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SOLVED Advice on molex cables

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D

data1

Member
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Joined
Oct 25, 2009
Hi
I have installed two HD 6870 for crossfire and now about to test it but I have small problem. I had to use two molex from the PSU with adapter to power the second card and this left no free molex for the fans of the case. (4-5 fans, need one molex for them).

(There's free molex from the ones that goto the graphics card but u see the problem? Manual says the card should have its own independant source.)


I could get power from one of the same molexes that powers the graphics card but manual said it should get its power from "independant connection to the power source"

What should i do?

thx
 
Be very careful, those 2 cards in Crossfire can pull around 470 watts on their own at full bore. I am not an expert on the Core I7's and their power requirements though. You may want to look at simply getting another power supply.
 
Its stated by ATI that 600w is enough for crossfire, I have 650w..

Do both the cables in cards draw as much?
 
Sorry, the review I was reading about the cards was showing 470 on crossfire for the entire system not just the vid cards. Thats my bad.

I would still be careful, I've had a power supply take out my vid cards before because while I was technically in the safe zone stuff happens. :p

As for your main question I honestly couldn't give you an answer on if its a safe move or not, but I would be more concerned with temps from the system from not running the fans than from a power spike causing damage.
 
Well right now after playing a game the meter is showing max draw of 300w. not much...

edit: furmark was able to raise it over 400w though and rising before i cancelled the burn in test..
 
Last edited:
Ok, I7 2600k draws in about 95 watts unoverclocked at 100%. HDD's tend to draw about 2 watts, and 3-5 fans draw roughly 35-45 watts(depending on the fans in question) you SHOULD be fine as long as you don't overclock anything, and use it at 100% for extended periods of time.

BUT...I do not recommend doing this, and recommend stepping up to a 750 watt power supply. While they may be rated for 650, it might only put out 510 stabily...if that's a word...Which it isn't. This means if the draw is 550 or 600, it could cause dangerous spikes in voltage.

A question to ask is how old is the PSU? Their rated power DOES degrade with time. Really good PSU's last for 10 years, mediocre lasts for like 4 years or so.

So...

95+2(X)+*.5(Z)SSD*+(Y)15+158(2)=

X=Number of Hard Disk Drives & Optical drives
Y=Number of fans
Z=Number of Solid State Drives

Always make sure there is a small headroom of 50-150 watts, for any other peripherals, like a fan controller, led's , pumps, Whatever...

Correct the equation where I missed anything important.
 
Hmm well the PSU has some protections:
OVP (Over Voltage Protection), SCP (Short Circuit Protection), and OCP (Over Current Protection)

its over 2 years old
 
What does Jonnyguru.com say about that PSU?
The marketing hype on a manufacturers page means squat, nada, nothing.


We have a sticky in the PSU section you might want to read.
 
Fans draw maximum power on start up, expect decent high air movement fans to pull say .4 amp each x 5 = 2 A at 12volt = 24 watts.
So put two fans on one line, three on the other. Adding 15 watt on one line and 10 on the other (most likely less) shouldn't matter.
If it bothers you that much a 12 volt 5 amp power brick can be had for $10-12. You can wire it internally or externally. I know I've seen UV sleeved molex splitters cheap/free shipping somewhere, splice one to the brick, plug one to each "leg" you four fan plugs, use four and have six.
Seriously the fans will be unlikely to draw much current except at start up, when the video cards will not.
Newegg still has the LEPA B850-MA for $120- $50 MIR = $70 if you must.
 
But if the watt limit isnt reached (~650w) then it should be ok? Im just concerned how many watts can single molex cable transfer without burning up or anything. because ive read something like that has happened to some people.

and im afraid i need just one molex for all fans because they are under speed control.
 
For certainty I would post the question on the jonnyguru forum.
For an amateur opinion both cards will be drawing power from the motherbord (around 75 watts a card) and the connectors, so you will be splitting power between rails.
The power supply has Overcurrent protection, it should shut down before damage.
You will be pushing the power rating under 100% stress testing, for gaming I see no problem.
 
For one, never EVER convert molex to PCI power unless you have to. that 650 could be only putting out 500 watts, and with it being over 2 years old, that makes sense. Like i said before, if it goes to like 620 watts, it could very well cause SHARP spikes in voltages, from 12 to 380. That will quickly kill everything in your pc. Time to replace my friend.

