BETTER 12V STOVE PROJECT

BETTER 12V STOVE PROJECT
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One of the reasons for undertaking this project was to provide
a better stove but equally is was my attempt to be able to cook
dinner legally during total fire ban days in Victoria.

(See Exploroz post 39298)

While there are a couple of alternatives, I came to the
conclusion that a generator setup driving 240v appliances
was an overkill for a tent camping setup out of the back of
the car. This especially as its hard to get 240v appliances now that
consume under a 1000w , making a large generator necessary.

12V stoves are available from about $30 at Dick Smith to hundreds of
dollars for stainless steel versions however all I have seen or reviewed
have been just barely adequate because there elements are less than 100w
and hence simply take to long to cook.

We have one labeled "Burton" from a camping store and its typical of a range
of these things that all look like they came out of the same Chinese factory.

It takes 35min or more to heat up a couple of already thawed out pies or pasties.

This project is about how I modified my stove to get more out of it.

Being into electronics I have often solved these issues by simply increasing
the voltage with a 12-15v convertor or similar. In this project I also
considered using resistors as supplementary heating elements by gluing
them with high temp glue next to the existing element.

However in the end I choose a different path which costs about $30 and is
probably a lot easier to implement for non-electronics people.
This approach provides a significant performance boost.

Whilst sitting under an apple tree and having a serious ponder about the
stove, an apple fell from the tree and hit the stove on the top lid.
(give me some slack here!)
I glanced again at the stove and then it dawned.
This stove probably consisted of two almost identical halves.
One half, the base, has a metal tray heated by an element and cable, and
the top half just has a metal tray blank of the same dimensions.
Certainly the moldings and food trays look the same.
If this was true then perhaps I could buy a second unit, and take off its
heated tray half and mate it with the heated half I already had, such that both the
top and base halves would then have heating elements.

Instantly, I would have doubled the heating power, and this, in effect is what
we did with success.


CONSTRUCTION
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Unfortunately you can't just get the bottom half off one stove and attach it
to the first because the top and base plastic moldings are different because
they incorporate opposite halves of a hinging mechanism.
What has to be done is to remove the heated metal tray from one stove and
substitute it for the non-heated top tray in the other unit.
This turns out to be dead easy as the trays are held in by just a push together
rubber seal around the top lip. It takes all of 10 seconds to remove the rubber
seal with a screwdriver, lift up the metal tray and then cut off the 12v
power lead attached.

You have to connect the 12v power between the new top half to the power
in the other base half and I did this by drilling holes in the back of
the black plastic cases in each and fitting rubber grommets (Jaycar Cat. HP0702).
On the electrical side, you just get about 300mm of the twin flex lead
you cut off and wire/solder it across the existing elements leads in the
base, then pass the wire out of the base thru the grommet and run it back
thru the grommet into the new top half.
Doesn't matter which way you connect the wires as the heating elements
attached to the base of the trays are electrically isolated from the trays.
I used a bit of heaksink over the connections to insulate them.

An alternate approach to paralleling the wires would be to just run
the two existing leads with plugs attached to each stove half.
This could give you the option of having a two speed stove, but would require
two power sockets unless you came up with a switch arrangement.

With the two trays now connected, you could just pop them back into there
respective cases halves however I decide to go one better.
When disassembling the unit, you will notice that they use insulating
pads, a sort of semi-rigid fibre glass batt. These fitted poorly in mine
but now with 2 sets I had more material. I cut up the second set and placed
the bits into both halves of the new stove to make a proper fit.
Further the original stoves had no insulation down the sides. I sliced the batts into
10mm thick wafers and put a piece down every side of both halves (8 extra pieces).

Adding the insulation made it tricker to push the metal tray sections back in with the rubber seal, you really need 3 hands, but with use of screwdriver I got it all reassembled correctly, once I realized that the rubber seal has lips which should go over the metal tray edges when re-fitting.

PERFORMANCE
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The elements in these stoves are thermostatically controlled at 150c, so the maximum temperature is no greater. Shorter cooking time comes from the fact that the long warmup time is reduced, the stove tends to have 150c all around it, not just at the bottom, and the heat coming from the top and sides tends to bake things not just heat.
However heating from the top is not as effective as bottom heating where food is in
direct contact with a hot surface.

My tests on pasties were that the cooking time was reduced from 35min to 25min
with better heat distribution thru the food. The cooking time is not much quicker
in my oven at home unless set to burn, as heat still has to get thru the food.

An unexpected bonus with this stove came when I realized that by leaving it open
I could actually cook 2 seperate dishes at once. This requires alfoil over each to
keep the heat in and of course takes us back to 40min cooking time - still two
elements in the same size package is great.
Well I thought it was as I cooked up rice in one tray and mixed
frozen vegies in the other tray for tea the other night.
But I think the family may have thought mum could have done
better seeing as we were actually at home.

POWER REQUIREMENTS
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The unit probably takes no more total power to cook as its still thermostat
controlled, and perhaps even less, however it can draw double the current at
(16 amps max) and your fuses need to be checked.

My "Burton" unit came with heavy power leads and a poor plug with a 15amp
internal fuse. I used this initially, still with its 15amp fuse, however
I consider the 12v cig lighter plug inadequate and changed it to one of
those "lion brand" versions which have 4 copper contact points and no inline fuse.
If sticking with an inline fuse it really should be 20-25amp.
I use a separately wired 12V (6mm sq copper) accessory lead in my car
fused at 30amps.

My Dick Smith stove had an undersized 12v power cable and I did not use it except
for the 300mm section to run between the two heated element sections.

SOME NOTES
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The 12V electrical wires should be keep on the outside of the insulation and not
touching the metal trays.

My stoves where branded differently (Burton & Dick Smith) but they are the same moldings.

CONCLUSION
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We were very pleased with the result achieved for about 3hrs effort and while
this stove is no substitute for the gas stuff its faster and better performance
means it is now acceptable. It is legal to use on total fire ban days.
The unexpected bonus of cooking two seperate foods without taking more
gear is really useful.
Combining this with the ability to begin heating food in the car before we get back
to camp and hence take less off-battery power has meant that a previously marginal device has become a useful camping accessory.

Robin Miller
10/11/2006

P.S. Exploroz does make make it easy to post projects , however the
project is on our Yahoo site as a word document with pictures.

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