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Old 01-29-2009, 10:43 PM   #11
Mini-Skoolie
 
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Re: Introduction and questions

I've read that many Walmarts allow overnight RV parking, but I think they might frown on parking a bus there and doing things like removing the seats or changing the oil. I suppose it couldn't hurt to ask, but I'm not going to count on being allowed to do maintenance in a parking lot.
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Old 01-29-2009, 11:08 PM   #12
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Re: Introduction and questions


Quote:
Elliot, your short statement is useful: it cuts right to the heard of the matter and advises me what to do. I would love to hear the reasoning behind that advice, if you don't mind spending the time to educate an ignorant newbie.
Well now.... You don't sound all that ignorant, so you probably know NOT TO place too much weight on so-called advice from some old bum in California.

As for the reasoning, you spelled that all out yourself -- I just summed up my impression of it for ease of reference.

If you buy one of these, it would make sense to have a competent shop examine the bus --since you, by your own admission, is no mechanic. You should ask for a basic safety inspection, which is a routine thing for commercial trucks and does not cost much. You are concerned about exessive wear in the steering, brakes, etc. You should also ask if they can evaluate the condition of the engine and the transmission; including oil analysis, which is not expensive. Oil analysis is most useful when you do it regularly so the results can be compared over time, but any analysis is better than none. And it could be very useful in a high milage engine, as they may be able to tell you if the bearings are worn thru to the backing metal. Look for a Caterpillar dealer, so you get a mechanic who is familiar with these engines.

I cannot say much about frost damage, since we don't have much frost around here. We get down in the low 20s some nights, then it warms to at least the 40s before Noon. Today (January 29), it was in the 60s. To protect against those frosty nights, I pour a couple of gallons of RV tank antifreeze in my tanks, and run it thru the fresh water pump and toilet. RV tank antifreeze costs just three or four buck a gallon in most auto parts stores. In colder climates, you need to do more, yes.

Refrigerators. Refrigerators draw a lot of electricity. My tiny RV refrigerator (which I have not inststalled yet) draws 10 Amps. I tested it with one 12 V deep cycle battery and inadvertantly left it overnight, and it killed that battery -- I mean, dead, buried, forever.

On the other hand, the propane feature in an RV refrigerator is said to be very cost efficient. I have no experience yet, but word is they use very little propane.

This makes sense, since RV refrigerators work on a different principle from house refrigerators. RV units work on -- strange as it may sound -- heat. A friend of mine found a discarded RV fridge at a recycling center, and the sun was shining on its exposed mechanism and... it was cold inside! Heating with electric resistance draws a lot of electricity. Heating with a propane flame, much cheaper. Yes, they need to be level so the liquid inside the cooling coils does not puddle. But I don't know the tolerance. I'm thinking of mounting mine in some sort of gimbal, so I can level it no matter how I'm parked.

Yes, you can tap into the air brake system for other purposes. Truckers do it all the time. But get a truck mechanic to show you where to tap in, and use proper hardware. Don't expect to get much use out of pneumatic tools though, as pneumatic tools draw a HUGE flow of air and the bus wil not be able to keep up.

That will have to do for now. You are doing a pretty good job of answering your own questions.
I suspect that nine out of ten skoolie projects are never finished. That's OK, so long as you are prepared to tow it to the scrap yard and give it to them -- as I did with my first bus (which cost $250,-).

Word is, many Wally-Worlds allow RVs to park overnight, because RV'ers are usually good customers. But don't even think of doing mechanical work in anybody's parking lot. Very bad for our overall reputation.
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Old 01-29-2009, 11:39 PM   #13
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Re: Introduction and questions

Lots of information, thanks!

I agree that propane refrigerators are an interesting and useful bit of technology, but I just don't like the idea of having to carry and refill propane!

Here's a link to the chest freezer to refrigerator conversion: http://www.mtbest.net/chest_fridge.html. This claims 0.1 kWh per day. A bit of searching turns up results from other people who have tried this; one person claims 0.264 kWh/day for a very large freezer, and another cites 0.125 kWh/day as their result.

It seems to me that 150 or 200 watts per day is pretty reasonable. That would easily be handled by a couple of large solar panels, or by running the generator once a week if you have a moderate sized battery bank.
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Old 01-29-2009, 11:50 PM   #14
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Re: Introduction and questions


Let's wait for some knowledgable electricians, but I'm worried about your "watts per day".

A Watt is a measure of energy flow at any given instant. Volts x Ampere = Watts.
My little Dometic draws 10 A at 12 V = 120 W. Continuously. Right? Wrong?
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Old 01-30-2009, 12:35 AM   #15
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Re: Introduction and questions

Yep, 10A at 12V would be 120 watts. Running constantly, that's 2880 watts per day. I doubt that the compressor would be running constantly though.

