semi-scientific experiment

[Optimistic Paranoid]

My brother found one of those tabletop electric induction cookers at a yard sale and bought it for only $5.

It's a NuWave2 made in China, natch.

I was curious, we have a stainless steel whistling tea kettle.  I emptied it and measured exactly 4 cups of water into it.  The NuWave2 has six temperature settings; low, medium-low, medium, medium-high, high, and Max-Sear.  I set it on high.  A digital readout came up and read 425 degrees - damn thing is a programmable cooking computer, too, apparently.

Anyway, I timed it. It took almost exactly six minutes to start whistling.

The next day, I put it on our Kenmore electric kitchen range, the same 4 cups of cold water, set the range on high, and timed IT.  14 minutes to start whistling.

The NuWave2 is marked as 1300 watts at 120 volts.  So that's 1300 / 120 = 10.83 amps.  At 12 volts, it would be 108.3 amps (ignoring inverter losses).

6 minutes is 1/10 of an hour, so since 108 amps for one hour is 108 amp-hours, 6 minutes would be 10.8 amp-hours from the battery bank.

Now you know.

[TedOnWalkabout]

It's interesting that you just posted this. About 2 weeks ago, I tried a cheap 800w induction cooker on my modified sine wave inverter. And promptly fried it. The smell of burning electrics was almost instantly overwhelming.

What kind of inverter are you using? I'm afraid of trying again. Thank you.
Ted

[Optimistic Paranoid]

Sorry, no inverter.  Tried it in a house.

[sternwake]

Got to love actual data.

The theoretical AH consumed does not account for Peukert's losses.

The 100AH battery cannot provide 100amps for an hour, the 100Ah battery can deliver 5 amps for 20 hours before voltage falls to 10.5v and is considered 100% dischrged.

A quality marine battery like the trojan group 27 at about 100 Ah capacity and a Peukert component of 1.15, which is likely generous as i cannot find any data on the peukert component of that battery.

Well that 100Ah battery under a 108.3 amp load, can provide only 49 amp hours, and that is disregarding inverter inefficiency, and also assumes starting with a healthy fully charged battery.

UNder that huge load the battery will likely be unable to support the 11~ volts the inverter needs to keep making that much AC wattage so even if somebody wanted to run such a load for 20+ minutes and abuse the living fuck out of the battery, they likely could not.

But at least the induction cookers are more efficient than the regular resistance heating elements, but still it is hard to do on battery power alone.

Not that anyone would likely try to do so on just one battery, i use the 100Ah group 27 12v flooded battery just as an example, but play around with different loads on different size batteries using this peukert calculator:

http://www.csgnetwork.com/batterylifecalc.html

The Peukert number of a battery also raises as the battery ages, and these numbers can vary pretty widely from battery to battery.

The Peukert component of an Odyssey AGM group 31 battery, which is a very low resistance lead acid battery is listed as 1.112. UNlikely any flooded battery has such a low peukert number.

That 1.112 Peukert component, as opposed to 1.15 estimation used in the example above, yields 59 Amp hours under the same load.

[Texjbird]

Thank You O.P.  

 I bought a brand new one over 2 years ago and have never used it.  It's nice to know their claim of less time/electricity is true.  I don't have a lot of patience so I rarely use a slow cooker.  I Want IT Now....whatever IT is....usually

TJB

[Scott7022]

Is it correct the Lithium has a different profile with respect to this law? 600 a/hr of Battle Born units through a Magnacharge 2000 hybrid inverter programmed for Lithium profile?

[sternwake]

Is it correct the Lithium has a different profile with respect to this law? 600 a/hr of Battle Born units through a Magnacharge 2000 hybrid inverter programmed for Lithium profile?

No personal experience with Lithium, but from what i've read Peukert's law can pretty much be ignored when using them.

[TedOnWalkabout]

On that 800w induction unit, it had multiple settings, using from 100 to 800 watts. I tried the 300 watt setting as I know that my rice cooker at 350w works just fine on my 300ah bank of el cheapo batteries.  The unit getting fried had to be something to do with the inverter, because the draw was pretty low.  The Peukert effect on that little draw on such a short duration should have been negligible.

[Optimistic Paranoid]

I'm sure you're right.  I personally think it was the MODIFIED Sine Wave that fried it.  A lot of stuff will run on MSW inverters, but there's also a bunch of stuff that won't.  You probably would have been fine with a Pure Sine Wave inverter.

[Optimistic Paranoid]

Is it correct the Lithium has a different profile with respect to this law? 600 a/hr of Battle Born units through a Magnacharge 2000 hybrid inverter programmed for Lithium profile?

The Wikipedia article on Peukert's Law included the following:

"Peukert's law was developed for Lead-Acid batteries, and works well in that application.
 
It does not necessarily apply to other battery chemistries, especially Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid discharge, and the Nernst Equation <https://en.wikipedia.org/wiki/Nernst_Equation> predicts battery voltage will increase with temperature. Thus, the effect of increased resistance is offset by the self-heating effect. This advantage of Lithium-Ion batteries is a well-known advertised feature, see <http://www.lithiumion-batteries.com/knowledge-base.php>.

In a research paper, a 50Ah lithium-ion battery tested was found to give about the same capacity at 5A and 50A; this was attributed to possible Peukert loss in capacity being countered by the increase in capacity due to the 30◦C temperature rise due to self-heating, with the conclusion that the Peukert equation is not applicable."