Depth of Discharge Myth?

[Dockhead]

Originally Posted by ramblinrod

.. .

For those disinclined to apply these charging technologies in favour of noisy, smelly ICE charging, I suspect boaters do hope they change out FLA batteries for LiFePO4 to reduce ICE running time.

However this doesn't likely change that they really wish those people would reduce or eliminate unnecessary ICE running by applying solar and/or wind charging systems.

Sometimes, the choices one makes can affect others beyond the confines of their own hull.

A while back, we were in a quiet and peaceful anchorage (Prinyers Cove for anyone who knows it), when a boat with "first rights" smack in the middle of the anchorage, raised anchor in the evening and moved away to the outskirts of the anchorage to run their generator without disturbing others.

Very courteous.

If all were so considerate, there prolly wouldn't be near the objection to those choosing to charge with ICE rather than with wind and/or solar.

My generator, a low speed heavy duty unit in a sound enclosure in a lead-lined soundproofed engine room, is entirely inaudible from the outside, even from the cockpit. It does not even make a water splashing sound, as it has a water separator muffler with below the water line water discharge.


Not all that rare.

[Pizzazz]

If people feel strongly about the cost of lithium vs FLA they should provide links instead of just statements. I think the cost of $1/AH for FLA vs. $7 for lithium is fairly well established in the US market. Useable capacity is not a good measure because it depends on the method of usage and personal choices such as how much solar to install, motoring style, etc.

[john61ct]

Originally Posted by Pizzazz

Useable capacity is not a good measure because it depends on the method of usage and personal choices such as how much solar to install, motoring style, etc.

No, only depends on your intended maximum-normal DoD.

If you stick to the 50% guideline for lead, the 400AH usable means an 800AH bank.

If 80% is your LFP number then a 500AH bank will do.

[ramblinrod]

Originally Posted by john61ct

No, only depends on your intended maximum-normal DoD.

If you stick to the 50% guideline for lead, the 400AH usable means an 800AH bank.

If 80% is your LFP number then a 500AH bank will do.

I agree with Pizzaazz.

If one applies the principle that some LFP reserve capacity should be maintained to accommodate variables in load or charge, as I have previously indicated, then the reality will most likely be that regardless of technology, approx. the same size bank should be employed.

[newhaul]

Originally Posted by ramblinrod

I agree with Pizzaazz.

If one applies the principle that some LFP reserve capacity should be maintained to accommodate variables in load or charge, as I have previously indicated, then the reality will most likely be that regardless of technology, approx. the same size bank should be employed.

sorry but I have to disagree with the both needing the same size banks
Due to the discharge voltage curve . My refrigerator would stop when the Fla bank reaches 60% DOD the Lfp will run it right up to the full 80%dod with no issues. Which equates out to be 20ah per 100ah in the bank.

On the reserve capacity it has been well discussed and established in this thread that a regular discharge of Fla to 80% DOD will do harm to the life expectancy of said bank however the same can't be said to a significant degree with Lfp.
Another established point is that Lfp will recover faster than Fla to a full state regardless of charging means.

[evm1024]

Originally Posted by ramblinrod

I agree with Pizzaazz.

If one applies the principle that some LFP reserve capacity should be maintained to accommodate variables in load or charge, as I have previously indicated, then the reality will most likely be that regardless of technology, approx. the same size bank should be employed.

Please define what you mean by reserve capacity.

Does it mean that you need 24 hours reserve with no charging? That would imply that your total usable (normal plus reserve capacity) equaled 2 days use.

Does it mean that you only need 12 hours reserve usage to cover you until solar start working in the morning?

Or does it mean something other. Please be as specific as you can be.

I know that you are a fan of small house banks (that meet the cruisers needs + reserve), smallish solar, wind and moderate alternators (80 amps for example).

So that we can compare apples to apples what daily usage are we talking about. Would it be fair to say 150 amp hours per day?
\
So what, 200 watts solar and what else?

[Delfin]

Originally Posted by ramblinrod

I agree with Pizzaazz.

