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A common problem for resistive loads, like household heating appliances, is that peak current is drawn on startup.

I have come across ICLs (inrush current limiters), which are cheap components. Do they solve the peak cold-start problem? If so, is there some other reason why they aren't frequently or always used in household resistive heating appliances?

Aside from the startup phase, I am wondering if "intelligent" (but still, household/countertop-level) appliances can be equipped with other countermeasures to overloading whatever circuit they're connected to. For example: is it possible to sense or infer line load? Perhaps based on voltage variations? And if so are there any common current-limiting components that can be put on a 120V 15A device to modulate its load in response to circuit conditions?


Original question, closed presumably due to the distracting example, but left here so the previous comments and answers make sense:

I have a toaster and coffeemaker – two resistive loads – on the same kitchen circuit. My old coffeemaker would trip the circuit if run together with the toaster. A new coffeemaker heats water even faster but does not trip the circuit when run with the toaster.

So is there a way that such a household device can intelligently regulate its current consumption to avoid overloading a circuit?

E.g., is there some reliable line indication that it is being overloaded, like a drop in voltage?

And is there any other common current-limiting component that can be put on a 120V 15A device to react to any line feedback?

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    \$\begingroup\$ Probably has something to do about how fast it starts drawing current. I'd guess it's the initial surge of current that causes the culprit. The new device simply slows down the initial draw. \$\endgroup\$ – Stihl Alighve Jul 1 '15 at 17:43
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    \$\begingroup\$ @StihlAlighve - Yes, sounds likely. I've come across "Inrush Current Limiters (ILCs)" in other devices. Is that a likely contender for this application and behavior? And is the "startup surge" just a function of resistance heaters having their lowest resistance when cold? \$\endgroup\$ – feetwet Jul 1 '15 at 17:47
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    \$\begingroup\$ @Passerby: Maybe (although I don't know how resistive heating can be made more efficient). But for the purposes of the question I'm really just using it as an example, and wondering if there is a way for an appliance to sense line load and regulate consumption accordingly. \$\endgroup\$ – feetwet Jul 1 '15 at 18:07
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    \$\begingroup\$ A coffee maker is a more or less ideal resistive load, as the heating element does not exceed 100°C by much. So the resistance does not change, and there is no current surge. (My water cooker: 18.3 Ohm at 230V when cold -> 2890W, plate says 3000W). On the other hand, the toaster could have a higher inrush current, depending on the material of the heating wire. The wire reaches about 900°C, where many metals will show a higher resistance. I also guess the new coffee maker needs less power. (No need to measure, just check the plates!) \$\endgroup\$ – sweber Jul 1 '15 at 19:59
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    \$\begingroup\$ @IgnacioVazquez-Abrams - "toasters and coffeemakers are usually far more resistive than inductive" Yes, and that's the problem. All practical heater alloys show a positive temperature coefficient of resistance. The result is most notable in incandescent light bulbs and called "cold filament inrush" and can be 10 times operating current or more. Heaters don't get that hot, but they do show a reduced version of the effect. I'd expect toasters to be worse than coffee heaters. \$\endgroup\$ – WhatRoughBeast Jul 1 '15 at 20:16
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No there's no easy way to do limiting in the way described at the end of the question. Some electric central heating equipment has exactly that feature, but then a centrally placed current sensor is used to sense total current used in the house. That information is simply unavailable to a stand alone appliance.

There is no way for an appliance to know how much current other appliances on the same circuit breaker are using, unless it has some other source of information than simply the voltage fluctuations on the line.

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  • \$\begingroup\$ Care to elaborate on the downvote? I'm always looking to learn! \$\endgroup\$ – avl_sweden Jul 22 '15 at 20:14
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If the loads are resistive then according to Ohms law: V = R.i, or i = V/R

Therefore the only way to limit the current to the loads would be to lower the voltage. I can't think of a way to do this without power electronics (a power supply with current limiting for instance) - although that would be an overkill for a house appliance I believe.

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  • \$\begingroup\$ Also got downvoted and would like to know the reason. Any limitation in the current from a resistive load MUST come from a lower voltage in the device. \$\endgroup\$ – SuperGeo Mar 28 '16 at 15:43

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