[Elecraft] OT: Quiet 12V-to-5V converter

[Jack Smith]

While a 6V battery may work, I would be concerned with voltage 
regulation. If the data logger is a true 5V device, a simple series 
diode may not keep the supply within acceptable limits over the typical 
range of battery voltage from full charge to discharge. An analog LDO 
regulator would be a better choice than a diode.

However, a 12V battery supply would, according to the original post, 
also allow the receiver to be powered from one source.

Jack K8ZOA


On 1/6/2012 12:49 PM, David Gilbert wrote:
>
> Why not just use a 6 volt motorcycle battery (two or three in parallel
> if necessary) with a series diode?  The total weight isn't going to be
> any different no matter what you do ... one battery for everything or
> separate batteries for receiver and data logging.   AH capacity is AH
> capacity.   The efficiency would probably be above 85% if a diode rated
> for a couple of amps was used, assuming a Vf around 0.7 volts, and it
> would be tough to beat for quiet.
>
> Dave   AB7E
>
>
>
> On 1/6/2012 9:34 AM, Jack Smith wrote:
>> There are quite a few simple switching regulator chips for 12V -->   5V,
>> requiring only a handful of parts to make a complete switching
>> converter. For example, National Semiconductor (now TI after the recent
>> purchase) LM2591HVT-5.0/NOPB. Stocked by Mouser and DigiKey at about $6.
>> This series is available in a through hole 4-pin TO-220 style device so
>> breadboarding up a one-off power supply isn't too difficult.
>>
>> With careful attention to detail, bypassing and shielding it should be
>> possible to build a quiet 5V, 1A supply around these parts. It can be
>> small enough to fit into a 2"x2"x1" Hammond die cast enclosure, and you
>> can use feedthrough caps for input and output, along with some internal
>> LC filtering.
>>
>> Still, 5V at 700 mA with a switching regulator and a 12V battery
>> (assuming 100% efficiency which isn't possible of course) the setup will
>> require 300mA from the battery. For 100 hours of operation, you're
>> looking at a 30 Ah battery requirement. While a battery will output more
>> Ah with a 100 hour discharge cycle, it's not that much more.  A 35Ah
>> sealed 12V gel-cel type lead acid battery will run you about $100.
>>
>> For serious long duration battery operation, I would look for a more
>> thrifty data logger.
>>
>> Jack K8ZOA
>>
>>
>> On 1/6/2012 10:10 AM, John Gibson wrote:
>>> Dear Elecraft list members,
>>>
>>> The recent thread on noisy switching power supplies leads me to a related question. My son n8fyk, who teaches radio astronomy, has set up a project with his students. They are using a 15m direct-conversion Radio Jove receiver in the field to monitor radio emissions from Jupiter, the sun, and the galaxy. The receiver operates from 12V, which is readily supplied by a portable utility 12V battery pack. Their problem is powering their data recorder, which needs about 5V at 0.7A.
>>>
>>> The data recorder is designed to operate from three internal AA alkaline cells, but these give a limited run time. My son would like to be able to leave the receiver and recorder for unattended operation for several days at a time.
>>>
>>> One solution would be to use a 12V-to-5V power converter between the 12V battery and the data recorder. For long battery life, it would be nice to have the efficiency of a switching converter. Such a converter would have to be RF-quiet, so as not to interfere with their weak-signal reception.
>>>
>>> I will be interested to hear what list members recommend.
>>>
>>> Thank you and 73,
>>>
>>> John, no8v
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