Alternator Size with LiFePo4

[john61ct]

Originally Posted by Q Xopa

Yes this last statement is what I was questioning you questionig last time. (If that makes sense).

Im not sure if you are suggesting the SOC cycling range makes no difference to cycle life, or negligable. And with practical economic considerations its not worth considering to any extent. I think the latter?

Yes. The former is very much not the case.

In thousands of threads across dozens of forums, I know of **no one** whose opinion I respect that advocates for oversizing LFP at 5-7x the cost of lead, just to get better longevity.

The longer the ROI period, the higher the inherent risk of a financial loss.

Longevity is already vastly improved by avoiding the shoulders, to the point a bank may last decades already even using 80% DoD every cycle, we just don't know yet.

Now for a solar-only setup, there are compelling reasons to build in a Reserve.

In my case I prefer to accommodate that need with a separate cheaper lead bank,

which I have for redundancy anyway for cruising full-time in primitive locations,

also eliminating dedicated banks for cranking engines, winching, thrusters etc, where feasible.

[rgleason]

Originally Posted by Maine Sail

I see a lot of focus on "replacing Ah" with ideals and thoughts of getting back to full .... (not what nebster is discussing, he gets it)

This is a lead acid mentality. Instead simply focus on replacing only what you need for the next 12, 24, 36, 48 hours etc. and shut it down.

If you have an opportunity to get back to near full, by all means take it, but don't fuss about it daily. Spend the money now to size the bank for a few days worth of silence and you'll really begin to appreciate LFP even more.

For example we leave our bank at less than 50% almost every-time we leave the boat. When we get back to the boat I fire up the engine & alt first. By the time we stock the fridge, bar, ready the vessel, stow our gear, leave the hook and get out of the harbor, about 40 minutes +/-, we have replenished more than an entire days worth of energy + what ever SOC we left it at.. The motor, if fully warm, then gets shut down and the PV flipped on.

With the addition of the new Balmar SG200 we will no longer need to guess at the accuracy of our SOC via a Coulomb counter. I doubt our bank will see 100% SOC all that often. It's just no longer necessary... LFP is really, really quite simple if you can leave the lead acid mindset in the 60's.

Yes SG200 is what I have.
I am planning LFP double my daily 100ah needs.
I wish to charge at .4C for 1/2 ÷/-hour morning and evening (40a total +/-) morning and evening. The alternator should be set to reduce charge rate to .2C at 85% charge and then shut off float (for longevity and safety) at the appropriate point.


Can this be programmed in Balmar and what would the settings be?


I don't mind not using all capacity if it is reasonable. I think BMS relay should be emergency use primarily.


Solar PV 100w with appropriate controller settings can provide house loads partial during the day. On the mooring, solarPV may have to be shut off.


I'd be interested in the balmar settings to do this.


Some of this discussion affects the practical size and requied continuous output required by my new alternator. I had wanted to restore 100ah in one hour and thought that 0.5C was a reasonable rate given many manuf show 0.5C-1C.



Now all the gurus are saying .3C max. Yet my alternator charging is not going to be at the shoulders where there is more resistance and where I think the damage to #cycles and capacity is done.

[john61ct]

Originally Posted by rgleason

I wish to charge at .4C
…
Now all the gurus are saying .3C max.

The difference in longevity between .3C and .4C will I bet be minor, but fact is no one knows for sure. And IMO only an issue as SoC get above the 85-90% range, so your solution above would work, leave that to solar, and as MS keeps emphasizing, no real compelling need for you to get to Full anyway!

> I had wanted to restore 100ah in one hour and thought that 0.5C was a reasonable rate given many manuf show 0.5C-1C.
Remember their motivation is not doubling the lifespan of your bank.
You may well be fine at that rate though, but I personally would not be increasing bank size just to decrease the C rates.

[john61ct]

Originally Posted by rgleason

The alternator should be set to reduce charge rate to .2C at 85% charge and then shut off float (for longevity and safety) at the appropriate point.

I believe this is only (maybe) possible with a non-mainstream regulator, exactly what I'm querying with Al wrt his SAR project

[Q Xopa]

Originally Posted by john61ct

Yes. The former is very much not the case.

In thousands of threads across dozens of forums, I know of **no one** whose opinion I respect that advocates for oversizing LFP at 5-7x the cost of lead, just to get better longevity.

The longer the ROI period, the higher the inherent risk of a financial loss.

Longevity is already vastly improved by avoiding the shoulders, to the point a bank may last decades already even using 80% DoD every cycle, we just don't know yet.

Now for a solar-only setup, there are compelling reasons to build in a Reserve.

In my case I prefer to accommodate that need with a separate cheaper lead bank,

which I have for redundancy anyway for cruising full-time in primitive locations,

also eliminating dedicated banks for cranking engines, winching, thrusters etc, where feasible.

Yes I think we are pretty much on the same page. However it will be interesting to see how Life Cycles and the factors effecting them play out over time.

I also have to agree that your boiler plate seems well thought out but perhaps a little complicated to practically impliment, particularly charging.

Never the less, as always, your efforts and sharing are muchly appreciated.

[john61ct]

Originally Posted by rgleason

Yet my alternator charging is going to be at the shoulders where there is more resistance and where I think the damage to #cycles and capacity is done.

No, the "shoulders" just refer to Voltage, at the bottom and top ends of SoC, looking where rate of change accelerates (steeper slopes) in the Volts vs SoC graphs.

