Alternator Size with LiFePo4

[john61ct]

Originally Posted by rgleason

So after 13.88v is reached the mode changes to CV (Constant Voltage) with proportionally declining current down to 0.2C or 0.3C which would get to 95%SOC, but this stage would not be as fast and will most certainly take much longer (1-2 hours)

Not at all, matter of minutes. Yes longer at high currents (**much** shorter CC/Bulk), but usually worst case well under 20min, depending on your endAmps.

With lower currents, may be 2-4min.

But even just doing CC-only, no way you need to stop at 75% even for high amp sources, just raise the setpoint a bit.

So this idea goes away:
> The Charging stage from 75%SOC to 95%SOC (20%C=40ah for a 200ah bank) is more appropriately charged by Solar PV at lower current levels.



> Hopefully the Solar Controllers are properly programmed to stop charging completely when the trailing amps reach the user set .2C to .3C (I do not believe that the current Solar Regulators can do this however.)

Yes if you're talking about allowing derating, many do, but why?

If you mean endAmps, many do, integrating with a shunt based remote / BM unit.

It's shore chargers where that feature is so rare, and on alt VRs, only the SAR project afaik.

[newhaul]

Originally Posted by john61ct

I did not say you didn't get excellent value. AGM is a low bar in that regard. Spending money on quality cells at least is IMO critical to getting a chance at ROI, which with all the ancillary gear, requires good longevity.

Remember stateside, lead is way cheaper and assured-quality LFP is way more expensive than in other markets, 5-7x AGM is my ballpark.

I'm glad I don't have to play in your ballpark
Mine is in the neighborhood of $2.50 per ah delivered.
Which seems to be about equal to agm per usable ah.

[tanglewood]

Originally Posted by john61ct

Recognized quality vendors:

Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Bare cells: ​Winston/Thundersky/Voltronix, CALB, GBS, A123 & Sinopoly

Just to clarify, Ocean Planet is a dealer for Lithionics, not a manufacturer. And I don't mean this to diminish Ocean Planet in any way, just to clarify their role.


Victron is a manufacturer, however OEMs their Lithium product line from MG Energy.


MasterVolt is a manufacturer, but I don't know if they design internally or OEM from someone else.


I've never heard of Redarc

[Maine Sail]

Originally Posted by tanglewood

Just to clarify, Ocean Planet is a dealer for Lithionics, not a manufacturer. And I don't mean this to diminish Ocean Planet in any way, just to clarify their role.

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

[rgleason]

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.

Thanks John, nice quide.
Newhull in answer to your question I think John has Winston or Thundersky.

[john61ct]

Originally Posted by tanglewood

Just to clarify, Ocean Planet is a dealer for Lithionics, not a manufacturer. And I don't mean this to diminish Ocean Planet in any way, just to clarify their role

Bruce designed their OPE-Li3 system, perhaps others.

[rgleason]

Originally Posted by john61ct

Not at all, matter of minutes. Yes longer at high currents (**much** shorter CC/Bulk), but usually worst case well under 20min, depending on your endAmps.

With lower currents, may be 2-4min.

But even just doing CC-only, no way you need to stop at 75% even for high amp sources, just raise the setpoint a bit.

So this idea goes away:
> The Charging stage from 75%SOC to 95%SOC (20%C=40ah for a 200ah bank) is more appropriately charged by Solar PV at lower current levels.

> Hopefully the Solar Controllers are properly programmed to stop charging completely when the trailing amps reach the user set .02C to .03C (I do not believe that the current Solar Regulators can do this however.)

Yes if you're talking about allowing derating, many do, but why?

If you mean endAmps, many do, integrating with a shunt based remote / BM unit.

It's shore chargers where that feature is so rare, and on alt VRs, only the SAR project afaik.

[I fixed the decimal places for the trailing amps above]

I've been reading somewhere (I think Marinehowto) that Sterling Pro Chargers do not measure trailing amps and thus are not well suited to LiFePo4 in this respect.

John, with respect to my reading the chart, that at a C-Rate of .5C Constant Current charging up to ending voltage of 13.88v (3.47vpc) will reach 75%SoC... the chart I was referring to when I drew the Bat Voltage, SOC, Charge Current diagram from Post #232 was based on a Powerstream graph here

How am I misreading that graph, or is it just different in the real world and this graph is a different battery type or something?

Is the problem I am having related to the long slope, so very small changes in ending Voltage affect SoC that much?

