high voltage high power transient voltage suppressor

[Frosty_47]

Hello,

I almost completed my HV defibrillator design and received my caps. Aside from protecting the capacitors with high power zener diodes, I would like to put a high voltage high power transient voltage suppressor in paralel with the load in order to protect my circuit from transient voltages that may arise from the various inductive coils that I plan to use for my experiments. There seems to be a deficiency of high voltage high power suppressors, so I would like to know if it's ok to combine several lower voltage transient suppressors in series to obtain the needed clamping voltage. Basically I need a transorb anywhere from 1600V-1800V.

Please help, as I cannot proceed with the project until I have this component.

Thanks

 

[dknguyen]

I think it's okay to put them in series. Series = higher voltage and power spread out over more components, and less capacitance. So I don't see a problem with voltage or response times (at least as far as capacitance is concerned. Lead inductance will be greater which will slow down response times)

 

[Frosty_47]

Oh and I also wanted to know, what energy or current ratting is needed for this application. Since my coil is practically a short circuit, there will be a serge of thousands of amps flowing through the coil. So I am not sure what current there will be in the inductor upon a sudden switch opening... How can I calculate the maximum serge current supplied by the coil upon a rapid switch opening? I have no way of measuring inductance of the coils. Should I just go ahead and buy the heftiest suppressor diodes and put as many of them in series as I need?

P.S. Highest ratted one I found is 15KW.

 

[crutschow]

Where is the energy in the coil coming from? If you know the source energy, then you know the energy in the coil.

For example, if its from a capacitor, then the caps energy is ½CV².

 

[Frosty_47]

Yes the source is a 1600V 3300uF capacitor bank. So thats just over 4000Joules of energy. The energy stored in inductor depends on it's inductance and the aplied potential. So there shoudn't be any more energy delivered to the transient supressor than the inductor can store. If I knew the inductance I could easily calculate the max energy. But I have no way of measuring the inductance of my coils, that are just a flat #8 AWG wire with very few turns. However thats only for inductrion luncher, I have no info yet on any other coils I am going to use.

 

[Optikon]

Yes the source is a 1600V 3300uF capacitor bank. So thats just over 4000Joules of energy. The energy stored in inductor depends on it's inductance and the aplied potential. So there shoudn't be any more energy delivered to the transient supressor than the inductor can store. If I knew the inductance I could easily calculate the max energy. But I have no way of measuring the inductance of my coils, that are just a flat #8 AWG wire with very few turns. However thats only for inductrion luncher, I have no info yet on any other coils I am going to use.

A defibrillator? as in for a heart? Is this design qualified to be used on a human patient? Since you asking some very basic questions, I have my doubts.

If you use series elements at high voltage how will you make sure that they share the voltage equally (as required for sharing power)?

Just throwing "as large as possible" part in is a great way to get your suppression not to work. You introduce alot of parasitic inductance that way and that renders the surge supression useless for all but the slowest events (none really)

 

[Optikon]

Where is the energy in the coil coming from? If you know the source energy, then you know the energy in the coil.

For example, if its from a capacitor, then the caps energy is ½CV².

1/2 CV^2 in an ideal, theoretical world yes. In the real world, we have to also consider the ESR of the capacitors and wire resistance etc.. a good deal of that energy is lost to those mechanisms... so 1/2 CV^2 can be considered an unrealistic maximum.

 

[Optikon]

Yes the source is a 1600V 3300uF capacitor bank. So thats just over 4000Joules of energy. The energy stored in inductor depends on it's inductance and the aplied potential. So there shoudn't be any more energy delivered to the transient supressor than the inductor can store. If I knew the inductance I could easily calculate the max energy. But I have no way of measuring the inductance of my coils, that are just a flat #8 AWG wire with very few turns. However thats only for inductrion luncher, I have no info yet on any other coils I am going to use.

You said,
"The energy stored in the inductor depends on it's inductance and the applied potential."

No, thats not quite right. The inductor stored energy depends on it's inductance (determined by geometry and materials) and the *current* through the inductor, not potential (volts)

 

[Frosty_47]

sorry meant current not potential. In any case, I have to limit the output current in order to calculate the largest inductor I can use. This is not going to be used on people (at least not yet ).