Advice 12/24v DC based vehicle build

msystems

Airflow Optimizer
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Apr 28, 2017
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Before I start spending $$$ I'm wondering if anyone has tried running a SFF system directly from their 12v/24v vehicle house batteries. I'm increasingly living in my vehicle these days and see no reason why I shouldn't make this switch.

I am planning to make a vehicle based sffpc, using straight DC from house batteries, since it has a number of advantages.
First, it should be more efficient than an AC system by preventing Inverter loss (although, voltage drop in the wires must be watched).
It also will be better on thermals. An internal AC-DC produces a lot of waste heat. An external DC-DC step-up converter won't produce much heat at all.
It will also be removable from the vehicle and can be connected to an external AC-DC Psu for use in the home.

The concept of the build is as follows:

Total system TDP: 250-300w, undervolting as necessary. In my experience, thermals/noise become increasingly bad as you start going above 200w on air
GPU: RTX 1060Ti Mini (200w TDP, but much less after undervolt. 850mv on Ampere seems to be a typical undervolt while sustaining factory clock)
CPU: TBD
Case: TBD. I only have 1 foot of vertical space, so ideally I'd need a Cube case that is exactly the footprint of a mITX board.

Electrical specs
It's a 12v system. 24v would be better but my battery bank and appliances are already configured for 12v.
-200AH Lifepo4 to stay within a healthy .2c discharge rate and lots of runtime
-Wiring - Power needs are 25 Amps@12v. I have a 10GA copper run already in place which I plan to fuse at 35A. It's more voltage drop than optimal.. but OK
-A 12->24v step up converter, 25a@24v rating (600w nominal) such as this. This is outside the case, but only inches away for the lowest voltage drop.
-Some sort of DIY soldering job on the step-up output, to create a male barrel connector compatible with the HDplex one
-HDplex 400w dc-atx accepting the 24v input


I don't think it will be that hard but I anticipate the tricky parts will be choosing a good step up converter, making the barrel connector, and confirming my wiring is not getting too warm. There's also a concern that vibration could damage it. Possibly would need to engineer some kind of anti-vibration mounting with foam or rubber grommets for the case. Also due to the vibration, I wonder if using a GPU riser would be better or worse. Im inclined to think that using a GPU riser-based case would be better than the gpu contacts constantly bouncing around in the fixed pci-e connector.
 
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Goatee

King of Cable Management
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Jun 22, 2018
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Are you tied to the 1660ti?

I have a travel build that takes 12v straight to the board (no 19v / 12v conversion) and is ~150w at full draw and the size of a hardback book.


This uses some pretty weird parts but is minimal work with nothing really fancy.
 

msystems

Airflow Optimizer
Original poster
Apr 28, 2017
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Are you tied to the 1660ti?

I have a travel build that takes 12v straight to the board (no 19v / 12v conversion) and is ~150w at full draw and the size of a hardback book.


This uses some pretty weird parts but is minimal work with nothing really fancy.
This is awesome. Could you go into detail about how you are delivering the power to the board? Are you using a 12v dc-atx like a Pico? I have heard of those 12v Pico before but I believe they have a bit less juice so I would need to trim down the power draw a ways.

One thing I'd have to consider if going this route is that it would mean finding a new 12v brick for AC if it was brought inside to run off mains, whereas the 19v laptop bricks are ubiquitous and can be adapted to hdplex
 
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confusis

John Morrison. Founder and Head writer SFF.N
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The concerns I would have (I've had a carPC in my dreams for a long term) is the voltage. Most 12V Pico-PSU variants just pipe the 12V straight through to the board. This would mean that when the alternator is charging the battery, the board is seeing 13.8-14v! Cranking the engine drops the voltage significantly too. If you have a standalone battery for accessories (think high end car audio style setup), you may be able to get away with it, as a properly configured engine battery to accessory battery feed would limit voltage variances.

"Wide Input" 12V Pico-PSU and similar tend to max out at 200W or thereabouts, alas.

Seeing as you are looking at upconverting 12V to 24V or similar, you may be able to find a power solution that works for that - 19V truck based laptop charger, etc. It does seem wasteful to go from 12 => 24 => 12/5/3.3V, though. Your linked 12-24 seems like a solid solution - and may indeed be the best option. The HDPlex accepts 16-30V so you're right in the sweet spot.

Regarding vibration dampening - remember cars have had optical disk readers in them for some time - a few rubber grommets and making sure the mounts are well designed - should work fine... Assuming the card's heatsink doesn't weigh tooo much.

In my instance, I have a couple of 12V to 230V 350W inverters spare that I was going to lean on to make life easy XD (I have one running a server in my solar powered carport -350WH of 12V SLA, "400"W of panels, and a 45w server doing hardly anything. Oh, and charging my DIY e-bike each night.)


What is your monitor/screen solution?
 
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msystems

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Apr 28, 2017
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Thanks for the ideas. To use Pico it sounds like I'd have to cut down the GPU options to hit 200w safely. But also since you mention it, the voltage could be questionable because of the battery chemistry which "likes" to be at about 13.6v. The battery system is isolated from the starter battery so the alternator isn't an issue, but it's the charger voltage at 14.4v. Estimating a .6v voltage drop on load from the DC wiring, the Pico would still be getting input of as high as 13.8v which could be out of spec.

For the screen I'm going to try to take my existing Dell U2415 (AC powered so this will be on inverter) and put it on an Ergotron arm and mount it in there for fun, since I haven't seen anyone try to put an Ergotron arm in a vehicle yet and I don't know why cause it seems cool as hell. I'll have to engineer some kind of tie-down system to secure it when driving so the arm doesn't swing around and break stuff. Ideally it can rotate and swivel up right against an empty portion of the wall to be secured.
 
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