1000w vs. 3000w kettle

[jbweston]

There should be a pressure sealed kettle option. With pressure you could easily exceed 100C and there would be no heat loss from vented steam. It would be much easier to insulate it as well.

Wouldn't the problem be how to get the water out of the kettle into your teapot or mug, as when the pressure was released it would explode messily and into a cloud of superheated steam and flying boiling water? I'm no physicist, but isn't this the problem with removing a car radiator cap when the coolant is held under pressure at higher than ambient atmospheric boiling point?

 

[Neeves]

The only caveat is I suspect it has lost some of its vacuum over the years as it does not keep water hot as well as it did when new.

If the vacuum had failed then it would fail totally and the exterior of the vessel, or the exterior of the vacuum chamber, would be hot (as the absence of vacuum would mean the 'vacuum chamber' is full of air). If your kettle exterior is still cool - the vacuum (its never a vacuum) will still have integrity.

Many, cheap, insulated pots are simply filled with polystyrene, not a patch on a vacuum (or Dewar) flask.

Jonathan

 

[MontyMariner]

The longer it takes to boil the more heat it will lose to the surroundings.

More to the point, only fill the kettle with the amount of water you intend to use. After boiling, excess water that's left to go cold has wasted supply power and time for it to boil.

 

[AntarcticPilot]

The amount of energy required to raise the temperature of the water from ambient to boiling is the same no matter what the wattage of the kettle. Assuming equal efficiency of heat transfer from the element to the water, a 1000w kettle will take 3 times as long to boil the same volume of water as a 3000w kettle. So it comes down to whether your system can support the higher wattage - which requires three times the current, with consequences for both cabling and battery capacity, as others more knowledgeable than I have already pointed out.

How about going halfway:? A 1500w or 2000w kettle would be faster. Another alternative MIGHT be a water boiler - there are two types; one boils a cup full of water on demand; the other maintains a reservoir of water at just below boiling (ideal temperature for tea and coffee!). The former only uses the energy required to boil the water required, and the latter only uses the energy required to replace heat lost through the walls of the reservoir once the water has reached temperature. Both are much more efficient than a kettle. The latter would be dangerous underway; the potential for harm of a large reservoir of boiling hot water is obvious. But it only draws 680w and that intermittently once the temperature is reached.

 

[PaulRainbow]

2.2 kW was just the size I chose. There are vacuum-insulated kettles of lower wattages available if you are limited by your battery or inverter size. The benefits I mentioned are still applicable.

I suspect it was a typo, but the OP actually indicated he had a 28 kWh battery bank.

That equates to about 2,000 Ah and weighs over 200Kg, so as you say, likely a typo.

Perhaps the OP can clarify ?

@GaryMiller

 

[wonkywinch]

I remember those 5/600 watt travel kettles that ran on 100-240v without switching.

It ran OK in the UK but plugged into a 110v US socket, took almost 25 mins to boil a cup of water as, of course, the power generated was a quarter of the UK, not the half you might assume by logic of half the volts equal half the power. Of course due to Ohms Law (V2/R).

 

[fredrussell]

... Your inverter itself will gobble power, even (or more so) on standby.

Most inverters these days will consume very little power whilst on standby- they sense load and switch themselves on automatically when you turn an appliance on.

 

[noelex]

The amount of energy required to raise the temperature of the water from ambient to boiling is the same no matter what the wattage of the kettle. Assuming equal efficiency of heat transfer from the element to the water, a 1000w kettle will take 3 times as long to boil the same volume of water as a 3000w kettle.

This assumes there is no heat loss to the air while the kettle is heating the water. A low-wattage kettle will take longer to boil and therefore will lose more heat to the air and surrounding surfaces. It requires slightly more total energy.

However, this is only part of the picture. I agree that the capabilities and efficiencies of the electrical system are usually a more important consideration for a boat.

 

[Alex_Blackwood]

That equates to about 2,000 Ah and weighs over 200Kg, so as you say, likely a typo.

Perhaps the OP can clarify ?

Agree, clarification required. Paul's figures are in line with the Delong unit mentioned in #6 Nowhere does the OP mention an inverter

 

[AntarcticPilot]

This assumes there is no heat loss to the air while the kettle is heating the water. A low-wattage kettle will take longer to boil and therefore will lose more heat to the air and surrounding surfaces. It requires slightly more total energy.

However, this is only part of the picture. I agree that the capabilities and efficiencies of the electrical system are usually a more important consideration for a boat.

Of course, perfectly correct - as I indicated, I was making simplifying assumptions! But the real bottom line is that heating water takes a LOT of energy; sadly water has a very high specific heat capacity, so it takes a LOT of energy to heat it.

 

[PaulRainbow]

Just how heavy is a 28KWh battery pack? If it really is that capacity no worries about any kettle as long as the inverter can cope.

Sorry, that's not correct.

What just about everyone keeps missing is the Lithium battery will have a BMS which limits the current, if that current is exceeded the BMS will shut the power out off.

The 2000Ah one in post #6 (which i can't see anyone fitting on a boat !!) has a 300A BMS. So unless absolutely everything else on the boat is turned off and the inverter is a decent quality/efficient one it will shut down when you turn a 3Kw kettle on.

The typical "drop in" Lithium battery being fitted to boats are fitted with 200A BMS, so even a 2Kw kettle would be unsuitable.

