Re: Wire-wound resistors as dummy test load

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

> Resistors in series will only have the wattage of the lowest

> rated resistor.

	In Each Resistor.

> In your case wiring them in series will give you 800 ohms at

> 200 watts.

	800 Watts for the assembly.  200 Watts per resistor.

	IF making a string of mixed wattages, say 3, 200W and
	1, 100W, THEN the 100W limit would set the limit
	for the string: 100W per element: 400W total.
	This gotcha can get you if mixing resistance values,
	as each will dissipate a different amount of power.


	In general, it is good practice to _not_ run XXX W

	resistors at XXX W, but at some value under that,
	down as far as 50%.  If operating is brief (as many
	Tesla Coil Systems are so operated...) then running
	to 100% of rated wattage is more acceptable, or
	if cooling is provided (fan...).  If used as a test
	load, such concerns are less critical.

 
> ----- Original Message -----
> From: Tesla list <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Monday, September 30, 2002 7:33 AM
> Subject: Wire-wound resistors as dummy test load

>>I found 4 200-Ohm, 200-Watt wire wound resistors all the

>>same brand, that I thought I would string together as an

>> 800 Ohm, 800 Watt, test load for my TC power supply.

>>while checking things such as PFC cap size, etc.  However,
>> when I checked them with my meters, I got these readings:

>>1) 205 Ohms 339 uHy
>>2) 206 Ohms 221 uHy
>>3) 210 Ohms 225 uHy
>>4) 208 Ohms 508 uHy

>>Physically, they all seem to be the same size, shape, and

>>construction, but the variation in inductance seems

>> unreasonable.

	Lead position during the testing?
	The stray inductance of the meter leads can be iffy,
	variable, especially in the uHenry region.

>> Has anyone looked into the inductance of wire-wound resistors

>>before?

	Any professional who uses them...

>> If so, is this reasonable? I know that at 60 Hz, this only

>>amounts to about 0.1 to 0.2 Ohms inductive  reactance,
>>but it seems strange.


	best
	dwp

...the net of a million lies...
	Vernor Vinge
There are Many Web Sites which Say Many Things.
	-me