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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: David Allred on March 12, 2018, 08:15:52 PM

Title: Load type and rating confirmation
Post by: David Allred on March 12, 2018, 08:15:52 PM

I did a little research and just need a confirmation of my  interpretation.  I need to force cool down periods for a fog machine that on some days can be on for up to 12 hrs.  6 hour rated.  Thinking about 3 on and 1 off.  Anyway, the relay of the timer as 2 ratings.  A higher resistive rating and a lower tungsten rating.  A fog machine falls in the resistive category, correct? 
Thanks.

Title: Re: Load type and rating confirmation
Post by: Nathan Riddle on March 12, 2018, 11:46:07 PM

Quote from: David Allred on March 12, 2018, 08:15:52 PM

I did a little research and just need a confirmation of my  interpretation.  I need to force cool down periods for a fog machine that on some days can be on for up to 12 hrs.  6 hour rated.  Thinking about 3 on and 1 off.  Anyway, the relay of the timer as 2 ratings.  A higher resistive rating and a lower tungsten rating.  A fog machine falls in the resistive category, correct? 
Thanks.

Mostly a toaster oven with some tubes. And a small ac pump.

So yeah, resistive; though I am unsure how tungsten is any less resistive than a resistor?

Title: Re: Load type and rating confirmation
Post by: Geoff Doane on March 13, 2018, 07:52:02 AM

Quote from: Nathan Riddle on March 12, 2018, 11:46:07 PM

though I am unsure how tungsten is any less resistive than a resistor?

A tungsten lamp has a high inrush current when it is first powered on.

The cold resistance is much lower than the operating resistance. The resistance of most materials goes up as they get hotter (like speaker voice coils), but it's particularly pronounced with tungsten light bulbs.

You can calculate what the operating resistance of a 100W lightbulb is (144 ohms), but if you measure a cold filament, it will be far less.

GTD

Title: Re: Load type and rating confirmation
Post by: Nathan Riddle on March 13, 2018, 08:18:26 AM

Quote from: Geoff Doane on March 13, 2018, 07:52:02 AM

A tungsten lamp has a high inrush current when it is first powered on.

The cold resistance is much lower than the operating resistance. The resistance of most materials goes up as they get hotter (like speaker voice coils), but it's particularly pronounced with tungsten light bulbs.

You can calculate what the operating resistance of a 100W lightbulb is (144 ohms), but if you measure a cold filament, it will be far less.

GTD

Ahh! Thanks for the explanation!