[arm-allstar] RPi3 - Allstar as Repeater Controller

[David McGough]

Hi Ramesh,

All these CPT 5v3A DC-DC converters I've gotten minimally work over the 
input voltage range of 8VDC to 20VDC. Some are advertised all the way up 
to 36V (or higher?). Also, they have synchronous rectification and high 
switching frequency, which leads to very good conversion efficiency--many 
advertise 96%.  And, I've confirmed these numbers, using a variable 
voltage bench PS for testing.

For ham-radio applications, I power the RPi3 boards (with DC-DC converter)  
from the 14V radio/repeater power supply. For non-ham applications, I
frequently use 18V or 19V 5A laptop-style power supplies as the
"pre-regulator." At 18V input, the current draw is perhaps 200mA, with the
RPi3 running "full tilt" (all cores maxed out), WiFi active, etc.

Another feature I've added in some cases is a series 10A Schottky diode in
the positive input lead before the DC-DC converter and then a fairly big
electrolytic capacitor to the negative lead (ground). This make a super
simple mini-UPS of sorts, usually saving the RPi3 from rebooting due to
some ut-oh event on the main DC power bus. This combo is incredibly 
stable, in my experience.


73, David KB4FXC





On Fri, 6 Jan 2017, "Ramesh Dhami via arm-allstar" wrote:

> On 2017-01-05 1:25 PM, "David McGough via arm-allstar" wrote:
> > Here is another photo, including a "blob FOB" which I was testing.
> >
> > https://hamvoip.org/photos/P1040276.JPG
> >
> > These "CPT" buck-mode DC-DC converters are cheap and work very well, in my
> > experience. I've got them installed everywhere.
> >
> <-- Hi , David:  I have seen these "CPT" DC-DC converters on eBay; the 
> thing that worried me about these is that every vendor spec's the input 
> as being 12VDC... there is no range or tolerance spec'd.  What is your 
> experience in terms of input voltage range and regulation of the output 
> voltage over the input range? - will these things handle up to 15V DC input?
> 
> Thanks!
> 
> Ramesh, VA3UV
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