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I know a washing machine and a coffee grinder are considered inductive loads so when doing math for wiring you would multiply wattage by 2x to be on the safe side. Just one plate of my inductive stove, apparently, is the biggest load in the house. It says 2100W on it. I wonder if I should treat it as a 4000W load when doing wiring. I have a strong grid connection so it was not an issue so far, but I am planning to add some batteries and the difference between 2KW and 4KW would be a major issue.

So the specific issues I'm concerned about:

  1. Power factor. Do typical induction stoves have a power factor close to a washing machine?
  2. Inrush / collapsing flux when you turn it on/off. I wonder if that might be even worse than in a washing machine. Once I had a plug come loose on that stove and before it switched itself off, it arc welded a few square millimeters off the plug and blackened the wall outlet.

Are there any rules of thumb about how to treat induction stoves when doing wiring?

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    \$\begingroup\$ I don't know for sure but it SHOULD be resistive. Watching with interest. \$\endgroup\$
    – mkeith
    May 24 at 5:07
  • \$\begingroup\$ As you have the stove put a meter on it and then you will know power factor, kVA etc exactly for that device. \$\endgroup\$
    – Solar Mike
    May 24 at 5:23
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    \$\begingroup\$ IKEA markets a induction hob as 1800W, 120V, 14-15A. This would certainly suggest a power factor close to 1. \$\endgroup\$ May 24 at 15:09
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    \$\begingroup\$ Many of them have PFC built-in, of various efficiencies and effectiveness in dealing with harmonics. As @mkeith says, the result is a would-be resistor. \$\endgroup\$ May 24 at 17:37
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    \$\begingroup\$ A 1200W table-top induction stove I use has a power factor of 0.99, so they must use a PFC circuit on the power supply. \$\endgroup\$
    – qrk
    May 24 at 21:32
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An induction stove isn't just an inductor connected across mains. A typical stove rectifies the mains power into DC, and drives the coils at a high frequency (tens or hundreds of kHz) through a resonant circuit. Ideally, the 'inductance' just provides a means for power transfer, and the load appears resistive. It is much like a voltage transformer. The main question is how the input rectifier & filter behaves.

enter image description here https://www.electronicsforu.com/wp-contents/uploads/2017/04/Screen-Shot-2017-04-14-at-3.22.46-PM.png

In the image above, the heating coil (cooktop) is represented by the inductor shown connected to the two IGBTs. The cookware itself (not explicitly shown here) is magnetically coupled to the heating coil. The 'resonant tank' refers to the combination of two capacitors, heating coil, and cookware. The MCU detects the resonant frequency of this group of components and drives the IGBTs near that frequency.

To answer your questions:

  1. A typical inductive stove would use active power factor correction within the rectifier to maintain a PF close to 1, which should be better than a typical washing machine.
  2. The coils are isolated from mains by the resonant power supply. You won't see the same inrush / inductive kick when turning the stove on /off as you would with a motor / inductor. These coils have a lower inductance and operate at a much higher frequency than a washing machine motor. Regarding your example, any loose electrical connection could cause arcing, regardless of the nature of the load.

I can't give professional wiring advice, but from an electronic perspective, an inductive oven should behave similarly to a other electronic loads, like your computer or TV. Which usually don't need special consideration.

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    \$\begingroup\$ I have a dumb question - where on the diagram is the actual hot plate? \$\endgroup\$
    – tilde
    May 25 at 13:56
  • \$\begingroup\$ @RichardtheSpacecat that would make sense - the IGBTs are for driving it, right? Is the "resonant tank" label for the pair of capacitors? Or does it include the inductor? \$\endgroup\$
    – tilde
    May 25 at 14:11
  • \$\begingroup\$ @tilde - edited to answer your questions \$\endgroup\$
    – jweeks
    May 25 at 21:21
  • \$\begingroup\$ thanks that's really clear! \$\endgroup\$
    – tilde
    May 26 at 15:21
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Found this from the 2014 report "Induction Cooking Technology Design and Assessment"

https://www.aceee.org/files/proceedings/2014/data/papers/9-702.pdf

It was presented at the 2014 ACEEE Summer Study on Energy Efficiency in Buildings.

Apart from energy consumption, the impact of any consumer electronics device on the power quality of the grid should be considered. Evaluation by EPRI (CEC 2014) found the current harmonics of induction cooking technology to be relatively low, below 6% THD (of current) for all load levels. In addition, power factor was measured at 0.98 and above. This performance is unlike that of switching power supplies, which draw current in large spikes. Although induction cooking makes use of high-frequency switching power electronics, these devices do not naturally exhibit poor power factor like switch-mode power supplies because their voltage is unregulated. Rather, power flow is controlled by varying the switching frequency of the resonant converter driving the magnetic coil.

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    \$\begingroup\$ That's because even cheaper stoves, nowadays, have PFC builtin. I've seen cheap Chinese ones that perform surprisingly well, and they're basically a boost PFC where the inductor is also the power inductor. How well they regulate the harmonics, that's a different matter, but the principle is there. \$\endgroup\$ May 24 at 17:34

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