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# Reduce current but maintain voltage? Answered

Do resistors reduce voltage or amprage? It's amprage as far as i know. I've got a power supply thag outputs 9kV at 300mA and I need to get it to 9kV at 0.2mA, someone suggested a 450kOhm resistor. When I phoned go get one they asked if I want a quarter watt resistor, what does that mean (1/4, 1/2 watt). I need to reduce the current comingfrom
the power supply because I'm using it to power a fusion reactor and the diodes I have to comvert
the AC to DC can only handle 0.02mA

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## 11 Replies

-max- (author)2016-03-26

I made this video just for you! (and everyone else who asks this question)

and a fusion reactor!?

verence (author)2016-03-25

Of course all those calculations with just a resistor don't take the resistance of the actual load (a fusion reactor? really!?) into account. You have to subtract that from the 45MOhm / 450MOhm / whatever.

And of course due to the voltage drop on the resistor, your load will not get the full 9kV any more. Check Kirchhoff's circuit laws.

Btw, I hope the diodes you mentioned can handle the ca. 14kV (peak voltage of a 9kV sine wave)

steveastrouk (author)2016-03-25

I have assumed that the plasma resistance is very low, compared to the dropper resistor stack....

rickharris (author)2016-03-24

resistors restrict current flow. however current isn't an issue as your load will consume the current it needs. The job of the power supply is to provide at least that required current.

JunaidA44 (author)2016-03-24

I know that the device will consume the power it needs but I'm using it for a fusion reactor and all of the current will flow through the two grids that's why I need to reduc it

rickharris (author)2016-03-24

How was I supposed to know that?

JunaidA44 (author)2016-03-24

yeah, sorry should've stated in the question

iceng (author)2016-03-24

Fluorescent lamps are a current limited high voltage mercury plasma devices...

Neon lamp transformers are 7KV to 15KV internally limited 15 to 30 ma...

To limit current placing an inductor on the AC side of your power supply is how plasmic arcs are controlled... The inductive reactance can be designed to limit any desired current with greatly lower power loss that is always imposed by a heating resistor...

The inductor saves the limiting energy in a magnetic field, which is returned when the current starts to alternate its AC direction making it the ideal device for control...

JunaidA44 (author)2016-03-24

***Correction 0.02mA not 0.2mA

steveastrouk (author)2016-03-24

Make that 450Meg ohms then, power dissipation is next to nothing. 45 10Meg, 250V resistors.

steveastrouk (author)2016-03-24

To current limit it, into a plasma, you'll need a very high voltage resistor, or a series of them, and 45 MEGOHOMS. Power dissipation is 1.8 Watts.

9000/200uA = 45Meg. Dissipation = 45 Meg x 200uA^2