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Old 04-08-13, 05:44 PM   #11
AC_Hacker
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Quote:
Originally Posted by Mikesolar View Post
Great, do you have a link to the unit you bought?

Yeah, the Avantco 1800w (or something less) IS HERE.



They also have a 3500w (or something less) RIGHT HERE.



But I also spotted another 3000w (or something less) RIGHT HERE.

It's very hard to get any really useful information about them.

More watts, more buzz I suppose, more fun.

-AC

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Old 04-08-13, 06:19 PM   #12
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Default more...

BTW, I did a temperature test, with a pretty good mercury column cooking thermometer (just try to find one of those, ha).

The temps weren't dead on, and I did notice that there seems to be some 'flutter' in the temp selection, like when I was setting the temp, the number readout was not quite congruent with the rotation of the knob, sometimes jumping up or down a bit. But once set, there was no flutter. I'll have to keep studying that one.

So my first run was:

Indicated Measured
140F 154F
150F 166F
160F 176F
180F 185F
190F 192F
200F 207F

Don't know yet what the repeatability is... that is important.

-AC
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Old 04-09-13, 03:33 PM   #13
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Default A First Look At Little Buzzy's Guts...

I have decided to christen my induction cooker, 'Little Buzzy'.

So today it seemed only fit that I should open Little Buzzy up to see what's going on inside.

[EDIT: 1200V are present in this unit!!!!]

I unscrewed the bottom and... there was a brief resistance that I overcame, and the bottom came right off.


This is a view of the layout of Little Buzzy's underside. Doesn't look so terribly complex, does it?

[EDIT: 1200V are present in this unit!!!!]



This is a view from about 45 degrees of the main induction coil and other parts.



This is a close up of Little Buzzy's induction coil, showing the low-mass plastic mounting plate that supports the coil. Looks pretty resonant, doesn't it?

Not so clearly shown in the photos is the fact that the air cooling fan looks pretty robust, but is forced to try to blow through thin slits in the bottom, thus reducing air flow by about 65% or better. The same situation exists at the back of the cooker... impeded air flow.

So, right off, possible improvements could be:
  • Open up the air flow
  • Add non-magnetic mass to the induction coil, with ceramic or brass plates
  • Investigate the knob encoder, and possibly replace with a better unit, that is made in a Chinese factory that is more good.

Also it should be noted that the initial resistance I felt when I took off the bottom plate, was due to some kind of heat transmitting pasty goo that put a heat sensor in touch with the bottom of the cooking surface. I'll have to test to see how that has affected the temperature sensing function.

[EDIT: 1200V are present in this unit!!!!]


Best,

-AC
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Old 04-11-13, 02:54 PM   #14
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Default Kids, do not try this at home!!!

KIDS, DO NOT TRY THIS AT HOME!!!

[EDIT: 1200V are present in this unit!!!!]

Look Ma, no safety interlocks, what fun!!


Here, I have opened 'Little Buzzy' up again to see where the buzzing might be coming from.

My idea is to actually heat something with the case off and listen through a tube to try to determine the origin of the noise. I realize that the electrons might spill out all over the floor, but it's worth a risk...



[EDIT: 1200V are present in this unit!!!!]

Here is the pot of water boiling merrily away, with the case off and electrons spilling out.

I don't really have a photo of myself with a tube to my ear, searching for the source of the buzz, so you'll just have to imagine it.

I did determine that the main location seems to be the induction coil itself. I really need a stethoscope with a contact tip to get a better idea of exactly where the sound is coming from.

[EDIT: 1200V are present in this unit!!!!]

I also let the cooker go long enough to boil some water, after which I measured the temperature of the coil to be about 147 degrees F.

Not such a high temperature, which allows for the possibility of gluing non-magnetic mass to the coil.

The arrow points to the spot where the Chinese thermal goo is suppose to go, just below the main 'goo-site' there is another off-center splodge of goo apparently left by some nameless Chinese forced-labor prisoner (probably in prison for dancing tango), who makes these units.

Through my dis-assemblies and re-assemblies the main goo-site is mostly empty, so I redistributed the orphaned splodge of goo carefully over the main 'goo-site', being very careful to rub it into the cooking surface smoothly and evenly.

Then I re-assembled the unit and tried another temperature test, allowing 10 minutes between temp change and measurement...

