Depth of Discharge Myth?

[john61ct]

Originally Posted by kmacdonald

What's the best brand of LA batteries?

FLA, AGM, or GEL.

Different lists.

[kmacdonald]

Originally Posted by john61ct

FLA, AGM, or GEL.

Different lists.

FLA batteries.

[kmacdonald]

There is also discharge efficiency. They heat up when being discharged due to internal resistance. Lithium excels at discharge efficiency also. Lithium ticks all the boxes except total cost and fault tolerance. Comes down to priorities I guess.

[john61ct]

Originally Posted by Dockhead

So the reason to avoid discharging too low is that one hour at 20% SOC is much more harmful than one hour at 50% SOC. But that even much more important than this is avoiding leaving the batts in those states for long periods of time.

Yes.

Going down to SoC 20% then immediately back to 100% endAmps is **much** less harmful than sitting even at 98% for a long period of time.

Sitting at 70% for X hours or days is better than 60% or 40%, lower you go worse it is.

And longer you go worse it is.

To optimize longevity, the default state is sitting at 100% Full.

Shallower the better, and shorter the better.

Really is not complicated.

But yes, there is no hard line B&W where the loss of lifetime cycles suddenly gets a lot worse.

It's greyscale sloping curves all the way.

The need for sitting at Full goes away with LFP, while sitting lower the better in fact

but the DoD vs lifetime curve is similar for LFP as lead **while cycling**.

[john61ct]

Charging efficiency has nothing to do with longevity.

And usually not a relevant concern in practice.

[john61ct]

Originally Posted by kmacdonald

FLA batteries.

Rolls Surrette, by far, worldwide.

Followed by, in the NA market: Crown, US Batteries, Superior

Then Trojan and Deka.

Of course not every line is designed for deep cycling, but all have good tech support including pre-sales.

Only Deka's Duracell FLA GCs are available in consumer big box, best value by far at ~ $1/AH

[kmacdonald]

Originally Posted by john61ct

And usually not a relevant concern in practice.

It's relevant. Charge efficiency of LA batteries from 80% SOC to 100% SOC is more like 60 or 70% efficient. That's when solar is used. The solar array sizing needs to take that into account. A solar panel putting out 10 Amps is essentially charging the battery at 6 or 7 Amps while topping off the battery.

[kmacdonald]

Originally Posted by john61ct

Rolls Surrette, by far, worldwide.

Followed by, in the NA market: Crown, US Batteries, Superior

Then Trojan and Deka.

Of course not every line is designed for deep cycling, but all have good tech support including pre-sales.

Only Deka's Duracell FLA GCs are available in consumer big box, best value by far at ~ $1/AH

I've been happy with Duracells from Sams Club. Cheap and last a long time.

[sailorboy1]

Originally Posted by kmacdonald

When you charge a battery it heats up. That heat is energy put in to the battery by the charger but not stored by the battery. It's that simple and obvious. Hope that helps.

Really, so in your world a battery doesn’t heat up much when charging below 80% soc

Btw the amount of heat is so minor that as far as an efficiency factor is a waste of time considering

But this has become a waste of time for me and I’m just going to save myself and inscribe to the thread

[john61ct]

Originally Posted by kmacdonald

It's relevant. Charge efficiency of LA batteries from 80% SOC to 100% SOC is more like 60 or 70% efficient. That's when solar is used. The solar array sizing needs to take that into account. A solar panel putting out 10 Amps is essentially charging the battery at 6 or 7 Amps while topping off the battery.

I did not think you meant the long tail phenomenon.

But again I think irrelevant IRL, unless you go LFP, you need to get to 100% Full one way or the other to get decent longevity.

And charging is often the lightest load for the last 3-5 hours.

Doesn't mean the energy isn't being used.

[kmacdonald]

Originally Posted by sailorboy1

Really, so in your world a battery doesn’t heat up much when charging below 80% soc

Btw the amount of heat is so minor that as far as an efficiency factor is a waste of time considering

But this has become a waste of time for me and I’m just going to save myself and inscribe to the thread

Well of course they heat up when charging below 80% SOC. The heat is not minor. It boils off electrolyte if charged too long at bulk charge voltages. That's why some battery chargers and voltage regulators have battery temperature sensors. It's OK, most people don't know much about batteries. If the beers cold and the lights come on (or not) they are happy.

[a64pilot]

If you take 200 amps out of a 1000 AH bank , it will take less time to recharge it, assuming a large enough charge source than if you take 200 amps out of a 400 AH bank, again assuming a charge source that is large enough.
It simply takes longer to recharge a battery that is deeply discharged than one that has been discharged to a much less degree. Why is that hard to believe or understand? We all charge our rechargeable drills etc, run it flat and it takes long than if it wasn’t run flat.

It’s this longer time to recharge that is in my opinion where the 50% rule comes from, average cruiser doesn’t usually completely recharge their bank as it is, if they pulled a much deeper discharge, then it’s way more likely that they won’t get it charged back up, and that is when sulphation creeps in and slowly murders the bank.

Geez, how often do you hear, “I’m fully charged before noon”? No matter what you try to tell these people they don’t want to hear it, they want to believe their bank is fully charged from their Solar panels before Noon, and won’t listen. To them everything is fine, they have been doing this for some time, so it must be true, right?

These same people if they had half the size bank and discharged it twice as far, would still be fully charged by Noon, want to bet?

[a64pilot]

People like Dockhead likely ought to cycle from something to about 85% SOC and then turn the generator off and just buy batteries more frequently, probably ought to invest into an auto start generator module. Most people, especially those without Solar are not full time, they cruise when they can, and of course nothing wrong with that, these people will still likely get years out of their banks, assuming that they equalize upon returning to the dock and shore power.
It’s the people that run the generator every day, day after day that seem to go to Solar and just accept the things are ugly and have windage, cause they get tired of that generator and know it only has X number of hours life in it.

[Training Wheels]

Great thread. Makes me happy I bought Firefly’s!

[john61ct]

Given a very high-amp source reasonably high CAR lead like AGM

The charging time difference to 100% between

50% depleted and 80% DoD for the same bank, or

as with your example

is not as great as you'd think.

Getting from 90% to true 100% endAmps can take much longer than from 50% to 90%.

Adding the extra 30% from 20% SoC may only be another 30-45min, compared to 6-7 hours overall.