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bhebby
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# Posted: 5 Dec 2011 20:20
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Does anyone have any opinion on me running the following.
rechargable 12 volt battery
power inverter
recylced chandelier from a friends renovation
4 -40 watt equivalent(use 9W)from Home Depot
I have about 100.00 into the whole thing. Mtn Don suggested 2 golf cart batteries in lieu of the one 12V which I have asked the guys at the battery shop to keep an eye for when they get reconditioned units. I hooked it up and it works like a charm and the cabin is small...one room 12x20. I guess my question is how long will it last using it 7 hours a day? Could I also run an ipod off it without worrying about losing juice?All I need is some lights and tunes I can get by with those alone.
Would I gain a lot by adding an extra battery?Thanks in advance for any advice.
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MtnDon
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# Posted: 5 Dec 2011 21:53
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Four lamps of 9 watts each for 7 hours a day works out to about 24 amp-hours a day on a 12 volt battery system and allowing for inverter conversion losses.
If you had 2 typical golf cart batteries in good condition connected in series you could run those lights for about 4.5 days. That would discharge the batteries to about 50%, the maximum safe level. That assumes a coldest temp for the batteries of 50 F; amount of time available would be less if colder, more if warmer.
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bhebby
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# Posted: 5 Dec 2011 22:04
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I know you feel that golf cart batteries are superior but is that close to or similar on a regular marine battery? I keep checking with interstate batteries becasue they sell blemish batteries very cheap. Can I gang up a few golf cart batteries with this one?What would be an economical way to keep these on a trickle charge? Thanks a lot I know nothing about this topic and its tough to ask a question when you cant desrcibe it intelligently,its nice to get answers from those who have just done it and understand it. thanks again-Bhebby
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MtnDon
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# Posted: 5 Dec 2011 22:19
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A golf cart battery has approximately twice the amount of lead in it as an RV/Marine battery. GC are normally 6 volts and weigh about as much as a 12 volt RV/Marine battery. You need two GC to make up the 12 volts but generally have twice the amp-hours as one RV/Marine battery. (figures rounded). So two RV/Marine batteries in parallel have more or less the same capacity as two GC batteries in series. But the GC are better longer lasting batteries.
If you already have a RV/Marine battery it may be best to stick with another of the same. Age differences can be a factor though when adding to an established system. One safe way to look at it is if you add a new battery to another battery that is, say 8 months old, you have just made the new battery "older".
Not a good idea to mix different types and capacities of batteries either. Not good for getting the optimum battery life.
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CabinBuilder
Admin
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# Posted: 6 Dec 2011 10:15 - Edited by: CabinBuilder
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Posted by Rob_O on 5 Dec 2011 21:04:
Well, let's do a little math here....
Your fixture uses 36 watts, at the input to the inverter that's 40 watts (assuming 90% efficient inverter)
40 watts at 12V = 3.33 amps * 7 hours = 23.3 amp/hours... let's call it 25 to make the math easy
A typical Group 31 RV battery is around 100 AH. Battery life is directly related to the depth of discharge. One day of use is 25% discharge which is fine. 2 days is 50% which is not good on a regular basis. 3 days is 75% discharge and you have seriously damaged your battery. Try it another day and your battery is now a doorstop
I get my tunes from a pair of computer speakers and a satellite radio receiver, it uses about half the power of a CFL. From experience I can tell you running the radio all day and a few hours of a 13W CFL for cooking/eating/cleanup uses 10 to 15 AH per day. One battery is barely enough for a weekend and I have maybe half the power usage you do
Hope that helps
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bhebby
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# Posted: 7 Dec 2011 15:05
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that does help and thanks for supporting it with data. Would I double my output by adding a second and or third battery that is the same?thanks a lot very helpful.
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TomChum
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# Posted: 7 Dec 2011 21:10 - Edited by: TomChum
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Quoting: bhebby Could I also run an ipod off it without worrying about losing juice?
An easy way to estimate relative battery capacity is to use weight. Assume your iPod weighs 4oz. Its probably half battery weight, so 2 oz, (=1/8 lb)
A golf cart battery might weigh 66 lbs. 66*8=528
I predict that a golf cart battery will run your iPod appx 500 times longer than the iPod runs on its own battery. If anyone wants to dispute this 500 I say listen to the iPod for 500 batteries' worth then get back to me.
Short answer: Don't concern yourself with the amount of juice used by the iPod. An iPod amp that the iPod plugs into, that runs external speakers, would use a lot more juice than the iPod itself.
For lighting, LEDs use appx half the power that CFLs use -----> that's another way to save on batteries. 12v LEDs cost $15-$20 each, but 4 LED bulbs (~$60) could eliminate the need to buy a $150 2nd battery.
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Rob_O
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# Posted: 7 Dec 2011 23:57
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Quoting: bhebby Would I double my output by adding a second and or third battery that is the same?
Doubling the number of batteries doubles your reserve capacity, and so on... You still have to recharge those batteries but that's another subject
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TomChum
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# Posted: 8 Dec 2011 00:16 - Edited by: TomChum
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Quoting: bhebby Would I double my output by adding a second and or third battery that is the same?
The way to decide this. Stay at your cabin, and use your lights and electricity as you normally would for one 24hr period. In the morning check your battery voltage with regards to this table.
Quoting: MtnDon more FWIW 
If in the morning you are down 20% (12.42v) consider adding a battery. If you are down 50%(12.06v) then you REALLY need to add a battery.
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MtnDon
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# Posted: 8 Dec 2011 01:03
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Good plan. Just remember to take the voltage reading after the battery has been sitting with no load, or very little load, for several hours, as in first thing in the morning. Voltages drop under heavy loads, but will likely recover some when "rested".
Cold battery temperatures will also affect the voltage reading; lower temps = lower readings.
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