[EDIT 4/12/2013: My first temp measurements allowed 10 minutes between tests. Turns out that it takes the unit longer than that to 'settle', so I did another series of measurements and allowed 30 minutes for the temps to settle. Results below are "Measured#30"]

Nominal Measured#10 Measured#30
140F 140F 152F
150F 150F 162F
160F 160F 170F
170F 170F 182F
180F 175F 190F
190F 192F 205F
200F 200F
210F 207F

Well now, let's hear it for the beneficial effects of careful splodge dispersion! I would imaging that had there not been that random bit of splodge, I certainly could have used CPU heat sink compound.

I have not yet solved the buzz problem, but I certainly have improved the accuracy of the temperatures.

[EDIT 4/12/2013: It looks like I didn't solve the temperature accuracy problem at all. In fact it looks like the algorithm that is used to control temperature is not a PID algorithm, as PID would have a much faster "ramp-up"]

[EDIT: 1200V are present in this unit!!!!]


Best,

-AC
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Old 04-22-13, 03:42 PM   #15
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Default Cook Top Shootout!

Cook Top Shootout!

I did some energy use comparison experiments this morning, and I thought I'd share the results.

The tests consisted of heating two pounds of water (very carefully measured) from 53F degrees to a rolling boil (212F). I used the same pot in each test, and re-cooled the pot before the next test. The power was monitored with a Kill-a-Watt, and I also used a kitchen timer to time how long it took to reach boiling.



I tested three cook tops, the first was a resistance cooker that had a measured wattage of around 900 watts.




The second was an induction cooker, 'Aroma', I bought from Target. It is sold as a 1500 watt cooker, but it's maximum power draw was about 1300 watts. In the tests, I reduced the power level to as close as I could get to 900 watts, which measured to be about 940 watts.



The third was an induction cook top, 'Avantco', I bought online. It is sold as a 1800 watt cooker, but had a maximum power draw of about 1500 watts. In the tests, I reduced the power level to as close as I could get to 900 watts, which measured to be about 860 watts.

Test Run #1:
Resistance Cook Top (aprox 895 watts)
Time to boil 2 pounds of water: 14 minutes
Kwh consumed: .2
Time for boiling to stop: 4 minutes

Avantco Cook Top (aprox 940 watts)
Time to boil 2 pounds of water: 10' 45"
Kwh consumed: .15
Time for boiling to stop: 6 seconds

Accent Cook Top (aprox 850 watts)
Time to boil 2 pounds of water: 9' 10''
Kwh consumed: .14
Time for boiling to stop: 9 sec
Test Run #2:
Resistance Cook Top (aprox 895 watts)
Time to boil 2 pounds of water: 14 minutes
Kwh consumed: .21
Time for boiling to stop: 4 minutes

Avantco Cook Top (aprox 940 watts)
Time to boil 2 pounds of water: 11' 00"
Kwh consumed: .15
Time for boiling to stop: 9 seconds

Accent Cook Top (aprox 850 watts)
Time to boil 2 pounds of water: 9' 00"
Kwh consumed: .14
Time for boiling to stop: 7 seconds
* * *

The 'Watts' reading on the Kill-a-Watt was very stable when measuring the resistance heating device, but was varying when measuring either of the induction heating devices. So the wattage readings from the induction units should be considered approximate. The Kwh readings, on the Kill-a-Watt, on the other hand, are cumulative so should be considered to be more reliable.

It is clear that water was heated much faster on either of the induction cookers than on the resistance cooker, in fact in about 70% of the time. Also, cool down time was very much faster on the induction cookers, calculated as about 3% of the time of resistance, compared to the resistance cooker.

Looking at the power used, it is also clear that the induction cookers used less power to heat water, in fact, about 75% of the power that was used by the resistance cooker, compared to the resistance cooker.

One explanation of the differences can be found in the cool down times, because the resistance cooker has substantial additional thermal mass to heat as it is heating water.

So, if cooking was done on a continuous basis, induction cooking might not show the same benefits as it does when we cook small batches.

But we actually cook in small batches almost all the time.

But interestingly, the cheap induction cooker heated the water fastest, while using least power... and it is much quieter. All very good qualities.

