Re: triggered SG

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Pete,

At 08:57 PM 8/7/2001 -0600, you wrote:
>For Terry,
>
>You suggest a 400 Watt resistive load for the dimmer and use 25 ohms.  I
>have several questions:
>
>25 ohms at 120 VAC is 576 Watts.

My resistors are rated at 400 watts.  Normally the dimmer is set to about
mid range so the power to the resistors is ~~288 watts.  The actual power
could probably go from 100 to 400 watts depending on where the dimmer is
set.  I just picked the 400 watt number off the resistors and my quick
mentral clct gave me 400 watts ;-) 

>
>With a dimmer is rated at only 600 Watts, isn't a 576 Watt load (not
>counting the coil) a bit much?  The load may not draw that much, but I would
>expect that the dimmer is rated that way (IOW, a load that draws 600 Watts
>at 120 volts is maximum for the dimmer, regardless of the actual wattage
>drawn with the dimmer in the circuit).    Also, 576 Watts seems like it is
>pushing the limit for 2-225 Watt power resisters.  BTW, I have run power
>resisters way over their limits, but not for long and they got HOT fast.
>

Normally the load will not get to the full power rating since the dimmer is
about 1/2 on.

>Does the dimmer reduce the load to 400 Watts?  Did you measure the power
>consumed by the resistance?  How critical is that load?

I need about 25 ohms but I don't have enough power resistor to refine it.
This load seems to vary between myself and others for some unknown reason...

>
>Would 36 ohms (400 Watts at 120 VAC) be OK or better?  Would 40 ohms do the
>job (360 Watts at 120VAC)?

I don't know 0;-)

>
>Digi-key has 300 watt resisters of 12, 16, or 20 ohms at about the same
>price as the 50 ohm, 225 Watt resisters.  Two of those in series should work
>and give a range of values near 25 ohms.  For example: a 16 ohm and 20 ohm
>in series would consume 400 Watts at 120 VAC.  The 20 ohm resister would
>dissipate 222 Watts.

I have not seen the 300 watts resistors...  I'll have to look again.  

BTW - power resistors at full load run about 350 degrees C =:O  They are
just heating elements...

Cheers,

	Terry

>
>Regards,
>
>Pete Komen
>
>I have a degree in Math; does it show? ;-)
>
>