Induction Cooking info and experience.

[s/v Jedi]

Originally Posted by rslifkin

We do use a good rice cooker at home. Only real reason the instant pot ended up on the boat (rather than buying another rice cooker) is limited galley space and it can do more stuff than a rice cooker. If I find space for it on the boat, I may buy a small rice cooker to keep aboard at some point.

One big thing for us is avoiding needing the stove more than once per day, as until I add more battery capacity and up-size the inverter (and probably need more solar too), the stove is generator-only when we're away from shore power (our stove is electric, but we haven't switched it to an induction unit yet). I don't mind cranking up the generator for a bit to make dinner (as it also heats water for showers), but I don't like having to run it multiple times in a day.

If not for the stove limitation and already having the instant pot, I agree, just get a stove top pressure cooker. But it's hard to justify buying one when the instant pot was already in a cabinet collecting dust. About the only advantage of an instant pot over a stovetop pressure cooker is that you can put it anywhere while in use, which might be good for those boats with a really small galley.

If you do end up needing to make rice in an instant pot, the best results I've gotten (at least for short grain rice) have been from high pressure, 4 minute cook time, and letting it depressurize on its own. The biggest thing I found was to use significantly less water than you otherwise would, as the instant pot is sealed and doesn't lose water as steam like a rice cooker does. So a normal quantity of water leads to soggy, awful rice. And if there's not a little oil or some other kind of fat in there, the rice tends to burn a little and stick to the pot. So I've been avoiding making just plain rice in the thing.

The little $50 appliance that I linked can also do many other types of cooking. I think everyone except pressure cooking.

I did the same as you: try to make do with what you have but at some point you will find that it’s just self torture because of a bad purchase and spending the $50 is a better option. Also, it is much smaller, very handy on a boat. So handy, that we actually bought one for use at home too… and this is why I have an InstantPot collecting dust in a cabinet haha

[Adelie]

Originally Posted by rgleason

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.

So i am interested in this and several years ago did very precise testing of an induction burner vs a butane catering stove. I weighed the whole stove to determine butane usage to the nearest gram and measured temp change to the nearest 0.1C for a mass of water to nearest gram.

Microwaves were 45% efficient
Butane was 50%
Induction was 75%.
I assume propane has similar efficiency to butane but have not yet tested it.
I assume that at lower heat settings the efficiency gap will be narrower but haven’t tested it yet.
I have not yet measured efficiency of propane oven vs convection oven, that’s coming.

Using the above efficiencies I created a chart so you can estimate daily electrical demand based on current propane usage. I would suggest using a luggage scale to weigh a propane tank just before you start using it and again after. This will give you a usage rate over a long term.
See chart below.

If you have 2 burners and a convection oven running on 120v, the biggest demand you could have is 3600W (2x1800W). That means you need a 4500-5000W inverter. Pure sine wave sine most induction burners can’t run on modified sine.

3600W is 300A at 12v.

Regarding battery bank. There are 2 things to consider:
A. Total daily demand
B. Instantaneous demand.

Personally I would want my bank capacity to be 3 or 4 times daily demand using LA batteries and 2-3 time using LFP.

So if I’m using 100Ahr/d cooking and another 100Ahr/d house loads that 200Ahr/d total which means I want 600-800Ahr lead acid or 400-600Ahr LFP.

LA batteries don’t like high draw rates. For extended periods. The burners and oven are only likely to run full power for a few minutes until everything is preheated. The only time you are going to leave a burner on high is when boiling water. Let’s assume it drops to 200A steady for design purposes.

I personally would want to limit draw rates to 0.15-0.25C for LA batteries and 0.25-0.33C for LFP.

So for a 200A draw you would want 800-1330Ahr capacity for LA batteries and 600-800Ahr for LFP. So issues with instantaneous draw govern over total daily draw.

Rule of thumb for MPPT controllers daily production in Ahr is 1/3 of solar panel nameplate capacity in Watts. Given a 200Ahr/d total demand you would need 600W of panels.

There are ways to cut you electrical or propane usage for cooking.

If you are doing rice, noodles or stewing something. Bring the food to a boil then transfer to a Wonderbag or thermal cooker to finish.

There are small solar cookers that can be had for about $100.

[Statistical]

Nice data but LFP can be pushed harder than that. Even 0.5C is modest for LFP. Now you may want more capacity anyways to avoid discharge depth and have enough stored capacity to ride out a few days of bad solar generation.

I really wish someone would make DC induction cooktop. To be clear all induction is alternating current but the input AC isn't used directly. Induction cooktops work in the 25,000 to 50,000 Hertz range so the AC is usually converted to DC and run through another inverter to up the frequency to 25+ kHz.

