hello everyone
I'm using a 3pst toggle switch to control the fans in a server: the switch alternates between three lines with resistors to lower the speed, and three lines without when I need the fans at full speed.
The problem is that I need the fans to run at full speed during the start up, otherwise the server doesn't boot, and since sometimes I will turn the server on remotely, I have to make sure that the 3pst switch is on his full speed position always when I turn the server on.
I was thinking to use a relay, but I have no idea of which one to use and how to connect the wires...any suggestion?

 

Are the three fans powered from three different power supplies, or are they fed from one supply (or could they be)?

A timer circuit followed by a relay (or a ready-made time-delay relay) could be wired so that the fans unconditionally run at high speed for a fixed time after power-up, and conditionally run at high or low speed depending on the setting of a toggle switch after the initial fixed time delay.

What voltage runs the fans? 12Vdc?
How long should the power-up time interval be?

ps: I just had a brilliant idea. How about this? Make the relay latch on its own contacts (hold itself in). With the relay latched on, the fans runs slow. If the power fails, or you power-cycle the server to force a re-boot, the relay drops out while the power supply is off, and when the supply turns back on, the fans run fast until you walk into the room and decide to initiate slow fans by pushing a momentary button which latches the relay. You can have a second (normally-closed) push-button to drop-out the relay to make the fans run fast again...

 

Are the three fans powered from three different power supplies, or are they fed from one supply (or could they be)?

A timer circuit followed by a relay (or a ready-made time-delay relay) could be wired so that the fans unconditionally run at high speed for a fixed time after power-up, and conditionally run at high or low speed depending on the setting of a toggle switch after the initial fixed time delay.

What voltage runs the fans? 12Vdc?
How long should the power-up time interval be?

ps: I just had a brilliant idea. How about this? Make the relay latch on its own contacts (hold itself in). With the relay latched on, the fans runs slow. If the power fails, or you power-cycle the server to force a re-boot, the relay drops out while the power supply is off, and when the supply turns back on, the fans run fast until you walk into the room and decide to initiate slow fans by pushing a momentary button which latches the relay. You can have a second (normally-closed) push-button to drop-out the relay to make the fans run fast again...

hi mike, tnx for the answer and sorry for delay
I think your second idea is the right one, the fans are 12v powered by the system board, but they have three different circuits (the cabling is a bit complicated and I have also modified it, but is not important for now).
I was thinking to a relay 3pdt that has two status, let's call them ON 2 (with resistors )and ON 1 (without resistors)...I need the relay to automatically switch to ON 1 when the system shuts down (and possibly when it reboots, but that's not fundamental), the problem is that my overall knowledge about electronics is quite poor, so I'd need someone to tell me which relay would do the job and how to actually set it up

 

Do you have a source of 12Vdc that goes on/off with the server power supply for the relay coil? The relay coil would require 0.25A or less.

 

yes, I have a molex 4pin with 12v and 5v, it should supply up to 5A

 

Ok, look at this. 12V1-4 might actually be coming from the same power supply.

The important thing is that 12V4 goes off when the server is rebooted...

 

I forgot something...

I would also add a 1N4007 diode, anode wired to the bottom of the coil, cathode wired to the top of the coil to suppress the inductive kick as the relay coil turns off. Without it, the inductive kick might do some mischief in the server....

 

first of all thank you very much,
sorry but I am having some troubles with internet nowadays..
I don't understand what you mean exactly with inductive kick, but, to give you more details, the fans get three continuous 12v all the time, and their speed is controlled via a manual pwm controller (that I added) and a switch with resistors to reduce the 12v (the one I need to change with the relay). When the system boots up it doesn't have any problem if the speed is reduced via pwm, but it gives an error if I switch the 12v line to the circuit with resistors.
The reason I had also to use the resistors is that, just with pwm, I wasn't able to get the fans silent enough.

 

just three more details:
1) every 12v line has got his own ground, can it be a problem?
2) the diode you suggested has to be in parallel with the coil?
3)the push buttons are the kind that keep the circuit closed, or that just close it for the time they are pushed?
thanks

 

I'm between flights at LAX. I'll answer when I get to my destination.

 

Made it to Hilo.

I do not follow what you are doing with the PWM controller. You would have to post a schematic.

Can you just wire three of the poles of the relay just like the 3pdt is wired now, and wire the coil of the relay, the diode, the NO button, the NC button, and the fourth pole of the relay to a separate 12V and 0V tap on a power supply as I showed?

The diode is wired across the relay coil with the cathode to the positive end of the coil.

 

well, the pwm is just one more thing I added, but let's forget about it as it doesn't affect the circuit of the relay..
most of the problem is given by the fact that I don't physically have the relay yet, and I have never used one (if you haven't understood yet I'm a newbie about electronics), that's why I don't fully understand your scheme. I am going to buy one tomorrow, so I can better figure out, but before I need to understand which kind of buttons I need as I will buy everything together:
do they have to open the circuit just for the time I press them, or do they have to keep it opened?
still thank you for your patience and help

 

Hi

If you don't mind me asking....what kind of server is that?
I never heard of a server that required manual control of its fans...especially to boot-up...

eT

 

the server is an old rack unit (HP proliant dl580 g5), normally it doesn't require a manual control, but I had to modify all the cabling of the fans to add a manual pwm controller and a switch with resistors, because it was very noisy, and it's not possible to control the speed of the fans via software (I keep it in the same room I sleep)..the server has a boot check, to make sure that all the fans are running and getting 12v, that's why it doesn't matter if I keep the speed low with the pwm, but it doesn't boot if I switch the 12v lines on the circuit with the resistors..the reason I have to use the resistor beside the pwm controller is that only via pwm I wasn't able to get a the fans silent enough, as this fans are a bit complicated to control..and, trust me, it has been more complicated that it looks like, but I don't want to confuse you with further details!

 

Right, I have finally managed to buy a relay and test it, and works pretty good, the only doubt left is about the rating, it is 10A 12v, but in the shop they also had a smaller one rated 5A 12v, considering that every single fan is rated 3.24A, would the smaller one works as well, or do I have to consider the rating adding the current for every single fan? And eventually, is the diode 1n4007 still good for the 10A one, or do I have to use a bigger one?
Still thank you very much for the scheme and help

 

"Momentary" as applied to a push-button switch is self explanatory...
The smaller relay would work... Just so the coil voltage rating is 12V.

 

"Momentary" as applied to a push-button switch is self explanatory...
The smaller relay would work... Just so the coil voltage rating is 12V.

Yes, about the buttons my bad, I didn't pay enough attention, and I thought that N.O. and N.C. was referred to the relay status, not the buttons, I realised once I looked for the diagramatic signs used for the buttons...your scheme was actually very detailed and explanatory, but I am just still too much incompetent...I am learning little by little, as nowadays I face this kind of small electronics issues quite often, and I really like to find a way to solve them...