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  #1   IP: 99.255.242.163
Old 01-28-2012, 09:07 AM
Jimmy Jimmy is offline
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Battery Charger Question

Guys.......I have a "TRUECHARGE 10" battery chargers that easily takes care of both batteries. I plan on adding a second battery to the house side to compensat for the new refrigeration unit. I will start with two new deep cycle batteries, and use my currently owned ,best as the starter battery.
Referencing the charger manual , I am aware I can't mix battery types, however , nowhere is it stated that I can't run with more than two......
Will my charger support this set up?
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  #2   IP: 67.78.241.34
Old 01-28-2012, 11:37 AM
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I ran a 10 amp Charles Industry with 5 and 6 deep cycle group 31 s for many years until the charger finally gave up the ghost. With 12 volt refrigeration you will most likely need to step up to something like a 30 amp charger.

Last edited by hanleyclifford; 01-30-2012 at 01:08 PM.
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  #3   IP: 199.173.226.236
Old 01-30-2012, 09:09 AM
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By mix "types", they usually mean mix chemistry. If all of them are wet, gel, or AGM you can use one charger.
That said, 10 amps is going to be marginal for what you are doing.
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Old 01-30-2012, 01:23 PM
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Lightbulb

Yes, you can. 12v batteries connected in parallel are still 12v..when connected in parallel, you add the Amp hours together of each battery to get a total Ah for that bank. (i.e.. two 85Ah 12v batteries in parallel = 170Ah.) You really should have them the same age & size and definitely the same chemistry.

People also often use two 6 volt golf cart batteries in series, which equals 12v. Usually, you get more Ah per pound with golf cart batteries (and supposedly more tolerance for deeper discharging), and they are available globally, even in less affluent countries. In this case, you don't double the Ah. Two 150Ah 6 volts in series = 150Ah @ 12 volts.

All other things already mentioned about charging capacity should be considered. A 10 amp charger may not fully charge a big bank overnight if you ran the refer all day long during the day.

Since boaters generally like to abuse their batteries, I think the best bang for the buck is still good old lead acid. I cannot see the advantages of high $$ AGM or even gel...& they have trickier charging profiles, which I think is the main reason they say not to switch chemistry..each type charges differently.
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  #5   IP: 67.78.241.34
Old 01-30-2012, 01:41 PM
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Quote:
Originally Posted by sastanley View Post

Since boaters generally like to abuse their batteries, I think the best bang for the buck is still good old lead acid. I cannot see the advantages of high $$ AGM or even gel...& they have trickier charging profiles, which I think is the main reason they say not to switch chemistry..each type charges differently.
What Shawn said +1. Don't waste money on fancy chemistry; spend it on more and bigger cheap wet cell from WalMart or NAPA. The sealed, gel, mat or whatever type only have marginal value if you plan on heeling 180 degrees.
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Old 01-31-2012, 06:26 PM
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Ok... So I simply need to compare the 3 elements......Amp Hrs vs weight vs cost and decide what I need.
How many Amp hrs capacity would be recommended for a vessel that is using 12 volt refrigeration and off a dock cord , for lets say no more than 48 hrs., and a few instruments at the helm?
( and Stanley, I am sure you weren't referring to your friendly neighbors to the north as " less affluent " Sorry could resist!
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  #7   IP: 67.78.241.34
Old 01-31-2012, 06:36 PM
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Refrigeration can kill a battery almost as quick as an inverter. In your situation I would have two deep cycle, group 27, 29 or 31s, switched separately.
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Old 01-31-2012, 07:26 PM
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See if you can look up power consumption for your refrigeration. Then you have to calculate how much time it is running at that power level and then work your calculations up to 48 hours. Take that amp hour value and make up a battery bank with at least twice that capacity. You might be better off running your engine twice a day for a few hours like the diesel people do to keep your battery system from becoming too drained.

If it were me I'd forget the refrigerator, just bring along a cooler for 48 hours. I've known people who have cruised the caribbean with no refrigerator, think out of the box, eat more fresh vegetables, etc.
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Old 01-31-2012, 07:45 PM
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Here is a sample calculation. I have a 2.5 cu ft Norcold which pulls about 4 amps. During a 48 hr period running at 50 per cent of the time, that is 4 amps x 24 hours = 96 amp hours. That will just about kill even a good group 31. In practice I run the thing overnight 12 hrs x 4 amps = 48 amp hrs, but this drainage is spread over 3 group 31s of, say 100 amp hrs each to be conservative. This means that the refrigerator is only drawing down each battery 48/3 = 16 amp hours. Many hands make light work. FWIW
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Old 01-31-2012, 09:25 PM
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Jimmy, no..the point is golf cart batteries are available worldwide..even in most 3rd world countries. The same may not be true of gel & AGM. I have a few Canadian friends you know..

One of the things we need to know is the duty cycle of your fridge unit and how many amps it draws when running, which is the example Hanley & Jonathon gave above.

I have a buddy with a fancy Beneteau 343. On a cruise this summer, I had to carry my battery over in the AM (and disassemble half my electrical system to get some 4# cable) to jumpstart his boat one day because his fridge was sucking all his batteries down overnight. There was an issue with the compressor, but nevertheless, these things need to be known & calculated ahead of time. I also think he left his switch on "ALL" (oops!) It was nice for the 35 year old boat with two 'little' batteries to save the day..

I have one 95Ah house battery and it serves all my needs..but I have an icebox and 90% of my lights are LED...I also only use the inverter for the PC and chartplotting when the engine is running.
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Last edited by sastanley; 01-31-2012 at 09:30 PM.
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Old 01-31-2012, 11:24 PM
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My EZ-Kold holding plate system draws 6 Amps at 12 V when running. The specs say that in a properly insulated icebox, it should only run about 6 hours total out of 24. That's 36 Amp-Hours per day right there.

A single group 31 runs around 97 AH rated capacity. BUT, you should never discharge it below 50% of capacity in order to maximize it's lifetime. This only leaves you with about 48 AH of _usable_ capacity.

And then there's the issue of charging profiles. With a smart charger, you can cram the first 80% of the battery's capacity in pretty rapidly at a high amperage rate, but the last 20% must be done at a much lower rate to avoid damaging the battery. This means extended charging time to get that last 20%. If you're using the engine to charge, it's likely that most of the time you'll only run it long enough to get the battery up to 80%. Thus, the available capacity is further reduced. Instead of 50%, you've only got 30% to work with! For a group 31, this works out to just 29 AH.

So, with my cold plate, lighting, and electronics, I need (and have) two group 31's in parallel to get through 24 hours, and need to run the engine a few hours every day to keep up. But my batteries are now 7 years old.

As a rule of thumb, calculate your total AH consumption for a single day, and multiply it by 3 1/3 to get the AH capacity of the battery bank you need to get through one day. If you need to go longer, further multiply by the number of days. You can go under this, but you'll be going through batteries a lot faster.
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