Don't you think that the load resistor was there to more quickly discharge capacitors when going downwards; perhaps also as a safety measure to make sure the device reaches 0 volts on power off quickly.
The added load resistor certainly caused the unit to return to zero volts much faster. However the current draw by the resistor was disproportionally high and it left little current for any connected load. I can always attach a resistor externally to the output if a situation required such.
Thx for sharing interesting overhaul-video Erik. ,,Wonder if the load-resistor (in addition to function as faster discharge) also reduces the max milliAmpere output to allow only for feeding high-impedance external circuitry..(..and maybe also reducing the 'hurt-factor' if the accident should occur. Just asking) //Again thanks for sharing this interesting unit, and overhaul. Have nice week.. br, from norway.
@@rolfts5762 Hi, glad you enjoyed the video. The resistor was across the output terminals so it only acted as a load on the supply leaving less current available for any normal external load. If it were in series with an output rail then it would have the affect you mention of increasing supply impedance and current limiting.
All of the high voltage generating circuity is inside the potted box. Everything outside the potted box is power supply, measuring, support, and control circuits. There are two power transistors on the back panel that are drivers for the high voltage potted circuit, basically a high frequency oscillator. The high voltage variation is done by controlling those power transistors, probably the pulse duty cycle although I have not investigated or measured that.
During the final end test, the minus clip of the multimeter was clipped to the chassis, and the multimeter showed a minus sign because polarity was swapped, but this also means that the entire chassis becomes positive at maximum 1000V. The chassis is also connected to the ground of your mains power grid, so that means that every device in your home with a metal chassis also carry that 1000V, this 1000V is normally not earth referenced because the high voltage module is powered by a transformer, but i don't think that this power supply is designed to work like that. That is the main reason that the high voltage connector has is own floating ground lead. Also swapping polarity done by a mechanical switch, i don't get the point of the benefits of that, when you can simply swap the output leads? Other then that, a nice video to watch. Grtz
Hi Grtz, the power supply did not originally have an isolated (floating) output. The output connector had been modified by a previous owner. Since this video was made I have installed an "N" connector which can withstand at least 1000 volts. It is safe to reverse the output polarity (making the chassis positive) because the high voltage potential only exists between the chassis and the internal HV module's other output terminal which is the center conductor of the output connector. True, other devices with a common earth ground would be at the same potential as this unit's grounded chassis but no shock hazard exists because a user of a separate device is not coming in contact with the high voltage modules other output terminal (center conductor of the N connector). The built in switch for polarity reversal is important because if you only reverse the power leads to an external device (to obtain polarity reversal) that also happens to have one side of the device earth grounded a voltage potential will exist between that external device chassis and the power supply chassis creating a shock and short circuit hazard.
Erik! I have a model 205a-03r high voltage power supply. I foolishly switched the polarity while it was still at -400V and now I am not reading any output voltage. The inside looks fine and I cannot find any signs of damaged components. Can I still save it? What can I check?
If your model is similar in design to mine, the potted/sealed high voltage module may have been damaged with the polarity reverse switch while on. But I would also check the power transistors on the heatsink for shorts or opens, drive signal to the power transistors and drive voltage to the high voltage module, and basic things like power supply DC voltages.
@@EriksElectronicsWorkbench Thank you for your swift response! Can I check the power transistors while they're still attached, or do I have to take them out?
@@BurakAhmetTufekci It depends on the surrounding circuit if it influences the readings to a great deal but you can try in circuit first. You should have a diode junction from collector to base and from base to emitter. And an open from collector to emitter. If you can unsolder just the base lead connection (depending on how they are mounted and wired) you may not need to remove anything else to get the C-B and B-E readings. In circuit may not give an accurate reading from C-E.
Thanks Erik, your explanations are very easy to follow and understand!
Thanks for the compliment.
Don't you think that the load resistor was there to more quickly discharge capacitors when going downwards; perhaps also as a safety measure to make sure the device reaches 0 volts on power off quickly.