The chest freezer to refrigerator conversions are claimed to be up to 10 times more efficient than regular fridges. Part of this is because freezers are usually insulated better than refrigerators. The rest of the efficiency comes from the fact that a top loading freezer doesn't spill all the cold air out onto the ground every time you open it, unlike a normal fridge.

I'm pretty sure that my math is correct. I understand all the voltage / current / power stuff pretty well. The only part I'm skeptical about is the figures that people have recorded after doing a freezer conversion, which is why I used 3 different sources for those numbers.

Edit: it just occurred to me that RV fridges don't have a compressor, right? So my comment was a little nonsensical. Still, I would hope that they don't draw power constantly, no matter what they do with it. Logically, they have to regulate how much cooling they do in some way. Otherwise a fridge couldn't maintain a constant temperature while the outside temperature fluctuates.
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Old 01-30-2009, 12:43 AM   #16
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Re: Introduction and questions

I've done a bit of research on the chest freezer to fridge conversions and I am quite impressed. There are also some very efficient production chest refrigerators you can buy, although they are very expensive. I will probably go with a homebuilt chest freezer conversion for my bus.

-Ray
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Old 01-30-2009, 12:47 AM   #17
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Re: Introduction and questions

Just playing with numbers some more:

If I had unlimited funds and no concerns about weight, I'd like to have a bank of 6 250AH batteries. At 50% usage (to preserve battery life), that would give me 9000 watt hours of usable energy. It would also weigh 1000 pounds and cost about $3500 (for AGM batteries and charger.)

More realistic would be a bank of 3 200AH batteries. This would provide 3600 WH at 50% discharge, weigh 400 lbs, and cost about $1600.

Going for a really simple setup, we could use just consider one single 200AH battery. At 50% discharge, this would give us 100AH at 12V, or 1200 watt hours. If the inverter is 85% efficient (which is a very conservative estimate), we could get 1020 watt hours of 120V electricity (8.5 amp hours).

If a converted chest freezer uses 200 watt hours per day (which is also a conservative estimate if we can believe reports), this battery would run a fridge for a little over 5 days.

If we consider the RV fridge using 10A of 12V power constantly, that would be 120 watts. We don't have the loss from the inverter, so 1200 watt hours being used at a rate of 120 watts should give you 10 hours of running time.
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Old 01-30-2009, 02:44 AM   #18
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Re: Introduction and questions

Elliot Wrote:
Quote:
Let's wait for some knowledgable electricians, but I'm worried about your "watts per day".

A Watt is a measure of energy flow at any given instant. Volts x Ampere = Watts.
My little Dometic draws 10 A at 12 V = 120 W. Continuously. Right? Wrong?
Yes.

Right - If it draws 10A at 12v then it draws 120 W.
Wrong - Not continuously (unless it's very poorly made or you always leave the door open). 120 W x 24 hours would be 2880 Wh (or 2.88 kWh) per day .

A load like a light bulb or fan left turned on WOULD be a continuous draw. Anything like a fridge that cycles draws the maximum only when it's running. Also, most (if not all) data plates list the peak instantaneous load, not the average. For example, if you got the 10 amps from a data plate, not from a meter, it might be 10 amps for a compressor start, and 5.5 amps when cooling. Add in a little draw between cycles if the control circuits are electronic.

The devil in the details on accumulated usage is how often and how long does YOUR fridge run? Everyone's mileage varies on this. How much stuff is kept in it? How often do you open the door? Are you always rotating warm food in, and cold food out, or just grabbing out a frosty beverage? Do you re-stock daily or weekly? Is the temperature outside the fridge 90 or 35? Some people gradually add jugs of water (like one per day) into the empty spaces in their freezers for thermal mass to hold heat, and to cut down on warm air exchange when the door opens. The goal is to reduce the number and length of the energy use cycles (but don't block the circulation of cold air).

The only way to tell what YOU use is with a run timer (think hour meter) or even better a watt-hour meter. If the fridge is 110 volts, an inexpensive Kill-A-Watt or Power Angel between the wall outlet and the load will display the accumulated usage for your personal equipment and style. If you have a DC system, a moderately-priced system meter like a Bogart TriMetric is very useful to show both usage and battery health.

[Note to self: Self, order that Kill-A-Watt you've been meaning to get, and go measure the freezer load.]
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Old 01-30-2009, 01:31 PM   #19
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Re: Introduction and questions


Thanks, Redbear! That certainly makes sense.
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Old 01-30-2009, 05:39 PM   #20
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Re: Introduction and questions

Well, no bus for me, at least not yet.

The buses went for $2550, $2450, and $2500. A similar one with a flat tire sold for $2485. Apparently 25 year old buses with over 300,000 miles are worth more than you might have thought.
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