Alternator Size with LiFePo4

[evm1024]

Originally Posted by john61ct

I think an endAmps setpoint of .02 or .03C is precise enough for most benchmarking purposes, and at lower current levels (well below .3C) I find that rarely means holding Absorb / CV for more than a few minutes.

As I said "stop at setpoint V" is all that's needed for normal cycling usage, Absorb serves no useful function in that context.

And if SG200 really is that accurate without ever needing 100% resets, then the only times I can think to Absorb at all would be load testing, and (if using top) balancing. Both are very rare events in most cases.

Agreed. Holding at CV for any length of time appears to give no significant advantage in capacity or longevity.

[john61ct]

Originally Posted by Q Xopa

Smaller alternator pulley and larger crank pulley will give a better low eng RPM performance.

Pretty sure around 2.5" is the lower limit for multi vee (serpentine) belts.

Other than specialty alts I think most need at least 1800rpm, 2400+ is probably better, to get to above say 60-70% rating.

[rgleason]

Here is a graph from MaineSail's MarineHowto website after a search on lifepo4



https://marinehowto.com/wp-content/u...4-On-Boats.jpg


https://www.powertechsystems.eu/home...ry-advantages/


Couldn't find it.

[john61ct]

Originally Posted by evm1024

Agreed. Holding at CV for any length of time appears to give no significant advantage in capacity or longevity.

My take:
gives no significant advantage in capacity, and is harmful to longevity, especially for those using higher voltages

[john61ct]

Originally Posted by rgleason

Couldn't find it.

this one?

Originally Posted by evm1024

I found the source as well. See: https://www.powerstream.com/lithium-...ge-voltage.htm

[evm1024]

Originally Posted by john61ct

My take:
gives no significant advantage in capacity, and is harmful to longevity, especially for those using higher voltages

Harmful to longevity when time in CV is measured in hours - perhaps less so when measured in minutes.

I was not thinking in hours which is "float" to my mind.

[Q Xopa]

Originally Posted by john61ct

There is no difference of opinion, on how to accurately measure total AH capacity, just different levels of correct knowledge.

Once you pick a given definition for 0% and 100%, then AH counters are just fine for measuring SoC on the way down, while **discharging**.

And let's say within those 0% and 100% points, normal cycling may be between 10% and 90%. If the owner-defined 100% rarely gets hit to reset the AH-counter, it's still good enough for guesstimating so the shoulders are avoided. As you point out Balmar's new SG200 may be more accurate at this than other meters, but for myself, I don't mind precisely hitting my 100%

for .2-.3C, 3.45Vpc, Absorb until endAmps @ .03C (3A per 100AH)

once a week or so.

However, as you get past 13.6-13.8V, depends on current level, an increasing amount of the AH being counted, is going into heat production, no longer actually increasing SoC.

As MS demonstrated with his documented test results, a load test is required to determine how many extra AH are **stored** by varying the two stop-charge parameters for a given charging rate, Voltage and Absorb endAmps (if any).

> It doesn't sound like you are so convinced

sorry, not convinced of what?

'You not being convinced' was referring to you being dismissive of a graph depicting Cycle life Vs Range of Capacity relationship.

I dont think anyone considers this factor to chase to the cost of all others. But it is a factor to consider and weigh. Like many others.

[rgleason]

Another well documented system by Tanglewood.
CatNewBee has also documented his system quite extensively.


It's worth following this thread for FLA/AGM start/reserve and House LiFePo4 operation.


Also Capt Pat

[john61ct]

Originally Posted by evm1024

Harmful to longevity when time in CV is measured in hours - perhaps less so when measured in minutes.

I was not thinking in hours which is "float" to my mind.

At high voltages (above 13.6V for low currents, 13.8 for high), going past .02 - .01C trailing amps would reduce some number of lifetime cycles off the back end.

More than I'd want to lose, shooting for maximum longevity hoping for many more thousands of cycles than mfg rating.

Many don't prioritize that.

But then, since there is nothing to be gained by pushing it, why do it?

From an automation POV, also much simpler / easier / cheaper to Just Stop at a voltage setpoint, using endAmps much more complex / difficult / expensive.

Especially given doing so accomplishes nothing useful?

