Hopefully someone can answer this question.

When connecting inductive loads (e.g. motors), a self-inductive recuperation diode (Schottky) and a 100 nF capacitor need to be connected to the consumer to prevent interference with the multiswitch.

What is the circuit diagram for this setup if I was connecting a fan to the multiswitch?

Sebastian,

Thanks for your reply and the link. So do I basically bridge the gap on the multiswitch with a Freewheeling diode and a 100 nF capacitor and then connect the fan as normal.

Trying to upload a small diagram to show what I mean but don't know how to do it here.

Thanks for the info and the link, the link looks more complicated than what is in the manual, do you think that is all needed? have you done this yourself?

SNIFFY

Thanks Shoggy,

This is what I think you mean. The terminals are from the Multiswitch, with the Schottky diode and 100 nF capacitor bridging the gap. Then the fan is connected as normal, is this correct or not?

Thanks again

SNIFFY

Hi there, tried this set up and it does not make any difference to the humm at the fan when the PWM signal cuts in.

Not really sure what to do now, any ideas, are the values of these components critical. I have a 3amp diode and a 100nF capacitor.

This is a shame as I will probably not use the multiswitch to control the fans now. So it is currently unused.


SNIFFY

Hi there,

Here is an update on my findings after experimenting with some components of various sizes.

The use empolyed for my Multiswitch was to control and vary the fan speed and so noise output of my cooling fans housed inside the case and a second set of 3 120mm very quiet permanant running fans on my Evo 360 radiator.

The Rad also has the supplied papst fans, controlled via the Aquaero in conjunction with the heat sensors. So in total that is 3 permanent 120mm fans controlled via the Multiswitch manually and 3 120mm fans controlled by the Aquaero automatically, to come on when the water rises above the threshold temps.

As the fans are Brushless they have some clever circuitry inside that changes the magnetic field in order to turn the fan. When a DC current is sent to the fan it works fine, but when the Pulse Wave Modulation (PWM) function of the Multiswitch supply is used, some of my fans were producing an audible humming/ clicking noise as it was interfering with the circuitry in the fan. Hence, destroying the purpose of the exercise!!

So in order to attempt fix the problem I have been experimenting with the circuit to try and find a set of values for the components which will hopefully reduce the electrical noise observed by attempting to smooth out the Square wave from the PWM output.




In the end the following circuit seemed to reduce the electrical humm in my worse offending fans significatly:



The circuit consists of:

1 x 1 Amp Schottky Diode (Allows the back EMF of the motor to dissapate and so not interfer with the Multiswitch cuircut)

1 x 50 Ohm variable resistor (Allows you to alter the resistance of the curcuit and so the charge rate of the capacitor which helps to smooth the PWM signal output to the fans)

1 x 47 uF electrolitic Capacitor (This essentially smooths the square wave PWM output so the fan's inside circuitry is effected less)


I found that if you altered the value of the variable resistor the worst effected fans would be almost silenced (you can still hear a slight humm if you put your ear right next to the fan, at about 15cm you cannot hear it), however this would reduce the top end RPM of the fan but only by a small amount. However the Humm was almost completely removed and was so acceptable to me.

Some fans did not need any resistance to remove the noise, so I considered using the variable resistors to give me the flexibilty to adjust the audible noise.

The capacitor used was a 47uF electrolictic type, although 10uF and 22uF capacitors all worked fine. However, with the 47uF capacitor I could start the fan when I set the Multiswitch to 3 from it being at a standstill. This happens about 14 with the 10uF, it will however turn at the lower settings provided it already has some momentum (spin). I therefore wanted the extra protection and it was slow enough at the low setting for my liking.



All items were obtained from Maplins in the UK, so it is easy to do if your having similar problems with your fans.

One word of warning, if you try this at home be extremely careful like the manual says, that you do not short circuit your Multiswitch outputs. This will damage the BSP250 MOSFET Transistor, I have destroyed 4 and so am hoping the replacements will restore my Multiswitch when they come in the post!

Apart from that setback, I now know I can use the Multiswitch as I had origianlly planned.


Fans tested:

AcoustiFan 120mm Fan (Humm improved)
AcoustiFan 80mm Fan (Humm Improved)
Scythe S-Flex 800rpm 120mm Fan (Humm Greatly improved)
Scythe S-Flex 1600rpm 120mm Fan (Humm Greatly improved)
Papst 120mm Fan (Humm improved)
Lian case Fan 120mm Fan (Humm improved)


Some Pics:






SNIFFY

Finnaly given up on the idea as I noticed the Power Supply was getting interference too, and making it's own humm. Jumpered the PWM jumper and connected straight to the Fan.