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Reply With QuoteAs long as you have a sufficiently big enough ground wire, yea... doesn't matter cept potentially for audio stuff if you have any noise.Originally Posted by BiohazrD
Ok, I am running a wire from my power supply in the trunk of the car, to my Lilliput in the front. So...
If I have the OPUS 150w:
150 watt = 12 volts * X amps
X = 12.5 amps
Y ohms = (5.254752 × 10^-09 Ohm feet) / (8.0 × 10-07 m^2)
(Resistivity of copper wire divided by crossectional area of 18 AWG wire)
Y = 6.56844 x 10^-3 Ohm / feet
Z ohms = (15 feet * 6.56844 x 10^-3 Ohm / feet)
Z = 9.85266x10^-2 Ohms
delta X volts = 12.5 amps * 9.85266x10^-2 Ohms
delta X = 1.2315825 volts
So, according to this, on the +12v rail, I will suffer a voltage drop of 1.23 volts, will this be enough for me to notice a difference on my Lilliput? Did I do these calculations right? Any help would be appreciated.
Edit: Also, do I have to have two grounds, can I just hook the two grounds on the Molex together?
Quick! To the Popemobile!
As long as you have a sufficiently big enough ground wire, yea... doesn't matter cept potentially for audio stuff if you have any noise.
2003 VW Jetta Wagon 1.9L TDI 5 speed
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CarNetix P1280 80w
EPIA TC10000 Mobo, 512MB SODIMM DDR, 160GB HD, Orinoco 802.11b, Hollux GPS (USB), 12dBi Omni Antenna
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how you did the math looks right.. as long as you're sure about the copper values and all that.. Also keep in mind you'll probably be putting ~13.8 volts and not 12V, AND it'll CAN suck more than 150W because it's not 100 percent efficient.
Of course it probably won't even suck up 150W most of the time..
Either way, you're running 18 AWG to your opus??
If so, that's bad. 10AWG is probably the least you want, if not 8.
If you mean that you have 8AWG or whatever going to opus, but then 18AWG to lilliput, you have to rethink this calculation:
delta X volts = 12.5 amps * 9.85266x10^-2 Ohms
Because that lilli isn't sucking up 12.5 amps, probably only 1 amp or so (just guessing).
Either way, if you didn't already do the wiring, use 14 AWG instead, just to be safe.
I was going to be wiring the 18 AWG to the Lilliput, I thought that when you calculated voltage drop, you just plugged in the total value passed through the wire, an the OPUS puts about 12.5 out on the 12.
All of this wiring is from the PSU to the Lilliput, I'm running the OPUS off of a 8AWG. (I have two amps for my system).
Quick! To the Popemobile!
nah, the math is that you do
12.5 amps * resistance of 8AWG wire = voltage drop from battery to opus.
This is probably only like 0.1 volts or something, if even that.
Then you do
1 amp (guessing) * resistance of 18AWG wire = voltage drop from *OPUS* to lilli
so total drop is 0.198 if we go by 0.1 volts + (1 amp * 0.098 ohms)
(assuming the 0.098 ohms which you calculated above).
Either way, since it seems you haven't wired the 18AWG yet, try to get some 14 if you can. Never hurts to have thicker wire.. assuming flexibility and size isn't an issue.
Good luck
I ran 3 x 12awg to a molex up to the front for xenarc and slim dvd. No probs yet.
Excellent, that was pretty much my plan exactly. So, did you hook both molex grounds to one of the wires?
Quick! To the Popemobile!
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