Highest power supply voltage for K2?

[Tom Althoff]

I see old messages about undercharging the K2's internal battery if you don't use more than 14VDC for the PS.    I had a nice 15VDC 20W wall wart that I thought would make a perfect PS/charger for the K2.   The trouble is while drawing 350ma in receive the K2 shows a supply voltage of 17.2 VDC.   I turned off the K2 immediately and turned to the Elecraft group for advice.

What is the absolute highest safe voltage you can pump into the K2 before you start overheating the regulators etc?    Could I squeek by with 17.2 VDC without worrying about letting the smoke out of any of the internal componants?

Tom K2TA
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[G3VVT]

 
In a message dated 30/11/04 02:01:23 GMT Standard Time, [hidden email]  
writes:

What is  the absolute highest safe voltage you can pump into the K2 before
you start  overheating the regulators etc?


Most manufacturers seem to give 16V as the upper sustained voltage limit  for
DC input on 12V equipment. The 2SC1969 PA transistors are rated at this in  
their data sheets and the regulators seem to come out at 25V as their maximum  
input so should not represent a problem.
 
Faced with the situation you have with 1.2V above the 16V normal limit a  
string of 1N4000 series 1A diodes could bring down the voltage to what you  
require. Normal forward voltage drop comes out somewhere near 0.6V per diode, so  
two in series would probably fit the bill. Used this technique to power a Sony  
2001 SW broadcast radio I had in the Middle East for over 20 years needing  
4.5VDC power source.
 
Bob, G3VVT
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[Ron D'Eau Claire-2]

[hidden email]  
writes:

What is  the absolute highest safe voltage you can pump into the K2 before
you start  overheating the regulators etc?

-------------------------------------------------------------

The K2 manual says "9 to 15 vdc"

I'd be inclined to believe them if you want to keep the smoke inside those
components...

Ron AC7AC


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[Tom Althoff]

Bob G3VVT wrote "...a string of 1N4000 series 1A diodes could bring down the voltage to what you require..."

I'm glad you mentioned it Bob.   It's my favorite way to drop a DC supply a few volts down.   I have four 10amp rectifiers here which would give me 2.4V drop..17.2 - 2.4 = 14.8.

The wall wart is rated at 15VDC but as Don pointed out the regulation on these things is pretty poor and under no load I was experiencing 17VDC.  Under a 1 amp load the voltage was 15.1.  Since most of the time I'm not transmitting under load I was hesitant to apply it until I checked here.

The manual that came with my K2 when discussing the output capacity of the PA stages states on page 102 of the Theory of Operation...

"The transmit strip is conservatively rated to provide excellent reliability and immunity to high SWR.  The same push-pull final could be pushed to over 40W on the lower bands."    

This is what let me to believe there might be some leeway.   I doubt they were talking about trying to draw 4 times as much current to get the 40W but to run it at a higher voltage than was in the specs.

I just need something to keep the battery charged while I'm at the cabin.   I didn't want to bring my 10AMP boat anchor supply so the wall wart was a small,  though less than optimum, solution.

I'll eventually add Don's smart charger hookup to help extend the life of the battery.

Thanks to all who answered.  

73 de Tom K2TA
  ----- Original Message -----
  From: [hidden email]
  To: [hidden email] ; [hidden email]
  Sent: Monday, November 29, 2004 9:29 PM
  Subject: Re: [Elecraft] Highest power supply voltage for K2?


  In a message dated 30/11/04 02:01:23 GMT Standard Time, [hidden email] writes:
    What is the absolute highest safe voltage you can pump into the K2 before you start overheating the regulators etc?
  Most manufacturers seem to give 16V as the upper sustained voltage limit for DC input on 12V equipment. The 2SC1969 PA transistors are rated at this in their data sheets and the regulators seem to come out at 25V as their maximum input so should not represent a problem.

  Faced with the situation you have with 1.2V above the 16V normal limit a string of 1N4000 series 1A diodes could bring down the voltage to what you require. Normal forward voltage drop comes out somewhere near 0.6V per diode, so two in series would probably fit the bill. Used this technique to power a Sony 2001 SW broadcast radio I had in the Middle East for over 20 years needing 4.5VDC power source.

  Bob, G3VVT
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[Dan Barker]

I've always done the following to see if I was going to toast something.
Maybe someone can tell me the error of may ways (the last thing I did this
on was a $1,400 Video Camera - if the method is dangerous, I'll stop!).

I hook the 6V Camera up to a 6V power supply (actually a variable voltage
PS) through an ammeter. I slowly advance the voltage (toward the 9.6V target
of the high-capacity batteries stolen from my Electric Zagi model airplane).

I figure if the current goes up, I'm going to cook something. If the current
decreases, then the power being dissipated is roughly constant so I'm not
cooking anything.

