Zimo function output to control fan motor

[Johngraham]

Hi, I was wondering if anyone can advise a way to set up a functional output on a Zimo MS440 decoder to suitably control a fan motor driving a radiator fan on diesel loco

i’m having difficulty getting the motor to run smoothly and start consistently at sufficiently low speed

many thanks, Graham

 

[Nigelcliffe]

Will depend on the motor being controlled, and how its responding to the PWM output of the function wire (which is how the output level is set).  

A crude adjustment method would be a resistor in series with the motor which drops the volts the motor sees, but needs to be adequate wattage for the power being dissipated in the resistor.  

If you've been around most of the function output settings (PWM "brightness", etc., as well as the type of output (there are things like "soft start")),  then the alternative is to make a small transistor drive for the motor, and run it from a "logic" output.  Thus your transistor drive can be better suited to the range of speeds of the motor.  

 

[Johngraham]

Hi Nigel, thanks for that I have been through a few of the function settings/dimming but wasn’t sure if there was a setting specifically for motor control I’d missed - I did try a low value capacitor in parallel with the motor and it certainly seems to stop the hum. I can try a mosfet as I’m familiar with using them with ESU decoders (will that work?) also wasn’t sure about using the 5v output from the decoder as an option? I read up in the manual, but I couldn’t quite get my head around it and obviously do not want to damage the chip

i’m using 6 of the full function outputs for the lighting so if I switch CV8 to 3  will I lose all the other full outputs?

appreciate your help

[Nigelcliffe]

As a basic rule, you can't use Logic outputs (5v) to drive anything other than a transistor circuit of some sort.  (exceptions obviously, but assume its extremely low current).    

 

If you've used FOF, FOR, FO1, FO2, FO3, FO4 as standard outputs, then there remains the option of changing either (FO3,4,5,6) or  (FO5,6) with the CV8 change to logic level outputs - see manual page 20 for various values.   Or could wire logic-level onto FO7, 8, or 9 (will require other CV's to disable Susi, etc..).    

If your mosfet circuit on ESU was for a logic level output (probably was), then same circuit will work.  With that you could also fit a lower driving voltage than the decoder blue wire. 

There is a 5v on the decoder, but the manual is unclear on the current.  Diagram on P7 says 200mA (plenty to run a fan through a transistor), but table on P4 says 50mA (marginal, depends on motor).  Either double-check what the German manual says, or ask Zimo's tech support which figure is correct.  

 

Off the wall - another suggestion,  with full power outputs, try another motor in series with the fan motor.  That will drop the voltage over the two motors. 

 

 

- Nigel

[melmerby]

12 minutes ago, Nigelcliffe said:

Diagram on P7 says 200mA (plenty to run a fan through a transistor), but table on P4 says 50mA (marginal, depends on motor)

Hi Nigel

If you use a MOSFET to control a fan the input current to the gate will be negligble, it's effectively a capacitor.

 

[Nigelcliffe]

26 minutes ago, melmerby said:

Hi Nigel

If you use a MOSFET to control a fan the input current to the gate will be negligble, it's effectively a capacitor.

 

 

Its not the gate current I was bothered about.   If the load supply through the Mosfet is taken from the 5v (so the motor only sees just under 5v rather than seeing around 12-14v from the decoder positive/blue wire).   Then the load current might be significant, depends on the motor and its starting draw - 50mA might be seen, 200mA would seem safe to me. 

 

 

[Johngraham]

I will experiment over the next few days and report back.
Cheers again

Graham

[Johngraham]

Brilliant - (Zimo MS440 decoder) using the 5V output as your suggestion but with a normal full powered FO = much more flexibility in setting the speed of the motor.

Starting and running perfect for my requirements, (it appears to be a 200 mA output after all - but that is unconfirmed) - I see the confusion in the manual - motor actually draws 50 mA in any case.

I am using a 100 µF capacitor in parallel with the motor, the smoothing appears to give more flexibility with the speed control (CV192) - going to see how many models I can convert.

Did not have much success with the MOSFET - (I really do like the idea) but will carry on experimenting

 

Thank you once again Nigel really appreciate your help

 

Graham