Keeping the Batteries up at Anchor

[Despacio]

I've always managed electricity on my boat by running the engine for one hour in the morning, and one in the evening. I knew that a fully charged 12 volt battery puts out 12.6 volts, so I believed, in spite of the evidence, that I was doing it correctly. When the meter showed 12.3 volts it's time to charge. After an hour it would read 12.6, and I'd shut it off.

I finally read the literature that came with the Smart Switch. An alternator should put out 14.4 volts with a fully charged battery, a battery charger (roughly) 13.8, and 12.6 at rest. There are marks on the Smart Switch for those values.

After a week I was fighting a losing battle, the meter went to 12.3 way too quickly. While running the engine the meter never got anywhere near 14.4. But it was 12.6 I had always been looking for.

So I did a lot of charging to get it up to 14.4, then every time I'd charge the batteries I'd watch the meter and run the engine until it said 14.4. When I shut the engine off, of course, it read the desired 12.6.

My charge time was about right in the morning, 1 hour, but far less in the evening, and the rest of the time I was at anchor the meter rarely fell to 12.3. I had always done this arbitrarily, an hour here, an hour there, and now do it by the output reading of the alternator.

I have four golf cart batteries for bank #1, and a 4D for the back up. I have never used the 4D. I put in a 100 amp alternator. I have a 1000 watt inverter and a 400 watt microwave. I'm trying to weed out the need for 110 volts everywhere I can.

I have no generator and appreciate it when my neighbors don't have one either.

[DougSea]

There's a lot of info out there, and some of it conflicts. The following is accurate to the best of my, untrained, knowledge.

I believe you have been undercharging your batteries, and if I'm reading your recent results correctly, they confirm that.

12.6v IS the charged voltage of a battery that, after being fully charged, has been allowed to sit for several hours being neither charged or discharged. Your batteries should have been reading closer to 13.5v right when you shut down the charger, and even higher (14.2+) during charging. Read up on "bulk" and "absorption" phases for more info.

At this point your batteries probably need to run through a de-sulfation cycle as the incomplete charging has reduced their max capacity. Many modern chargers have this ability.

[Despacio]

My four golf cart batteries are one month old.

Yes, I have been undercharging them, that's my point. But it seems fairly common for people I know to run the engine arbitrarily instead of up to that 14.4 number that says, "fully charged." Your results may vary.

[psneeld]

What is fairly common for people to do with boats, motors, etc...etc is often quite incorrect. Mainly because all the systems on a boat often work quite differently than sytems found elsewhere. The basics are the same but not necessarily the use/application.

Batteries are a good example. People think their boat batts get used much like their car batt. Not even close. Even the batts are a bit different some being start and some deep cycle.

A good understanding of batteries and their associated systems only comes after reading literally thousands of pages on the subject. Mostly in books where chapters are dedicated to the electrical system..not some 5 paragraph story written in a boating mag. Topped off with perusing tech info from battery manufacturers and charger/inverter manufacturers that go a little deeper into their own specifics and how those batts should be treated or "total system" operated.

[crowra]

I agree with DougSea (and it sounds like you) that you are undercharging your house batteries. A fully charged wet-cell battery is 12.6v. BUT that should be after it has gone through 'bulk', 'absorb' and finally 'float' stages of charging. Think of filling up a water jug. You can run the water into the jug full flow -- that's the bulk charge up to usually 75% of the battery's charge. To fill the remainder of the jug, you need to reduce the flow of water -- that's the remaining absorb charge. When fully charged from those two stages, a typical wet-cell battery should be at 14.2-14.4v. If taken to a lesser voltage level, some of the sulfate deposits that form during discharge will remain on the plates.

Once the batteries are fully charged, they should be maintained at a lesser voltage, typically 13.2-13.4v (float charge) to prevent gassing, etc. Hopefully you have a 'smart' voltage regulator for your alternator to take your batteries through the charging stages (sounds like you do). Once the float charge stops, i.e., you turn off your engine, the battery should be approx. 12.6v.

I'm assuming your 'golf cart' batteries are 6v, deep-cycle wired in series and parallel to create one 'big' 12v battery. Deep-cycle batteries can be discharged to 80% their capacity so taking you batteries below 12.3v is fine. It also depends on your battery's amp hour rating for how long your battery's charge will last. If your golf-cart batteries are 100ah, then you have 200ah total capacity. You mentioned weeding out the need for 110 but your DC loads will still need to be factored into how many total amp hours your batteries are good for.

Unfortunately (for you), we have a generator although the majority of charging our batteries comes from shore power or the alternator while underway. We rarely stay anchored in the same place for more than one night.

[psneeld]

While discharging Golf Cart Batteries beyond 50% isn't fatal...oyu do significantly lengthen their lives by sticking to the 50% rule...

Average Life Cycle Chart
Depth of Discharge Cycle Life Cycle Life Cycle Life
% of AH capacity Group 27/31 Group 8D Group GC2
10 1000 1500 3800
50 320 480 1100
80 200 300 675
100 150 225 550

The chart gets reformatted but the GC2 batts have 1100 cycles at 50% discharge and only 675 at 80%.

http://www.cartsunlimited.net/How_Batteries_Work.html

[jleonard]

And of course there is always the screw up finding out your alternator is putting 20V into the batteries. Yes that happened to me last week with the new Balmar alt and regulator.
Lucily none of the batteries boiled over and now that my old Leece Neville is back in service the batteries and the system are doing fine as long as I run 4 hours or so per day.

[N4QC]

How is the 20V problem being rectified (pun intended)...

Have fun,

[jleonard]

The Balmar is in the trash bin and the old Leece Neville is back in service.

[bccanucker]

Despacio: psneeld is very right. You need to continue to read on this subject. When you get to reading about amphours you are getting close to understanding how full a battery is when you are at anchor. You cannot use a voltmeter to know the state of charge a battery is at when it is being used. You need an amphour monitor.
A battery is full when the voltage is 12.6 AFTER THE BATTERY HAS BEEN SITTING FOR 24 HOURS WITHOUT BEING USED. That's pretty much not something you can do when you're using the boat.
You cannot charge a battery full with an engine alternator. You say you don't want to use a genset. I agree but using your engine is the same thing. Noisy.
Three years ago I installed 3 135Watt solar panels. We, and now many of my friends have found this to be the silent answer.
See the pictures on my blog of the installation at
http://www.blueheron-albin.blogspot.ca/

[Captn_Dwt]

Most of the answers to this question are correct. I'd like to add just a bit;
1) a 12v deep cycle battery will have a lower finish voltage than two 6v deep cycles connected in series. (an example: the 12v batt will be +/- 14.2v. The two 6v, at 7.2 each, will be 14.4v finish) The finish voltage (v @ full charge with charging pressure applied) is specified by the manufacturer. You must have that value to properly manage the battery. Call the battery mfg. if needs, but know this value.
2) This is a subject where the knowledge required is lots, but not insurmountable nor voluminous. The solar power industry and "off the grid' folks (like me) have found many excellent articles on battery use and maintenance. It's chemistry and 10ths of volts. It's very reasonable to work with. But, you need the knowledge and tools to do it. There's way to much info needed to post here, sorry.
3) Here's a sample link : http://www.homepower.com/articles/solar ... -re-system
Home Power is a wonderful source for detailed information for those who want to do it themselves. The began publishing in the early 1980's and have always focused on sharing knowledge. Great folks.

So, read, read, learn and enjoy!