The added load resistor certainly caused the unit to return to zero volts much faster. However the current draw by the resistor was disproportionally high and it left little current for any connected load. I can always attach a resistor externally to the output if a situation required such.
Thx for sharing interesting overhaul-video Erik. ,,Wonder if the load-resistor (in addition to function as faster discharge) also reduces the max milliAmpere output to allow only for feeding high-impedance external circuitry..(..and maybe also reducing the 'hurt-factor' if the accident should occur. Just asking) //Again thanks for sharing this interesting unit, and overhaul. Have nice week.. br, from norway.
@@rolfts5762 Hi, glad you enjoyed the video. The resistor was across the output terminals so it only acted as a load on the supply leaving less current available for any normal external load. If it were in series with an output rail then it would have the affect you mention of increasing supply impedance and current limiting.
Is in the green box is resistor divider for voltage setting ? looks like was potted ? Thanks for the video
All of the high voltage generating circuity is inside the potted box. Everything outside the potted box is power supply, measuring, support, and control circuits. There are two power transistors on the back panel that are drivers for the high voltage potted circuit, basically a high frequency oscillator. The high voltage variation is done by controlling those power transistors, probably the pulse duty cycle although I have not investigated or measured that.
During the final end test, the minus clip of the multimeter was clipped to the chassis, and the multimeter showed a minus sign because polarity was swapped, but this also means that the entire chassis becomes positive at maximum 1000V. The chassis is also connected to the ground of your mains power grid, so that means that every device in your home with a metal chassis also carry that 1000V, this 1000V is normally not earth referenced because the high voltage module is powered by a transformer, but i don't think that this power supply is designed to work like that. That is the main reason that the high voltage connector has is own floating ground lead. Also swapping polarity done by a mechanical switch, i don't get the point of the benefits of that, when you can simply swap the output leads? Other then that, a nice video to watch. Grtz
Hi Grtz, the power supply did not originally have an isolated (floating) output. The output connector had been modified by a previous owner. Since this video was made I have installed an "N" connector which can withstand at least 1000 volts. It is safe to reverse the output polarity (making the chassis positive) because the high voltage potential only exists between the chassis and the internal HV module's other output terminal which is the center conductor of the output connector. True, other devices with a common earth ground would be at the same potential as this unit's grounded chassis but no shock hazard exists because a user of a separate device is not coming in contact with the high voltage modules other output terminal (center conductor of the N connector). The built in switch for polarity reversal is important because if you only reverse the power leads to an external device (to obtain polarity reversal) that also happens to have one side of the device earth grounded a voltage potential will exist between that external device chassis and the power supply chassis creating a shock and short circuit hazard.
@@EriksElectronicsWorkbench , thanks for the quick reply. Grtz
Erik! I have a model 205a-03r high voltage power supply. I foolishly switched the polarity while it was still at -400V and now I am not reading any output voltage. The inside looks fine and I cannot find any signs of damaged components. Can I still save it? What can I check?
If your model is similar in design to mine, the potted/sealed high voltage module may have been damaged with the polarity reverse switch while on. But I would also check the power transistors on the heatsink for shorts or opens, drive signal to the power transistors and drive voltage to the high voltage module, and basic things like power supply DC voltages.
@@EriksElectronicsWorkbench Thank you for your swift response! Can I check the power transistors while they're still attached, or do I have to take them out?
@@EriksElectronicsWorkbench Also, yes it's practically the same model as yours, but it goes up to 3kV and 10mA.
@@BurakAhmetTufekci It depends on the surrounding circuit if it influences the readings to a great deal but you can try in circuit first. You should have a diode junction from collector to base and from base to emitter. And an open from collector to emitter. If you can unsolder just the base lead connection (depending on how they are mounted and wired) you may not need to remove anything else to get the C-B and B-E readings. In circuit may not give an accurate reading from C-E.
@@EriksElectronicsWorkbench You're right. Also, how could I check the sealed high voltage module? Thank you so much!