Hi Everyone,

I was asked to design a solenoid "that can operate with a back EMF limited to -37.6 VDC". My first thought is, this doesn't make sense. why design for a back EMF when you can just get rid of it? Is this number to calculate which diode to use to prevent EMF? Can you help me interpret what this means?

 

Which one do you mean you'll remove, the EMF or the solenoid?
If you remove the solenoid where would you get your power start?

 

http://farside.ph.utexas.edu/teaching/em/lectures/node82.html

Somewhere in this is the answer to your question and also lots of useful equations too!

 

I used to have a rule of thumb for snubbers across inductors that I went by but it was recently shot down due to some further study.

The EMF can rise as high as 10x the normal operating voltage peak (I used to go by 4) thus the diode should be able to handle fairly repetative pules of current also about 10x the peak current the inductor normally sees.