Thursday, January 1, 2015

Powering the "Driveby" System

Initially I brain-farted on the 12vdc power requirements for the "Driveby" system's hardware.  I hadn't really thought about the 12vdc from the Truck actually being more like 13.8 with surges and dips in voltage that are normal for any "12vdc" system in an automobile.  Doh!

Equipment like one of the USB powered Hubs is 7-24vdc input (self regulated) would probably be just fine.  However, the Nvidia TK1 that is 12vdc, and the Netgear Network Hub which is 12vdc probably wouldn't be so happy with 13.8+/- varying all over the place.  

To be "safe" I've decided that the SIMPLEST, not necessarily the cheapest or smartest or most power-economical way to deal with this issue is to simply purchase a 12vdc to 120v (AC) power inverter.  These things are fairly cheap, and just plug into the 12vdc (read: 13.8+/-) cigarette lighter outlet in my Truck.  This gets me to a regulated 120v AC.  So at this point I have options where I can simply use a 120vac power strip and the walwart 12vdc regulated supplies which come with the TK1, and the Netgear Hub ~OR~ I can use a "Mean Well" 120vac to 12vdc regulated supply and power everything from that one 12vdc source that requires 12v.  I prefer the later method.  As in the past it's been much simpler to control noise issues in systems similar to the "Driveby" system I'm currently working on.

While I agree (probably with most folks) that it seems ridiculous to take 13.8vdc and ramp it up to 120vac and then back down to 12vdc (regulated)....It's SIMPLE.  I tend to lean towards 'simple' when I can, and save my brain and time for the things that are more difficult.

At the start of all of this I had decided NOT to go this route, and then completely forgot about the issues of 13.8v vs. 12vdc and 'computer equipment' that *expects* 12vdc exactly (more or less) being finicky about it's input 12vdc.  Being this close to actually getting on the road with the entire system I didn't want to waste a week or even a few more days ordering parts, and then building and testing a 13.8vdc to 12vdc power regulator/stabilizer.  I searched around for 2 days looking for something that could do about 10 amps @ 12vdc like this, but came up with nothing that looked like it wasn't 'sketchy'.

So I've decided to use a simple 12vdc to 120vac inverter like the Tripplite PV375 which can handle 350 watts continuous and surges to 600 watts.  I found one on Ebay for $57.00.

I already have several Mean Well 120v to 12vdc, and 5vdc supplies on had in the junk box which I'll use for this.  

These two items are small, and easy to wire up, and the problem is solved for cheap, without spending a lot more time having to think, order/wait, build, and test something.

I've used one of these PV375's before.  They're reliable at least.  Albeit a tad bit noisy on it's cooling fan under load at times.  I intend to place this unit inside the large metal box with the rest of my gear for this project so that will insulate some of the noise I suspect.  The metal box has vents already in place for air-flow, and I intend to add a few more strategically placed with (12v) 120mm and (5v) 60mm cooling fans to force air in/out of the box.

So that's the current plan to power all of the items for this mobile project.  It's not my first choice!  But I'm sick of waiting at this point and just want to get out on the road to test things.  This will accomplish that in the simplest way I can think of at this point.


Tripplite PV375 on Ebay (13.8vdc to 120vac)


120v to 12v @ 10amp on Ebay (cheap maybe not the best, but it'll do I suspect)


12vdc to 5vdc @ 10amp on Ebay (tested here, these work fine!)