Boiling water efficiently

[Pete7]

Originally Posted by coopec43

Absolutely!!

I was looking around for a 500ml kettle but found they were around $60. Two liter kettles are only $17 so now I do as you do and just half fill the kettle

That's a shame. Like Franziska, we use a small 0.8L kettle half full to make two cups of tea, saves anyone over filling it (me). Its plastic and we don't let it run to the full 4 minutes it take to boil and then turn off. As Noelex points out, not much gained in the last minute of heating. Takes 4m 15s to boil 0.5L with a1Kw element if you let it bubble away. Perhaps 3m30s to hot enough for Government work.

This is the cheap and cheerful approach and accept that a kettle may last 3 or 4 years in full time use, then replace.


https://www.argos.co.uk/product/4821...kettle:1:117:1

[Franziska]

Originally Posted by coopec43

Absolutely!!

I was looking around for a 500ml kettle but found they were around $60. Two liter kettles are only $17 so now I do as you do and just half fill the kettle

We paid 19€ for our 1/2 Liter one..

[noelex 77]

Originally Posted by seandepagnier

where did you get your vacuum insulated 12 volt kettle?

The ones I find all have teflon and other toxic coatings.

Our vacuum kettle was from Amazon and is made by Vektra model VEK-1504. The body is double walled vacuum insulated stainless steel. The lid is plastic. There does not appear to be any coating. The manufacturer claims it is “BPA-Free”.

[noelex 77]

This particular kettle does have some advantages and drawbacks compared to most regular models.

Advantages:
Energy savings.
Variable temperature.
No (or almost no) steam released even when boiling (100°C) selected. This is due to the sealed lid and a special pulse boiling program.
Low power (1800w) so will work on a smaller inverter.
The contents stay hot enough that you can have a second cup without reboiling anything.
The lid is locked and sealed (until you press a button). This means no water (or only a few drops) spills if the kettle is knocked over, reducing the risk of burns, especially while sailing.
The base is large making the kettle very stable.
There is a continual temperature readout of the contents.

Drawbacks:
Expensive.
Larger than normal for the volume. The double wall insulation adds bulk.
Larger than normal base. Therefore more bench space used.
Low power (around 1800w) although due to high efficiency it boils as quickly as conventional 2200w model)
There is no external indication of the water level ((this would compromise the insulation).
Without removing the lid the pour rate is slow.
The lid needs to be removed to fill.

[seandepagnier]

Originally Posted by noelex 77

Our vacuum kettle was from Amazon and is made by Vektra model VEK-1504. The body is double walled vacuum insulated stainless steel. The lid is plastic. There does not appear to be any coating. The manufacturer claims it is “BPA-Free”.

It looks nice but a high price.. but it does not run on DC. I am looking for something that uses DC power. I do not have an inverter. Everything I have runs without inverters, and this would require quite a large inverter as well. The inverter is 85% efficient so would negate a lot of the advantage of vacuum insulation.

[noelex 77]

Originally Posted by poiu

How much more power is used with a conventional boil-to-switch-off kettle?

Good question. It will obviously be worse than the energy used by the variable temperature, but uninsulated kettle I measured for the above test.

By keeping the temperature just below boiling, the variable temperature models save the energy that would be lost converting the liquid into steam. Just as important it also avoids extra water vapour released into the boat interior. It can also make drinks taste better by avoiding the burning of coffee or tea.

I would expect the power savings to be worthwhile, but I have not tested this.

Out of interest, the insulated kettle avoids some of the above drawbacks by having a sealed lid to avoid the water vapour release (and recyle the energy). It uses a pulse program in the final stage of boiling to avoid any pressure build up.

[noelex 77]

Originally Posted by seandepagnier

It looks nice but a high price.. but it does not run on DC. I am looking for something that uses DC power. I do not have an inverter. Everything I have runs without inverters, and this would require quite a large inverter as well. The inverter is 85% efficient so would negate a lot of the advantage of vacuum insulation.

I am also a fan of running everything on DC if possible. However, running high power devices such as these kettles on DC has many practical problems.

With a DC kettle you are limited to low power, typically 150w or less. The very slow boil is not very efficient, as a lot of heat will be lost during the long heating time.

A bigger problem for many smaller boats with simple electrical systems and no inverter is how to generate sufficient electrical energy to support heating water electrically. Unfortunately, DC kettles do not solve this issue.

[seandepagnier]

Originally Posted by noelex 77

I am also a fan of running everything on DC if possible. However, running high power devices such as these kettles on DC has many practical problems.

With a DC kettle you are limited to low power, typically 150w or less. The very slow boil is not very efficient, as a lot of heat will be lost during the long heating time.

The loss is not as much as you think. A typical alcohol stove uses the least amount of fuel if boiling water in 30 minutes even though most are designed to do so in 5-10 minutes. This is with a typical pot not vacuum insulated and no wind. It is not a direct comparison, just pointing this out as it surprised me to learn this.

The losses for vacuum insulated are very low for long heating times. They stay burning hot for hours. The extra losses in the battery at high power are probably more unless you have tens of kwh, which you may very well have, but a smaller battery you end up with an optimal speed to balance battery losses vs very low thermal losses from vacuum insulation.

You are not limited to 150 watts on DC. This is 12-13 amps. I dont really think 30 amps at 12 volts is unreasonable. Furthermore, you are making the AC from DC, so either way its the same amount of power, somehow you supply the inverter with this, it isn't limited to 150 watts, so why not the cooker instead?

I also have a 48 volt battery that weighs 10 pounds and stores 1.3kwh. It can probably supply 50 amps, but at only 20 amps, this is still 1000 watts, and no problem to supply for 5-10 minutes.