[john61ct]

Originally Posted by Q Xopa

'You not being convinced' was referring to you being dismissive of a graph depicting Cycle life Vs Range of Capacity relationship

Do not recall that, nor that latter term.

What was the overall point you think I was disputing?

[nebster]

It's been mentioned a couple of times in passing, but charging only in CC (to a simple voltage stopping point) at higher rates will not result in a full charge, for whatever "full" means for you.

If your typical charging happens at say 0.15C or less, the amount of excess voltage rise due to charge rate is pretty small in most LFP prismatics, so the amount of CV time available is pretty small and simply stopping before CV is a close approximation.

As you move up in charge rate, the excess voltage rise grows substantially, and you can end up not storing as much energy as you planned, unless you do in fact add CV time.

A typical cell will reach only ~90% true SOC at 0.2C to 3.45V, whereas it will reach 96% SOC at 0.1C to 3.45V. If you are so brash as to select a charging system capable of something like 0.40C (ahem), the numbers decrease much further, and you simply must elect to enter absorption if you want to get full use of your battery pack.

My suggestion is: if you plan to do any charging above 0.1C, you should test and verify the charging results yourself before committing to a solution that only uses a CC charge strategy.

[nebster]

Originally Posted by john61ct

My take:
gives no significant advantage in capacity, and is harmful to longevity, especially for those using higher voltages

Incorrect, for higher charging rates.

By the way, it would be great to hear what rate you like to use for charging your battery.

[newhaul]

Originally Posted by nebster

It's been mentioned a couple of times in passing, but charging only in CC (to a simple voltage stopping point) at higher rates will not result in a full charge, for whatever "full" means for you.

If your typical charging happens at say 0.15C or less, the amount of excess voltage rise due to charge rate is pretty small in most LFP prismatics, so the amount of CV time available is pretty small and simply stopping before CV is a close approximation.

As you move up in charge rate, the excess voltage rise grows substantially, and you can end up not storing as much energy as you planned, unless you do in fact add CV time.

A typical cell will reach only ~90% true SOC at 0.2C to 3.45V, whereas it will reach 96% SOC at 0.1C to 3.45V. If you are so brash as to select a charging system capable of something like 0.40C (ahem), the numbers decrease much further, and you simply must elect to enter absorption if you want to get full use of your battery pack.

My suggestion is: if you plan to do any charging above 0.1C, you should test and verify the charging results yourself before committing to a solution that only uses a CC charge strategy.

Ok my charge profile is .2C on solar and a potential for .25C with wind which combined is possible to hit the .5C point am I not charging my 100ah Lfp bank to its maximum potential?
Do I need to add another 100ah?

[nebster]

Originally Posted by newhaul

Ok my charge profile is .2C on solar and a potential for .25C with wind which combined is possible to hit the .5C point am I not charging my 100ah Lfp bank to its maximum potential?
Do I need to add another 100ah?

If you're charging at continuously at 0.5C with a CC-then-stop (bulk only) charge profile, you will put a lot less energy into those cells before you reach the stopping point then if you charge them at 0.1C on a windless, partly-cloudy day at the same profile. Possibly 20-25% less total energy.

That's because faster charging rates push the internal voltage*higher at any given achieved SOC. It is likely entirely due to internal heating and the ensuing reaction kinetics, but I'm not an electrochemist so I can't say for sure.

On the other hand, if you are charging with a CC-then-CV (bulk, then absorb) to a reasonable CV voltage threshold and with a reasonable tail current stopping value, then you should end up at the same stored energy regardless of how much solar or wind you have.

[newhaul]

Originally Posted by nebster

If you're charging at continuously at 0.5C with a CC-then-stop (bulk only) charge profile, you will put a lot less energy into those cells before you reach the stopping point then if you charge them at 0.1C on a windless, partly-cloudy day at the same profile. Possibly 20-25% less total energy.

That's because faster charging rates push the internal voltage*higher at any given achieved SOC. It is likely entirely due to internal heating and the ensuing reaction kinetics, but I'm not an electrochemist so I can't say for sure.

On the other hand, if you are charging with a CC-then-CV (bulk, then absorb) to a reasonable CV voltage threshold and with a reasonable tail current stopping value, then you should end up at the same stored energy regardless of how much solar or wind you have.

with purely renewables I am actually charging with variable current and stopping at designated voltage Via the controller setpoints.