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Old 11-29-2008, 11:06 AM   #1
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Re: 12V vs 110V

IMO any efficiency differences running the pump and propane alarm are not really worth considering, since they run intermittently (pump) or draw very little juice (alarm). If you are running 12vdc through an inverter to run a 120vac fridge, you're losing maybe 5-15% to inverter losses. Any inverter manufacturer should be able to tell you the efficiency numbers for their products. Also note that an inverter is more efficient the closer it gets to its capacity....i.e., a 600-watt inverter is more efficient inverting 500 watts than 100 watts.
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Old 11-29-2008, 06:02 PM   #2
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Re: 12V vs 110V

I would try and get an LP alarm that runs on dry cells like 9 volts. I just like the idea of them being totally independent of all other systems from a safety standpoint. It also makes it much easier to eliminate parasitic battery draws. When you store the bus you could just pull the battery out of it rather than have to disconnect wires.

As for what is more efficient for everything option is really more efficient. If the fridge draws 250 watts at 120 volts it will draw 250 watts at 12 volts for the most part. What's important is to design around your camping style. I think you're going to find that most pumps are 12 volts and I think that would be fine. They are low enough draw that I wouldn't even worry about it if you didn't have house batteries.

So...that leaves only the fridge to worry about. That's where it really comes down to where you are staying and such. If you plan to mostly camp where you can tie into shore power or you're going to haul a generator around then I think a 120 volt fridge will be the easiest, cheapest solution. The downside is that you will see those inverter losses when running off your battery bank going down the road as was posted above. But you won't need a big battery bank so long as you're staying close to shore power.

On the other hand, if you're going to be boondocking a lot I would suggest a 12 volt or propane fridge (or any combination of the 3 power sources). The reason for that is that you will have a large battery bank if you're boondocking. You might also have solar or wind generation, both of which operate at 12 volts. Basically, you would be eliminating that 10-15% inverter loss which could mean the difference between needing an extra solar cell or not. The downside will be when you park near shore power. If you don't have a 120 volt option you're going to be stuck relying on your battery bank, propane, alternative energy, or using an expensive converter to go from 120 volts to 12 volts.

I run my fridge strictly on 120 volts. Typically I'm not too far from shore power. I also have a generator I can use, albeit very loud. If I'm boondocking I can go for 2 days on my battery bank. I can recharge it to ~90% with the bus alternator if I choose or I can recharge it with my tractornator (as well as supply real time power) which is a surprisingly quiet and fuel efficient option.

The point is that you really need to decide for yourself what is going to work best I guess.
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Old 11-29-2008, 07:22 PM   #3
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Re: 12V vs 110V

These folks have some that run off of 12 volts. Claims that this one will run on 8-14 volts, more like they're saying that they'll still function no matter the state of your house batteries than that they're intended to run off of a transistor radio battery. They've got several others - pricey tho', like all things 'RV'.
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Old 11-29-2008, 08:38 PM   #4
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Re: 12V vs 110V

Or just pick up a RV style LP detector that runs on 12v and a pair of 6 volt flashlight batteries and run them in series...
The only problem I see with this, is the batteries will constanty run down, so it would make more sense to use a 12v converter with house battery back-up...


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Old 12-05-2008, 07:05 AM   #5
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Re: 12V vs 110V

I'm not sure that I would agree with smaller. Voltage doesn't matter when it comes to the physical size of the wire (only the insulation), but current does. Watts are volts times amps so if your voltage is 10% of 120 like 12 volts would be then your current has to be 10 times as high.

Let's say I want to run my desktop computer 20 feet away from my batteries. I'm going to say I need 500 watts between the tower's power supply and the monitor. That would require about 4.16 amps at 120 volts. 18 gauge wire could easily handle that so the much more commonly available 16 gauge would certainly do it. But if I wanted to run it at 12 volts I would need to supply 41.6 amps and over a distance of 20 feet (DC suffers from line loss much more than AC) I'm going to need a pretty darn healthy power cable. Now I might be able to get away with 8 gauge, but I would be at its limits and 6 gauge or 4 gauge would be a much better choice. Big cable like that isn't cheap or easy to run!
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