Solenoid Back EMF

[Arouse1973]

Now I don't know if I am on the right track but I think I might need to include a damping factor into the formula.
L=20mH
C= 400pF (not unrealistic value)
Dp=R/2*L=600
Then the V= -L*di/dt (t=5*RC) = 208*10^3 Volts divide this by 600 = 346V. I was getting about 350V.
Does this seem plausible?
Thanks
Adam

 

[(*steve*)]

I was going to post earlier about stray capacitance and even inductance, your post does that more formally.

 

[Laplace]

Instead of guessing what the value of the distributed capacitance might be, could you estimate the value from the resonance frequency of the coil? Look at the ringing on the scope and measure the time between zero crossings; from that calculate the resonance frequency. Since you already know the inductance of the coil, use the formula F=1/(6.28sqrt(LC)) to calculate the capacitance. Is it anywhere near your assumed value?

 

[Arouse1973]

Yes I was going to do that, but I was at home when I wrote this and wanted peoples feedback initially. I'll do this and let you know.
Cheers