# AC current limiting

Thread Starter

#### Da iawn

Joined Nov 17, 2019
1
The context is a kettle supplied at 220v AC from an inverter. The kettle is rated at 850 watts, resulting in a current of about 75amps on the 12v side.
I would like a circuit I can plug in between the inverter and the kettle to limit the current on the 220v side, and consequently reduce the current on the 12v side down to around 40 amps.
This is to protect a lead acid auxiliary battery in s camper.

I know the simple answer is to get a lower wattage kettle, and it's not the most effective way of heating water in this context but due to a combination of real life factors it would be very convenient to be able to plug the kettle in to the inverter and run the engine for the time it takes to boil at times where naked flames are banned.
Any suggestions.
For background my electronics experience is mainly from the 70s although I'm confident with circuit con

#### AlbertHall

Joined Jun 4, 2014
8,846
Maybe a phase controlled lamp dimmer would do the job?

#### ElectricSpidey

Joined Dec 2, 2017
784
You could cut the power in half on the 220 side with a high current diode, assuming the kettle doesn't need the other half of the cycle. (for a timer or something)

#### drc_567

Joined Dec 29, 2008
751
... Wondering if it would be feasible to reduce the high side 220 vac to 110 vac using a 2:1 transformer rated at 1 kva. The 12 volt battery load amps should be about half the original at 37 amps or so. The transformer might weigh 5 or 10 lbs. The heating wattage would only be about half at maybe 425 watts. There should not be any critical problem with running a resistive load at half voltage. The only difference would be an extended heating period necessary to achieve the required temperature.

#### LesJones

Joined Jan 8, 2017
2,420
Re post #4
NO. The current at at 12 volts would be about 19 amps (Probably a little more due to losses in the transformer.) The power to the kettle would be 212 Watts. Remember P = V^2/R. To reduce the power to half would require a transformer with a secondary voltage of about 155 volts.

Les.

#### drc_567

Joined Dec 29, 2008
751
... I am correctly corrected in post #5.

#### BobaMosfet

Joined Jul 1, 2009
893
A capacitor might work, but need to know what your load's impedance is.

Last edited:

#### AlbertHall

Joined Jun 4, 2014
8,846
The dimmer has the advantage of being easily adjustable.

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