RadioBanter - View Single Post

January 25th 05, 05:55 PM

On 25 Jan 2005 08:22:59 -0800, wrote:

When looking for a power supply for my Alinco dr-590, what type of
power supply would I look for? The radio says 13.8 v dc but if I get a
12 volt power supply will it put out the same wattage at the radio?

Hi Don,

Do the math. You have the same load - less voltage. The power laws
describe this simply as E²/R.

However, it is very, very, very unlikely that you have 12.0 V of
anything as this is a "nominal" voltage, and almost never an actual
voltage. The 12 V label is derived from the common application of the
Lead-Acid Edison Battery. The cells of this battery develop 2.1 V
potential, and with their common combination into batteries of either
3 cells or 6 cells, those bring the total up to 6.3 V or 12.6 V. Many
here will recognize these values as common filament voltages for
tubes. So even here, common transformers that are either 6 or 12 V
specified, actually supply more voltage under load (because they were
originally filament power transformers).

The specification for 13.8 V is derived from the automotive electrical
system that was designed (with its voltage regulator and
generator/alternator) to supply a "float" voltage that would keep the
battery topped off while simultaneously carrying the load. Hence,
mobile applications are designed for this configuration and the source
should be robust enough to support the load.

Now, it seems to me you were using a deep discharge battery, or you
were planning to do so. This is a common application in the shack, I
have two batteries in parallel held up with a 20A trickle charge
(voltage adjusted to the optimum value). The charger (actually a
precision source from Acopian) is not large enough to supply my HF
rigs under full power out (my Drake TR-7 is rated well above 100W) but
the combination of batteries and charger manage quite well. Also, I
have connectored everything so that I can strip down, transport and
reconfigure for field day operations (sans charger).

73's
Richard Clark, KB7QHC