VERY Hot 12v-7v Reducer Cable? Normal??

Hi guys,

I have a 12v-7v reducer cable that came with my Aerocool DS 120mm fans, which will be replacing my San Ace fans. Damn they are loud as heck. Anyways, I have never used these reducer cables before, and would like to use them. The problem is that the rubber sheath or end where the fan cable connects to the reducer cable is quite hot. I actually burnt my finger. I immediately discontinued using that reducer cable until I can get more insight/advice. I am no electrician, but that burning hot end doesn't seem right. I tested this on my streaming PC and wife's PC, and still got the same result. I tried the molex to 3 pin connectors, fan controller (only on main rig), and directly from mobo fan headers. Still the same.



The above picture has the same look, except the pic is a simple fan extension cable. The rubber end or sheath on the left side, if you're looking at the picture, gets VERY hot.

Is this normal, and if not, what can I do to remedy this? I know that fan is relatively quiet already. I don't mind ditching the reducer cable, but wouldn't hurt to get it a bit lower in sound/decibels. Thanks much!

Yes, that's completely normal... its the resistance doing the job reducing the voltage. some reducer cables have the resistance in the middle of the cable to avoid connector overheat but its normal the temperature, even some manufacturers inform about to have caution with those cables while in use, I can't remember exactly where but I think was Noctua and Corsair..

Thanks, Araxie! That's reassuring. I'll go ahead and connect them and seal the comp up then.

the cable uses resistance to reduce the voltage and in the process creates heat.....and this is of course for powering a fan to help cool the pc? Am i the only one scratching my head?. Ya think they just design it to run off the 5 volt rail?

I had no idea any of the manufactures were using resistance to lower fan speeds? Course all my antec 120mm have built in speed controls but i admit i run them on full speed so honestly i never even entered my mind how they change speeds with a switch........ but honestly adding resistance would not have been my first guess. (since that would consume more power, not less)

No disrespect or trolling indented....just wondered what others smarter than myself thought ...i suspect my fans determine speed by have different coil taps running to the fans coil and in theory no wasted power or heat but its just a guess....its just added heat in my mind equals wasted power, even if its very small about....or it could be im just overly ocd

I tried one of those 9v reducers. It got hot as balls and burned out really quickly.

Its easier to just rig up a 7v adapter.

http://www.overclockers.com/forums/showthread.php/372297-Guide-to-the-7v-Fan-Mod

I've been wondering why no one has been using the LlM7800 series three terminal voltage regulators to control fan speeds below twelve volts. Adding a variable resistor to the center third lead would allow a wide adjustment of voltage.they are very cheap. They will conduct one amp and most fans pull much less.lm317 and others could be used.One of those and a common npn power transistor,like a 3015 would give you 15 amps. Only a small heatsink would be required for a 7800xx

Resistors die if they get too hot, that's just the way it is. A larger surface area (in the LIM7800) would allow greater heat dissipation, and it's sending the excess current to ground instead of generating rf/heat, but there will still be some heat generated. You would need a decent heatsink or some sort of feedback to control temperature or voltage (in addition to your pot) in order to keep the current constant, or else thermal runaway would be almost as likely (assuming lack of airflow was the cause of the other resistor burning up).

I found a datasheet for the uA7800 Series Volt. Regulators--wasn't able to find LIM7800 using google-- and it mentions current-limiting and thermal-shutdown features...which means it should continue working up to a certain temperature (and maybe prevent temperature from affecting output up to that point), but I'm not sure how to interpret the data in there, and it's really late.

This is what a fan controller is for.

Those reducer cables get way too hot for my liking.

Fan controllers can either use a variable resistor or PWM design. The PWM design will use less power and run way cooler.

cyclone3d said:

This is what a fan controller is for.

Those reducer cables get way too hot for my liking.

Fan controllers can either use a variable resistor or PWM design. The PWM design will use less power and run way cooler.

Click to expand...

yeah, that's why its always advertised like this:



one or two fans don't hurt, but after that point its always advisable the use of fan controller or PWM fans.. I always try to avoid RPM reducers like the noctua's LNA.

Or you could just use a 7v mod. Works fine unless you have a shitty psu like my old bgf 850w.

I prefer a fan controller as well but there are times where a fixed voltage is probably the better option. For example my large external rad. I never needed the fans over 1000rpm.

If you need variable voltage and don't mind doing a bit of work, you can splice a 3A buck converter in. They cost less than $2.

http://www.ebay.com/itm/291247572887?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Feeding it off a 12v source will give you an output between 1v and around 6.5v. That may be a bit too low for some fans, but there are buck converters that have less of a voltage falloff on the regulated side.

They're still way more efficient than burning off the extra power with a resistor and are less of a fire hazard.