Depth of Discharge Myth?

[kmacdonald]

The alternators on cars and trucks continually output 14.2 to 14.4 volts and never go to float. When the batteries are full the acceptance is low and it causes little to no damage to the battery. Above 14.4 excessive gassing can occur and water will need to be added more frequently.
For LA banks of about 200 to 400 Ah I would use a 8MR internally regulated 90 amp alternator. I would limit the output to about 60 amps by picking a pulley of appropriate diameter. A larger charge current wouldn't decrease total charge time by a lot. At higher charge currents the battery will reach absorption at a lower SOC thus reducing most of the perceived advantage of a larger alternator. Charge to 85% SOC with engine and size solar to top it off keeping in mind the 50% charge efficiency above 85% SOC. Total cost for 4 6V duracells and the 8MR alternator is less than $600.
Note: Trojan recommends a charger of 12 to 15% of Ah capacity for LA batteries. 60 amps is at the high end for a 400 Ah bank.

[thinwater]

I wonder if the motion of the boat has an influence on stratification. When I take a cat or tri out for a vigorous sail, everything gets mixed. I have to believe that is true for cars and trucks. Perhaps it is less true for larger monos (slower motion, even when rolling) and it is certainly untrue of off-grid installations; the only mixing will come from off-gassing and convention, that latter trivial due to the viscosity of battery acid.

[kmacdonald]

Originally Posted by thinwater

I wonder if the motion of the boat has an influence on stratification. When I take a cat or tri out for a vigorous sail, everything gets mixed. I have to believe that is true for cars and trucks. Perhaps it is less true for larger monos (slower motion, even when rolling) and it is certainly untrue of off-grid installations; the only mixing will come from off-gassing and convention, that latter trivial due to the viscosity of battery acid.

Interesting. Using data from one application to another may not correlate exactly or even closely. Looks like asking one question opens up a lot of cans of worms. I still say batteries are too cheap to worry about too much, unless you go overboard on them.

[kmacdonald]

I just hope Dockhead posts what he decides on so everyone can give their opinion on where he went wrong.

[Paul L]

Originally Posted by kmacdonald

I just hope Dockhead posts what he decides on so everyone can give their opinion on where he went wrong.

Law school😯

[Dockhead]

Originally Posted by leftbrainstuff

Deep discharges also consume the chemical life. ..

What does that mean? Consume the chemical life?

[Dockhead]

Originally Posted by Paul L

Law school😯

Ha, ha!


That was not the only "went wrong" point in my life, I'm afraid

[newhaul]

Originally Posted by Dockhead

Ha, ha!


That was not the only "went wrong" point in my life, I'm afraid

bought a hole in the water another major one

[Dockhead]

Originally Posted by newhaul

bought a hole in the water another major one

Which one?

[sailorboy1]

Originally Posted by newhaul

bought a hole in the water another major one

I consider myself a water hole that lives on a boat

[newhaul]

Originally Posted by Dockhead

Which one?

is that an admission of your mental illness?

[newhaul]

I admit I have 5 including the kayak but I'm a shipwright so its ok to be mentally challenged with boat ownership

[Dockhead]

Originally Posted by newhaul

is that an admission of your mental illness?

Thank God I know about the 5th Amendment.

[newhaul]

Originally Posted by Dockhead

Thank God I know about the 5th Amendment.

I would rather drink it than plead it.

[missourisailor]

Originally Posted by a64pilot

Read this,
Then go back and read it again, go do something and read it again.
I’m not trying to be an Ass, but it says a whole lot, and explains why even with a kilowatt of Solar, I cannot get to 100% charged on Solar alone, and that is locking my Outback 80 into absorption voltage only, never letting it get to float.

A64,

You are very correct on this and I feel that it can’t be stressed enough.


To the folks that say “... my solar system goes to float before noon”, either don’t have much Ah usage through the night or don’t realize that their “bulk” stage is timed. Or both.

With my modest 180Ah usage and meager 500w’s of solar, assuming perfect sun for 12 hours, I need 6 hours of charging with NO other loads just to replace the previous usage. This is assuming 100% efficiently. So it will be longer with normal electrical losses.
Add in normal house loads during the daytime charging time, now I’m up to 9 hours or more.

So factoring in real world electrical losses, even with perfect sun, I never get to “full” under solar alone.

This has noting to do with Dockhead’s OP. But maybe why folks whom observe the 50% myth are still killing their banks.