Need PSU with single +12V rail, nothing else

**aindfan** · 05-10-2011, 10:25 AM

Hello everyone,

I have a nano-ITX board on the way that takes a round 12V DC plug and works out all of the rest (for USB and hard drive connection). I would like to feed it clean 12V power and use the same power supply for a Lilliput 669, TDA7850 amp, and Visteon HD radio. Let me start by running some numbers:

Motherboard: power requirements unknown (board description is here, but it has an AMD Fusion setup with a Radeon 6250 which will also power the SSD and any other
Amp: Does 4x25W sound ok? I think my stock speakers are 4Ohm, but I'm not sure.
Radio: Don't know the power requirements for the 12V Visteon... any help here?

So let's add all that up and say I'm at or around the 200W area.

The reason that the ATX-based supplies don't meet my requirements is their many voltage rails. I'm not looking for 15A on 5V and 3.3V, or anything on -12V; I need all of the power available on the +12V rail. The only decent option that I found so far is the Opus 180W dual-output supply, which is split between two 12V 90W supplies. The amp could get one 90W side all to itself, and the rest of the components (motherboard, monitor, radio) could sit on the other 90W.

To the best of my understanding of this supply and my power requirements, such a setup *should* work. But do I have any other options?

Thank you very much!

**nivanov** · 05-10-2011, 10:54 AM

I'm running a similar setup, only my all-in-one nettop takes 19V DC. I purchased a DCDC-USB power supply. It takes power from Battery and IGN lines and gives you a clean line of any voltage of your choosing (I forget the actual range, but 12V is one of the presets for it). It should handle the mobo and the monitor no problem. The output plug is a 4-pin molex plug, which can be easily cut off and split into 2 round DC power connectors (one for monitor, one for mobo)
Visteon Radio is designed to work without a clean DC power source - it can be hooked up directly to Batt / ACC lines

I'm not sure how to go about the amp - I'd have it powered from the battery over a 12V relay that gets triggered by the AUX power line from DCDC. AUX power line can have variable timing, so you can set it to turn on 20 seconds (or more) after the ignition - that should give your computer enough time to boot and prevent any thump.

I wouldn't hang the monitor, the amp and the computer on DCDC-USB - I'm pretty sure it's not gonna be powerful enough. If you get Opus 2x90W, one line can go to the amp, the other one can power the computer and the monitor. I don't think AMD Fusion board with an SSD and a couple of USB devices will eat more than 40W. Monitor is about 10W max, so you are looking at 50W on one of the lines. Amp will probably eat about 40W total, so Opus should do just fine.

**aindfan** · 05-10-2011, 01:27 PM

Thanks! I just spent some time on the phone with Opus tech support, and the man on the phone did a good job understanding my requirements and explaining that the "Motherboard" firmware option is what I need to provide the PS ON pulse to the motherboard turn-on header.

**DarquePervert** · 05-10-2011, 02:03 PM

The amp & Visteon unit shouldn't need regulated 12v, as nivanov points out.. They should operate just fine from the car's electrical system, which will fluctuate.
So that leaves just 12v for the PC.

A couple options:
1. Find a laptop car power adapter that outputs 12vDC with sufficient amperage.
2. Go with a Carnetix P2140 (pricey) or DSX12VD or Opus 80w for your 12v.

**nivanov** · 05-10-2011, 02:26 PM

Originally Posted by DarquePervert

The amp & Visteon unit shouldn't need regulated 12v, as nivanov points out.. They should operate just fine from the car's electrical system, which will fluctuate.
So that leaves just 12v for the PC.

A couple options:
1. Find a laptop car power adapter that outputs 12vDC with sufficient amperage.
2. Go with a Carnetix P2140 (pricey) or DSX12VD or Opus 80w for your 12v.

Darque, any objections to DCDC-usb? It's cheaper and smaller than DSX12VD, and for his wattage requirements, seems enough.

**aindfan** · 05-10-2011, 02:33 PM

Thanks for the replies. I'm not too confident about the amp... has anyone used the TDA7850 unregulated?

Unfortunately (or fortunately), I already ordered the Opus.