If I'm WAY off in left field, let me know. I'll spring for the $60 camera
batteries that don't last worth a poop instead of the [already on hand]
airplane batteries that hold up nicely.

If I'm NOT off in left field, this is a nice way to check out a circuit
without a diagram or any disassembly/tracing.

Dan / WG4S / K2 #2456

I a message dated 30/11/04 02:01:23 GMT Standard Time, [hidden email]
writes:

<snip>
What is  the absolute highest safe voltage you can pump into the K2 before
you start  overheating the regulators etc?
</snip>

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[Jack Brindle]

Guys, there are several things to consider when raising the input  
voltage to the K2 family.

First, power loss in the regulators. There are several 5V, 6V and 8V  
regulators on board. If you have a 12V source to a 6V regulator, you  
will be burning up as much power in heating up the regulator as in  
powering the circuit. At 15 volts you will be wasting twice as much  
power in the 5V regulator as the circuitry it feeds. I'm sure you would  
much rather have that power go out the antenna port or the speaker than  
to warm the case.

The other big thing to consider is the voltage rating of the  
components. Some of the electrolytics in the K2 or its various  
accessories are rated in the 15 to 20 volt range in order to keep the  
size down. Do you _really_ want to risk popping these things?

The max rated input voltage to the K2 and its accessories is 15 volts  
for a very good reason. Your K2 will last much longer if you keep the  
power supply below this level...

On Nov 29, 2004, at 11:53 PM, Tom Althoff wrote:

> The wall wart is rated at 15VDC but as Don pointed out the regulation  
> on these things is pretty poor and under no load I was experiencing  
> 17VDC.  Under a 1 amp load the voltage was 15.1.  Since most of the  
> time I'm not transmitting under load I was hesitant to apply it until  
> I checked here.
>
> The manual that came with my K2 when discussing the output capacity of  
> the PA stages states on page 102 of the Theory of Operation...
>
> "The transmit strip is conservatively rated to provide excellent  
> reliability and immunity to high SWR.  The same push-pull final could  
> be pushed to over 40W on the lower bands."
>
> This is what let me to believe there might be some leeway.   I doubt  
> they were talking about trying to draw 4 times as much current to get  
> the 40W but to run it at a higher voltage than was in the specs.

- Jack Brindle, W6FB
------------------------------------------------------------------------
---------------------

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[Don Wilhelm-3]

Dan,

You method will work in some cases, but can result in component damage in
others - there is no one answer, it depends on the device and its design.  I
personally wouldn't try that with my digital camera (it is not a throw-away
expense to replace it).

Far better to use a regulator or even a string of diodes to bring the
voltage to something less than the max specified for the device in question.

73,
Don W3FPR

----- Original Message -----
From: "Dan Barker" <[hidden email]>
To: "Elecraft" <[hidden email]>
Sent: Tuesday, November 30, 2004 8:29 AM
Subject: RE: [Elecraft] Highest power supply voltage for K2?

> I've always done the following to see if I was going to toast something.
> Maybe someone can tell me the error of may ways (the last thing I did this
> on was a $1,400 Video Camera - if the method is dangerous, I'll stop!).
>
> I hook the 6V Camera up to a 6V power supply (actually a variable voltage
> PS) through an ammeter. I slowly advance the voltage (toward the 9.6V
> target
> of the high-capacity batteries stolen from my Electric Zagi model
> airplane).
>
> I figure if the current goes up, I'm going to cook something. If the
> current
> decreases, then the power being dissipated is roughly constant so I'm not
> cooking anything.
>
> If I'm WAY off in left field, let me know. I'll spring for the $60 camera
> batteries that don't last worth a poop instead of the [already on hand]
> airplane batteries that hold up nicely.
>
> If I'm NOT off in left field, this is a nice way to check out a circuit
> without a diagram or any disassembly/tracing.
>
> Dan / WG4S / K2 #2456
>
> I a message dated 30/11/04 02:01:23 GMT Standard Time, [hidden email]
> writes:
>
> <snip>
> What is  the absolute highest safe voltage you can pump into the K2 before
> you start  overheating the regulators etc?
> </snip>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
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> Elecraft web page: http://www.elecraft.com
>

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[Jessie Oberreuter]

      If the airplane batteries are clearly superior in performance, you
should consider making a pack of them that meet the voltage requirements
of your camera.  In almost every circumstance, the excess voltage is being
dissipated as heat and/or causing more direct damage.