 

[johnalison]

Of course, perfectly correct - as I indicated, I was making simplifying assumptions! But the real bottom line is that heating water takes a LOT of energy; sadly water has a very high specific heat capacity, so it takes a LOT of energy to heat it.

Heating water takes no energy if you are using waste heat from the engine. As I said, a boat's hot water tank contains potable water and if you have spent part of the day motoring you are getting free energy, at least in part. We are so accustomed to only drinking water from a dedicated cold source in our homes that many people don't consider drinking hot water on their boats.

 

[PaulRainbow]

Heating water takes no energy if you are using waste heat from the engine. As I said, a boat's hot water tank contains potable water and if you have spent part of the day motoring you are getting free energy, at least in part. We are so accustomed to only drinking water from a dedicated cold source in our homes that many people don't consider drinking hot water on their boats.

That's a good point John. We always fill the kettle from the hot tank.

 

[wonkywinch]

Of course, perfectly correct - as I indicated, I was making simplifying assumptions! But the real bottom line is that heating water takes a LOT of energy; sadly water has a very high specific heat capacity, so it takes a LOT of energy to heat it.

And a lot more to boil it. To raise water from 0C liquid to 100C liquid takes around 420 joules per gram. To then raise it from 100C water to 100C steam, it takes another 2,260 to boil it, ie over 5 times as much to change it's state without changing it's temperature as it did to get it from zero to 100 degrees. It's how steam engines and the weather works. Like scientific magic.

Motto, don't leave the kettle boiling, that wastes a lot of energy!

 

[jwilson]

Sorry, that's not correct.

What just about everyone keeps missing is the Lithium battery will have a BMS which limits the current, if that current is exceeded the BMS will shut the power out off.

The 2000Ah one in post #6 (which i can't see anyone fitting on a boat !!) has a 300A BMS. So unless absolutely everything else on the boat is turned off and the inverter is a decent quality/efficient one it will shut down when you turn a 3Kw kettle on.

The typical "drop in" Lithium battery being fitted to boats are fitted with 200A BMS, so even a 2Kw kettle would be unsuitable.

PaulRainbow is right, as usual. But I think the OP in suggesting fitting a 28Kwh battery pack is thinking of a domestic installation, not a normal boat one. I don't think there are any 12 volt 28KwH battery packs made - googling this seems only to show up 48 volt ones for connection to large solar panels on a house roof etc. The OP has not posted since.....

 

[PaulRainbow]

PaulRainbow is right, as usual. But I think the OP in suggesting fitting a 28Kwh battery pack is thinking of a domestic installation, not a normal boat one. I don't think there are any 12 volt 28KwH battery packs made - googling this seems only to show up 48 volt ones for connection to large solar panels on a house roof etc. The OP has not posted since.....

He does say in post #1 John, it's for his boat. I think the 28Kwh is either a typo or he's misunderstood something.

Shame he hasn't come back to the thread he started.

 

[noelex]

Motto, don't leave the kettle boiling, that wastes a lot of energy!

Absolutely.

Some of the efficient kettles save further energy by "sneaking up" on the boiling point. Heating up and then shutting off in quick succession to more accurately detect the first point when the water just starts boiling. Some also have a semi-sealed insulated lid, so a minimal amount of steam (and therefore latent heat) is lost to the air.

You can save even more energy by selecting a temperature just below boiling.

If you are trying to manage without propane/butane in areas of marginal solar insolation, these measures are helpful.

 

[GaryMiller]

Sorry for the delay in coming back to this - I didn't anticipate that a mundane subject such as kettles would generate such a response .......................
Yes, complete typo in my part - the lithium battery pack is, in fact, a Ecoflow Delta 2 that has a capacity of only 1kwh and I plan to keep it charged when the engines are running (very slow I know) and/or using the same procedure as with our electric OB battery - by taking into anywhere convenient (usually a HM office) and imposing on their goodwill.
Useful information all round - I wasn't aware of insulated kettles and a previous suggestion of aiming for a halfway point (say 200w) will probably be the next step.
Many thanks for all the responses - I hadn't realised how complicated the whole thing could be ..........

 

[Tranona]

That seems a very expensive and clunky way of making a cup of tea (or coffee). You don't say what battery capacity you have, but with 2 engines and 2 alternators, a decent size house bank and an inverter would seem a better way of getting a small amount of 240v. The combined charger/battery/inverter is aimed at the portable market, but a boat has all the ingredients to build a simple permanent installation. Cuts out the regular need to hump it ashore to recharge.

 

[PaulRainbow]

Sorry for the delay in coming back to this - I didn't anticipate that a mundane subject such as kettles would generate such a response .......................
Yes, complete typo in my part - the lithium battery pack is, in fact, a Ecoflow Delta 2 that has a capacity of only 1kwh and I plan to keep it charged when the engines are running (very slow I know) and/or using the same procedure as with our electric OB battery - by taking into anywhere convenient (usually a HM office) and imposing on their goodwill.
Useful information all round - I wasn't aware of insulated kettles and a previous suggestion of aiming for a halfway point (say 200w) will probably be the next step.
Many thanks for all the responses - I hadn't realised how complicated the whole thing could be ..........

See post #31 you cannot run a 2Kw kettle from this battery. If you found a 1.5Kw kettle you could use that, providing you didn't have anything else on at the same time. A 1KW kettle still makes the most sensible choice, IMO.