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20-10-2017, 17:14
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#1
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Marine Service Provider
Join Date: Aug 2011
Location: St Augustine
Boat: '87 Irwin 43
Posts: 245
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Battery charger...the "correct" size
35 - 40 - 50 Amp charger...it doesn't really matter, does it?
I have two 12V 8D, wet cell, 200 Ahr batts in parallel providing 400 Ahrs as my house bank (I typically discharge no lower than 50% and currently boat is frequently connected to shore power most of the time).
I need to replace the batt charger and a fair amount of research indicates its not really important that I "correctly size" the new charger to my batt bank...
- because any charger between say 35 to 50 Amp capacity will work fine recharging my two 8Ds - the only real difference is that the 35 Amp charger will possibly take just a bit longer than the 50 Amp charger to recharge the batt bank back to 100%....correct?
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20-10-2017, 19:37
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#2
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Battery charger...the "correct" size
Yes, to a point. First don’t forget to subtract your house load from the charger size, so if your using 10amps, the first ten amps from the charger is just to break even, then your 35 is only a 25, but the 50 is a 40
Then some battery chemistries do better if they are hit pretty hard during recharge, like AGM and even regular ole flooded batteries may benefit as being charged hard can get the electrolyte stirring around preventing stratification.
Then if your ever away from the dock and on generator, a larger charger can reduce gen run times somewhat, however since battery acceptance rates fall off so fast, it may not reduce total charge times by as much as you may think.
Sorry to talk around in a circle, I guess biggest thing is to not to forget to subtract your house loads
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21-10-2017, 16:48
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#3
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Registered User
Join Date: Feb 2010
Location: Long Beach Ca.
Boat: Westsail 28
Posts: 353
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Re: Battery charger...the "correct" size
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21-10-2017, 19:02
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#4
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery charger...the "correct" size
No 20-30% of AH even with flooded, take into account may upgrade the bank later on.
AGM 50-60%.
And not necessarily much faster overall, but when powered by the genny (still need some solar) any reduction of daily runtime is worth the extra investment.
Plus required for AGM longevity.
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22-10-2017, 08:12
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#5
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Registered User
Join Date: Feb 2010
Location: US
Posts: 219
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Re: Battery charger...the "correct" size
Make sure that your battery charger has voltage settings (bulk charge voltage and float voltage) that match your battery type or battery vendor recommendations at the various average temperatures.
Monitoring amps may help for reasons given by others, but maintaining proper voltages will assure longer battery life.
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22-10-2017, 08:24
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#6
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery charger...the "correct" size
Best is custom adjustable profiles, future proof for whatever chemistry bank down the road.
Sterling ProCharge Ultra or ProMariner Pronautic P
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22-10-2017, 08:28
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#7
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S/V rubber ducky
Join Date: Jul 2007
Location: heading "south"
Boat: Hunter 410
Posts: 20,362
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Re: Battery charger...the "correct" size
Unless you plan to regularly discharge to less than 60-70% it will make little difference whether you have a 60 amp charger or a 40 charger. Even if using your generator the real world run time difference will only be 20-30 minutes. If you are spending a day in a marina on shore power it wouldn't any difference at all as the charger has all day.
This is personal real life experience.
__________________
Don't ask a bunch of unknown forum people if it is OK to do something on YOUR boat. It is your boat, do what you want!
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22-10-2017, 08:36
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#8
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery charger...the "correct" size
Yes obviously if always on shore power 10-15% is fine for flooded.
But 20-40% still needed for longevity for AGM.
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22-10-2017, 09:16
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#9
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,113
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Re: Battery charger...the "correct" size
Dyno batteries recommends charge rate of 6% of 20 hour ah rating up to 10% is allowed .
https://www.google.com/url?sa=t&sour...D6QV-maNrqIf_V
( deep cycle batteries)
__________________
Non illigitamus carborundum
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22-10-2017, 09:24
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#10
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,113
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Re: Battery charger...the "correct" size
East Penn is a bit ambiguous in their charging specs.
Here is what they say .
Proper charging is essential for maximum battery life. In gener-
al, the proper charging rate for lead-acid batteries is any rate
which doesn’t produce temperature higher than 115°F (46°C),
and any rate which doesn’t cause excessive gassing.
https://www.google.com/url?sa=t&sour...tZN-24JajLBc4J
__________________
Non illigitamus carborundum
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23-10-2017, 06:14
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#11
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Registered User
Join Date: Jun 2008
Location: Tampa, FL
Posts: 5,009
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Re: Battery charger...the "correct" size
To kind of summarize some of the things already said...
10% of total battery capacity is considered a minimum for effective charging of lead acid batteries. A bigger charger doesn't hurt, but getting a monster charger for a small battery bank is rather a waste of money. Of course, if you intend to increase the size of the bank in the future, then a bigger charger might be a good idea.
You pays your money and takes your choice.
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23-10-2017, 06:24
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#12
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cruiser
Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 5,030
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Re: Battery charger...the "correct" size
Quote:
Originally Posted by denverd0n
10% of total battery capacity is considered a minimum for effective charging of lead acid batteries. .
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Anyone know where or why this bit of perceived wisdom came about?
Can see it for trojans where the majority of t105's have a hard life and any less could lead to batteries not getting to charged over night. But when there's lots of time do the batteries know or care if the current going in is less?
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23-10-2017, 07:14
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#13
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery charger...the "correct" size
Yes certainly for AGM as stated above.
Have not seen minimums for FLA nor statements that longevity is affected, but you do want to get to true 100% Full.
Equalization protocol, which I only do manually I believe benefits from higher rather than very low current rate.
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23-10-2017, 07:17
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#14
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery charger...the "correct" size
Note unless it were a critical longevity factor, mfg would not state minimum charge rates, since that implies their product is not suitable for millions of potential customers.
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23-10-2017, 08:33
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#15
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,113
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Re: Battery charger...the "correct" size
Quote:
Originally Posted by denverd0n
To kind of summarize some of the things already said...
10% of total battery capacity is considered a minimum for effective charging of lead acid batteries. A bigger charger doesn't hurt, but getting a monster charger for a small battery bank is rather a waste of money. Of course, if you intend to increase the size of the bank in the future, then a bigger charger might be a good idea.
You pays your money and takes your choice.
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I have to question the 10% to be the minimum for charging .
I have just provided the spec sheet from a major deep cycle battery manufacturer who's stated that optimum for their batteries was 6% of ah capacity. I actually have never seen the 10% number actually stated in any manufacturer spec sheet for Fla charging.
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Non illigitamus carborundum
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