# nick in a variac dimmer wiring



## ship (Dec 18, 2007)

Had a Mole Richardson fan come back from a tour today. Said something about the dimmer sparking and the dimmer area getting really hot when on a low setting for a while.

This fan has a semi-exposed variac dimmer that is easy to see within the housing. Somewhere at about 90% there seems as if some kind of nick in the dimmer wiring. When the brush hits this area it sparks but continues working. No sparking or anything unusual observed about the lower dimmer setting.

What’s the possible theorized problem that caused the extra heat while on a low dimmer setting yet not on other settings persay in relation to the sparking at the higher dimmer setting? 

Splain please how the sparking at a higher dimmer setting could overheat while the dimmer is on a lower setting..


----------



## David Ashton (Dec 19, 2007)

How about it being a straight thermal problem, the variac depends on the fan airflow for cooling, low speed low cooling.
Nick on 90% is a red herring.


----------



## wolf825 (Dec 19, 2007)

ship said:


> Had a Mole Richardson fan come back from a tour today. Said something about the dimmer sparking and the dimmer area getting really hot when on a low setting for a while.
> This fan has a semi-exposed variac dimmer that is easy to see within the housing. Somewhere at about 90% there seems as if some kind of nick in the dimmer wiring. When the brush hits this area it sparks but continues working. No sparking or anything unusual observed about the lower dimmer setting.
> What’s the possible theorized problem that caused the extra heat while on a low dimmer setting yet not on other settings persay in relation to the sparking at the higher dimmer setting?
> Splain please how the sparking at a higher dimmer setting could overheat while the dimmer is on a lower setting..




I would say it has to do with how the coils conduct the electricity in a Variac system...and how a simple short or break or even dirt can create inductance or added electrical resistance in the flow thru the coil which can cause an excess thermal build up in the coil by the electricity, under even the lowest of settings... ? amperage being constant, and voltage being adjusted in that style of coil...??

-w


----------



## David Ashton (Dec 19, 2007)

Problems with that theory, current is not constant it reduces with voltage and the nick would give localized heating then burn out.
the bit about dirt creating inductance makes no sense.


----------

