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Supply Voltage Range Elecraft K2 transceiver

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rolf

Supply Voltage Range Elecraft K2 transceiver

Elecraft specifies the voltage supply range for the K2 transceiver to 9-15 Volts.

This range is suitable for lead or nickel batteries. Using Lithium rechargeable batteries it gets somewhat problematic. The voltage range with a single Lithium Ion (or Li-Polymer) Cell is from 4.2 V (fully charged) to 3 V (lower limit). Using in a power supply battery pack 4 cells in series, the voltage ranges from 16.8 V (max) to 12 V (min). With the K2 as a load to the battery pack the maximum voltage drops fast down to the plateau voltage of about 14.5 V. The upper voltage of 16.8 V, however, exceeds the maximum supply voltage as given by Elecraft.

Using 3 Lithium Cells in series, the voltage range will be from 12.6 V to 9 V. This is within the specified supply voltage of the K2. However, this voltage range is not very suitable for getting the maximum RF output.

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?

Especially for portable operation the use of Li-batteries reduces the weight in the "rucksack" considerably.

Any answer is appreciated.

Thanks and 73, Rolf, DL3AO

John Huggins, kx4o

Re: Supply Voltage Range Elecraft K2 transceiver

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?

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Eric Swartz - WA6HHQ

Re: Supply Voltage Range Elecraft K2 transceiver

Administrator

In reply to this post by rolf

16V is the specified maximum. We do not recommend operating above that level.
73,
Eric

www.elecraft.com
_..._

On Jan 12, 2012, at 1:49 AM, rolf <[hidden email]> wrote:

> Elecraft specifies the voltage supply range for the K2 transceiver to 9-15
> Volts.
>
> This range is suitable for lead or nickel batteries. Using Lithium
> rechargeable batteries it gets somewhat problematic. The voltage range with
> a single Lithium Ion (or Li-Polymer) Cell is from 4.2 V (fully charged) to 3
> V (lower limit). Using in a power supply battery pack 4 cells in series,
> the voltage ranges from 16.8 V (max) to 12 V (min). With the K2 as a load to
> the battery pack the maximum voltage drops fast down to the plateau voltage
> of about 14.5 V. The upper voltage of 16.8 V, however, exceeds the maximum
> supply voltage as given by Elecraft.
>
> Using 3 Lithium Cells in series, the voltage range will be from 12.6 V to 9
> V. This is within the specified supply voltage of the K2. However, this
> voltage range is not very suitable for getting the maximum RF output.
>
> 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?
>
> Especially for portable operation the use of Li-batteries reduces the weight
> in the "rucksack" considerably.
>
> Any answer is appreciated.
>
> Thanks and 73, Rolf, DL3AO
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Supply-Voltage-Range-Elecraft-K2-transceiver-tp7179694p7179694.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html

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Vic Rosenthal

Re: Supply Voltage Range Elecraft K2 transceiver

In reply to this post by rolf

Would it work to use 4 cells with a couple of series diodes to reduce the voltage?

On 1/12/2012 1:49 AM, rolf wrote:

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/

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Chip Stratton

Re: Supply Voltage Range Elecraft K2 transceiver

As a better and even safer solution, Use LiFePO4 cell x 4 pack for no mote
than 14 Volts from the pack. . Fully charged each cell is 3.3 to 3.5 volts.
At 2.5 volts they are depleted. This type of Lithium rechargeable us also
far more tolerant of overcharging and overdischarge than original LiPo
technology. It is far less prone to catching fire or exploding with
physical or electrical abuse It is a little more expensive, and not quite
the same power density as regular LiPo, but still beats Lead acid.

I use these for my K2 and KX1 with good results.

Chip
AE5KA

On Thursday, January 12, 2012, Vic K2VCO <[hidden email]> wrote:
> Would it work to use 4 cells with a couple of series diodes to reduce the
voltage?
>
> On 1/12/2012 1:49 AM, rolf wrote:
>> Elecraft specifies the voltage supply range for the K2 transceiver to
9-15
>> Volts.
>>
>> This range is suitable for lead or nickel batteries. Using Lithium
>> rechargeable batteries it gets somewhat problematic. The voltage range
with
>> a single Lithium Ion (or Li-Polymer) Cell is from 4.2 V (fully charged)
to 3
>> V (lower limit). Using in a power supply battery pack 4 cells in
series,
>> the voltage ranges from 16.8 V (max) to 12 V (min). With the K2 as a
load to
>> the battery pack the maximum voltage drops fast down to the plateau
voltage
>> of about 14.5 V. The upper voltage of 16.8 V, however, exceeds the
maximum
>> supply voltage as given by Elecraft.
>>
>> Using 3 Lithium Cells in series, the voltage range will be from 12.6 V
to 9
>> V. This is within the specified supply voltage of the K2. However, this
>> voltage range is not very suitable for getting the maximum RF output.
>>
>> 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?
>>
>> Especially for portable operation the use of Li-batteries reduces the
weight

>> in the "rucksack" considerably.
>>
>> Any answer is appreciated.
>>
>> Thanks and 73, Rolf, DL3AO
>>
>>
>>
>> --
>> View this message in context:

http://elecraft.365791.n2.nabble.com/Supply-Voltage-Range-Elecraft-K2-transceiver-tp7179694p7179694.html

>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

N7UN

Re: Supply Voltage Range Elecraft K2 transceiver

In reply to this post by rolf

Or use a step-down adjustable voltage regulator from http://dimensionengineering.com/DE-SWADJ3.htm

Popular among the R/C crowd, I've used this regulator (set to 13.0v) for over a year now without any problems to power my K2 from a "older" 4S LiPoly battery (fully charged to 16.4v and a flat operation voltage of 15.6v). The battery has still got a lot of re-charge cycles left so don't want to replace it yet with an A123 battery.

Plus, I add fuses for both leads and a crowbar diode for reverse polarity protection. Everything fits in a 2.5" x 1.5" x 1.15" plastic box.

Email me directly if you want more information. 73, Guy/N7UN