[Elecraft] Supply Voltage Range Elecraft K2 transceiver

[John Huggins, kx4o]

Hi Rolf,

Judging from the K2 schematic, there is no over-voltage protection, save 
for the SB530 (D12) reverse protection diode which, in normal hookup,
won't do much until the bus hits ~30V; This is clearly meant for reverse
protection only and really that's taken care of with D10.  I guess D12 is
there in case someone drives power reversed into P3.  Smart.

A related question concerning whether the K2 can handle high voltages is...

Did the K2 designers have automotive power systems in mind when designing
the rest of the circuitry that touches their "12V" internal bus?

This implies 9-15 nominal voltage, as their spec. sheet suggests, but also
implies the ability to handle the addition of power bus ripple up to ~16.5
Volts peak and temporary spikes/surges up to 25 volts or more... the real
world of vehicle power busses.  9-18 Vdc is the usual nominal rating for
anything that connects to a "12V" automotive power bus.

A quick glance at all the parts touching "12V" or "12V IN" finds items
with ratings of 20V (6V Reg.), 22V (Audio Amp), 25 V (Finals), 26V nom.
40V peak (8V reg.), etc.  I suspect nothing will "punch through" those
higher rated parts when run at 16V.  However, I would have concern over
the power dissipation of those finals and voltage regulators when running
more than 15V.

Given the voltage ratings of the K2 parts on the 12V bus, I wouldn't
connect a K2 to an automotive power bus without a peak clamping circuit
inline... similar to D28 in the K3 design.

However, you are asking about 4S Lithium Battery Packs.

Until someone runs a stress analysis on the key warm parts in the K2, I
would not run it beyond 15V.  You can do what other 4S Lithium converts
from many industries (who face this exact same problem) do... put a low
dropout regulator in series with the pack and set it to 14V or so.  This
ensures you are not pushing power dissipation in the K2's parts beyond
their design limits.

John, kx4o


On 1/12/12 4:49 AM, rolf wrote:
> Elecraft specifies the voltage supply range for the K2 transceiver to
9-15 Volts.
> <snip>
> Question: Keeping the RF power output and the DC Current of the K" below
the maximum limit, is it possible to apply a supply voltage exceeding 16 V
without causing a failure to the electronic components in the K2?