On Tue, 28 Jul 2015 08:19:32 +0100, N_Cook wrote:

On 27/07/2015 22:32, Cursitor Doom wrote:
Thank you, gentlemen.

So we're all agreed:

1. there's no problem using wire-wounds for a load provided the power
output measurement is carried out with sine waves from a suitable
external generator.

2. Even low rated power resistors can be used for the load provided their
case temperatures are kept low by some effective means of external
cooling (something more than mere heat sinks and fans, IOW).

Many thanks.

2) only if you know the current carrying capacity of their winding wire

Nope. A fuse works by heating the wire high enough to where the wire
oxidizes and turns into an metallic oxide which then crumbles. If you
can extract the heat from the wire to maintain a temperature below
this point, the fuse will last indefinitely. Dumping the load
resistor into a bucket of water does this quite nicely. To do this,
the wire is in intimate contact with a refractory ceramic which then
transfers the heat to a metal case and finally to the water. No air
gaps allowed.

You can demonstrate the principle with a common coffee cup heating
coil:
http://www.ebay.com/itm/171376872247
If you bypass the internal thermostat and run it in open air, it will
blow up rather quickly. However, if you immerse it in water, the
water will conduct most of the heat away, thus preventing the heater
wire from fusing.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558