Where can I get a simple on/off 3-pin switch?

Kerosene · Post by **Kerosene** » Wed Oct 31, 2007 4:11 am

Is it possible to buy a simple on/off switch for my 3-pin fans?
Something like a Fanmate that goes down to zero.

Or is there some wonderful law of electricity that makes this impossible?

alleycat · Post by **alleycat** » Wed Oct 31, 2007 5:18 pm

A cheap switch from Jaycar and a bit of soldering would do the trick.

Felger Carbon · Post by **Felger Carbon** » Wed Oct 31, 2007 5:54 pm

A fan motor is inductive. Suddenly opening the circuit can cause very large voltage spikes. That's why it's not a good idea to pull the fan wires off a mobo header with the fan running.

Kerosene · Post by **Kerosene** » Wed Oct 31, 2007 6:31 pm

@ alleycar - that's what I was thinking, but I knew there would be a catch... I know nothing's ever as simple as a trip to Jaycar

What about a simple rotary switch? Would that minimize any voltage spike problems?

To complicate things even more, I was hoping to run 2 fans off the same motherboard header and run them thru a single switch. Would it be any safer to power 2 'on/off' fans from a PSU molex connection?

The Australian summer is fast approaching and I'm looking for a simple way to fire up 2 extra fans at the flick of a switch, either for when I'm not here, or for when the aircon is off.

Felger Carbon · Post by **Felger Carbon** » Wed Oct 31, 2007 7:24 pm

Kerosene wrote:The Australian summer is fast approaching and I'm looking for a simple way to fire up 2 extra fans at the flick of a switch, either for when I'm not here, or for when the aircon is off.

If you substitute "the turn of a dial" for the flick, you're golden. Aspire makes single-channel fan controllers...

Kerosene · Post by **Kerosene** » Wed Oct 31, 2007 7:55 pm

I just looked up the Aspire controllers, seems that they don't go down to zero:
Specifications: ...DC Output: 5.0V-11.70V...

Any other ideas?

Bluefront · Post by **Bluefront** » Wed Oct 31, 2007 8:34 pm

Sure....Buy a cheap DD5 (digital doc 5). Hook up the fans you want to control. Set the sensors to turn on at whatever temp you want. The fans turn on at 12V.....easy.

Link

Kerosene · Post by **Kerosene** » Wed Oct 31, 2007 8:53 pm

Bluefront wrote:Sure....Buy a cheap DD5 (digital doc 5)......

$33.99 USD? All I want is an on/off switch for one of my old boxes. I was hoping I could do this with the spare change in my pocket and a trip to my local electronics store.

Is there such thing as a 'soft start' resistor that I can use in a DIY switch to avoid voltage spikes?

Felger Carbon · Post by **Felger Carbon** » Wed Oct 31, 2007 10:40 pm

Kerosene wrote:Is there such thing as a 'soft start' resistor that I can use in a DIY switch to avoid voltage spikes?

The problem isn't a start surge. The problem is suddenly interrupting current that's flowing in the inductive fan motor. In other words, the problem is the sudden stop.

Kerosene · Post by **Kerosene** » Wed Oct 31, 2007 11:12 pm

Felger Carbon wrote:
Kerosene wrote:Is there such thing as a 'soft start' resistor that I can use in a DIY switch to avoid voltage spikes?
The problem isn't a start surge. The problem is suddenly interrupting current that's flowing in the inductive fan motor. In other words, the problem is the sudden stop.

I know nothing about electronics, but surely there must be something that can create a 'slow stop'.

I can't believe somebody (e.g Zalman) don't make a kill switch for fans.

Bluefront · Post by **Bluefront** » Thu Nov 01, 2007 2:48 am

Well look....A DD5 can be usually found for <$20 in the USA. Cheap enough for the features.

Now if you really want cheap.....a simple on/off switch spliced into the red wire to the fan will work. To be safe, don't flip the switch when the computer is running. Hardware stores, automotive parts stores, electronic parts stores.....all have such things usually <$5.

Kerosene · Post by **Kerosene** » Thu Nov 01, 2007 5:08 am

Bluefront wrote:Well look....A DD5 can be usually found for <$20 in the USA. Cheap enough for the features.

Now if you really want cheap.....a simple on/off switch spliced into the red wire to the fan will work. To be safe, don't flip the switch when the computer is running. Hardware stores, automotive parts stores, electronic parts stores.....all have such things usually <$5.

I do want 'really cheap' - I'm not running NASA here

But I will need to start the fans while the PC is running (it's on 24/7).

Are there any fans that will STOP DEAD at =< 5v?

Felger Carbon · Post by **Felger Carbon** » Thu Nov 01, 2007 6:13 am

There's a two-switch solution. Switch #1 connects a resistor in parallel with the fan. Then switch #2 interrupts the +V feeding both the resistor and the fan. The inductive surge is suppressed/absorbed by the resistor, which remains in parallel with the fan.

If you don't mind the extra power drain, switch #1 can be dispensed with and the resistor can remain in parallel with the fan at all times. The resistor should draw about as much current as the fan's run current.

Inelegant, but sometimes inelegant works best.

truckman · Post by **truckman** » Thu Nov 01, 2007 9:55 am

Felger Carbon wrote:
Kerosene wrote:Is there such thing as a 'soft start' resistor that I can use in a DIY switch to avoid voltage spikes?
The problem isn't a start surge. The problem is suddenly interrupting current that's flowing in the inductive fan motor. In other words, the problem is the sudden stop.

A cheap solution would be to add a diode or RC snubber circuit. The diode version is simpler, but you have to be careful to connect the diode with the correct polarity to avoid letting the magic smoke get out.

