Saturday, January 17, 2015

Driveby System - Inverter Noise

If you want to just skip to what I've decided on this is it:

http://www.mini-box.com/DCDC-USB-200  (update 2015-01-20 this item has shipped and I'm awaiting it's arrival!)  I can't wait to see how this affects the Driveby System.

Problem Solved (I think)

2015-01-22 the DCDC-USB-200 has arrived.  I am feeding it with just about 14vdc and the DCDC regulator is working!  The whole assembly is also about 1-2 lbs lighter after removing the AC/DC supplies and replacing them with the DCDC.  

Systems are up, and happy (amazing little device!)  WAY more power available then this system will ever require I suspect.  

Here are some pictures of the swap-process I did and some results:







If you still wanna read why please feel free to continue.


The Tripplite PV375 when turned on even with nothing connected to it generates a butt-ton of RFI on 50 Mhz, I didn't check other bands but I suspect there is some there too.  In yesterday's drive test I used a Yaesu VX8 to monitor 50.485 Mhz "AM" mode.  As soon as I turned on the inverter I notice a huge amount of RFI into the little handheld radio.  At the time it was running on it's own internal battery and connected to the new external radio point off the Big Box's 8 port splitter which is fed from the Discone antenna feeding the Driveby System.

So .... This is something I was afraid of when I decided to try to use a 13.8vdc to 120vAC inverter to power the system.


So now I need to go back to the drawing board in order to provide regulated 12vdc and 5vdc.  It's important that whatever I use is as highly regulated to 12.0 - 12.3vdc and 4.95 to 5.15vdc so that the motherboards I'm using are happy.


When I first was thinking about power requirements for the Driveby System I thought I would need about 8-9 amps @ 12vdc.  Turns out that even with 6 internal fans, 1 Nvidia TK1, and 3 USB hubs all running off the 12vdc rails all of that only draws 2-3 amps.


The 5vdc is only running the Odroid XU3 and that only draws < 1 amp.


So the problem here is how to get a regulated 12vdc and 5vdc from a voltage that can fluctuate between 12.3 and 15v and is nominally around 13.8v.  When I was spec'ing things out for 8-9 amps @ 12vdc this was  fairly difficult to find an off the shelf regulator at that high an amperage.


I'm sure some SMART folks out there think resolving this would be easy.  But I've been finding it difficult so far to 1.) find an off the shelf solution or 2.) find a design I could build.


My requirements for the Driveby System appear to be:

  • 12vdc regulated @ 4-5 amps (to have a bit of buffer over the nominal 2-3 amp requirement) that can run off 11-15vdc from the vehicle.
  • 5vdc I can resolve by using a 12vdc to 5vdc converter that I already have if I can get a regulated 12vdc source