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Old 18-05-2012, 18:07   #1
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Battery Charging Questions.

I am sure the answers to my questions are buried somewhere in this forum, but I have read so much about batteries, solar charging, alternators and AC chargers, the waters just keep getting more muddy.

My current plan:
- use two group 31 AGM 12 V batteries in parallel for the house bank.
- use a group 24 battery for the starting battery, could be either a standard lead acid or an AGM. (Daily load: 115 to 125 AH) (6 Volt batteries will not fit in the available space.)

Charging:
- Solar -- Already have two 80 Watt and two 55 Watt panels. (Panels are 12 Volt.)
- Alternator -- Standard 55 amp.
- AC charger -- to be determined.

Questions:
- Would it be better to set the system up using all AMG Batteries or to save some money and use a standard battery for the starting battery?
- What parameters should the AC charger have to satisfy the charging needs?

Your help in clearing up the water will be greatly appreciated.
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Old 18-05-2012, 19:03   #2
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Re: Battery Charging Questions.

If you mix battery types you will want a shore charger that can charge mixed batteries. Not all do. Beware.

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Old 18-05-2012, 19:19   #3
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Re: Battery Charging Questions.

Is there any reason I should not use an AGM Bat. for the starting Bat?
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Old 18-05-2012, 20:59   #4
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Re: Battery Charging Questions.

AGM's make fine starter batteries. Just make sure what ever battery you chose has enough cold cranking amps (CCA) available. Your engine manual will tell you what minimum you need.
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Old 18-05-2012, 21:38   #5
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Re: Battery Charging Questions.

I am not so shure about AGM batteries. For standard lead acid flooded types, avoid ferro resonant chargers, and go for three stage chargers that can respond to the need for bulk charge, and taper down to a float voltage. Avoid discharges below 50%, and keeping them fully charged is key to long life. The cheaper chargers will cook batteries that are up to charge and kill them. I got 13 years out of my house bank before retiring them when they were still functional.
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Old 19-05-2012, 04:30   #6
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Re: Battery Charging Questions.

Thanks for the good advice
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Old 19-05-2012, 05:49   #7
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Re: Battery Charging Questions.

If you buy a device like the Balmar Digital Duo-Charge, you can set up your system to charge the house bank only, and the Digital Duo-Charge will use the house bank to keep the starting battery charged. Then it won't matter what type battery you choose for starting.

Two group 31 AGMs = 210 Amp-hour capacity. Your daily load of around 120 AH will draw them down more than 50%, unless your solar panels are really putting out. Can you add one or two more AGMs?
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Old 19-05-2012, 06:33   #8
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Re: Battery Charging Questions.

A lot depends on how you are going to use the boat. What you have now will work for occasional use, but if you are going to live on the hook, you need to do a bit more. Your proposed battery bank is too small for 120 amp-hrs/day, and your solar panels will not keep up, as they are probably going to put out about 75 amp-hrs on sunny days. If its just for weekend use plus occasional cruises, you can make up the difference by running the engine (with a 55 amp internally regulated alternator, it will take about 2 hours to make up 50 amp-hrs).

In a boat your size, its getting hard to find room for more batteries and solar panels, so you should probably work first on cutting consumption. On my 45 foot sailboat, I generally consumed about 60 amp-hrs per day at anchor (refrigeration, VHF, computers, lights)and 120 amp-hrs per day underway (add autopilot and sailing instruments). If you haven't already done so, convert to LED lights, select all radios and instruments with an eye to power consumption, and put some more insulation inside the fridge.
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Old 19-05-2012, 07:57   #9
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Re: Battery Charging Questions.

I agree the battery capacity could be increased, but findidng the space for more batteries is a challenge. Plus, I still need a means to keep them charged.
I have thought of adding a portable generator,but then, Where can it be securly stored? Because the generator will have gas in its tank, I have to be concerned with gas vapors. Also, where to store the extra gas? I have a 400 watt KISS wind generator, but its shadow would no doubt affect the solar panels.
I am adding solar powered vents. This will cut down on some of the fan use. We do not have a frig. So, our at anchor AH's should drop below 70.
"I know of no greater challenge than trying to make a silk purse out of a sow's ear. It's kind of like owning a boat."
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Old 19-05-2012, 09:05   #10
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Re: Battery Charging Questions.

Optima red top is agm. Apparently a very good starting. I believe as long as the battery can deliver adequate CCA one is fine.

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Old 19-05-2012, 09:10   #11
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Re: Battery Charging Questions.

Living on the hook in the Tropics, we used about 120 AH per day and we had a Frigoboat keel-cooled freezer and reefer which accounted for a good part of that. What's sucking up all your juice?
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Old 19-05-2012, 11:11   #12
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Re: Battery Charging Questions.

