Camping power requirements

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Camping power requirements

Post by Peter Connan » 08 Dec 2018 11:58

I have now been camping for several years. And a common feature of most trips is that the electricity runs out at some point in time. And I suspect I am not alone in this...

This has at long last driven me to the point of mathematics. This is always a bad sign, but bear with me.

I guess the most important camping accessory in terms of electricity supply is the fridge, as it probably uses more power than any of our other accessories and also because if it stops working it has the most detrimental effect on the holiday.

Now it's pretty easy to find out how much power one's fridge uses at full draw, but far harder to find out how much it uses in any given set period of time (keeping in mind that they basically use full power or nothing, because they switch on and off to regulate the temperature).

The one thing I did find which helped was a test done by WegRy magazine years ago. May 2012 edition, page 50-56 to be exact. In this test, they tested how much power 7 fridges used to cool down from 32C to 0, and how long it took. Then they measured how much power those fridges used to stay on temperature, and also how long it took them to get back up to 25C afterwards.

But this is not how I use my fridge. I tend to pack it at home and get it down to temperature on Eskom's finest and scarcest before setting off. But then I start opening it up, rooting around in it and closing it down again fairly frequently. Fortunately they also published some graphs of how the fridges cooled down, so I was able to figure out how long it took those fridges to get from 5 degrees to zero.

I thus set up a spreadsheet which calculates how much power each of those seven fridges would use in a 24-hour period if it was opened a number of times, assuming that each time it is opened 5 degrees is lost (I hope this is conservative, but guess if you have to dig something out the bottom or add something which is warm into the load it could be about right).

I also had a go at guessing how much more power would be necessary if the set temperature was lowered to -5 and the ambient increased to 40 degrees. Now I realize that ambient temps of 40 degrees are very rare and basically unheard of over a full 24hour period, I do think the temperature in a car parked and closed may easily exceed that, and I have been in many campsites where you basically have to keep your car closed to geep the monkeys out. And the ultimate aim of the process is to figure out how much power is needed to keep everything going under the worst scenario...
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Re: Camping power requirements

Post by Peter Connan » 08 Dec 2018 12:01

Here is a screenshot of the fridge power calculations:
FridgePowerUsage.JPG
FridgePowerUsage.JPG (104.41 KiB) Viewed 423 times
As you can see, opening the fridge makes a huge difference to how much power one needs. It makes far more difference than increasing the temperature differential.

This goes a long way toward proving that the best way to conserve power is by careful planning of how you pack you fridge and keeping it closed as far as possible.
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Re: Camping power requirements

Post by Peter Connan » 08 Dec 2018 12:26

The reason I started doing calculations at all was because of a conversation with a friend about solar panels, and the ensuing desire to figure out how much solar panel one actually needs.

This is is thus an attempt to determine how much solar capacity I would need to be able to park my trailer effectively indefinitely and keep the electrical system going, but I also calculated how long the battery would last. For this, I also added a few other loads, being a little bit of water pumping, lights and some charging of batteries.

Here are the results of a couple of scenraios:
Solar power requirements.JPG
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Re: Camping power requirements

Post by Peter Connan » 08 Dec 2018 12:27

And here is the spreadsheet, if anybody wants to have their own fiddle:
Camping Solar.xlsx
(17.42 KiB) Downloaded 14 times
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Re: Camping power requirements

Post by Kagiso II » 08 Dec 2018 13:45

With our Outreaches [up to 8 per year, Botswana Richtersveld and that in hot months I am totally dependent on the freezer to stay alive.
We bought a Waeco 55 wayyyy back, and it still works fine. The Royal deep cycle battery really kept it running for days without much re-charge. The new Willard is NOT that good, second day it is flat AND just alternator power does not get it up enough
I start at home by bringing it down to -18 c with pre-frozen foods, whilst freezing the trip food in the eksdom powered big boy.
I do NOT put cold drinks or water in the Waeco. Only the food that must be frozen. On top of the food box I put 5 pages newspaper [onder die deksel ja] and I have a "Picnic blanket" with one side a silver [almost like thermal blanket] That is folded double and draped over the Waeco.
I too, Like Peter, delve for what is needed. Pack in "Use sequence" is NOT my strong point

Last year I spent money on a 120 watt solar panel [17,5 volt max] (once it is mounted, it will be supporting the Willard all day.
I will buy Waeco again
I will NEVER buy Willard again.
Maybe Varta but definitely Royal again

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Re: Camping power requirements

Post by David M » 08 Dec 2018 15:36

The assumption I am making is that you are talking about spending an indefinite period in one place.
As with most things overkill works quite well as long as you have the space for it.
About to spend 21 days off the grid in the Transkei with no access to electricity our "Hotel Mdumbi" consists of the following;

In the trailer I have 2 X 80 W panels that I hinged and fitted under the tent (had to raise the tent by 20 mm which was a mission and a half) connected via a CTek D250S to two 105 Ah deep cycle batteries (got them with the trailer but will change to AGM once they are kaput).
SP.jpg
This runs the pump, LED lighting and a double door Snomaster 76 l Expedition Series (thick insulation). This fridge is used purely as a deepfreeze, ice storage and for ice making. Ice is only made during the day on sunny days. At worst this fridge is opened 6 times a day. Under ideal conditions the panels give me 9 A and the fridge draws 5.5 A at it's worst so I am safe.

