good diode for CG clamping?
Quantum Singularity, Sat Apr 01 2006, 05:48AMOne of the last components I need for my new 'lytic powered cg projects are clamping diodes. I have found a few beefy ones for reasonable prices. My question is will a standard recovery work or does it need to be an ultra fast recovery type. The specs on the ones i have found cheap that are standard recovery are:
DO5 stud mount
800V
80A avg
133A rms
I(fsm) 1800A - I assume this is max single pulse
I^2T 14000A - not sure what this is
Will these work? My caps are 250V and I may or may not series a pair or three so it is a good idea I get a high enough V rating that I can series some if I want.
Re: good diode for CG clamping?
Wilson, Sat Apr 01 2006, 08:24AM
I think it doesn't matter whether it is a normal diode, or an ultra fast type. The only distinction between the 2 is the turn off characteristics.
Wilson, Sat Apr 01 2006, 08:24AM
I think it doesn't matter whether it is a normal diode, or an ultra fast type. The only distinction between the 2 is the turn off characteristics.
Re: good diode for CG clamping?
Quantum Singularity, Sat Apr 01 2006, 06:48PM
Well I have never used diodes yet in my EM launchers so its kinda new to me. I was thinking that if the diode couldnt turn off fast enough then maybe when the pulse reversed it would kill the diode. Not sure how much V reversal there is after the first reversal that should be clamped by the diode. Is there a turn-on characterisitc? I mean if the diode cant go from off to on to clamp the pulse before it builds up to say 100V then your caps might be in danger? Not sure if this is somethign that can happen or not.
Quantum Singularity, Sat Apr 01 2006, 06:48PM
Well I have never used diodes yet in my EM launchers so its kinda new to me. I was thinking that if the diode couldnt turn off fast enough then maybe when the pulse reversed it would kill the diode. Not sure how much V reversal there is after the first reversal that should be clamped by the diode. Is there a turn-on characterisitc? I mean if the diode cant go from off to on to clamp the pulse before it builds up to say 100V then your caps might be in danger? Not sure if this is somethign that can happen or not.
Re: good diode for CG clamping?
EN, Sat Apr 01 2006, 07:27PM
Diodes have negligible turn on times that are governed by the inductance of their terminals etc. So even slow diodes turn on extremely fast, and there is no chance of the voltage rising to any dangerous values. (and many people don't even care about those 100V in reverse as long its only for a small amount of time)
The turn off (reverse recovery time) of slow diodes is slow, but still in the microseconds. So you'd only get problems here if you would re-charge your cap bank within a few microseconds after the discharge. (the coil can't do this because it is clamped by the diode)
EN, Sat Apr 01 2006, 07:27PM
Diodes have negligible turn on times that are governed by the inductance of their terminals etc. So even slow diodes turn on extremely fast, and there is no chance of the voltage rising to any dangerous values. (and many people don't even care about those 100V in reverse as long its only for a small amount of time)
The turn off (reverse recovery time) of slow diodes is slow, but still in the microseconds. So you'd only get problems here if you would re-charge your cap bank within a few microseconds after the discharge. (the coil can't do this because it is clamped by the diode)
Re: good diode for CG clamping?
Quantum Singularity, Sat Apr 01 2006, 08:08PM
Ok sounds good. So a really high power standard recovery rectifier like the stud mount I described above would singly handle any coil so long as I dont approach the 800V limit right? And will 1800A be able to handle the inductive kick for any reasonable cg coil powered by up to a few kJ at 800V or less that I might build? Its hard enough to calculate the actual surge current let alone what the coil will surge once the magnetic field collapses... I dont know if this info is out there maybe I just havent found it yet.
I asked about the recovery because I beleive all the diodes mentioned from digi-key by someone in another post were all ultra-fast type I think.
Quantum Singularity, Sat Apr 01 2006, 08:08PM
Ok sounds good. So a really high power standard recovery rectifier like the stud mount I described above would singly handle any coil so long as I dont approach the 800V limit right? And will 1800A be able to handle the inductive kick for any reasonable cg coil powered by up to a few kJ at 800V or less that I might build? Its hard enough to calculate the actual surge current let alone what the coil will surge once the magnetic field collapses... I dont know if this info is out there maybe I just havent found it yet.
I asked about the recovery because I beleive all the diodes mentioned from digi-key by someone in another post were all ultra-fast type I think.
Re: good diode for CG clamping?
EN, Mon Apr 03 2006, 07:02AM
The current the diode sees is slightly less than the peak current (dependant on the damping factor of you RLC curcuit). However this current can last much longer than the current that the thyristor sees(also dependant on the damping effect of the coil's resistance).
In my picture, i marked the place, where the diode takes over the current.
Edit: Here 's the scope pic of my diode clamped coilgun:
[Edit: Go here
to learn how to post pictures]
EN, Mon Apr 03 2006, 07:02AM
The current the diode sees is slightly less than the peak current (dependant on the damping factor of you RLC curcuit). However this current can last much longer than the current that the thyristor sees(also dependant on the damping effect of the coil's resistance).
In my picture, i marked the place, where the diode takes over the current.
Edit: Here 's the scope pic of my diode clamped coilgun:
[Edit: Go here
to learn how to post pictures]Print this page