Quote:
Originally Posted by Hud3 View Post
...What's sucking up all your juice?
I agree, you need to get some real numbers to determine what your electrical load is; otherwise, you could spend more money than you need to or else not have a sufficiently large storage and/or charging setup. Be sure to get a marine battery charger that will handle two banks. If you have a bow thruster you will need one for three banks. Marine chargers are expensive, maybe $200 for twenty amp and two bank, but you need one because automotive chargers connect the 12 volt ground to the shore power ground because it is cheaper to make the transformer all in one winding instead of one widing for 120 volts and another for battery voltage. This means electrical current can flow from one boat to another with huge increase in the likelyhood of electrolysis (severe corrosion)

I got on the internet and found some information on AGM batteries and flooded cell. Deep Cycle Battery FAQ
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Old 19-05-2012, 12:38   #13
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Re: Battery Charging Questions.

Quote:
Originally Posted by Duke 48 View Post
I am sure the answers to my questions are buried somewhere in this forum, but I have read so much about batteries, solar charging, alternators and AC chargers, the waters just keep getting more muddy.

My current plan:
- use two group 31 AGM 12 V batteries in parallel for the house bank.
- use a group 24 battery for the starting battery, could be either a standard lead acid or an AGM. (Daily load: 115 to 125 AH) (6 Volt batteries will not fit in the available space.)

Charging:
- Solar -- Already have two 80 Watt and two 55 Watt panels. (Panels are 12 Volt.)
- Alternator -- Standard 55 amp.
- AC charger -- to be determined.

Questions:
- Would it be better to set the system up using all AMG Batteries or to save some money and use a standard battery for the starting battery?
- What parameters should the AC charger have to satisfy the charging needs?

Your help in clearing up the water will be greatly appreciated.
Whatever you do I would get a small 2-5watt trickle charging solar panel for the starting battery and leave it mostly separate from the house system. A panel that small doesn't even need a regulator. This panel is to maintain the starting battery thru long periods disuse. It may be able to keep the battery changed if the engine is only started once a day or less.

IF the trickle charger can't keep up with the starting requirements either mount a second small alternator on the engine for it or get an echo charger (about $140). Personally I would go for the second alternator for redundancy.

For the house side it kinda depends on what you are going to do.

If you are not going to live aboard then the AC charger is not so important, you have plenty of solar wattage to keep up with weekend use, the solar panels will have 5 week days to make up whatever you took out over the weekend. Even if you take the boat out for 2-3 evenings a week plus all weekend the panels should be able to keep up. To get the most out of them get an MPPT solar controller.

If you are living aboard the situation changes. Then you need to consider how much time you will be at the dock. If you are living at the dock or coastal cruising and spending most nights in a marina, then an AC charger makes more sense. If you are spending 4 or more nights a week living aboard at anchor or underway on passage then you need to be looking at upgrading the solar panels and batteries, not getting a high end charger.

If you are spending 3 or 4 nights a week with AC available, then it would be a toss up to me, I would wait and see if I had problems with the amount of power I was consuming.

If you are not currently sure exactly how much you are going to be on the boat, try a wait and see approach.

Battery choice:

If you are going cruising away from developed countries, get flooded batteries, you don't want to mix and match and gels and AGM's are not very available in developing places.

My understanding is that gels and AGM's do not have the life expectancy of flooded and they are more expensive. The tradeoff is that flooded require periodic maintenance: you want to check electrolyte levels and densities monthly, top up with distilled water and equalize every 6mo or whenever there is a disparity between cell densities of >.020. I suspect the reason for the difference in life expectancies is that the gel and AGM batteries are manufactured as maintenance-free batteries when really they are reduced maintenance batteries, though how you would maintain them if you had access is something for a battery scientist to explain.

If you are staying in the developed world then AGM's will decrease the maintenance load at the cost of replacing them more often at higher cost.

Check this link for a long-term cruiser's take on the battery choice issue:Systems.


In summary:
Get a small panel to maintain the starting battery.
Get an MPPT controller for the solar panels.

Cruising away from the developed world:
Get flooded batteries.
Get a jug of distilled water and a good battery density meter
Make sure you have some means of doing an equalization.

Cruising the developed world:
Get whatever batteries suit your fancy
Make sure your controller will deliver the appropriate voltages for the type of battery you have chosen.

Wait and see how you actually use the boat before investing in a charger that may see little use.
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Old 19-05-2012, 16:59   #14
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Re: Battery Charging Questions.

Quote:
Originally Posted by Hud3 View Post
Living on the hook in the Tropics, we used about 120 AH per day and we had a Frigoboat keel-cooled freezer and reefer which accounted for a good part of that. What's sucking up all your juice?
Having not done extended time aboard away from the manira, I am making all of my estimates high.. It is one thing to do without some things for a short period of time, but I am trying to predict what it will take to keep the wife satisified after we have been aboard for a while. Depending on the cercomstances, I trully expect our electrical demands to go down after we have some experience.
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Old 19-05-2012, 17:12   #15
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Re: Battery Charging Questions.

Re MPPT regulators, should they be expensive where you live, it is good to weigh them against their cash equivalent in solar panels. Once you are up to the solar panel area limit and when this limit is big numbers, an MPPT regulator adds a little extra on top.

For small installations, more panel area is often the cheaper / watt solution.

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