Re: OLTC primary loss measurement

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 02:02 PM 8/30/2002 -0600, you wrote:
>Original poster: "tesla by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><tesla-at-paradise-dot-net.nz>
>
>Few Further thoughts on last post re this:
>
>1) The only thermal resistance you need to know is heatsink to air if you
>measure heatsink temp. This is normally published for each heatsink type


But that number is only a "design guide", used for sizing the sink in the 
first place, not an actual measured or reliable number.  A huge amount of 
things can affect the sink<>ambient resistance.. small amounts of air 
movement (as from thermal gradients) dramatically reduce the thermal 
resistance.  If you think electromagnetic stuff is complex, it's nothing 
compared to heat transfer, where the transfer medium is non-linear, has 
varying flow regimes (turbulent/laminar), and all sorts of other weird effects.

Putting it in a big box (to reduce the effect of external air currents) and 
doing a power replacement calorimetric measurement would be your only hope




>2) You can reduce time to reach equilibrium if you preheat the heatsink with
>a hairdrier. (you need to have a feeling for this as to how much to preheat
>it)
>
>3) Smaller heatsinking would much reduce time to reach equilibrium if that
>is a problem.
>
>Good Luck
>Ted L in NZ