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Faster capacitor bank bleeder
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OM222O:
simplest and safest way: use a constant current DC load, fairly cheap and simple to build.
Use an IGBT with suitable high voltage rating, any basic rail to rail op amp (I've had good results with MCP6002) and high power resistors.

I strongly recommend you use a heat sink for the IGBT and have a fan blow over the whole setup. you can increase the load by using dual/quad op amps and copying the schematic over. in your case precision doesn't seem to matter which makes it extremely easy and cheap to build.


Instead of a fet use the IGBT. the load current would be Vref/Rshunt and that should allow you to pick suitably rated resistors for the task.
This way you should be able to discharge the caps in 3 seconds if your load can handle about 200 watts! for a more moderate 100 watts, that'll still be only 6 seconds. not too shabby if you ask me.

Edit: why are you looking for constant power? your main target is to discharge the bank ... constant current would be even better
Circlotron:
For those suggesting mosfets and igbts as part of an electronic load, beware that igbts and recent hv mosfets don’t always have a very good safe operating area. A mosfet might have a dissipation rating of several hundred watts but this rating goes right down the toilet at high voltages. Seems more of an issue with newer types than for ones 20 years or so ago.
David Hess:

--- Quote from: langwadt on March 07, 2019, 12:11:31 am ---
--- Quote from: David Hess on March 06, 2019, 11:02:59 pm ---You need some of those negative value resistors which draw current inversely proportional to the voltage across them.  The same store which sells prop wash and blinker fluid carries them.  :)
--- End quote ---

a light bulb sorta does that
--- End quote ---

It does but over a limited range.


--- Quote from: Circlotron on March 07, 2019, 12:36:57 am ---For those suggesting mosfets and igbts as part of an electronic load, beware that igbts and recent hv mosfets don’t always have a very good safe operating area. A mosfet might have a dissipation rating of several hundred watts but this rating goes right down the toilet at high voltages. Seems more of an issue with newer types than for ones 20 years or so ago.
--- End quote ---

That would need to be taken into account which a constant power load sort of does by making the current inversely proportional to voltage.  Of course the secondary breakdown curve is nonlinear so a nonlinear slope would be used unless the part is derated.  It is easier just to derate the part for the worst case part of the curve; power semiconductors at this voltage level are not that expensive.
OM222O:

--- Quote from: Circlotron on March 07, 2019, 12:36:57 am ---For those suggesting mosfets and igbts as part of an electronic load, beware that igbts and recent hv mosfets don’t always have a very good safe operating area. A mosfet might have a dissipation rating of several hundred watts but this rating goes right down the toilet at high voltages. Seems more of an issue with newer types than for ones 20 years or so ago.

--- End quote ---

That is exactly why I suggested high power resistors  ;D you let them take the brute force while keeping the IGBT/FET almost fully on. let's say for each 100 watt dissipated by the resistor, the IGBT dissipates 10 watts  ??? that seems pretty coolable and SOA won't be an issue. again this is not a matter of accuracy as the resistance of the the Rshunt will change! but who cares if the load is drawing a bit more or a bit less current? the fan will keep the resistors safe.
DBecker:

--- Quote from: Circlotron on March 07, 2019, 12:36:57 am ---For those suggesting mosfets and igbts as part of an electronic load, beware that igbts and recent hv mosfets don’t always have a very good safe operating area. A mosfet might have a dissipation rating of several hundred watts but this rating goes right down the toilet at high voltages. Seems more of an issue with newer types than for ones 20 years or so ago.

--- End quote ---

That's why I suggested a power supply chip such as a LinkSwitch powering a low voltage incandescent indicator lamp.  They use a hard-switching MOSFET well within in the SOA.  The bulk of the power is dissipated in the lamp, which serves as an indicator as well as a power sink.
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