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Discussion Starter #1
I acquired an electric uncapping knife from an elderly beekeeper. In comparison to my nearly new one, it overheated quickly. Heated enough that the blade began to arch back like a bimetal thermometer. Melted the cappings.

I am curious if this indicates a fault in the heating element -- which I assume is nichrome wire wrapped on mica. I put it on a "wall dimmer" box, but it still ran hot (though not as excessively). The 600w wall dimmer is likely undersized for the knife.

Is this a characteristic failure mode for the electric knives? Don't want to invest in a larger (15 amp) dimmer switch if the knife is fundamentally at fault.
 

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I don't know whether the issue is characteristic of impending element failure, but if the dimmer isn't overheating it may not be undersized. The dimmer may not be cutting the voltage down far enough, so the knife still overheats.

I might try putting a suitable diode 'inline' with one of the wires to the element. Here is a example of a suitable one:
http://www.amazon.com/Amico-Molded-...=8-3&keywords=10+amp+diode#productDescription

That will eliminate half of the the AC cycle and effectively cut the power in half. See how that works, and then decide whether you want to try dimming as well.

I wouldn't leave any home-made fix like this plugged in and unattended - even for a little while. :eek:


UPDATE: A simpler plan than above would be to wire an ordinary lightbulb socket in series with one of the wires to the heating element. Then you can experiment with various wattage incandescent bulbs in that socket. Bigger bulbs will result in less power to the heating element.
 

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If it is a speed king knife there is an adjustment on it. If there is a "bump" on the top side of the blade about as big as the end of your thumb, look on the bottom side (will require cleaning the wax out) of the bump and you will find a tiny hole with a screw in it for adjusting the temp. Post up a pic of the knife.
 

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Discussion Starter #5
Hey thanks for explaining the "bump" on my newer knife.
The 2nd hand one is a "Pierce" and doesn't have any obvious adjustment. Looks like the handle rivet is just that. This has a hand stamped number of "1860 ", the plug is a molded, grounded one which manufacture date of the 1970's possible. The blade looks like it has some fatigue marks (likely from the arching that occurs when it heats).
 

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You can check the element itself by using an ohmmeter, and measuring from the ground to either of the flat spades on the plug. If you get resistance to ground, then your element has gone bad, and it will stay on all the time.
 

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That light bulb socket trick that Radar (#2) mentioned is a very neat trick for reducing electrical power. I have used it many times during my 35 years as an electrician. Great for testing without blowing too many sparks.
Charlie
 

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Discussion Starter #9 (Edited)
Thanks for walking me through the element test.

I had 700 ohm to ground from either spade. Spade to Spade (hot to neutral) was 40 ohm
My newer knife had infinite (open) from ground to spades, and 40 ohm spade to spade.

So it looks like the old knife has a circuit to ground, and is toast. Confirm?
Plugging into a GFI outlet throws the local breaker.
 

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Thanks for walking me through the element test.

I had 700 ohm to ground from either spade. Spade to Spade (hot to neutral) was 40 ohm
My newer knife had infinite (open) from ground to spades, and 40 ohm spade to spade.

So it looks like the old knife has a circuit to ground, and is toast. Confirm?
Plugging into a GFI outlet throws the local breaker.
The element itself has shorted to ground. That is why it overheats, and that will also trip your GFCI's.
 
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