On 26/01/13 10:48, Chris Green wrote:
On Fri, Jan 25, 2013 at 07:16:40PM +0000, Anthony Anson wrote:
So puting it another way: if a PSU says it can deliver 1A @5V, then I should be able to stick a 5ohm (R=V/I) resister across the terminals and the voltage shouldn't drop substantially below 5V?
Theoretically. Remember that the resistance of a component is often temperature sensitive, and a resistor's value is probably measured at expected working temperature. While it's unlikely to vary a lot over the range, if the PSU is working at its limit, it could be put at risk.
Any 'purpose made' resistor will have (for the case in point) a negligable temperature coefficient. It's only things that *aren't* 'resistors' that will change value significantly with temperature.
Even a crude bit of 'resistance wire' (as in constantan, I think that's one of the names) will have a temperature coefficient of a tiny fraction of a percent per degree and will maintain essentially the same resistance up to red heat.
Try testing a wire-wound resistor...