If one applies the principle that some LFP reserve capacity should be maintained to accommodate variables in load or charge, as I have previously indicated, then the reality will most likely be that regardless of technology, approx. the same size bank should be employed.

That's interesting, since I've replaced a 1200 amp AGM bank with a 600 amp Li bank and have the same usable capacity at a more stable, higher voltage that requires 1/3 the time to replace during recharge. But maybe I'm missing something.

[Delfin]

Originally Posted by Dockhead

My generator, a low speed heavy duty unit in a sound enclosure in a lead-lined soundproofed engine room, is entirely inaudible from the outside, even from the cockpit. It does not even make a water splashing sound, as it has a water separator muffler with below the water line water discharge.


Not all that rare.

I guess that makes at least two of us. We can barely hear the genset running on the boat, much less 75 yards away because we have a similar setup.

[Delfin]

Originally Posted by ramblinrod

Has anyone made that blanket statement?

I know I haven't.

Originally Posted by ramblinrod

I am not making categorical blanket statements.

"To me, the only real benefit I see to switching from FLA to LifePO4 is the ability to say, "I have LiFePO4s"."

-Ramblinrod

[john61ct]

Yes a reserve is important, as in handling poor solar weather conditions, or worst case raining with kids aboard.

But that can be built into the sizing, so with lead can usually only cycle 20-30% DoD, going down to 50% is the reserve.

Or with LFP, if you think the LFP system is more fragile, a separate Reserve lead bank can replace dedicated Starters in the design.

___
But with an on-demand ICE charge source,

not depending on a mostly-solar design,

the reserve is in the fuel tank,

in which case regular 80% DoD from LFP is just fine, one hour ICE runtime may be enough energy for days

With a routine ICE usage for other reasons scenario, no added runtime at all is required.

[StuM]

Originally Posted by Delfin

That's interesting, since I've replaced a 1200 amp AGM bank with a 600 amp Li bank and have the same usable capacity at a more stable, higher voltage that requires 1/3 the time to replace during recharge. But maybe I'm missing something.

You have the same regularly usable capacity.
You don't have the same reserve capacity in the event of problems with your charging system(s).

[Delfin]

Originally Posted by StuM

You have the same regularly usable capacity.
You don't have the same reserve capacity in the event of problems with your charging system(s).

Assuming the genset and engine anternator and shore power cord all fail at the same time, and the starter bank takes a header, you're right.

[newhaul]

Originally Posted by Delfin

Assuming the genset and engine anternator and shore power cord all fail at the same time, and the starter bank takes a header, you're right.

That why i carry a lipo jump pack jjst in case.

[kmacdonald]

Originally Posted by StuM

You have the same regularly usable capacity.
You don't have the same reserve capacity in the event of problems with your charging system(s).

If you run out you just do without for a while. Not the end of the world.

[ramblinrod]

Originally Posted by Delfin

That's interesting, since I've replaced a 1200 amp AGM bank with a 600 amp Li bank and have the same usable capacity at a more stable, higher voltage that requires 1/3 the time to replace during recharge. But maybe I'm missing something.

In all individual cases it would take an individual energy needs assessment to come up with an answer for that particular individual case.

That said, there are general rules of thumb. Others have suggested that it is
Not appropriate for me to post generalizations using such terms as “in most cases”.

That is ridiculous. It is unreasonable to suggest we not post generalities. Almost post of anyone trying to offer general advice would be prohibited or shunned.

If one doesn’t accept the general
Advise given, because they believe their circumstance is unique then just
Ignore the general advice rather than attempt to stifle the poster, whose advice may be valuable to others, perhaps even most.

Now, IN GENERAL TERMS...one needs to perform an energy needs assessement.

This will include average A-hrs per day consumed, while under way or at anchor,
Including anticipated variance.

Then one has to determine what reserve capacity is desired.

I believe the concept of no reserve capacity for LFP is very bad design. If loads are higher than average, alarms may go off forcing one to get up at 0230 to start a generator. Or worse, have a disconnect and all power be off until intervention.

When one considers that one can dip a FLA bank below 50% on occasion, then there is inherrent reserve capacity in that system.