Defining Heat Generation Rate for Solenoid & Motor in thermal simulation

How to define the heat generation rate for Solenoids and Motors for thermal simulation. I know the power rating for these components, but again some of the energy is used for mechanical action rest is wasted as heat.
Do I have to use the total wattage or fraction of it while defining the Heat Generation Rate. I am using Solidworks Flow simulation.

 

[MikeHalloran]

It would be conservative to assume that all energy that _could_ go in, shows up as heat.

Since solenoids only produce mechanical work intermittently, you should definitely not bother to subtract that.

For motors, it would be conservative to use whatever current is allowed by the motor protection, which probably exceeds the nameplate rating of the motor.

... assuming you're interested in generating some 'worst case' data with your simulation. I'm not clear what value a 'normal' condition would have for most engineering.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Seems to me that you need to talk to the EE responsible for the design and get an accurate operational scenario for the simulation. While worst-case design is an approach, if the WC is substantially worse than the worst nominal operation, it may result in needlessly complicating the design, both in weight, and cost.

TTFN
faq731-376

 

[MikeHalloran]

IRStuff is right; selecting what to simulate involves deciding what constitutes a failure, and how the system is expected to respond to each and every possible mode. E.g. maybe you don't care if something sags, so long as it doesn't catch fire. ... or maybe even a small permanent deformation is unacceptable, ... or maybe you care about touch temperatures on some surfaces.

I.e., you can probably get a worst case now, but the thermal simulation should proceed in coordination with your FMEA.



Mike Halloran
Pembroke Pines, FL, USA

 

[BMDesign]

I have the duty cycle of the solenoids, but the stepper motor is on all the time. And it generates a lot on heat, on ambient both motor and the solenoids shoot up to 65-70 deg C.

 

[MikeHalloran]

Because steppers and solenoids are 'always on' and don't have an internal cooling mechanism, many applications go to some trouble to reduce the current going through them once they have changed state, e.g. using dual voltage supplies or switching resistors into the circuit once the solenoid has reached its mechanical stop or once the stepper has reached its next position and doesn't need to move for a while.

You can oversize the components, or use high temperature insulation systems, or provide heat sinks, but it's usually cheaper and more compact to add a few transistors. Talk to your system design people about the issue, and to resolve what operational or failure modes you are expected to simulate.


Mike Halloran
Pembroke Pines, FL, USA