I decided to see if I could find an isolated DC-DC. I have some Tyco 1/2 brick DC-DC converters which would run from pack voltage but it seemed a bit overkill to use a 150W unit to power something which draws in the mA range of current. Not being an EE I didn't have much to go by as to where to look or what kinds of parts are available. I found that Jameco Electronics had a small isolated DC-DC converter which took 9-18V input and had 9V output. I ordered this, two 3.5mm terminal blocks, a small ABS case, a PCB which fit the case, and some stand-offs to mount it.
The DC-DC said it had filtering built in but I decided to install an inductor and capacitor on both the input side and the output side to smooth out the current. I didn't find out if I need an inductor in both the positive and negative leads. I only put the inductors in the positive leads. I used two small inductors out of a dead PC power supply. The fuse holder, 1/2A fuse and 22uF capacitors came from a dead digital mulit-meter. Here is a picture of the finished board.
I mounted the box portion of the case to the underside of the dash in the Gizmo. There is a little fiberglass tab which was unused in my Gizmo. Looking at another Gizmo I see that this tab is where the fuse block used to be mounted. I put some soft wide weatherstripping on the underside of the box, drilled holes to match the holes in the fiberglass tab and then ran a large zip-tie through the holes to mount the box. I figured that mounting in this way would lessen the sharp jarring and vibration that Gizmos get on rough roads. I then mounted the PCB to the lid of the box and drilled a small hole in the lid for the wiring. This allows me to get to the unit by merely removing the lid to the box making installation/removal much easier.
So far, this has worked flawlessly.
My parts list:
- CONVERTER,DC-DC,5W,9V@0.556A 9-18Vin,REGULATED,ENCAP,FCC/CE Jameco PN:2107477
- CASE,ABS SPEEDY,3.125 x2 x.875 Jameco PN: 18922
- PROTOTYPE BUILDER,1.6 x2.7 Jameco PN: 105100
- MOUNTING HARDWARE KIT,CIRCUIT BOARD Jameco PN: 106551
- HEADER,3.5mm,TERM BLOCK,2 POS, TOP SCREW Jameco PN: 2094506
- Two 50V 22uF capacitors
- 250V Fast Acting 0.5A fuse and holders
- Two small inductors