25 Aug
2014
25 Aug
'14
3:33 p.m.
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.
25 Aug
25 Aug
3:43 p.m.
In the past when I?ve needed low inductance loads (for transmitter testing as opposed to
power supply testing), I?ve used carbon resistors in a jar filled with water. Water
cooled resistors can be dramatically overloaded without suffering in obvious ways. Wire
wound resistors of course can be had with higher power ratings so this isn?t so
interesting for power supplies. Still, if you have a set of plain old carbon resistors
you can arrange in parallel, and get to, say, 20% of the power rating you need, just dunk
them in water and test away. Even if you fry them, they will fail open (so no harm done)
and carbon resistors cost next to nothing.
paul
On Aug 25, 2014, at 3:33 PM, Marc Verdiell <marc.verdiell at gmail.com> 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.
4:14 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
26 Aug
26 Aug
10:45 a.m.
On 08/25/2014 1:14 PM, Chuck Guzis wrote:
On 08/25/2014 12:33 PM, Marc Verdiell wrote:
This was called a "Keep-Alive", and not only does it protect the drive
transistor this practice also increased the life of the lamp by
pre-heating the filament so it lasted far longer than it would have
otherwise. The thermal shock of being turned on from the cold state is
the time when filaments normally fail - we've all seen that - turn a
house light on and it glows extra bright and pops open...
John :-#)#
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
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