As for being under speed control(fans) it STILL kicks up to 100% power at start. Everything does.

I'd recommend looking up jhonny guru, find a psu in your watt range(750+) that is at least an 8 in performance. From there, it is a matter of how much you want to spend.
 
Suppressor1137, please take your own advice. Read the review. The Antec EA650 received a very good review from jonnyguru. It is a an older design, but solid.
It will do 650 watts continuous. It will not have aged significantly in 2 years.
Using molex to PCIe connectors is not optimal, but it works. Some cards come with adapters for that reason.
You will get a startup "spike", not to the extent you mention.
 
I don't go around reading reviews for every power supply on that site, but from what I understand, he has issues connecting both video cards+fans, Regardless, I still recommend getting a new power supply, since his current one does not meet his needs any longer.

With SLI, not having any airflow save the cpu fans is hardly safe. It will have a runaway effect, video cards get hot, air around soaks the heat, heat causees vid cards to get hotter, releases more heat.

The only reason I pushed it so hard is because my father's computer ran off molex, which somehow shorted, and caught fire. the culprit was the converter.

Just because it comes with it, does not make it recommended.

Its like saying you have a 99 pathfinder which gets the job done, or a 2012 GTR, which does the job well. sort of...
 
I find it peculiar that molex cable can burn. If it did then warrant should be accepted on possible damage.

however i got this repply from antec:

You do not have to worry about the power supply or your components being damaged when there is too much power draw. There are protective measures in EarthWatts series power supplies that will prevent any damages effectively. If one of the protective functions should become active, your system will not be able to turn on, unless you disconnect all power, turn it off and leave it unplugged for at least 10 minutes. This way the PSU will recover and can be used again.

650W is plenty though for even SLI/CrossFire systems.
Click to expand...

So, what do you think, is it ok to put those 5 fans on one the molexes that power the GPU ?
Since theres that protection.
Or can the cables still fail over too much wattage?
 
it will be fine, just get a molex splitter thing that will give you one more molex to daisy chain your fans, and enjoy.

I'm just saying from past experience that it can turn out bad in a few more years as it degrades.

i wouldn't plan on keeping it for more than 3 years as of today, by then, it would effectively be over 5 years old, and THAT is pushing it, no matter who says otherwise.

good luck, and wish you the best on safe operation.
 
Suppressor1137 said:
Ok, I7 2600k draws in about 95 watts unoverclocked at 100%. HDD's tend to draw about 2 watts, and 3-5 fans draw roughly 35-45 watts(depending on the fans in question) you SHOULD be fine as long as you don't overclock anything, and use it at 100% for extended periods of time.

BUT...I do not recommend doing this, and recommend stepping up to a 750 watt power supply. While they may be rated for 650, it might only put out 510 stabily...if that's a word...Which it isn't. This means if the draw is 550 or 600, it could cause dangerous spikes in voltage.

A question to ask is how old is the PSU? Their rated power DOES degrade with time. Really good PSU's last for 10 years, mediocre lasts for like 4 years or so.

So...

95+2(X)+*.5(Z)SSD*+(Y)15+158(2)=

X=Number of Hard Disk Drives & Optical drives
Y=Number of fans
Z=Number of Solid State Drives

Always make sure there is a small headroom of 50-150 watts, for any other peripherals, like a fan controller, led's , pumps, Whatever...

Correct the equation where I missed anything important.
Click to expand...

Added note on this HDD is 3-7W Max, SSD is .5-4W Max This is idle and full tilt on cards. They are not that low. Most 120mm fans are 6-12W a piece to give an idea. Though its not the constant load that is the issue, its the spike in power on startup that causes more issues than not, besides the PSU holding the voltage rail on long loads.


I got my 750W PSU and its going plenty strong still, 4.5 years old now I believe maybe longer now. Solid, and most of my systems that I've run with it barely broke 400W even with dual video cards in the past.

As for PSU degrading. Estimate around 1-5% of capacity every year or so that it will decrease. Give or take a little. Though I don't know if its more so usage or time that really kills these.
 
Thx it has been working fine in crossfire. I havent run furmark burn test yet but no problem playing games.

thx all!
 
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