12v water boiler / kettle?

shirk

Active member
Is there any of these that don't suck? Looking to boil about 750ml of water for morning coffee on days when breaking out the stove is undesirable. We were out this past weekend and it was raining changing over to wet snow before heading off to go ski. Just needed a coffee and nothing else needed to cook. Being bear country here in BC everything get's packed away at night, nothing left out. Being able to plug in some water to boil while feeding the kids and packing away sleeping gear would be handy.

We're in a VW Eurovan weekender, so poptop with no inside kitchen. No plans to add an inside kitchen as we're happy to cook outside or if the weather is too crappy just eat no cook meals inside. Need to figure out the coffee.
 

workerdrone

Part time fulltimer
Would be pretty cool if someone would make a standalone water kettle with induction technology, even if you had to run it off an inverter at 120v
 

Herbie

Rendezvous Conspirator
The problem with 12v water heating is the damned laws of thermodynamics.

Just some basic back-of-the-envelope calculations:
750ml water, raised from 65°F to 210°F (cool room temp to just off the boil), using a typical 1000W heating element (~70% efficient), would take about 7 minutes.
This is, not coincidentally, about the wattage of a standard $30 countertop electric kettle.

1000W @ 12vdc is > 80A, which is an absolutely massive draw for that amount of time. Everything between battery and heater would need to be like 2-gauge (large jumper or welding cable sized) just to avoid turning the wire into a separate (very inefficient) space heater. (Or worse, a fuse.)

Slightly more practical would be to use a 120v (or better yet 240v) electric kettle with a ~1500w or 2kw inverter. (Remembering that you lose even more efficiency in going from 12vdc to 120v or 240v AC, but at least you only need giant cables between the battery and the Inverter.)

So that's probably your best answer. Get a good 1.5kw-2kw inverter, wire it up to a good deep cycle battery (preferably LiPO since you'll be pulling big amps on it), and plug in a standard home electric kettle.
 

workerdrone

Part time fulltimer
I was thinking that induction would be much more efficient than resistance heating but that may not be the case for a dedicated water kettle where all the heat gets directed into the kettle basically via closed insulated device.

For stovetop and separate pans, it's much more efficient than resistance or gas, at least at home.

For campers, gas is still cheap and easy on the budget end of things
 

Herbie

Rendezvous Conspirator
I was thinking that induction would be much more efficient than resistance heating but that may not be the case for a dedicated water kettle where all the heat gets directed into the kettle basically via closed insulated device.

The problem isn't the efficiency so much as the amount of energy that's needed. Rerunning the same calculation I posted above, but changing to an ideal 100% efficient heater (impossible, but as a theoretical limit) changes the run time to 5 minutes. So on the one hand, you've saved ~30% of your total watt-hours versus a less efficient heating method, but since the goal is still to raise the same volume of water by the same number of degrees, that extra 2 minutes probably doesn't mean much in terms of re-designing the power-supply part of the heating system.

You could play a lot of games, and say "What if I have a perfect, 100% efficient heating method, and I'm willing to wait 10 minutes for the water to boil?" That would let you use only a 500w "perfect" heater - so it will "only" draw about 42A at 12v. You've used roughly the same watt-hours as before (half the amps but for twice as long), but at least now you're in the 6-gauge cable ballpark, and maybe a cheaper inverter will do. (Although a cheaper inverter might give away more efficiency...) Mind you, 42A is the kind of draw that absolutely tortures AGM batteries, so you're still shopping LiFePo, etc.

The short version is that Ma' Nature is a tightwad, and she don't give nothin' for free.
 

shirk

Active member
Thanks for the info @Herbie.

I was hopeful that there was something but appears not. Would be nice to not have to carry a second small stove like a Jetboil or MSR Recator and deal with the fuel canisters for very limited use.
 

plh

Explorer
Thanks for the info @Herbie.

I was hopeful that there was something but appears not. Would be nice to not have to carry a second small stove like a Jetboil or MSR Recator and deal with the fuel canisters for very limited use.


Watts is watts - a Jet Boil is around 3,000 watts (10k BTU) but energy is directly from dino (no conversion to electrons first). Dino makes great heat.
 
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