EDIT: Oh, and one more thing, a subsequent reader did the math on efficiencies, here's what he said:

Quote:
Originally Posted by ELGo View Post
Ignoring the container, the water took up 88 * 900 * 4.2 = 332640 Joules = 0.0924 kwh. This works out to 66% efficiency for the better induction device, and 46% for the resistive device.
Best,

-AC
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Old 04-22-13, 04:37 PM   #16
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AC,

Great comparisons on induction cookers. The cool down is very likely largely a result of the thermal mass of the pot or pan you are using. When you turn off an induction cooker, it is like turning off a microwave oven - the power is off instantaneously (except for the small thermal mass of the ceramic directly above the induction element).

My son loves his induction stove and his heavy cast iron pots work very well as not only is there the even heat put out by the element, but then that element heats a large thermal mass of the pot. He feels that the heavier the pot (larger amount of ferrous material) the more even the heat.

He has pointed out to my wife (who loves gas cooktops) that it is FAR easier to simmer on an induction as he can literally dial in a specific temp. The same with a gas element means that the heated area is very small (leading to scorching in that small area) and the very low flame can easily blow out.

But she LOVES her Revere copper clad cookware and being able to "see" the heat. Yup, she doesn't like the microwave either . . .

I may just buy one of these units and recess it next to the stove where we can also cook stews etc. Since I do most of the cooking, I should have something to say . . . .

You may have mentioned this, but what price rance are the units and which one would you recommend?

Thanks again for your "Consumer Reports" feature.

Steve
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Old 04-22-13, 06:20 PM   #17
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Quote:
Originally Posted by stevehull View Post
...The cool down is very likely largely a result of the thermal mass of the pot or pan you are using.
As you will see when you get yours, cool down is incredibly fast. The reason that the resistance unit in the tests was slow to cool down is that the resistance element itself, and in this particular case, there is an iron plate that the element is attached to. In all the tests I did, I used the same pan. So, it might be possible to cool down in less than 7 seconds with a lower mass pot.

Quote:
Originally Posted by stevehull View Post
...He feels that the heavier the pot (larger amount of ferrous material) the more even the heat.
I think that a properly made pan would have ferrous material in combination with copper or aluminum. That's the way the Ikea pots are made, and they're the best I have encountered so far with regard to even heating. And they aren't so heavy.

Quote:
Originally Posted by stevehull View Post
...it is FAR easier to simmer on an induction as he can literally dial in a specific temp.
Yeah, that's the whole thing in a nutshell. I have even discovered that you can dial in a sub-simmer temperature and cook almost as quickly, and not create the humidity load.

Quote:
Originally Posted by stevehull View Post
The same with a gas element means that the heated area is very small, leading to scorching in that small area...
The cooking coil diameter determines the immediately heated area. Some units have larger coils, some smaller. My 'Aroma' is about 4.5" my 'Avantco' is about 5.5". I looked inside the Avantco and saw that there was room on the support plate for a larger coil... wish they'd kept winding.

I have seen units with larger, segmented coils that sense the diameter of your pot and adjust themselves to your pot... for a price.

Quote:
Originally Posted by stevehull View Post
You may have mentioned this, but what price range are the units and which one would you recommend?
You want:
  • Variable Power
  • Variable Temperature
  • Timer

I was looking for the cheapest I could find. The first one was $70 (power control, timer, but no temperature control, bad). The other was about $130 (timer, temperature control & power control).

I'm impressed with the possibilities of induction cooking, but I'm not 'all in' with either of the units I tried.

If you got a full-on cook top, you'd have hobs with power capability like 3600 watts, 1800 watts, 1200 watts.

I really do like having a knob to change the temperature settings, even though the knob on mine is a bit flakey.

Having many steps of temperature control is very important.

Ditto many steps of power control.

To cook a stew for a family, having 1500 watts would be plenty, so you should get 1800 watts, because the advertised power is not accurate. More power will heat up the water faster, but after that, holding a simmer temp only takes maybe 600 watts, cycling on & off.

There are also some sleek one and two hob flush mount units, very nice.

I heard all these tails of amazingly fast heat ups with induction cookers... well it is because they were using really high wattage cookers, like maybe 3600 watts.

The really good units are made by Cook-Tek and Vollrath, but be prepared to bleed.

Quote:
Originally Posted by stevehull View Post
Thanks again for your "Consumer Reports" feature.
Yeah, I like to think of it as a 'Technology Reports' kind of thing, keeping the 'Eco' attached to the Renovator.

