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post #221 of 301 Old 04-01-2014
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Re: safe cooking

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Its proven fact that LED causes brain cancer, Sorry
Gotta reference?

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post #222 of 301 Old 04-01-2014
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Re: safe cooking

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Originally Posted by SVAuspicious View Post
Units are important. There are a couple of people on this thread with near saintly patience. Kudos to Puddin' Tain and GeorgeB who have been getting it right.

Units are important. If you are using units like amps/hr (or /min or /sec) you don't understand. If you use amps to measure power (W, kW) or energy (Ws, Wh, kWh, or (unfortunately since it adds voltage dependance) Ah) you don't understand. Carry the unit terms through your calculations and you'll see you the error of your ways. This is Jr High School algebra and you should understand it.

I don't intend to offend anyone directly. I hope to help you understand just how important this material is, and that if you get the units straight you will be an electrical rock star.



This is a great example. Lets walk through it.

First remember that watts are a measure of power that is NOT voltage dependent. That makes them great for dealing with voltage conversions that happen at inverters or battery chargers. Let's use my little Tappan microwave instead of the undefined one above. It is sold as a 600W microwave because that is the output of the microwave transmitter in the oven. If you read the label on the back you'll see it draws a maximum of 850 watts; the difference is due to the efficiency of the transmitter, losses in the power supply, and the control board, clock, etc. So we use 850 watts.

Actual RMS AC voltage (what you read on a volt meter) for US spec appliances should be between 117 and 120 VAC at 60 Hz (Hertz is just the frequency of the alternating cycle (AC) power). Let's use 120 to keep things simple.

850 watts (volt·amperes neglecting power factor which isn't relevant until we talk about refrigerators, air conditioners, or other device with significant rotating loads) / 120 volts = 7 amps ON THE AC CIRCUIT supplied by the inverter. We'll go back to watts to work our way through the voltage conversion in the inverter since it is voltage independent. My Mastervolt 2kW inverter has an efficiency of 95% - actually pretty decent. 850 watts on the AC side turns into 850 watts/0.95 = 895 watts on the DC side. If my batteries are fully charged and providing 13.6 VDC the microwave will draw 895 watts / 13.6 V = 66 amps. That's a lot of amps. If I heat up a casserole for 8 minutes I'll use 66 amps * 8 minutes / 60 minutes/hr = 8.8 Ah from my 675 Ah battery bank, about 1.3% of capacity. Not bad at all.

Lets look at a spaghetti dinner on an induction cooktop. Assume 3 minutes at 1500 watts to boil the pasta water and 11 minutes to cook the pasta at a lower setting - say 600 watts. We also heat canned spaghetti sauce (I'm making this simple so we don't have to saute meat and mirepoix, and sauce and paste, yadayadayada) at about 300 watts for the same total time.

3 min * 1500 W + 11 min * 600 W + 14 min * 300 W = 15300 W·min (aren't watts wonderful?)
Through the inverter 15300 W·min/.95 efficiency = 16105 W·min
Again with fully charged batteries that means 16105 W·min / 13.6 V / 60 min/hr = 20 Ah
Not the end of the world, but that does mean that if spaghetti is representative of a cooked meal and you make two a day aboard and that if refrigeration draws about the same 20 Ah you could cook with propane and have two big refrigerators and a separate freezer and come out ahead. If that's a good trade-off for you, fine - just make the decision with your eyes open and don't kid yourself that there is some magic efficiency changing the rules of physics.

Now one watt is roughly 3.4 BTUs, so a 1500 W induction hob is equivalent to a 5100 BTU propane stove burner. It can't be different. Force 10 and Eno propane cookers (for example) have large burners that run between 8000 and 8500 BTUs. The smaller burners hover around 3400 BTU. So in our spaghetti example above, the propane stove will boil the water faster than the induction hob, but that only reduces the initial 3 minutes. It isn't relevant to heating the sauce or cooking the pasta at reduced heat.

In fairness, most propane cookers have an electrical solenoid in the propane locker that draws a surprising amount of power. Many draw about 1 A the entire time they are switched on. So our spaghetti dinner on a propane cooker consumes 14 min * 1 A / 60 min/hr = 0.23 Ah. Not much, but it should be counted.

All the efficiency claims of induction are relative to electrical resistance heating, not gas.

Exercise: look up and understand current (amps), power (W), and energy (Wh, Ah, BTU).
Nothing like keeping it simple.

1000 watts AC out of an inverter takes 100 amps DC - a bit conservative but easier numbers to use. 1000 watts for one hour out of the inverter consumes 100 AH from the batteries. That is really all you need to know.

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Re: safe cooking

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Gotta reference?
I'm really sorry, I was just teasing, i shouldn't joke about that ****.
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post #224 of 301 Old 04-01-2014
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Re: safe cooking

Hmmm...alcohol stoves can't cook pasta? I must have imagined all those pasta dinners and lunches I've cooked on my boat.

"If a man must be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most." --- E.B. White
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post #225 of 301 Old 04-01-2014
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Re: safe cooking

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I'm really sorry, I was just teasing, i shouldn't joke about that ****.
I thought so. But ya' never know what wacky things people will believe.
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Re: safe cooking

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Hmmm...alcohol stoves can't cook pasta? I must have imagined all those pasta dinners and lunches I've cooked on my boat.
Alcohol stove + pressure cooker =YUMMI
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Re: safe cooking

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Originally Posted by hellosailor View Post
Coal? No good for boats, too hard to get good coal in most of the developed world, and too easy to have a monoxide problem.

But speaking of spaghetti, that's a classic "ain't gonna happen" on a 6800btu burner. Can't boil a big pot of water on that. Although, most of us were taught how to cook pasta the rich way, with a big pot of rolling boiling water. If you just bring the water to a boil, and then shut the burner and come back to stir the pasta every few minutes, it cooks up just fine. May take 20 minutes instead of 10, but it cooks just fine without the need for copious amounts of boiling water. Great way to save fuel, whatever kind it is.
FYI copied these specs from a force 10 propane marine stove.

3,400 BTUs per small top burner

8,200 BTUs per large top burner

5,100 BTUs oven burner
5,500 BTU Broiler

So you can see that the Origo alcohol stoves burners are right inline for marine stoves

Sure Marine Service, Inc. | Force10
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post #228 of 301 Old 04-01-2014
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Re: safe cooking

Propane = risk of boom.

CNG = risk that you can't find a fill station... or boom.

Alcohol = risk of burn (or blindness if you drink it)

Kerosene = risk of CO poisoning.

Electric and genset = risk of being murdered by your neighbor in a quiet anchorage

Wood = risk of setting fire to your boat

Diesel = risk of wood and kerosene combined

fission = risk of cancer

fusion = risk of the CIA murdering your for your technology

cold food = risk of suicide

Everything has risk. You make your choices, you CHOOSE WHICH RISK you prefer and go with it. If propane were really all that dangerous don't you think that the drunken idiots all over America that are operating poorly maintained, made in China BBQs would be blowing themselves up all time? Yet somehow they're not....

MedSailor

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post #229 of 301 Old 04-02-2014 Thread Starter
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Re: safe cooking

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Originally Posted by barefootnavigator View Post
Not me, I shut my cell phone off two years ago. But then there is wifi Dman!


i suppose, you could always start wearing a tin foil beanie to keep all the bad stuff out of your head.

The only rules that really matter are these: what a man can do and what a man can't do.---Captain Jack Sparrow


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Re: safe cooking

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Originally Posted by barefootnavigator View Post
Alcohol stove + pressure cooker =YUMMI
you've eaten alcohol stoves and pressure cookers?! that can't be easy on your teeth!
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