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Old 12-06-2023, 08:17   #1
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Induction Cooking info and experience.

I'd like to learn more about this topic.

How much energy kwh does it use to boil 1 gal of water?
Is there a way to bake bread for example?
What equipment is best on a boat?
With light use, say morning (2) coffee & oatmeal for 2 people, salad light lunch, and perhaps a cooked dinner for two (fish, beef, or stew) what would the kwh/day likely be?
How much bigger would the batteries need to be?
Do inductive stoves require 120v/240v? Thus requiring a big inverter?
Some photos of systems and inductive cooking for boats when at sea might help.
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Old 12-06-2023, 08:21   #2
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Re: Induction Cooking info and experience.

Some of the big induction units are 240v, but there are 120v systems available.

As far as calculating your expected power usage, if you've got propane now, how much propane do you use in a typical month or other period of time? From there, the energy contained in that amount of propane can be translated into an amount of equivalent electrical energy. An induction stove will be a bit more efficient at getting heat into the food, so actual use will be lower than the straight conversion indicates.
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Old 12-06-2023, 16:10   #3
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Re: Induction Cooking info and experience.

Thanks. (2) 5lb Tanks each containing a little more than 1gal of propane can last two to 1.5 summers of use.

Propane Tank Lifespan = (Tank Size (in lbs) ÷ 4.25) × 91,500 BTU per gallon ÷ Consumption BTU =

https://learnmetrics.com/how-long-do...ane-tank-last/

5 lbs ÷ 91,500 btu per gal ÷ consumption btu =

A single burner could use about 10,000 btu/hr. Thus a single 5 lb propane tank could last for 10 hrs. depending on use (how high the burner knob is set and if it is windy, if grilling out)

One tank contains about 91,000 btu so two is about 182,000 btu.

This btu then gets converted to kwh.
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Old 12-06-2023, 16:24   #4
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Re: Induction Cooking info and experience.

A kwh is 3412 btu. And I'd figure an induction stove will use 80% or less of the power of a gas stove to heat an equivalent amount of food due to better efficiency. So you're looking at about 42 - 43 kwh to do an equal amount of cooking to your 2 propane tanks. So for your usage pattern, you're likely well under 1kwh/day.
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Old 12-06-2023, 16:47   #5
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Re: Induction Cooking info and experience.

1 kWh = 3412 btu
So 182,000 btu ÷ 3412 btu/kwh =
53.34 kwh

So. basically it will cost about 3 kWh to provide the same heat as 1 propane burner on full for 1 hour.

How how much would this kind of load increase the size of the lfp?

Assuming a 120vac induction burner is used, which will require an inverter?

Would a 400ah 12vdc LFP be unreasonable for refrig, radar, nav, lights and cooking?

I expect to recharge going in and out of harbors when cruising and with 100w to 300w solar. When cruising we use 90ah=100ah. When at sea we use more power, more like 150ah/dat not including stove.

It is not a large boat.
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Old 12-06-2023, 17:42   #6
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Re: Induction Cooking info and experience.

Quote:
Originally Posted by rgleason View Post
1 kWh = 3412 btu
So 182,000 btu ÷ 3412 btu/kwh =
53.34 kwh

So. basically it will cost about 3 kWh to provide the same heat as 1 propane burner on full for 1 hour.

How how much would this kind of load increase the size of the lfp?

Assuming a 120vac induction burner is used, which will require an inverter?

Would a 400ah 12vdc LFP be unreasonable for refrig, radar, nav, lights and cooking?

I expect to recharge going in and out of harbors when cruising and with 100w to 300w solar. When cruising we use 90ah=100ah. When at sea we use more power, more like 150ah/dat not including stove.

It is not a large boat.
Realistically your power consumption will be lower than 53 kwh, as induction puts more of the heat into the food and less into the surrounding air, so you'll need less energy input to cook the same food.

Based on your usage, 400ah is likely adequate provided it can handle the short term draw of your chosen stove setup (2 burners will mean more peak draw than 1). 400ah in a 12v lfp setup is about 5kwh of stored power. Figuring you're using 2 kwh/day now on the worst days, you'd probably be 3-4 kwh on your most intensive cooking days, less on most days. Producing enough power with the solar you can fit is likely the biggest challenge, but you can help that with more batteries (meaning you can survive more days of power shortfall before a good recharging opportunity shows up).
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Old 12-06-2023, 17:55   #7
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Re: Induction Cooking info and experience.

If you can supply the power for induction cooking from surplus solar power, then it is a good deal. Some boats can do this (usually catamarans with acres of deck space), but not most.

If your solar power is already maxed out, and the incremental cooking energy usage needs to come from burning fossil fuels for a drive engine driven alternator or genset, then induction cooking is going to be WAY more expensive than propane, generate more CO2, and just be generally much less efficient.

You still might want it--but be prepared to pay for it.

I do use electric for some cooking tasks because it is convinient, and I am willing to pay for that. I heat 1 liter of water to boiling every morning for my coffee. It takes 2800 watts for 3 minutes (round numbers). Converting that to other units, that would be about 140 Watt-hours. or 12 Amp-hours at 12 volts, or 6 Amp-hours at 24 Volts, or about 480 BTU. That (obviously) consumes pretty much the full capacity of a 3kVA inverter. That is a net efficiency of about 60% from stored energy in the battery to heat in the water. You'll be hard pressed to do better than that in the real world.