-AC
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Old 04-22-13, 07:11 PM   #18
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2/1.5 - 1.33, meaning the resistive element is using about 33% more juice to heat your water. The reported efficiencies are 72 and 84% for resistive and induction respectively, or 84/72 = 1.16.

I'm not sure why your shoot-out came out so much more efficient for the induction device, but container coverage of the heating element and a flat contact surface affect heat transfer.

Ignoring the container, the water took up 88 * 900 * 4.2 = 332640 Joules = 0.0924 kwh. This works out to 66% efficiency for the better induction device, and 46% for the resistive device.

Conclusions: if hot water is really what you want, an immersion heater in a container with low heat capacity has advantages. That actually is true for my home where we drink a lot of hot fluids and cook in the pressure cooker. My choice will be to buy a good thermos that I heat 1.5 liters of water in to boiling every AM and use through the day. I figure that should keep my electric consumption for hot water to something under 200 Wh a day. It will also let me use the pressure cooker for longer into the summer season since very little heat will escape inside the home (cooling down phase outside.)
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Old 04-22-13, 08:07 PM   #19
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All good points. I did have similar thoughts about immersion heating as I was doing the testing.

In fact, one of the best parts about induction cooking is the addition of microprocessor capabilities, giving you a timer and accurately variable heat... both features could be incorporated into a resistive devices.

But a couple of questions:

Quote:
Originally Posted by ELGo View Post
2/1.5 - 1.33, meaning the resistive element is using about 33% more juice to heat your water. The reported efficiencies are 72 and 84% for resistive and induction respectively, or 84/72 = 1.16.
I didn't use a lab, I used an actual kitchen with actual an actual pot.


Quote:
Originally Posted by ELGo View Post
I'm not sure why your shoot-out came out so much more efficient for the induction device, but container coverage of the heating element and a flat contact surface affect heat transfer.
The pot I used was a very good fit to the resistance hob and the induction hob(s).

Flat contact surface? I suppose I could have lapped the bottom of the pot to better fit the resistance hob, but is that how people actually cook?

Quote:
Originally Posted by ELGo View Post
Ignoring the container, the water took up 88 * 900 * 4.2 = 332640 Joules = 0.0924 kwh. This works out to 66% efficiency for the better induction device, and 46% for the resistive device.
I like this so much that I hope you'll forgive me for editing it into my previous post.

Quote:
Originally Posted by ELGo View Post
if hot water is really what you want, an immersion heater in a container with low heat capacity has advantages.
It's actually soups and stews I'm looking for, and the ability to quickly and precisely change temperature... and now that I'm used to it, a timer.

Quote:
Originally Posted by ELGo View Post
It will also let me use the pressure cooker for longer into the summer season since very little heat will escape inside the home (cooling down phase outside.)
Are you saying that you have an immersion type resistive-heated thermos style vacuum insulated pressure cooker? I really want to know more about that.

Thanks for your comments.

Best,

-AC
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Old 04-22-13, 08:52 PM   #20
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Quote:
Originally Posted by AC_Hacker View Post
Are you saying that you have an immersion type resistive-heated thermos style vacuum insulated pressure cooker? I really want to know more about that.
-AC
Ah, so much more low tech

I don't have it yet, but the grand plan is to buy a 48 oz Nissan Thermos and an immersion heater. In the AM I'll heat up the liquid *in* the thermos, and use it throughout the day. I'm not really in any rush at the moment because summer is fast approaching and our hot water for cooking is much less for the next 5 months. Definitely on my to do list for next winter.

I'll probably contrive some sort of doohickey for the heater so that it sits flush with the thermos lip so that I do not scorch the side of the thermos,do not have to hold the thing, and have less heat loss while heating. I'm thinking glass, so that I can see when the water comes to a boil. I'll measure how long it takes to boil the 48 oz and set a timer so that I am called back to turn it off.

--
Re: your test protocol,
As was posted before me and you realized since you measured how much time the water continued to boil after the power was turned off, some of your resistive heat went to heating up the plate. I wonder if you could have turned off the resistive element say at 12" and then let the water come to a boil from the latent heat in the plate.

I completely agree with you -- go induction for the heat control and timer, not for efficiency. Not that efficiency is bad, just not superior enough to other methods to justify on that basis alone.

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