So on a boat running off battery power behind the scenes we have this:

DC battery bank -> AC inverter -> AC circuits (50/60Hz) -> cooktop input -> DC rectifier -> high frequency AC inverter (25+ kHz) -> induction coils.

It would be a lot of amps at 12V but 24 or 48V banks would be doable. Could skip two of those steps.

48VDC battery bank -> cooktop input -> high frequency AC inverter (25+ kHz) -> induction coils.

[s/v Jedi]

Originally Posted by Statistical

Nice data but LFP can be pushed harder than that. Even 0.5C is modest for LFP. Now you may want more capacity anyways to avoid discharge depth and have enough stored capacity to ride out a few days of bad solar generation.

I really wish someone would make DC induction cooktop. To be clear all induction is alternating current but the input AC isn't used directly. Induction cooktops work in the 25,000 to 50,000 Hertz range so the AC is usually converted to DC and run through another inverter to up the frequency to 25+ kHz.

So on a boat running off battery power behind the scenes we have this:

DC battery bank -> AC inverter -> AC circuits (50/60Hz) -> cooktop input -> DC rectifier -> high frequency AC inverter (25+ kHz) -> induction coils.

It would be a lot of amps at 12V but 24 or 48V banks would be doable. Could skip two of those steps.

48VDC battery bank -> cooktop input -> high frequency AC inverter (25+ kHz) -> induction coils.

They may run on DC if you try…. but you need 110V of DC. To make that, you do exactly the same.

[Statistical]

Originally Posted by s/v Jedi

They may run on DC if you try…. but you need 110V of DC. To make that, you do exactly the same.

They would need to be designed with an high frequency inverter that operates as 12V or 24V or 48V vs 120V or 240V. That is probably why it doesn't exist. Marine uses are an ultra tiny niche compared to all the AC based uses globally. Even ones designed "for marine" can piggyback on economies of scale with high frequency inverters designed for high voltage. If you open up a 120V "marine", "rv", and "residential" induction hob they likely have the exact same components.

[s/v Jedi]

Originally Posted by Statistical

They would need to be designed with an high frequency inverter that operates as 12V or 24V or 48V vs 120V or 240V. That is probably why it doesn't exist. Marine uses are an ultra tiny niche compared to all the AC based uses globally. Even ones designed "for marine" can piggyback on economies of scale with high frequency inverters designed for high voltage. If you open up a 120V "marine", "rv", and "residential" induction hob they likely have the exact same components.

That would make the cooktop as big as a 2000W inverter…. not very realistic

[Statistical]

Originally Posted by s/v Jedi

That would make the cooktop as big as a 2000W inverter…. not very realistic

Most of the cooktop is the inverter regardless. Raising voltage of AC is quite trivial it is called a transformer. Nothing about induction cooktops requires the AC used for induction to be at 120V or 240V or any particular voltage it just requires very high frequency.

Now realistically due to economies of scale and the tiny niche that is marine induction cooking I think it is unlikely it will ever happen but it would be nice to avoid double conversion with losses.

[s/v Jedi]

Originally Posted by Statistical

Most of the cooktop is the inverter regardless. Raising voltage of AC is quite trivial it is called a transformer. Nothing about induction cooktops requires the AC used for induction to be at 120V or 240V or any particular voltage it just requires very high frequency.

Now realistically due to economies of scale and the tiny niche that is marine induction cooking I think it is unlikely it will ever happen but it would be nice to avoid double conversion with losses.

If you want a cooktop that runs on 12V DC, then your conductors are the same size as for a 2,000W inverter. Imagine the 150A MOSFET’s chopping it up.
It is very tough to convert 12V at 150A to a high frequency AC. It is very easy to convert a 120V 15A power feed to high frequency AC. Ten times easier.

[Statistical]

Originally Posted by s/v Jedi

If you want a cooktop that runs on 12V DC, then your conductors are the same size as for a 2,000W inverter. Imagine the 150A MOSFET’s chopping it up.
It is very tough to convert 12V at 150A to a high frequency AC. It is very easy to convert a 120V 15A power feed to high frequency AC. Ten times easier.

You don't convert 12VDC to 120VAC (at any frequency). You convert a variable ~12VDC input to a specific low voltage and then invert it and then step it up with a transformer. 12VDC is non-ideal for the same reason a 12V inverter is non-ideal simply massive input cables but 24V or 48V would be more manageable. Your "120V" induction cooktop is also not running at 120V internally in order to optimize the coils. At 25 kHz only the skin of the wire is being used so you will want to step the voltage up a lot internally anyways to bring the amps down.

The issue isn't that you can't do. You could build one in your garage. The issue is economics. Of the millions of induction cooktops sold each year marine usage isn't even a rounding error. First of all the marine market is tiny and then a tiny fraction of that is using induction cooktops. The market is simply too small to warrant an induction cooktop with a DC input and likely a custom designed low production run. Too small today in the future who knows.