And, by the way there is no such thing as an "induction oven" unless you consider a microwave to be such a beast, which a physicist might....
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Old 12-06-2023, 18:52   #8
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Re: Induction Cooking info and experience.

I have a 2 quart induction pan that I've used on natural gas on a house stove and moved it to the boat. On the boat is boils in about 80% of the house time.
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Old 12-06-2023, 19:26   #9
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Re: Induction Cooking info and experience.

Your mathematical comparison is assuming a 10k btu hob. Thats a big hob, usually you would use smaller, and run that smaller hob at a medium flame, not full flame.

Without my measuring my usage, i know my solar produces 2.2kwh per day. That is enough for me to run my induction hob at a medium setting for about an hour, in addition to my normal boat loads.

I would guess about 600 Wh to run my hob at a medium power for an hour. I never use the high power setting(1200W). Medium (900W) is plenty.
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Old 12-06-2023, 19:31   #10
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Re: Induction Cooking info and experience.

Keep in mind 2800W for 3 minutes, 1400W for 6 minutes, and 700W for 12 minutes all use the same amount of stored energy. I have no reason to boil water in 3 minutes. It takes about 10 minutes on my propane stove, and i set my induction power levers to match that.
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Old 12-06-2023, 19:54   #11
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Re: Induction Cooking info and experience.

Using the numbers from the propane tank this way is misleading. Far simpler and more accurate to ask how long a tank currently lasts then use that number to get your actual daily average energy use (assuming it's only used for.vooking).

Then multiply that number by 0.8 or even down to 0.6 to allow for the MUCH greater efficiency of heat transfer from induction cooking.

FWIW, I came out at 1.3 kWh of gas heat per day, leading to a probable energy budget of 1kWh for the induction cooker.
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Old 12-06-2023, 20:23   #12
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Re: Induction Cooking info and experience.

Quote:
Originally Posted by rgleason View Post
I'd like to learn more about this topic.

How much energy kwh does it use to boil 1 gal of water?

.47 last time I ran the experiment.


Quote:

Is there a way to bake bread for example?

Several. You can use an electric oven or a bread machine. Or steam the loaf on an induction cooktop though this will not produce a crisp crust. Or make flatbread in a pan.



Quote:

What equipment is best on a boat?

The 1 or 2 burner flush-mounted (in-counter) cooktops.


Quote:

With light use, say morning (2) coffee & oatmeal for 2 people, salad light lunch, and perhaps a cooked dinner for two (fish, beef, or stew) what would the kwh/day likely be?

In my experience using both, think in rough terms of 10 kwh = 1 gallon of propane for practical cooking. Obviously the theoretical btu content of propane is higher than that but the heat transfer to the cookware isn't as efficient. Propane efficiency is worst with high heat vs. low and narrow pans vs. wide so you will get different conversion ratios depending on what you're doing -- which pan and heat setting.



Anyway for most people around 1-2 kwh per day is typical.


Quote:

How much bigger would the batteries need to be?

Think in terms of 200-400 Ah, for 12v.


Quote:

Do inductive stoves require 120v/240v? Thus requiring a big inverter?

All the ones I am aware of are 120v/240v.
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Old 12-06-2023, 20:29   #13
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Re: Induction Cooking info and experience.

Using my induction cooktop, I can make coffee and some oatmeal for 2 using 1800W over 3min, or 90 Wh. That's peanuts and the solar used to refill it in 30min (but now in 2min with our extra solar!).

Cooking with induction makes a ton of sense, it's not a constant high load, it's a high load only while it brings the food to temperature and then it reduces to a much lower load to just keep the temperature there. And since most of the cooking happens quite quickly, it's really not a big amount of power overall, as long as your inverter can handle the 1800W load.

Now for baking using an oven, it's an entirely different thing and I actually haven't done that offgrid yet. But at home we mostly use a small counter-top oven for cooking and that's 1800W as well. We cook for maybe up to an hour each day, probably less. So you're talking, in a worst case scenario, 1800Wh, which at 12V is 150Ah. That's nothing to scuff at but again, if you have enough solar it's also not insurmountable. And realistically I doubt that the oven actually uses 1800W for the entire hour. Probably just for the first few minutes and then less so. Also the insulation would play a big factor, and that would be a per-oven thing along with the installation method.

Anyhow, induction cooking is peasy if you've got a bit of solar and an even small surplus power budget.
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Old 12-06-2023, 20:36   #14
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Re: Induction Cooking info and experience.

Quote:
Originally Posted by rgleason View Post
I expect to recharge going in and out of harbors when cruising and with 100w to 300w solar. When cruising we use 90ah=100ah. When at sea we use more power, more like 150ah/dat not including stove.

On monohulls, especially smaller ones, this is the problem -- there's only room for so many solar panels. If (as is common) you already have a shortfall most days, now you're going to add another 1 kwh or so shortfall, which on most boats means an extra hour of running the motor or the genset every day.


I use induction at my house but still use propane on the boat for this reason (among others).
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Old 12-06-2023, 20:50   #15
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Re: Induction Cooking info and experience.

You're not going to use 1kWh if you just do light cooking with induction, to be sure. You'll use far less than that.
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