NI 9472 Circuit Protection

[Fifty60]

Hello everyone, I have a NI-9472 sourcing digital output module that I recently had to replace because of a bad output.  I would like to know what kind of circuit protection to use on the outputs.  I know that the module is internally short-circuit protected by a 12 amp protector, but the individual outputs are only rated at 0.75 amps so this internal protection does not provide any overload protection to the individual outputs.  Would a 0.75 quick blow fuse work, or is there something more specific that I should use to protect the outputs from overloading?

[santo_13]

Do you mean 14A protection?

What is connected on the other side that caused the 9472 to fail? you need to fix that instead of adding a fuse.

[Fifty60]

It is being used as a PWM output.  

I would like to add some protection so that if the device it is connected to does fail, then the module is at least protected.  I am not sure if a KTK class CC quick blow fuse would help or not, or if they would operate quick enough to protect the 9472 if it was overloaded.  

[santo_13]

You still haven't provided info about what is connected as load to the 9472.

Yeah, a quick blow fuse is a good option, now, once you install it, what if the fuse blows every time you use your setup, what would you do?

[Fifty60]

Thank you for the response.  It is being used as a PWM signal for an HVAC Blower motor.  There are 2 machines this is working on, and both worked well for several months before the one machine burned up its NI 9472 card.  I was able to literally smell the module to detect that the 9472 had "burned up".  I replaced the 9472 card and it started working correctly again.

So whatever the issue is it is intermittent.  Not sure if there is a loose connection or something that requires a certain star alignment to cause problems, or if there is some kind of design/application issue.  

My goal would be to have a fuse to replace when the starts align, and not have to procure a new module again.

[santo_13]

Do you have a motor controller for the HVAC blower motor? What model?

If this is just a PWM signal, you could insert an Opto isolator to be safe.

[AnalogKid2DigitalMan]

I 2nd Santhosh's opto-isolator approach.

-AK2DM

[Fifty60]

Could you possibly recommend an opto-isolator that would work for this application?  I am familiar with what they are but I have never used them for this type of application.

[santo_13]

Please share if you use any motor driver to control the blower motor.

What motor do you use? ratings?

[Fifty60]

Sorry if I have been confusing.  The 9472 is just providing a control signal for the PWM, it is not actually powering the motor.  The 9472 sends a control signal to a separate power supply, and that separate power supply is what controls the motor.  So I do not think the blower motor specs are in play.

With it only being a control signal, there is no actual load on the 9472 so I am not sure why it was damaged.  As I mentioned, the other 9472 module is working fine, but the one burned up.  Not sure if this is just something that happens from time to time with these modules, or if something other happened.

I am trying to protect against the "something other" scenerios.  I see there is short circuit protection, but nothing for overloads.  So that is why I am considering adding a 0.75 quick blow (KTK class CC) fuse to it.  Wasn't sure if there was another recomendation to protect the module.