Battery Life ...

[Buccaneer]

I've a '83 48' MY with the original Frigidair Fridge, an ice maker and an 18 bottle win chiller on the sundeck. I installed an inverter this year, and find I get about 4-5 hrs in the two 8D house bank batteries.

ok, the point of the inverter was to not have to run the damn genny all night long.

4-5 hours... Does that sound right?
Should I be thinking about an additional one or two 8D house bank batteries?

Thoughts from the collective?

 

[bostonhatteras]

do the math. find out the running wattage of each appliance and how long each runs. figure this out for a 24 hour period. take the number of charging periods in the same 24 hour period and divide appliance wattage by this number of charging periods and you'll have the ac load between charges. now divide this resulting number by 12 (for 12 volts) and you'll get a reasonably accurate amp-hour demand on the batteries. now figure out how much amp-hour demand you are putting on the batteries from all the dc lights blowers pumps etc and add this to the approx ac amp-hour load. take this number and multiply by 3 or better yet 4 and you'll see how many amp-hours you need your batteries to have. cheapo lightweight 8d batteries will die very fast tied to an inverter, use top quality DEEP cycle, not starting batteries. dont forget even the inverter uses a certain amount of juice to do the conversion, its not free so to speak. it even uses juice doing nothing! also bad dc connections use electricity by converting it to heat!

 

[bobk]

I get easy 12 hours from 6 Workaholic golf cart batteries. No battery monitir so I have no idea how low they get, but the low battery light has not come on. Newer Whirlpool double door self defrosting refrige and a wine cooler on aft deck. The wine cooler is in a cabinet which holds the heat, so I have a muffin fan to exchange the air. Make sure everything is well vented.

Bob
Chateau de Mer
1981 48MY

 

[bobk]

I should have also mentioned that I use a Yandina battery combiner to keep the house bank charged underway without running the generator.

Also the 48's have a very convenient spot for the extra house bank. Mine are right above the forward engine room bilge pump. I have a shelf above them which makes ER access very convenient. WaltP thought it might even be easier than without the shelf.

Bob
Chateau de Mer
1981 48MY

 

[Vincentc]

How would series 31 batteries serve as starting batteries for 671's. The 31's I looked at had 950 cca's which appears to meet DD specs for the engines.

I currently have 4 8d's paired in parallel between the engines. One pair starting the port engine and generator and the other starting the stbd engine and providing the "house" Want to add an inverter and thinking about having seaparate individual starting batteries for the 671's and the generator and a separate bank of golf cart batteries for the inverter and house. I would like to eliminate the individual weights of the 8d's.

Any experiences to share regarding 31's as starting batteries?
Thanks,
Vincent
43DC Lilly Marie

 

[Sonny]

Vincent - give the genny it's own starting battery, let the mains share a battery for starting that is charged by one of the mains. The other main can charge the deep cycle house battery. When starting your mains, start the one that charges the starting battery first. This system ensures you can start your engines in all but the worst unimagineable combination of events.
Buc - if you use your boat a lot then your inverter battery should be sized so that it is drained no more than 25% after the desired time of eight hours, so a battery bank 4x larger than your 24hr draw is required if you want any decent life out of the batteries. If you only plan on doing this a couple times a year, then a 50% drain after eight hours might be acceptable and give you decent battery life. Draining beyond 50% will drastically shorten your battery's life span. The easiest/cheapest way to tell how low your batteries are getting is by monitoring the inverter's charge and how long it takes to replenish the battery ie 100amp charger takes 1 hour to top up a 200ah battery means you drained it 50%, but as mentioned there are losses so this is only good as a general idea of how much you're using and chargers charge on a curve to further complicate your math. The better way is a battery monitor that tells you how much you've used and how much you've got left. I installed a freedom 2000 with the link 2000 panel in my previous boat and it told me everything there was to know about my battery bank.

 

[Pascal]

i get about 20 hours out of an 880AH bank (@ 12 v) for the GE fridge/freezer and other misc. stuff, down to almost 50% discahrge which Golf Cart batteries can handle.

the fridge is the big draw... you can extend run time by lower the T stat when you're going to be relying on inverter. also, a 20 year old fridge is not going to be as efficient as newer ones...

another issue is at what voltage does your inverter cut off? usually this can be adjusted, depending on the batteries you use, you can sometimes push them a little more and increase run time. as mentioend above, GC batteries can take a 50% cycling.

2 8Ds (200/240AH each i assume?) arent enough for such a load, you might get thru the night but i'd definitely increase the bank.

dont overlook charging, how big is the charger? inverter-chargers usually put out faster charging rates than stand alone. If you're using a stand alone, maybe you're not recharging the bank enough between runs.

 

[Buccaneer]

OK, so I need to research more and read Calder more. I'll get back to ya'll.
Thanks.

 

[REBrueckner]

Bucc.. they simple answer is: if you add another pair of 8D batteries you'll get twice the service from them...and if you have large enough charging capability, you'll be able to charge them faster as well....as noted its a good idea to avoid discharging below about 40% to 50% of battery amp hour capacity to maximize the power you'll get from a battery over it's life....deep discharges reduce overall life cycle amp hours delivered.

AGM batteries are superior but cost more...they recharge about three times as fast as wet cell and do so more efficiently and provide more amp hours over their life than most wet cells...in other words the cost per amp hour is less but they cost more up front...

 

[REBrueckner]

And here is the complete design answer from my prior post:

Revisit: Reducing Genny Run time for Battery Charging - 06-05-2008, 01:26 PM
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I originally posted the following as shown below.....except for a few minor editorial changes for clarity here. Today it's especially relevant since if your burn say $1 gal per hour running your genny for battery charging, and can reduced that by, say, two hours daily, you not only save about $9 or $10 daily on fuel, maybe $300 monthly, but likely another few dollars daily on wear and tear and maintenance, maybe $350 or $375 total over a month.

DC System Design - 12-03-2005, 04:32 PM

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When your dc battery charging source (amps) is properly matched to your battery bank capacity (amp hours), and your battery bank capacity is matched to your daily load in amp hours, you can reduce genny run time to a minimum.

This is VERY valuable for long term cruising away from shorepower because a balanced dc (battery) system reduces genny run time (and wear and tear), limits noise periods, and extends battery life. It pays for itself in marina fee savings.

Design steps are NOT rocket science:
(1) Determine your daily amp hour load, (say, 150 amp hours, is typical).

(2) Pick the number of batteries (amp hour capacity) of your choice at least three or four times the capacity of your daily load, or more, (This limits daily discharge cycle depth resulting in longer battery cycle life, permits more rapid charging, and daily charging reduces sulphation.) (4 x 150 daily amp hours is about 600 AH, about three or even four 8D's to serve a 150 amp hour daily load.

(3) Size your charging source to about 20 or 25%% of the battery amp hour capacity for wet cell, 40% for gel, 100% for AGM. (If wet cell, you should size your charger(s) at about 20% or 25% of 600 or about 120 amps to 150 amps for three 8D batteries. AGM's will take close to 600 AH!)

You should be able to recharge from, say 50% to 85% or 90% or so in an hour!!!.

Poof: you have a well balanced dc system! Of course you need the genny power (size) to charge at this level, and perhaps power AC loads at the same time (such as a water heater and microwave) if so desired.
One way to help this along: perhaps eliminate electric cooking (a heavy draw) and convert to propane. If you run your genny all day anyway, as for air conditioning, the above accomplishes little.


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Rob Brueckner
1972 48ft YF for sale