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post #1 of 18 Old 07-07-2014 Thread Starter
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Battery charger - small, medium, or large?

Talking to some friends and we were talking about chargers. Is it better to get a 40 Amp charger than a 10. Both being 3 stage chargers.

It's my thought that after the "bulk" charging, the remaining time to get a full charge is about the same for all chargers. AND, a bank can only accept so much during bulk without doing damage.

SOooo, unless you have a big bank (200 Ah or more), a bigger (read that as bigger $$$) will not save you all that much time.

So I guess my question is, is it worth it to spend the extra $ for the higher capacity charger?

Greg

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post #2 of 18 Old 07-07-2014
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Re: Battery charger - small, medium, or large?

The real question is how much time do you have? At anchor with a gen, or at a dock with shore power? What are your DC loads when at the dock or charging?

Too small a charger, asked to do high an output duty for long periods, will result in shorter life, especially the fan less "waterproof" variants that are ideally designed for small bass boats...

Flooded batteries enjoy long slow charges at about 10% to 15% of "C" but can certainly be charged faster than that with no issues.

Ignore the term "smart" with chargers. Most chargers that claim smart are still as dumb as a box of rocks.... There is one well known charger brand that enters float at 4 hours from the time it turns on. That is, turn it on and in four hours it will be in float whether your bank should be there or not. With a large bank it may NEVER attain absorption voltage before dropping to float. SUPER DUMB...

Lots of other chargers use the simple "egg timer" approach to absorption timing. Smarter chargers use adaptive algorithms that calculate time in bulk, % of output etc. to determine time needed for absorption charging. Better "smart" chargers also revert to absorption voltage every few days or weeks to gas the batteries to prevent stratification and limit sulfation. Staying in float indefinitely can be bad for batteries and some charger makers have finally figured this out..

Some chargers will pop out of float with as little as 10% of the chargers capacity and then start an egg timer again. A good charger will run to 90% or more of capacity and hold float before triggering absorption. A good charger will also recognize that "bulk period" was very short and will drop back into float quickly as opposed to running out an egg timer.

Sadly most charger manufacturers are not open about their chargers true operational status and the vast majority of chargers actually suck at being smart.......


The Sterling ProCharge Ultra or ProMariner Pronautic "P" are two of the smarter chargers out there... (identical chargers jointly developed by Sterling in the UK and ProMariner in NH).

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post #3 of 18 Old 07-07-2014
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Re: Battery charger - small, medium, or large?

10% of the battery bank is standard. 200 amp bank, 20 amp charger.
Here's a great article about marine battery chargers and installation..

Installing A Marine Battery Charger Photo Gallery by Compass Marine How To at pbase.com

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post #4 of 18 Old 07-07-2014 Thread Starter
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Re: Battery charger - small, medium, or large?

THANKS for the quick replies!

I am not thinking about this for a full time cruising boat. More than a day sailor, but less than full time. I was also thinking about a boat that most likely goes into a dock that has power, and will stay at least the night or more.

I was just thinking about the real world difference in time required to charge a battery between a 10 or a 40 A charger. AND, the real value if the boat was going to spend a lot of time at a dock.

I HAD a 10 A charger in my boat for quite a while. I then put in a 40 A charger and just do not see that it did much better at charging, just emptied my wallet a bit faster.

Greg

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post #5 of 18 Old 07-07-2014
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Re: Battery charger - small, medium, or large?

In your use 10 amps may be fine but it would depend on your loads. I'm installing a 10 amp charger on a family members 30' shortly. The boat lives on a mooring and has no refrigeration the only draws are a small gps vhf and a few cabin Lts and a 140AH bank. Basically the charger will top of the batteries when he's at the dock for a day two at the most, and to some times turn on when the boats on the hard being worked on. If the boat had refrigeration and lived on a dock I would up that to the 20 amp range of charger to better keep up with the more constant power draw.

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post #6 of 18 Old 07-08-2014
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Re: Battery charger - small, medium, or large?

I agree with Maine on the Pronautic P or Sterling - great charger.

Size can mean a faster charge if you need to charge quickly during a short dock stay. Regardless of charger size the batteries are the determining factor - they will accept what they need and no more for a given voltage.

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post #7 of 18 Old 07-08-2014
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Re: Battery charger - small, medium, or large?

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Originally Posted by Delezynski View Post
SOooo, unless you have a big bank (200 Ah or more), a bigger (read that as bigger $$$) will not save you all that much time.
I guess we all have our reference points. A pair of 6 volt golf cart batteries in series is a 225 Ah 12 VDC bank. I don't think that's a big bank. Now eight golf carts in series-parallel is a 900 Ah bank, which I think is a big bank. *grin*

500 to 700 Ah banks are pretty common in the cruising boats I see, even weekenders.

sail fast and eat well, dave S/V Auspicious

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post #8 of 18 Old 07-08-2014
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Re: Battery charger - small, medium, or large?

It also depends on the type of battery used in the bank. AGMs can take more charging current than other batteries. Full River recommends 25% of the Amp Hour capacity for the initial charge current (65A @ 14.5-14.9V) for my 260AH batteries.

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post #9 of 18 Old 07-08-2014 Thread Starter
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Re: Battery charger - small, medium, or large?

I guess what I was sort of trying to get a feeling for was something like;
Given the same battery bank of 200 Ah, 30% discharged
Given two of the SAME smart OR dumber chargers, one 10 Ah one 30 Ah

How long does it take each charger to bering the batteries to 100%

Something like (and this is just an example and has NOTHING to do with reality)
8 hours for the 10 Ah charger and
6.5 hours for the 30 Ah charger????????????

My point would be (IF the above was even close to real, and I am sure it's not) that if you were spending the night at the dock, the difference in time to charge would NOT make much difference! And if one charger was $100, and the other $300, I'd rather spend the extra $200 on sundowners

That is just me and I am NOT trying to tell any one what to do, just look at it logically.

Greg

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post #10 of 18 Old 07-08-2014
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Re: Battery charger - small, medium, or large?

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Originally Posted by Delezynski View Post
the difference in time to charge would NOT make much difference! And if one charger was $100, and the other $300, I'd rather spend the extra $200 on sundowners
Greg
Problem is that good quality chargers (Pronautic P for example) are not cheap. The chargers that are kind to your batteries are both larger and more expensive usually. I do not know of a really high quality charger that is low amperage and inexpensive.

If it is oversize there are no issues as the battery determines acceptance, not the charger.

Brian
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