How much does battery temperature affect this point/ending voltage?


Also Post #353 shows how C-Rate to a certain ending voltage affects SOC. The faster you charge the lower the SOC at that voltage. This graph is interesting to think about.

For a C-rate of .4C using CC ending volts 3.45vpc reach 77%Soc. A C-rate of .5C would be less, about 75% SoC.
This chart shows that if I charge at C-rate .35C to ending volts of 3.45v I will be at about 82% SoC
If I charge at Constant Current C-rate .30C to ending volts of 3.45v the batteries will reach 87% SoC
It would be nice to know what estimated number of cycles are for each type of charge.
Will all C-rates above result in more than 2000 cycles? (Since it is within the specs of the manufacturer?)
How many cycles would you gain by reducing the C-rate to .2C and reaching 95%SoC while increasing charge time (add 1/3 time)?

[rgleason]

Originally Posted by newhaul

I'm glad I don't have to play in your ballpark
Mine is in the neighborhood of $2.50 per ah delivered.
Which seems to be about equal to agm per usable ah.

Newhaul, I know you posted the specs somewhere in this forum, can you post them again or point me to them? I think you said they were packets? Also what do you know about the company and your dealer?

Wouldn't 240ah LiFePo4 x $2.50 = $600 be good if it was as spec'd?

[john61ct]

Originally Posted by rgleason

Sterling Pro Chargers do not measure trailing amps and thus are not well suited to LiFePo4 in this respect.

The setpoint adjustability is more important for me. I don't know of any non-combi chargers that offer both. That functionality - if you really feel required (I don't, for my use cases so far) can be implemented by using an external control relay to handle the stop-charge.

> at a C-Rate of .5C charging up to ending voltage of 13.88v (3.47vpc) will reach 75%SoC
Can't over-generalize, so many factors involved. 75% of what definition? Are you doing CC only, or holding some CV / Absorb? Are you really going to charge at that high a rate? If so, you saw my 3.50 reco, if being careful, constant amps, could bump up even a little higher with CC only.

Or hold Absorb to .03C if you think the extra SoC gained important, but base your decision on the behaviour of your cells under that charge source.

I don't need answers to the above, just reminding you of the many factors under your control, a given graph can be useful to illustrate a principle, but you tweak your own setup as needed and **your** graph will be quite different.

A foolish consistency is the hobgoblin. . .

[john61ct]

Originally Posted by rgleason

Wouldn't 240ah LiFePo4 x $2.50 = $600 be good if it was as spec'd?

Yes if consistently excellent quality,

it takes several years and hundreds of positive IRL reports to establish that AFAIC,

would be a huge breakthrough, maybe even the basis for a profitable business importing.

There is no local dealer afaik you have to import directly yourself, pays your money takes your chances.

So many scammers out there in this niche.

Companies sort the results of QA testing, how do you know you're not getting C or D level rejects, maybe from some midlevel factory manager? Or secondhand, or returned output.

Can't really tell without thorough testing, even sawing a case open. . .

[rgleason]

Since we've been talking about charging exhaustively, some thought should go into the lowest discharge, with respect to cycles, voltage, etc.

Winston Specs I linked to further below have this line

Cycle Life
80%DoD >- 5000 times,
70%DoD >-7000 times

Could someone please explain this to me. These DoD number of cycles are also dependent on other use aspects as well aren't they?

Does this mean we should never go below 70% Dod or we will never get 7000 cycles? I am trying to understand how this is relevant to actual use of the battery.

What is the lowest SoC and Voltage that the batteries should be allowed to go practically? How much does this level improve/decrease the number of cycles?

Let's assume the BMS settings are separate and lower. When should the Discharge Alarm sound and the alternator start charging?


Can we go down to 90%DOD without losing lots of cycles?

[rgleason]

Originally Posted by john61ct

The setpoint adjustability is more important for me. I don't know of any non-combi chargers that offer both. That functionality - if you really feel required (I don't, for my use cases so far) can be implemented by using an external control relay to handle the stop-charge.

So you use a Sterling Pro Charger?
We need a simple System manager that measures volts and current at several shunts and turns on and off relays, with user set values. Then let the BMS do its own thing.



You would have thought that Balmar in its wisdom would have built that into is SG200, but all it does is Critical Alerts, no controls. They do support multiple shunts and locations. I suppose the control module is coming and that also gets purchased along with a fancy new regulator specifically designed for LiFePo4....