The current rate vs longevity issue may well be a completely separate mechanism chemically, but as I speculated above, likely less of an issue within the flatter areas of that curve

[newhaul]

Originally Posted by john61ct

Just to reduce your C rate?

Buying a bigger bank IMO should only be driven by an actual need for the higher AH capacity, because you feel you're hitting too close to your 0% point too often, and don't have the ability or desire to replenish via ICE on demand.

Increasing your charging voltage a little will get you to higher SoC.

But the only way to calibrate the impact is through load testing.

this I do believe is the first time I have ever been told I have to much solar .

On the other hand if I add another 100ah to the current setup to keep my charging in the low .15C +/- it will also increase the number of days I can go without charging.

And just an fyi I do have the potential to mount and use the 55amp alternator I carry on the boat for emergencies.

[john61ct]

Originally Posted by nebster

Well, in an example charging strategy being discussed earlier, the endAmps was set to bulkAmps

I find that last term confusing.

Again, my daily cycling charge profiles are To a Voltage then Stop, no Absorb/CV at all.

If I were concerned about getting to Full in that context - which I am not - I could do so by varying voltage.

The **only** time I use a CV stage / hold Absorb V, is for benchmarking purposes, and that (of course) requires using a shunt to stop-charge based off endAmps.

_____
In any case I'll not dispute your claim that CC-only charging **in itself** leads to significantly lower SoC when charging stops, since I don't see that as a downside anyway.

However the high-current rate just makes a higher voltage **safer** (less impact on longevity) with CC-only profiles. With an Absorb stage, higher current does make shunt-based stop-charging based on endAmps **more** important, since that point will be reached much more quickly than at low currents.


> The threshold should be set as low as possible.

Well too low and you're charging much more slowly, both for extracting max power from solar, and if ICE is running for the sole purpose of charging, that is not ideal.

I think my "13.6 for low rates, up to 13.8V for high" strikes a decent balance and is easy to both understand and to implement.

Note I am **not** taking a hard line on CC-only, that just for the ease of understanding and implementation.

[rgleason]

Sorry, I missed the "NOT going to be at the shoulders", and went back and edited in. Sorry for any confusion.

[john61ct]

Originally Posted by newhaul

this I do believe is the first time I have ever been told I have to much solar

No such thing. 8-)

Just means adjusting the output profile **if** you both

believe the higher rate will significantly reduce longevity, **and**

care that much about optimizing for maximum longevity.

> On the other hand if I add another 100ah to the current setup to keep my charging in the low .15C +/- it will also increase the number of days I can go without charging.

The latter is a valid reason to increase bank size, but greatly reduced by any ability to charge on demand via ICE.

[rgleason]

John's request to Al Thompson for his programable regulator, adjusted for 200ah bank (as measured). See this post
http://www.cruisersforum.com/forums/....php?p=2794301

Sample:

Start out at 0.35C x 200ah= 70A, hold as long as V < 13.72, then drop to 53A

when V < 13.77, drop to 35A

at 13.82, 18A

at 13.85, 7A

Stop charging (or open the remote solenoid) at 13.95V.

[rgleason]

Newhaul wrote:

this I do believe is the first time I have ever been told I have to much solar .

Thats ok! You are a lot greener than my dirty approach and I would do that in an instant but the boat is not designed for solar. There is no clean suface anywhere, so its the small dodger and some stern wings probably.

[Maine Sail]

Originally Posted by john61ct

In thousands of threads across dozens of forums, I know of **no one** whose opinion I respect that advocates for oversizing LFP at 5-7x the cost of lead, just to get better longevity.

John, what exactly is over sizing? I suspect by your standards I over-sized... I won't lose any sleep if you don't respect me in the morning...

Our lead bank was approx 400Ah. We only used about 30% of it before recharging. When I switched to LFP I stayed at 400Ah and gained multiple days without having to hear an engine. We also lost the need to ever get back to 100%.

I don't consider that "over-sizing" just being realistic that when the family & I are at anchor, in an idyllic spot, I don't want to listen to the drone of an engine and I am not going to make our boat look like the clown-car of solar, wind gen, no thanks.....

Rated Lead Ah to Rated LFP Ah = Same


Usable Ah Capacity = Vastly Different

Piece & Quiet = Priceless

If I had to do it over I would do the exact same.... If my design goal was up to five days with no ICE charging and only a small solar array that's not really over-sizing it is a design goal.....

[Maine Sail]

Originally Posted by rgleason

John's request to Al Thompson for his programable regulator, adjusted for 200ah bank (as measured). See this post
LFP's Charging Voltage and State of Charge - Page 5 - Cruisers & Sailing Forums

Sample:

Start out at 0.35C x 200ah= 70A, hold as long as V < 13.72, then drop to 53A

when V < 13.77, drop to 35A

at 13.82, 18A

at 13.85, 7A

Stop charging (or open the remote solenoid) at 13.95V.

Why......? CC/CV charging will do all this for you. Set it at 13.8V - 14.0V and have it stop at .03C - .025C & you're done.

You're over complicating something that is actually quite simple.

[john61ct]

Originally Posted by rgleason

John's request to Al Thompson for his programable regulator, adjusted for 200ah bank

Note I just WAG'd those setpoints as an example, feedback welcome on what they should actually be.