Battery state of charge

[smj]

We have 460 watts of solar at an investment of about $1k. Usually fully charged by noon on a sunny day and late afternoon on a cloudy day. Our Honda 2000, the backup for our solar, has been sitting idle for the last 6 months. Since we have outboards with small alternators we don't have an option of using the motors for charging. My question is to those who use their diesels for charging. Probably the worst thing you can do to a diesel is run it with only a light load such as charging the batteries. I understand some people can't fit a large array of solar on their boat, but wouldn't something
Like a Honda 2000 running your battery charger be a better solution? It burns a gallon of gas about every 8 hours and would take an unnecessary strain of the diesel.

[Dockhead]

Originally Posted by Tropic Cat

I'm not familiar with the term 'stratification' when talking batteries. Does this mean the battery electrolyte has broken into layers? If so, will shaking the battery un-stratify it?

Yes, that's when the electrolyte settles in layers with the sulfuric acid not evenly distributed through it. This considerably reduces capacity since only part of the plates are explosed to the strong acid.

I've never heard of anyone shaking batteries to solve this (sounds dangerous), but a good equalization charge with vigorous gassing for an hour or two is supposed to take care of it. The hydrogen bubbles are supposed to stir up the electrolyte and evenly distribute the acid. One of the main purposes of the equalization charge altogether.

[Hyprdrv]

There are a number of variables as a lot have pointed out. The type and Manufacture of the batteries is the determining factor as to the state of recharging however the standard answer is 50%. Standard Lead/Acid batteries are known to be good to 50%. My AGM's from Northstar are good to 40% discharge. LiPo4 batteries are good to 80% DOD so the type and manufacture has a lot to do with the point of recharging.
Yes running a generator or the motors to FULLY recharge the batteries is not good for the ICE nor efficient. Running these to get up to 80% is the correct and most efficient way to charge and then completing the charge with solar or wind. If neither of these is on board then run the motors to get the last 20% while under power in transit. Not fully charging the batteries is going to hurt them for a few days.

Steve in Solomons MD
Lagoon 410 SE

[Tropic Cat]

Well, I've got a dumb charger pumping lot's of current and I clearly see the electrolyte bubbling happily. However, I've been at this all morning off and on (stop as battery becomes warm to the touch) and no joy. at rest voltage is 11.5v and 12.62v. (two deep cycle group 27 batteries 4 years old)

What surprises me is these have never been cycled. No discharges of more than 5% and yet still it looks like I'm off to buy new batteries (yes, it's both of them)

[Dockhead]

Originally Posted by Tropic Cat

Well, I've got a dumb charger pumping lot's of current and I clearly see the electrolyte bubbling happily. However, I've been at this all morning off and on (stop as battery becomes warm to the touch) and no joy. at rest voltage is 11.5v and 12.62v. (two deep cycle group 27 batteries 4 years old)

What surprises me is these have never been cycled. No discharges of more than 5% and yet still it looks like I'm off to buy new batteries (yes, it's both of them)

Count your blessings that you only have to buy two. I have ten (10) heavy duty batteries on board. I've replaced nine of them this year.

[Tropic Cat]

Final note. new cheap wet deep cycle batteries have been installed.

I did play with the 'dead' batteries for a bit and put in a constant current charge into the old batteries for 3 days. Varying it from 1 amp to 3 amps. One battery did begin responding. I gave up when it would run my car head lamps for at least an hour, but could not be charged enough to turn the car's starter. Apparently dead is dead, even if the batteries aren't abused. Sulfation sucks.

One note, after reading what our forum experts had to say about solar charge controllers, I revisited my decision to buy the one I bought 4 years ago. What I thought I bought was a fancy new digital controller for complete battery maintenance. However, what I actually came home with turns out to be one of the infamous 'shunt' controllers. Apparently these just are not up to the task. I'm looking at replacing it with one of the Genasun GV-10-Pb controllers as folks here seem to think highly of them.