[Elecraft] K3 - Power cable voltage drop

[Bob McGraw K4TAX]

Yes true.   However seeing they way some hams configure their stations, 
building or modifying and implementing a power supply with voltage 
sensing, is of serious questionable nature. Likewise, in conditions 
where power supplies are buried under the desk.  One needs to see the 
volt meter when the supply is first turned on to assure the voltage is 
correct.   And that should be done before the radio is turned on.     Oh 
I know about crowbar circuits, but if that $2.50 part fails it will 
likely take out a $3000 radio.   This just isn't smart.

Having worked with equipment that was supplied with 35 ft or 50 ft power 
cables for loads of 20A to 30A at + & - 18 volts, I understand just a 
wee bit about voltage sensing circuits and what makes them oscillate.

Just err on the safe side.    And for ham radio, it likely is not 
necessary to have or implement remote voltage sensing.  Wire and 
connectors are cheap.   Use a shorter length of wire or larger gauge 
wire.   There's no likely component failure with this approach.

73

Bob, K4TAX


On 12/24/2019 8:25 PM, K9MA wrote:
> Typically, there are small resistors at the power supply between the output and sense terminals to prevent the voltage from rising if a sense wire opens up.
>
> 73,
> Scott K9MA
>
> ----------
>
> Scott Ellington
>
>   --- via iPad
>
>> On Dec 24, 2019, at 5:39 PM, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:
>>
>> Yes, but one screw-up on the remote sensing system and it will take advantage of the voltage overhead on the pass transistors and likely wipe out every piece of equipment.       I strongly do not advise it.   And you make a valid point for NOT using remote sensing.
>>
>> 73
>>
>> Bob, K4TAX
>>
>>> On 12/24/2019 3:22 PM, Jim Rhodes wrote:
>>> I have thought about doing that. Just requires a 2 wire hookup with small
>>> gauge wire. But I run all of my small items like the remoterig box, LP-pan
>>> box, VHF/UHF rig and so forth off of the main supply and if I have a larger
>>> than anticipated voltage drop on rig power cable the voltage on the other
>>> tings could go fairly high. The power supply is a HB thing with at least a
>>> 50 amp capacity and plenty of voltage overhead before pass transistors.
>>> (Used to run 2 HF rigs before downsizing.)
>>>
>>>
>>>> On Tue, Dec 24, 2019 at 2:25 PM Rose <elecraftcovers at gmail.com> wrote:
>>>>
>>>> First, it would require some basic technical skill ... (;-)
>>>>
>>>> 73
>>>>
>>>> K0PP
>>>>
>>>> On Tue, Dec 24, 2019, 13:20 Karin Johnson <karinann at tampabay.rr.com>
>>>> wrote:
>>>>
>>>>> Why hasn't anyone used remote sensing at the radio voltage input?
>>>>> As far as I know all of the Astron supplies don't have external sense
>>>>> wiring.  Many so called professional grade high current supplies provide
>>>>> For external connection of the voltage sense back to the regulator chip.
>>>>> I've toyed with this idea a bit but haven't had the time dig in to the
>>>>> Astron supply I have.  If this were implemented then one could maintain
>>>>> 13.8 volts or whatever you desired at the radio power supply inputs,
>>>>> Regardless of the current draw.
>>>>>
>>>>> Karin Anne Johnson K3UU
>>>>>
>>>>>
>>>>> ______________________________________________________________
>>>>> Elecraft mailing list
>>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>>> Post: mailto:Elecraft at mailman.qth.net
>>>>>
>>>>> This list hosted by: http://www.qsl.net
>>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>> Message delivered to elecraftcovers at gmail.com
>>>>>
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:Elecraft at mailman.qth.net
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>> Message delivered to jimk0xu at gmail.com
>>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to k9ma at sdellington.us
>