25 Aug
2014
25 Aug
'14
1:14 p.m.
On 08/25/2014 12:33 PM, Marc Verdiell wrote:
I use 10 Ohm 10 or 25W resistors, 2 or more of them in
parallel,
depending how much current you want to draw. They look like white
rectangular bars. They have them on the shelf at my Fry's electronics
store. For what it's worth, on the latest power supply I tried, just
one resistor was not enough to start the supply, I needed 2 to draw
at least 1A from the 5V and then it was OK.
A wirewound power resistor in series with an incandescent lamp is
perhaps a better solution than the incandescent alone, particularly if
you're loading close to the overcurrent limit of the PSU.
An incandescent (tungsten) lamp can have a hot-to-cold resistance change
of 10 to 1 or more. When incandescents were used for panel indicators
and such, one technique was to add a resistor to keep the lamp faintly
glowing "warm" to avoid the shock on the driving transistor.
Globar resistors are probably the best loads. Negative temperature
coefficient, non-inductive; gives a nice "soft start"
characteristic--and used extensively as RF dummy loads. Sandvik Kanthal
seems to be big vendor of these nowadays.
--Chuck