Kerosene · Post by **Kerosene** » Fri Nov 02, 2007 1:19 am

truckman wrote: A cheap solution would be to add a diode or RC snubber circuit. The diode version is simpler, but you have to be careful to connect the diode with the correct polarity to avoid letting the magic smoke get out.

This sounds like exactly what I want. Assuming I'm going to be running a single fan off a molex connector - could you give me a bit more info on what kind of diode I'd need to buy, and where exactly it should go in relation to the switch?

Somebody should be making these and selling them.

truckman · Post by **truckman** » Fri Nov 02, 2007 3:00 am

Kerosene wrote:
truckman wrote: A cheap solution would be to add a diode or RC snubber circuit. The diode version is simpler, but you have to be careful to connect the diode with the correct polarity to avoid letting the magic smoke get out.
This sounds like exactly what I want. Assuming I'm going to be running a single fan off a molex connector - could you give me a bit more info on what kind of diode I'd need to buy, and where exactly it should go in relation to the switch?

For use with a 12V fan, any of the 1N400x (1N4001, 1N4002, etc.) series of rectifier diodes should be suitable. You should be able to purchase these from your nearest Radio Shack or equivalent electronics store.

The diode should be connected across the fan terminals, with the cathode (banded) end connected to the positive fan wire. If you connect the diode backwards, you'll short the power through the diode, and probably let the magic smoke out of the diode if you are powering the fan with the molex connector. If you are powering the fan with a motherboard connector, reversing the diode polarity could fry the motherboard.

Kerosene · Post by **Kerosene** » Fri Nov 02, 2007 5:14 am

Thanks truckman! My simple switch idea is becoming more complex by the minute

I'm not entirely clear on what your mean by "The diode should be connected across the fan terminals, with the cathode (banded) end connected to the positive fan wire"

Forgive my pathetic diagrams... but are either of these correct?

I'll be running the fans from molex connectors from the PSU. If the dreaded blue smoke appears, will it damage my PSU, or just trash the diode?

alleycat · Post by **alleycat** » Fri Nov 02, 2007 5:32 am

I don't think this needs to get too complicated. I've unplugged and switched fans before, without any noticeable consequences. I've made a two-position switch that switched between 12V and 5V. I've also made a 12-position rotary switch with diodes, which you'll find in the "Building your own fan controller" sticky. I had no problems with any of these.

Kerosene · Post by **Kerosene** » Fri Nov 02, 2007 5:46 am

Have any of your switches gone down to zero though?

truckman · Post by **truckman** » Fri Nov 02, 2007 8:08 am

Kerosene wrote: Forgive my pathetic diagrams... but are either of these correct?

The first diagram is the correct way to connect the snubber diode.

The second diagram shows how to decrease the voltage to the fan by about 0.7V (connect more diodes in series to increase the drop). This works better than a dropping resistor because the voltage drop is not very dependent on the amount of current drawn by the fan.

Kerosene wrote: I'll be running the fans from molex connectors from the PSU. If the dreaded blue smoke appears, will it damage my PSU, or just trash the diode?

The PSU is overcurrent protected, so it should just shut down without damage, but I don't know if the PSU will shut down quickly enough to prevent damage to the diode, which has a 1A maximum continuous current rating if it is one of the 1N400x series.

alleycat · Post by **alleycat** » Fri Nov 02, 2007 7:34 pm

A switch that "goes down to zero" is one that breaks the circuit. Most switches are of the "break before make" variety, breaking the circuit before selecting the other position.

truckman · Post by **truckman** » Fri Nov 02, 2007 10:00 pm

Now that I think about it, I wouldn't bother adding a snubber diode.

One reason is that the fan motor controller chip in the fan hub inherently has a reverse biased diode connected exactly the same way as an external snubber diode would be connected, though I can't be totally certain that it is thermally capable of handling the long duration current spike caused by unplugging the fan as opposed to the brief, high-current spike caused by an ESD event.

The second and more important reason is that the motor coils are not connected directly to the fan power terminals. Instead, they are switched on and off once or twice per revolution of the fan by transistors in the motor controller, and these transistors are definitely being protected by snubber circuitry connected to the motor coils, and this circuitry should also handle the case of the fan being suddenly disconnected from power.

Kerosene · Post by **Kerosene** » Sat Nov 03, 2007 4:33 am

Well you've all totally succeeded in making my head spin

So, alleycat and truckman - are you both suggesting that it may actually be safe to simply install a switch? Although, if soldering in a diode will add some extra protection, then I'll do it.

If I'm running the fans from my PSU (using a switch WITHOUT a snubber diode) and something goes wrong - what's going to get damaged? If it's just the fan, then I'm happy to roll the dice...

alleycat · Post by **alleycat** » Sat Nov 03, 2007 6:22 am

Just cut the red wire and solder in a switch like this. The switch has only two connections; doesn't matter which way around it is. I doubt anything could go wrong. About the worst I can think of is you might get a dry solder joint, in which case the fan won't turn on. If you're really worried you can PM me, and if you're not far away I could give you some help. As it happens, I'm only a block away from Jaycar in the CBD.

truckman · Post by **truckman** » Sat Nov 03, 2007 11:52 am

Kerosene wrote:If I'm running the fans from my PSU (using a switch WITHOUT a snubber diode) and something goes wrong - what's going to get damaged? If it's just the fan, then I'm happy to roll the dice...

The most likely thing to get damaged would be the fan, and since I've never seen any reports of fans being damaged by hot-plugging, I'd say that you're unlikely to have any problems if you just use a switch.

Kerosene · Post by **Kerosene** » Sat Nov 03, 2007 4:40 pm

OK thanks for the help everyone. I'll give it a shot using a switch without a snubber diode. I'll be using some cheap spare fans anyway, so if they crash and burn it's no big deal.