I took a $3 vacuum insulated mug from walmart.. and put test tube in it with 4x 3d printer 60 watt heaters (in series for 48v instead of 12v) so 240 watts, but.. it just boils whatever liquid I put in the test tube and overflows them, so its not viable, I need a better heating element. I was considering running power through the right length and gauge of heating wire, like stainless or nickel wire submerged in the water.. but I am not sure if this is safe to drink the water?

A bigger problem for many smaller boats with simple electrical systems and no inverter is how to generate sufficient electrical energy to support heating water electrically. Unfortunately, DC kettles do not solve this issue.

The DC kettle helps by eliminating inverter loss. I think it is obviously more suitable for people who dont use grid power.

This is not a bigger problem. I have plenty of power most of the time. I have 4 out of 6 solar panels stored below, and even still too much electricity I disconnected one of my 2 solar panels that is out and even covered the other one with a towel and battery is still full today.

I also built a tow generator, it can supply 3 amps underway. Its not enough to cook continuously, but hours of this should store up enough to cook.

I have always had excess power onboard most of the time except with several days of overcast, when I have just enough. After 3 days without sun I would stop cooking with electric.

[rslifkin]

Originally Posted by seandepagnier

The loss is not as much as you think. A typical alcohol stove uses the least amount of fuel if boiling water in 30 minutes even though most are designed to do so in 5-10 minutes. This is with a typical pot not vacuum insulated and no wind. It is not a direct comparison, just pointing this out as it surprised me to learn this.

With a flame-based heat source reducing heat can help efficiency as you've found. The smaller flame means more heat goes into the kettle instead of up and around the sides of it. But if the heat is being put directly into the water (induction stove or an electric kettle) then heating faster is more efficient as there's no extra heat loss from increasing the heat source output but the shorter heating cycle means the kettle loses less heat to the surrounding air.

[grantmc]

For the best results when making coffee most baristas would be looking for water temperature less than boiling; in the range of 92-95 degrees.

Here's amusing little video that explains what an electric kettle actually is for our American cruisers.

Kettles

[noelex 77]

Originally Posted by seandepagnier

You are not limited to 150 watts on DC. This is 12-13 amps. I dont really think 30 amps at 12 volts is unreasonable.

30A @12v is still only 360W so this is going to be a very slow kettle. Most commercial 12v kettles are even worse. 150w or less is typical. This is not enough for most boat owners.

Originally Posted by seandepagnier

Furthermore, you are making the AC from DC, so either way its the same amount of power, somehow you supply the inverter with this, it isn't limited to 150 watts, so why not the cooker instead?

There are a few reasons:
High power 12v inverters are readily available, but high power 12v kettles are not.
Inverters can be located close to the batteries, but this is difficult to achieve with kitchen appliances.
The large power cables supplied to an inverter will run many other high power devices. The power can distributed with thin cables.
Connecting the kettle with large cables is impractical and unwieldy.

Originally Posted by seandepagnier

I took a $3 vacuum insulated mug from walmart.. and put test tube in it with 4x 3d printer 60 watt heaters (in series for 48v instead of 12v) so 240 watts, but.. it just boils whatever liquid I put in the test tube and overflows them, so its not viable, I need a better heating element. I was considering running power through the right length and gauge of heating wire, like stainless or nickel wire submerged in the water.. but I am not sure if this is safe to drink the water?

This type of experimentation is great to see. Please keep going and post the results here.

[PaulCrawhorn]

A 12V kettle? No, even an immersion coil in a single cup is too slow.

Jetboil is great, use with small bottle topside.

[Kit_L]

We have not made the full transition to a big solar system yet, so we run a hybrid system that requires that I run the generator once a day for an hour (cooking, water heater, heating fan, charge batteries) and a small solar system to finish the batteries off the next day (weather permitting). So, when running, I boil water in a conventional kettle then. But we have a $19 AUD camping stove for the morning cuppa, and as @rslifkin mentioned above, ¾ flame boils faster than full. Saul Griffiths ("The Big Switch") claims that 67% of gas heat heats the room, and only 33% heats the water when boiling a kettle, but that must only be a rough average, because careful flame adjustment both heats the water faster, and saves gas.

We are looking forward to installing a 2 x 440W panel setup, and we were planning a 3,000W inverter (this is the de facto 'standard' setup in this area), but careful monitoring of power use over the last year suggests that we will do fine with an 800 or 1,200W inverter, and adding two or four more Trojan T-105s to our bank of two. Very old school in this era of LiFePo4 batteries, but we have found these reliable and simple.

[Simi 60]

Originally Posted by Kit_L

We are looking forward to installing a 2 x 440W panel setup, and we were planning a 3,000W inverter .

We found that a 5000 was only a few hundred dollars more if going victron multiplus.
Charge increased from 70amps in the 3000 to 120 amps in the 5000
Well worth the extra coin imho.

[SV_FlyingTigress]

Originally Posted by Sea Beezy

Sounds like kettle boiling and general cooking need to be segregated when it comes to induction. If you have enough solar the convenience of induction is alluring but requires conductive cookware so all the old pots and pans are replaced. I prefer espresso made Italian style but the bialetti coffeepot is not induction compatible. So I had to get a little plate adapter. Who has room for all this stuff?

Just want to relax and enjoy a coffee for 20 minutes and not think like an engineer but its so hard.

Bialetti induction compatible moca pot.. I use mine all the time. Works great set temp for 220 to warm up and 212 deg F once espresso starts showing:

https://www.amazon.com/Bialetti-Indu...13722473&psc=1