On Tue, 30 Nov 2004, W3FPR - Don Wilhelm wrote:

> Dan,
>
> You method will work in some cases, but can result in component damage in
> others - there is no one answer, it depends on the device and its design.  I
> personally wouldn't try that with my digital camera (it is not a throw-away
> expense to replace it).
>
> Far better to use a regulator or even a string of diodes to bring the voltage
> to something less than the max specified for the device in question.
>
> 73,
> Don W3FPR
>
> ----- Original Message ----- From: "Dan Barker" <[hidden email]>
> To: "Elecraft" <[hidden email]>
> Sent: Tuesday, November 30, 2004 8:29 AM
> Subject: RE: [Elecraft] Highest power supply voltage for K2?
>
>
>> I've always done the following to see if I was going to toast something.
>> Maybe someone can tell me the error of may ways (the last thing I did this
>> on was a $1,400 Video Camera - if the method is dangerous, I'll stop!).
>>
>> I hook the 6V Camera up to a 6V power supply (actually a variable voltage
>> PS) through an ammeter. I slowly advance the voltage (toward the 9.6V
>> target
>> of the high-capacity batteries stolen from my Electric Zagi model
>> airplane).
>>
>> I figure if the current goes up, I'm going to cook something. If the
>> current
>> decreases, then the power being dissipated is roughly constant so I'm not
>> cooking anything.
>>
>> If I'm WAY off in left field, let me know. I'll spring for the $60 camera
>> batteries that don't last worth a poop instead of the [already on hand]
>> airplane batteries that hold up nicely.
>>
>> If I'm NOT off in left field, this is a nice way to check out a circuit
>> without a diagram or any disassembly/tracing.
>>
>> Dan / WG4S / K2 #2456
>>
>> I a message dated 30/11/04 02:01:23 GMT Standard Time, [hidden email]
>> writes:
>>
>> <snip>
>> What is  the absolute highest safe voltage you can pump into the K2 before
>> you start  overheating the regulators etc?
>> </snip>
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>
>
> _______________________________________________
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>

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[Hisashi T Fujinaka]

I worked in the semiconductor industry and I remember frying a bunch of
chips when I reached a knee in the current draw. You can increase the
voltage until something breaks down, and then you're hosed. Lots of
current flows and your semiconducting device is no longer conducting at
all since you let all the magic smoke out.

I'd suggest the correct batteries, but I worked in a ham radio repair
shop years ago and I know how *(@#*&$ cheap hams are so I know telling
you to pay any extra to use the correct batteries will fall on deaf
ears. :)

>> ----- Original Message ----- From: "Dan Barker" <[hidden email]>

>>> I hook the 6V Camera up to a 6V power supply (actually a variable
>>> voltage PS) through an ammeter. I slowly advance the voltage (toward
>>> the 9.6V target of the high-capacity batteries stolen from my
>>> Electric Zagi model airplane).
>>>
>>> I figure if the current goes up, I'm going to cook something. If the
>>> current decreases, then the power being dissipated is roughly
>>> constant so I'm not cooking anything.
>>>
>>> If I'm WAY off in left field, let me know. I'll spring for the $60 camera
>>> batteries that don't last worth a poop instead of the [already on hand]
>>> airplane batteries that hold up nicely.

--
Hisashi T Fujinaka - [hidden email]
BSEE(6/86) + BSChem(3/95) + BAEnglish(8/95) + MSCS(8/03) + $2.50 = latte
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[Bob - W5BIG]

Hi Dan,

I would be very hesitant to use this technique on expensive equipment.
Gradually turning up the voltage while watching the current can lead to a
problem that doesn't show up immediately since components can be operated at
a higher than normal temperature for a while but their failure rate goes up.
After a few hours, days, weeks, your circuit may be damaged.

The determination of absolute max input voltage depends on a lot of factors
and it's a major engineering problem to determine the safe value.  For
example, the power rating of the regulators depends on how they are mounted.
It may not be convenient to measure their case temperature to characterize a
particular application. Alternatively, one can be conservative and use the
databook values.  Since the guys at Elecraft say 15V, I would go along with
that.  If the power supply is not well regulated, consider the max value
with no load.

73/ Bob - W5BIG


----- Original Message -----
From: "Dan Barker" <[hidden email]>
To: "Elecraft" <[hidden email]>
Sent: Tuesday, November 30, 2004 7:29 AM
Subject: RE: [Elecraft] Highest power supply voltage for K2?


> I've always done the following to see if I was going to toast something.
> Maybe someone can tell me the error of may ways (the last thing I did this
> on was a $1,400 Video Camera - if the method is dangerous, I'll stop!).
>
> I hook the 6V Camera up to a 6V power supply (actually a variable voltage
> PS) through an ammeter. I slowly advance the voltage (toward the 9.6V
target
> of the high-capacity batteries stolen from my Electric Zagi model
airplane).
>
> I figure if the current goes up, I'm going to cook something. If the
current
> decreases, then the power being dissipated is roughly constant so I'm not
> cooking anything.
>
>



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