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Old 02-25-2009, 12:25 PM
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nilrehob nilrehob is offline
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Join Date: Nov 2008
Location: Sweden
Posts: 689
I just did a test using components that I had lying around: coil ~166mH, cap 47uF, diode 1N4007, bat 12V and a switch.
The amp draw of the coil was ~500mA.
Battery, coil and switch in series.
Coil, diode and cap in series.
Switching on/off a few times the cap easily reached 80V.
Doing this repeatedly and emptying the cap each time it reached around 80V I took the average of the changes in voltage for each on/off-cycle squared and got ~550V^2. (Edit: max change squared = 688V^2)
The energy in each forward EMF spike captured by the cap would then be about (47*10^-6*550)/2=0.013 J. (Edit: max energy = 0.016 J)
The energy in the coil before switched off would be near (166*10^-3*0.5^2)/2=0.021 J
The difference in energy I blame resistance and other losses and me calculating the inductance wrong (using supposed length of the wire and the physical dimension of the coil).

What is wrong with my assumptions in this exercise?
Hob Nilre

Last edited by nilrehob; 02-25-2009 at 12:44 PM.
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