Originally Posted by john61ct

> at a C-Rate of .5C charging up to ending voltage of 13.88v (3.47vpc) will reach 75%SoC
Can't over-generalize, so many factors involved. 75% of what definition? Are you doing CC only, or holding some CV / Absorb? Are you really going to charge at that high a rate? If so, you saw my 3.50 reco, if being careful, constant amps, could bump up even a little higher with CC only.

Or hold Absorb to .03C if you think the extra SoC gained important, but base your decision on the behavior of your cells under that charge source.

I don't need answers to the above, just reminding you of the many factors under your control, a given graph can be useful to illustrate a principle, but you tweak your own setup as needed and **your** graph will be quite different.

A foolish consistency is the hobgoblin. . .

Well, I believe this is a Winston chart, but I am not sure. If it is I expect it would be using their "A" values for C, not our "B" or "C"


I am just looking for some idea of how much the number of cycles will change with different charging rates. 2000 cycles would be fine, that would last me over 10 years I believe.


The way you treat your cells John, how many cycles do you think you "miight" get? - sorry to get so personal.


The problem is I need to get the batteries and use them, to learn what they can do and then get a new alternator sized properly.
I'd rather do it the other way round.

[CatNewBee]

Originally Posted by rgleason

Since we've been talking about charging exhaustively, some thought should go into the lowest discharge, with respect to cycles, voltage, etc.

Winston Specs I linked to further below have this line

Cycle Life
80%DoD >- 5000 times,
70%DoD >-7000 times

Could someone please explain this to me. These DoD number of cycles are also dependent on other use aspects as well aren't they?
...

Can we go down to 90%DOD without losing lots of cycles?

It is an idealistic Lab scenario, that postulates, you can charge the battery full and discharge it 5000 times to 20%SOC (or draw 80% of the nominal capacity) before the battery degrades to 80% of nominal capacity considering it dead. So to speak, if you use it always 80% of its capacity and re-charge to 100%, you can store / draw energy of 5000*0.8*C, before the battery loses 20% - for 100Ah this would be 5000*0.8*100Ah = 400000Ah or 400kAh - in other words she must provide 80Ah each cycle.

The second figure means (lab)-cycles using 70% of the energy and re-charging to 100%, so 7000 cycles until the battery degrades to 70% of nominal capacity or 7000*0.7*100Ah = 490000Ah or 490kAh - providing 70Ah each cycle.

The battery is considered good, as long as she can provide the DOD capacity, but this is a definition gray area, this also explains part of why a shallower discharge leeds to more cycles, a battery that must deliver 80% of nominal capacity can only lose 20%, a battery that must only deliver 50% of nominal capacity can be used longer until the capacity drops below 50% and in our example the 100Ah battery cannot do a 50Ah discharge any more without going below 2.8V per cell.

As you see, you get an advantage of 90kAh or 22.5% more usable energy if you stop 10% earlier to discharge.

You can extrapolate, and if you come to the point of 0%DOD, you'll have infinite (non-) cycles ;-) and the battery will leave forever.

[john61ct]

Originally Posted by rgleason

When should the Discharge Alarm sound and the alternator start charging?
…
Can we go down to 90%DOD without losing lots of cycles?

Do not allow below 2.99Vpc, that's absolute 0% SoC.

10-20% SoC is fine IMO, but size the bank so that's rarely required.

All batteries have a cycle lifetime vs DoD chart, but the slope of the curves and endpoints vary.

Based on the mfg specs for other factors like charge profiles.

Lab conditions, actual numbers little to do with IRL.

Lots of disagreement on whether oversizing for that reason only is economic, but of course LFP vs lead, both cost and weight may change your position between the two.

Some people don't even believe in the causality itself! For sure there is no one right number, like the "50% guideline", knowledgeable owners can set their own.

For sure do not pay attention to the "counting cycles is silly, only total AH throughput over lifetime matters" crowd.

Pretty well hashed out here http://www.cruisersforum.com/forums/...th-206151.html

[john61ct]

Originally Posted by rgleason

their "A" values for C, not our "B" or "C"

Nit pick on my benchmark scheme

A is nameplate AH rating.

B is whatever you choose for "theoretical" or vendor 100%

C is your usage 100%, where you reset your BM.

Which may be different from your actual stop-charge point in daily use cycling.