So I guess the consensus is to power the LCD off the PSU...

**ThePistonDoctor** · 06-01-2009, 08:42 PM

Is this the standardized way of doing it? I have a 7" Xenarc 705TSV and it is the final piece in my CarPC puzzle.

I have an M4ATX 220W supply and am hardly using any of it. Do I need to regulate the power supply in any way or just splice into the yellow power cable? I have a few free HDD connectors and work at an electronics manufacturing company so I'm sure they have some molex pins or something I could solder on and plug them into one of the free HDD connectors.

Would that also work so I don't have to cut the power cable? In other words, is there any difference between tapping the main 12V wire from the M4ATX harness, tapping one of the 12Vs from the smaller 4-pin harness, or plugging it into a HDD connector?

Lastly, do I just cut the cig lighter cable that came with the screen and use that? Seems like that's a long distance for such a small gauge wire; should it be fused?

Sorry, I know this is a lot of questions but I have seen more than one car go up in flames because of shorts...lol

**colin** · 06-01-2009, 09:09 PM

Okay here's where it depends. If your screen comes with an egg (regulator) and a lighter socket, it's saying HINT HINT, you can power this off of the lighter socket. That may be misleading though.

In reality, it never hurts to feed these guys regulated 12v. The eggs have a bad reputation and because of this, they fry screens every here and there. It probably won't fry yours, but I mean, what do you have to lose by hooking it up to a molex?

There is no difference between the M4ATX harness, the smaller 4-pin harnesses, or the HDD connectors, UNLESS your power supply has 2 or more separate +12v lines, which I don't think it does. Don't hold me to that though. EITHER WAY, you're safest powering it off the main harness or the molex harnesses because those small 2x2 (4-pin) harnesses are the ones that specifically power the CPU, and you don't want to be stealing power from there.

Hope this answers your question!

**Bugbyte** · 06-01-2009, 09:59 PM

Anything downstream of the M4 is regulated, so you can use that.

**ThePistonDoctor** · 06-02-2009, 10:30 AM

Alright, I'll grab some molex connectors from work here and use the HDD socket. Guess I was just hoping I wouldn't have to run more cable all the way to the back...but I'd rather do it right the first time. Should I just chop the cig lighter plug, fuse the + and run it to the power supply?

Thanks

**Maheriano** · 06-02-2009, 11:15 AM

My 700TSV has a regulator in it and SHOULD NOT be powered off of the power supply for said reason. Check and see if the 705 does, which I assume yes, and act accordingly.

**ThePistonDoctor** · 06-02-2009, 11:28 AM

^why should it NOT be powered off the PSU? And how do I find out is my 705TSV has a reglator? IIRC the cig lighter plug is just the plug, no additional boxes or "eggs" as noted above.

**Sicarius** · 06-02-2009, 02:30 PM

Regulators require a certain amount of head-room to provide their rated output so a 12v regulator might require 13v or more to provide its rated output. The alternator running voltage is somewhere around 13.5v (edit: or more) so the regulator would output its rated voltage. If you hook it to a pre-regulated 12v source, then it will output somewhat less than 12v which may (or may not) cause problems for your screen's circuitry.

Another issue that has me leaning towards direct power is that if you hook it direct to your PSU, the screen will lose power when you shut down and lose its settings memory. My screen defaults to a brightness of 50 on power-up and I would have to reset it to 100 every time if I power it from the PSU. My only worry is how much standby current it draws.

**DeltaFX** · 06-02-2009, 05:26 PM

Isn't alternator running voltage around 14.4 V ?

**ThePistonDoctor** · 06-02-2009, 06:27 PM

^yes, and it depends on the car. In fact I have a voltage monitor on mine and it actually sits pretty steadily around 14.8-15.2V...

**mayhembdm666** · 06-03-2009, 05:29 AM

Im not sure why this seems to be such a debate?
When it comes to powering the screen, I know there are different models and ratings as such. But the screens have generally been supplied with their own power supply and were never designed to use a PC PSU. This does no hard in running the screen from the PSU but if your going to run it from your PC PSU then your better off building a regulated PS from just a few 7812's or direct from the Car battery with a relay.

Running the Screen from the PC PSU is just an extra load on the PSU which really is not needed. I know there are other points going against this.. But with the pros n cons.. I would not be using the PC PSU.

Same goes for hubs and other devices, If it is not internal to the PC like mainboard/hdd/cd/pci/sata then it should have its own power supply/source as this be less waste as well.