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Is Ice the Best "Battery" for Mobile Living?

Since the last post ended with a bit of a downer, let's see if we can crawl out of the slough of despair today. Let me be a good sport and admit that I am temporarily stymied in finding an economical, high-ground-clearance tow vehicle for pulling my 3000 pound converted cargo trailer/travel trailer and storing two bicycles inside.

Usually when a problem has you temporarily beaten, it is best to put it aside and work on something else.  So let's get to work on reducing the weight of camping gear and personal possessions. One way or another, lighter loads will pay off when it comes time to select a new tow vehicle, whatever it is.

After water -- be it clean, grey, or black -- batteries are the heaviest factor that an RVer has any control over. I am using four 6-volt, golf cart, flooded, lead acid batteries: model GC-2, made by Interstate. With cables, clamps and boxes, let's round off their weight to 70 pounds each.

Downsizing from 4 to 2 such batteries reduces the weight of the trailer by 140 pounds. Imagine how many clothes, dishes, and toys you would have to get rid-of to add up to 140 pounds! 

Unfortunately I don't have an energy-summing device to give you exact numbers. Suffice it to say that my DC-voltage-powered refrigerator is the biggest energy-draw in my trailer, and therefore that is where the improvement must come from. (It's a 12 Volt-DC, compressor-based refrigerator: the Whynter 45 quart model, sold at 

Let us not think of a battery as an electrochemical device, but as an example of the more general category of "energy storage devices." There aren't too many other examples of energy storage devices besides the battery, but one that we usually overlook is the heat capacity of water and the heat exchanged in freezing water.

During the day, my nearly 500 (nominal) watts of solar panels usually charge up the four golf-cart batteries by mid-morning. Then, the rest of the day, the whole system is just maintaining a full charge on those batteries. Therefore much of the capabilities of the solar system is being wasted.

Wouldn't it make more sense to run the solar system full blast, all day? If I used my Whynter refrigerator as a freezer for various jugs of water (rather than as a refrigerator for food), all of the solar capabilities will be "soaked up" during the day, freezing water. Then, at night, I could just turn off the Whynter frig/freezer, in order to get by on merely two golf cart batteries. The ice jugs would then be transferred to a common inexpensive "Igloo" or "Coleman" cooler chest, which would serve as the refrigerator for my food. 

The Whynter unit has thus gone from being a food refrigerator to purely an ice manufacturing machine. I have done something like this before. Basically it works, but well enough to downsize 4 golf cart batteries to 2?

If the reader knows any success stories (or failures) with this technique, please comment.


Unknown said…
Sounds like enough work. Check into LiFePo battery. Do some research first and don't just buy. the marine travelers use them a lot.
have you checked any of the smaller vehicles equipped with a "camper package" or towing package. I had a Chevy S10 that was rated same as a 3/4 ton payload.
John V said…
We do something similar with our solar all the time. During the day, we run the refridgerator and freezer off the inverter using the solar panels. We'll also turn up the cooling setting higher. When the sun stops, we convert back to propane and lower the cooling setting on the unit. It usually doesn't need much if any propane in the cool of the evening. We also do all of our electronics charging during the day. So we get our batteries back up to 100%, get our fridge/freezer extra cold, run our well pump if needed, and recharge anything needed by maxing out our solar use during the day. At night we rarely see our batteries drop below 80% and we use about 4 gallons of propane a month. Since our batteries get back to 100% almost every day, we also don't need to equalize them. Shallow draw down and not needing to equalize equal longer battery life.
Yes, that is the same energy-storage principle I am talking about. I'm considering taking it to the next level.
Oh Chester, don't get me started! If only they still made the S10, Sonoma, the Ford Ranger, and the Chevy Astro.
edlfrey said…
I am thinking that you would freeze two 1 gal or two 1/2 gal containers of water the first night then put them in the cooler for the day. I would further assume that they would stay in the cooler for 24 hours with you froze two more containers and would then cycle them.
The added water will reduce your 140 pounds or weight reduction some but even at 140 pounds that would be less than a 5% weight reduction on a 3000 pound trailer. What is the weight goal? Why?
Anonymous said…
I'd say, wire up just two and see if they survive an abnormal run of cloudy days. If they have no issues, you can stop carting around the unneeded extras. Personally, I'd first look at how long it takes for your freezer to cool down whatever water you need to a good freeze. I'm not a big fan of adding complexity and inconvenience just to gain theoretical efficiency, unless whatever system I already have is not cutting it, but that's just me and I see the attraction of losing weight. But, I'd frequently forget to turn on/off the freezer at the right times, or be home to transfer the jugs by 6PM. I'd need daily alarms, I guess. Not gonna happen. Good luck with your experiments!
5% ? Correct, but you are thinking with the Linear Model. The Threshold Model would be better for this case.

The trailer weighs in at its GVWR. Now there is nothing exact, absolute, or god-given about that number, but it IS a useful discipline to pretend that it is. We need that discipline. So taking off 5% when you have 0% "safety margin" is a big number, in a sense.
Good, sensible advice, DougB.

It would have made the post too long to describe how I revere ice. Remember, I camp in the Southwest. Let me try to be succinct: have you ever watched the movie, "In Quest of Fire?" There is something primal in playing the ice game, just as they played the fire game in the movie. It captures my imagination.

But when push comes to shove, I will suppress my fun and games and choose the path of ruthless utilitarianism and frugality. Does anyone know how long a 12 volt DC compressor-based refrigerator is supposed to last when used on a daily basis? I have no idea -- this is my first one. Therefore the cautious thing is to use it as a refrigerator rather than a freezer.
edlfrey said…
Yes, if you are at the Threshold then any reduction is worthwhile. I did not realize that was the situation with your trailer.

I think the batteries that you have are rated at 232 amp hours for a pair of them. The 12v compressor refrigerator uses about 65 amp hours/day which would leave you about 50 amp hours/day for all other power demands. If you can live within that 50 amp hours restriction then a two battery bank would not usually exceed a depth of discharge of 50% and you should be fine without doing any water freezing or have a separate cooler.
Transfer Efficiency of energy produced from renewable energy sources to storage batteries can significantly influence cost of the overall system. Poor transfer efficiencies of lead acid require 20% larger solar installations when compared to LYP lithium storage systems. Lead acid batteries due to their high internal resistance have a transfer efficiency of 72 - 76% compared to 96% transfer efficiency of the LYP battery. A 50W, Solar panel installation can produce 400 whr of energy during an 8 hour period, but only 304 whr of this energy will be stored by lead acid batteries, meanwhile a 40 watt solar panel installation with LYP batteries would store the same amount of energy during an eight hour period.

now you can ditch 1 panel & 2 batteries if you switch to Lithium