Of course what about the drinks, rabbit food, dairy etc??? I have a second Snomaster single door 65 l fridge (Classic Series with normal insulation) on the back of the bakkie connected to a 115 Ah AGM that used to be in my 4.5 and is charged via a solar regulator from a 125 W panel. The panel is stored in the folded bed above the trailer while travelling and it is a mission to offload the fridge and battery from the bakkie but worth it for 21 days. I tested this setup for a couple of days in the garden and to simulate the constant opening and closing I left the door slightly open permanently. The battery actually gained ,2 of a volt over a couple of days.
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Re: Camping power requirements

Post by gupster » 08 Dec 2018 17:54

As always Peter, a very interesting article including the facts you meticulously provide. I think that there are many variables to the equation, as you pointed out, and I can only submit my experience. In my travels through Africa I was very happy with my NL 40 twin and never experienced the freezer section defrosting despite the extreme temperatures. I did find however, that I needed to run the engine for at least an hour a day to supplement the 80 W solar panel when I was camping for extended periods. The problem with solar panels is that they need to be in the sun, but you need to park your truck in the shade and the cable is quite short. I have subsequently fitted a regulator that allows a greater distance between panel and battery. But still, the arc of the sun makes a big difference to the amperage from the panel. I penciled a sketch of a frame that would tilt the panel for the best results but never made it. Perhaps this is your field of expertise Peter? I have had buy 3 deep cycle 120 AH batteries, during the 6 years of my travels and found the Royal to be sub standard. It is cheap and useless, in my opinion, letting me down after only 6 months of use. You get what you pay for. After my alternator expired when I was camping in Die Hel, I switched to the Delco deep cycle battery running my fridge and managed to get all the way back to PE. In my case, I probably used up the amount of times a battery can be deep cycled and am considering Gel as an longer alternative, but thats another debate
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Re: Camping power requirements

Post by Peter Connan » 09 Dec 2018 06:00

Thanks David and Barry

David, yes, this is for parking the trailer up for an extended period, but the fridge in the trailer will be the high-use one. There will eventually be a second fridge in the car, which will be used as the deep freeze and opened only once a day.

Barry, many solar panels come with built-in feet to get a 45 degree angle, but I recently read a couple of articles about solar panel angle. It seems here in JHB and further north, the ideal angle during mid-day hours is actually flat on the ground. In the afternoon, one should ideally angls it toward the west, but it seems the gain is only around 10%.

You will see in my calculation there is a safety factor of 0.35. This is to compensate for things like panel angle, dirt on the panel and the fact that thas panels actually get less efficient at high temperatures. Oh, wnd a good long lead as well.
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Re: Camping power requirements

Post by David M » 09 Dec 2018 06:41

Yes - Angle is important and once in the tropics flat is best (and hopefully no one stands on it). For further south it is easy to make up some adjustable legs that fold into the panel.
SPL.jpg
Secondly not all panels are created equally when it comes to efficiency when it is cloudy. After much trawling of the internet for panels available in SA I found that the German Solarworld panels seemed the most efficient and then they promptly stopped making the smaller panels. At the moment I would buy Renewsys.

Foldable panels are available which are great for space saving but I can not motivate the current cost of R 8,5 k for 80 W. Hopefully like all technology the price comes down as it would then be quite easy to transport 300 to 400 W.
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Re: Camping power requirements

Post by offroadbiker » 10 Dec 2018 09:00

And that is also where personal preferance comes in, I run 2 of them a 40L as a freezer and a 42L as my fridge (Both Engel) as I hate frozen vegies or melted ice so I prefer a dedicated fridge and freezer. But this also meens that I am constantly running 2 compresors which equates to a higher power usage....


River trip, and overlanding with one day stay overs does not create any problems as the alternator seem to keep up with the power requirements (If a remember correct I have to 90A batteries), but 2 days or more and power goes belly up.

I have a solar panel (dont know the size - probaly 80W) need to get it to Mr Forgey as for some reason it does not charge through the CTeck 250S, but I am also sure that 80W is not going to give me the required power to keep the 2 batteries happy......
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