performance and capacity. I consider a battery a consumable item like fuel, water, food, sheets, ropes, sails. When one day in the future she needs a replacement, new technology for a better price will be around, until then I have what I think I need.

[kmacdonald]

Originally Posted by kmacdonald

OK, some real numbers to chew on. I'm charging a 12V deep cycle LA battery, as I type. It was put in service on 5/2016, so two seasons use. In 7 hours it has gone from 3.1 Amp to 2.9 Amp acceptance @ 14.8 volts. I'll let you know what it is in the morning. It's a 90 Ah battery so that's 0.0322C or about 3% C. I said in another thread that a lot of batteries won't get to 0.5% C (magic tail number according to some) no matter how long they charge at 14.8 volts. We'll see.

Ambient temp is 75 degrees F and the battery is 85 degrees F.

A quick update. 3.5 Amp @ 14.8 volts. Ambient temp is 75 and battery temp is 92. Just when you think you know how it works you get thrown a curve ball.

I'm going to apply an equalization charge. I only have a 10 amp power supply and at 15.6 volts it's outputting 10.5 amps. I'll increase voltage up to a max of 16 volts if the current drops.

[CatNewBee]

Originally Posted by kmacdonald

A quick update. 3.5 Amp @ 14.8 volts. Ambient temp is 75 and battery temp is 92. Just when you think you know how it works you get thrown a curve ball.

I'm going to apply an equalization charge. I only have a 10 amp power supply and at 15.6 volts it's outputting 10.5 amps. I'll increase voltage up to a max of 16 volts if the current drops.

You'll gonna kill it...

Is it a flooded plain lead acid? 14.8V are way too high for absorption, it is for AGM Type 2 batteries only. If you run equalization, do not expect a high current, the battery will boil any way, when all cells produce gas equally, you can stop boiling it. It is normal, that the battery gets warm when charged. Check the electrolyte level and top it up with distilled water if necessary after the equalization.

Is the battery isolated of the loads when charging and measuring the current? Otherwise you may get wrong figures, when the charger also powers your fridge and other stuff on board.