Makinhg 7V fan power from 12V + 5V, OK?

[DaveSimmons]

Directron has these rewired 4 pin plugs that use 5V + 12V power to make a 7V fan power connector, that are cheaper and simpler than a Zalman fanmate:

Directron

Any reason not to use these for undervolting fans, or to make my own? I seem to recall some vagueness about it putting a strain on the PSU.

 

[Bobthelost]

The 5V rail is not supposed to sink current, in practice i've never heard of any problems with them.

 

[lenjack]

This commonly done with no problems.

 

[vanvock]

There used to be an article over at SilentPCreview I think that recomended not to because of a risk of feeding current back to the supply as I recall. It may still be there.

 

[SparkyJJO]

I can see that being a problem in the long run, you are essentially backfeeding current into the 5 volt rail. Not a good idea IMHO

 

[vanvock]

http://www.silentpcreview.com/article6-page1.html


http://www.cpemma.co.uk/7volt.html

 

[DaveSimmons]

Originally posted by: vanvock
http://www.silentpcreview.com/article6-page1.html


http://www.cpemma.co.uk/7volt.html

Thanks! One thing I'm not sure of after reading MikeC's SPCR note though: does the other 5V load need to be on the same cable from the PSU, i.e. using a Y-splitter on the cable with one going to a hard drive or something else, or is it just some 5V load on any other cable from the PSU?

Though I'll probably wimp out and just use a fanmate instead 😱

 

[Aluvus]

Originally posted by: DaveSimmons

Originally posted by: vanvock
http://www.silentpcreview.com/article6-page1.html


http://www.cpemma.co.uk/7volt.html

Thanks! One thing I'm not sure of after reading MikeC's SPCR note though: does the other 5V load need to be on the same cable from the PSU, i.e. using a Y-splitter on the cable with one going to a hard drive or something else, or is it just some 5V load on any other cable from the PSU?

Though I'll probably wimp out and just use a fanmate instead 😱

Any cable is fine, as far as the power supply is concerned they're all just parallel loads.

I've heard it said that if a fan connected in this way were to fail into a short-circuit condition it would be problematic, but that such a failure is very uncommon. A failure that causes the fan to look like an open circuit is no big deal.