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Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

Here's the situation: I have a small inverter generator (1200W peak, 1000W continuous. It's a Zipper STE1200IV) and I'd like to be able to run certain high-powered kitchen equipment in case of power cuts. Specifically, a 1600W sandwich toaster and a 1300W convection oven.

I was thinking of using a high-power dimmer (like this one) in-line with the load and setting the knob such that the load only consumes 1000W.

I have purchased and wired-up said dimmer and tested the toaster, and it works fine at 1000W (measured using an inline wattmeter on the dimmer input), though it buzzes audibly at a pitch of 50Hz when "dimmed". This is the kind of toaster where a thermostat constantly cycles it on/off to maintain a fixed temperature - so the loss of 600W of heating power just makes it warm up more slowly and lengthens the ON period of the duty cycle.

In my testing however I noticed that the power factor when "dimmed" is quite low (0.5 to 0.7). I understand that it is to be expected because of how an SCR dimmer chops off part of the sine wave, but what I want to know is, would this setup be safe to run with the generator? As a mechanical engineer my knowledge of reactive power is a little limited - I know the piston engine will have no problem handling the demand as the setup will only load the flywheel with circa 1000 real watts (plus overhead for losses)... but I don't know whether the inverter board can deliver 1600VA?

A second concern is, in the case of the convection oven, it uses a fan to blow air over the heating element. Since the dimmer will reduce power to both the heating element AND the fan, would the heater overheat due to the reduced airflow (despite it dissipating less power)?

RE: Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

I would use a buck transformer. Just a 10% drop in voltage will give a 20% drop in power, 15% drop in voltage would give just a little over 1000W. That non standard voltage would likely take two transformers. there are international conversion transformers 120 to 100V and 240V to 200V.

RE: Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

The problem with the dimmer is it's full power during all the parts of the power cycles that the dimmer is conducting. Since your generator is an inverter generator that's all going to impact the semiconductors not a mass of copper that gets to cool between ON periods.

Opera's idea is superior in that you will continue to load the generator in a balanced 'efficient' manner instead of an asymmetrical inefficient manner with horrid form-factor power factor.

As for the fan.. It depends. Look at the oven and figure it out. If the oven has heating rods and a fan to just circulate the air and then allows the maker to call it "convection" then it should be fine. If instead they put the heating element in some tube and the air has to blow thru it to get the heat out into the oven then low flow may toast the element. Chances are the fan is a shaded pole motor and it may not slow down with reduced voltage. In that case a tubed-heater could still work.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Using dimmer (SCR/Triac) to power oversize resistive load with small generator?

Thank you

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