[rgleason]

rslifkin: If your current fridge has a Danfoss compressor there's a good chance it can already run on 24v.

It is a danfoss!

I suppose I'd have to change the new delco remy si28 rotor to be 24v? or modify another one. Then what victron multipass inverter size? and I suppose I would need a dc-dc converter 24-12v for house panel, nav, nav lights, starter bat etc.

Probably worth considering

[rslifkin]

Originally Posted by rgleason

rslifkin: If your current fridge has a Danfoss compressor there's a good chance it can already run on 24v.

It is a danfoss!

I suppose I'd have to change the new delco remy si28 rotor to be 24v? or modify another one. Then what victron multipass inverter size? and I suppose I would need a dc-dc converter 24-12v for house panel, nav, nav lights, starter bat etc.

Probably worth considering

You'd want to go though each piece of equipment on the boat and figure out what can already accept 24v input, what can easily be swapped for a 24v version, and what needs to stay 12v with converters.

Sizing converters, inverters, etc. will depend on what you decide each one needs to power.

[Grith]

We use an induction cooktop, 240v electric storage hotwater service and compressor refrigeration/freezer along with charging torqeedo batteries and have a variety of occasional use 240v appliances and chargers.
We do all this via a portable lithium power pack hooked into our shore power system with a transfer switch which is connected to our solar panel array.
We have left our conventional AGM yachting systems batteries in place and just use the lithium power pack to replicate being connected to shore power whilst out extended cruising.
It has been working very well whilst the EcoFlow Delta Max power pack also transfers to our slide on truck camper and home as a UPS when we are not cruising our trailerable yacht.
The ability to remotely monitor (via phone app) solar input, all outputs, state of charge, and switch on and off the inverter (limiting losses) and adjust parameters remotely makes it a very neat package in my view.
The portable power pack is neatly and securely tucked away under a settee berth in a vented by water resistant location.
This system has allowed us to remove all propane from our yacht along with its heavier than air leak accumulation risk.

[s/v Jedi]

Originally Posted by Statistical

You don't convert 12VDC to 120VAC (at any frequency). You convert a variable ~12VDC input to a specific low voltage and then invert it and then step it up with a transformer. 12VDC is non-ideal for the same reason a 12V inverter is non-ideal simply massive input cables but 24V or 48V would be more manageable. Your "120V" induction cooktop is also not running at 120V internally in order to optimize the coils. At 25 kHz only the skin of the wire is being used so you will want to step the voltage up a lot internally anyways to bring the amps down.

The issue isn't that you can't do. You could build one in your garage. The issue is economics. Of the millions of induction cooktops sold each year marine usage isn't even a rounding error. First of all the marine market is tiny and then a tiny fraction of that is using induction cooktops. The market is simply too small to warrant an induction cooktop with a DC input and likely a custom designed low production run. Too small today in the future who knows.

We must be miscommunicating. I was addressing someone who wished for 12V DC powered induction cooktops. I am an electronics design engineer.

[rgleason]

Adelie. Thanks for the great analysis and info. The loads seem to be too high for me to consider induction, but I will continue to study it.

[Grith]

Originally Posted by rgleason

Adelie. Thanks for the great analysis and info. The loads seem to be too high for me to consider induction, but I will continue to study it.

I have lived with our portable induction cooktop for around 8 weeks now. It cooked two meals a day for two to three people and around 12-18 cups of tea/coffee per day. On average we consumed around 1500kwh per day doing this.
We also ran a 40litre compressor fridge at 2 degrees and separate 20 litre freezer at minus 10 degrees. These both consumed around 400 kWh a day a total of 800kwh.
On around every third day we heated our 22litre hotwater system to 60 degrees via electricity consuming again around 400kwh.
All of these outputs run from a pair of EcoFlow Delta Max lithium power banks totalling 3500kwh of storage.
These are being charged by a 720w solar array (generally averaging around half rated production for 6 hours a day but often more if sunny) and a 12-24v vitron voltage increaser which provides 360w of charge when the outboard is running.
I have another 200w of solar charging my AGM’s which power all the conventional yacht systems.
The load of the compressor fridges is being handled by the powerbanks 12v outlet (not requiring the inverter to be activated)
Without the fridge freezer loads the AGM’s are coping very well with powering all the normal yacht systems. The EcoFlow powerbanks are producing shore power equivalent 240v with remote switching of the sine wave inverter.
In fact the systems are working well enough now that I am confident to leave my Honda eu2.2 behind and rely on solar with the outboard alternator giving a further top up when occasionally running.
As can be seen below our meals are not minimum power usage ones.