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Splicing Grounds

J

jadawgis732

Gawd
Joined
Jun 18, 2009
Messages
536
Hi guys. So I want to run my DVD off a 3 pin fan cable. This will allow me to run almost every component off a hub built out of a hammond box. Here's the image of what I'm trying to do.



So what I did was spliced the grounds, ran them to one of the 3 pins, and had 5v and 12v each using one of the other pins. Here's an image.



Either I didn't run the pins to their correct locations on the 3 pin connector or this cannot be done because smoke came from the back of the DVD drive and I don't think that was the desired effect. (ha ha). Can anyone please tell me which of those is happening?
 
Don't let the similar colours fool you into thinking fan wiring and drive wiring are compatible.

3 pin fan cabling carries 12V (usually on a red wire) ground (usually on a black wire) and a speed sense line (usually on a yellow wire).

Drive power wiring has 5V (usually on a red wire), 12V (usually on a yellow wire) and two ground (usually on black wires). Sata power cables direct from the PSU also have an orange wire for 3.3V but afaict virtually no drives use this because of the fact that molex to sata adaptors don't supply it.

So if you match the colours between fan wiring and drive wiring you will end up putting 12V on the 5V line which is likely to cause stuff to go bang :(
 
It sounds like you connected the 12v rail from the fan connector to the 5v pin on the DVD drive.
 
plugwash said:
Don't let the similar colours fool you into thinking fan wiring and drive wiring are compatible.

3 pin fan cabling carries 12V (usually on a red wire) ground (usually on a black wire) and a speed sense line (usually on a yellow wire).

Drive power wiring has 5V (usually on a red wire), 12V (usually on a yellow wire) and two ground (usually on black wires). Sata power cables direct from the PSU also have an orange wire for 3.3V but afaict virtually no drives use this because of the fact that molex to sata adaptors don't supply it.

So if you match the colours between fan wiring and drive wiring you will end up putting 12V on the 5V line which is likely to cause stuff to go bang :(
Click to expand...

I know all this. The 3Pin fan leads were all connected to the appropriate sources.


Sick Willie said:
It sounds like you connected the 12v rail from the fan connector to the 5v pin on the DVD drive.
Click to expand...

I heard this somewhere else too. Does this mean that the idea SHOULD work in theory, if I had connected everything the right way?
 
jadawgis732 said:
I heard this somewhere else too. Does this mean that the idea SHOULD work in theory, if I had connected everything the right way?
Click to expand...
Yes, it should work in theory if I am understanding correctly that you were attempting to connect the 3-pin connector's wires to the appropriate +12V and +5V sources.
 
I guess I misread the first post. Yes, in theory, if you have the ground, 5v and 12v rails wired correctly, you won't smoke the DVD drive. However, the contacts in the 3 pin fan connector are much smaller than what should be used for the current required. I would still be skeptical of continuous operation of the drive.
 
Those black wires are not 12v- and 5v- (and it's not a question of semantics since there are rails with those names - the position of the "-" in the name is irrelevant), they are grounds. Otherwise, it looks good.
 
Your diagram looks like it would work, I can only conclude that you were either very unlucky and had a DVD burner die randomly on you or (more likely) that you messed up the wiring somewhere.

Still ab(using) fan style connectors for drive power seems like a bad idea to me. It's just asking for something to get misconnected in the future.
 
That's exactly what I think Plug. These images should give you an idea of why I'm using 3Pin connectors (I just don't have room for more than that). The box will house 5 3Pin headers and 1 Molex Connector which the PSU plugs into. I soldered up a circuit board I found at Radio shack in order to avoid using a terminal strip, or just splicing in each wire. The other option for the 4 pin requiring devices is Floppy connectors or PWM connectors, but I don't have any, and from what you guys are saying, it's not even necessary. Plus the pin locations on a 3 pin are going to be 5v, 12v, GND whereas a fan is RPM/12V/GND. So I don't think it's really asking for trouble as far as that goes, but it is if you're too stupid to put the pins in the goddamn correct locations.




And yes, my soldering skills are sorely lacking.
 
Do I even need to splice the ground wires from the PSU or can I just run one up to 1" before the DVD drive and have the two GND wires going to the SATA connection spliced?

Also, I just realized. Those 4 wires coming off the circuit board. Yea, 22AWG. Problem? The power will only be traveling over them for a few cm at most, but after that, it's probably drawing about 125W. (That's a guess, I'm not sure but 2 pumps, 1 fan controller controlling 7 fans, 1 DVD drive, a few trucolor light bars, 1 12" CCFL, a few LEDs, aaaaand that's probably it. So do I have to switch it?
 
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