[Elecraft] laptop power supply to power KX3

Tue Sep 18 19:08:34 EDT 2012

Bill,

If it sits on the floor, what is the problem.   No meters in your face, 
just good DC power provided to the rigrunner.  The fuse sets the current 
supplied to the transceiver.  The KX3 will only draw 3 amps on transmit 
at full power.  The maximum current available from the power supply has 
no meaning other that the requirements of the load  cannot exceed the 
power supply ratings.  In other words, one cannot power a 100 watt 
amplifier from a 6 ampere power supply.

I detect that there are many monitoring this thread who do not 
understand the voltage, current. power relationship as it relates to 
DC.  I do not want to enlighten all, but some of the questions have gone 
below the level that all radio amateurs  should understand from basic 
principles of Ohms Law - some of the most fundamental equations relating 
voltage, current, and power.  If there is not a basic understanding of 
those parameters, there is a great communications loss.  I am sorry, but 
I cannot "spoon feed" those who do not have a grasp of those basic 
electrical parameters.  If it was not on your amateur radio exam, then 
you can find it in the ARRL Handbook Electrical Laws and Circuits chapter.
It is simple - voltage equals current times resistance, Power equals 
voltage times current - fundamental formulas, but I feel that many hams 
do not have any concept of those parameters - this is basic, entry level 
stuff.

73,
Don W3FPR

On 9/18/2012 6:40 PM, Bill Tubbs wrote:
> I actually have a 20-amp Astron, as well as a 20-amp Icom supply, but I was hoping for something in the middle. If I were just going to consider using only the KX3 i suppose a 6-7 Amp supply would do the trick, and I would think it might be no bigger than the KX3 itself, no?
>
> Bill
> WK6A
>
> Sent from my iPhone
>
> On Sep 18, 2012, at 2:16 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:
>
>> Bill,
>>
>> I would suggest an Astron 20 amp supply (or even the 35 amp linear).  Yes, it is overkill for the 12 watt KX3, but that is no problem, the current will not exceed what the connected device (the KX3) needs even though the supply is capable of much more current. When you also have the KXPA3, you will need that extra current.  You also have other 12 volt powered devices around the shack, so the extra current rating will help with powering those devices.
>>
>> For those who want to homebrew for the basic KX3, I suggest you look at the article in QST from November 1993 page 27 for a 5 amp regulated 13.8 volt 5 amp power supply with crowbar overvoltage protection.  We are hams, so think "build your own"  It is a good philisophy/
>>
>> 73,
>> Don W3FPR
>>
>> On 9/18/2012 4:53 PM, Bill Tubbs wrote:
>>> After sending my note about using the little MFJ power supply at 2.89 amps, I realized that it works fine on my FT-817D at 5 watts but would obviously be taxed at the full 12 watts of the KX3. So fuggetabowdit.
>>>
>>> Now I'M looking for a sufficient supply for the KX3 ;-)
>>>
>>> Bill
>>> WK6A
>>>
>>> Sent from my iPhone
>>>
>>> On Sep 18, 2012, at 4:44 AM, Johnny <vr2xmc at yahoo.com.hk> wrote:
>>>
>>>> Yes , correct , laptop supplies are often RF noisy.
>>>>
>>>> Sent from my  iPhone 4
>>>>
>>>> "Fred Townsend" <ftownsend at sbcglobal.net> 於 2012年9月18日 下午2:04 寫道：
>>>>
>>>>> Jeff, caution.  Laptop power external supplies are designed to be followed
>>>>> by precision internal regulators that handle the logic voltages and charging
>>>>> the battery. The external supplies are not well regulated and can be quite
>>>>> noisy.  They may not be the best supplies for ham rigs.
>>>>> 73
>>>>> Fred, AE6QL
>>>>>
>>>>> -----Original Message-----
>>>>> From: elecraft-bounces at mailman.qth.net
>>>>> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jeff Herr
>>>>> Sent: Monday, September 17, 2012 6:40 PM
>>>>> To: 'Elecraft Reflector'
>>>>> Subject: [Elecraft] laptop power supply to power KX3
>>>>>
>>>>> While at work I went through our stock of power supplies for the various
>>>>> makes of laptops we use.
>>>>> I found that Toshiba supplies are specified 15v and ranged in current
>>>>> capability from 2.5 amps and up.
>>>>>
>>>>> Dell, Lenovo, HP, Acer, Asus all use 19v supplies.
>>>>>
>>>>> Those Toshiba supplies are very small.
>>>>>
>>>>> WW6L
>>>>>
>>>>>
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