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Transformer/Capacitor question

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George L. said:
ok, I get it....... :D

Do the resistors need to be able to handle high voltage???
I would like to use the 100K 1/2W resistors from radioshack because it is 2 minutes from my house.

Also, this is my first time using voltage balencing resitors for caps. Where do I put them??? I remmember you said I need three.

For the diagram above (with the three in parallel and three in series) you would need three resistors - you put then in series from +ve to -ve, with their junctions connected to the junctions of the capacitors.

The resistors need to be able to handle the voltage, and also dissipate the heat they generate - you can simply work that out from VxV/R - for 300V it comes to just under 1W, I would advise using two watt resistors!.
 
sorry nigel,

I dont really understand what you are saying, could you provide a simple diagram like ljcox did, it would be really helpful.

Also, radioshack only has 1/2 watt resistor, could I in some way, combine those to make a 1 or 2 watt resistor.

Thanks,

George
 
George L. said:
sorry nigel,

I dont really understand what you are saying, could you provide a simple diagram like ljcox did, it would be really helpful.

Also, radioshack only has 1/2 watt resistor, could I in some way, combine those to make a 1 or 2 watt resistor.

You could use four 100K 1/2W in series/parallel to give 100K 2W.

Here's the diagram you asked for.
 

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thanks Nigel :D

the diagram is much more helpful.

according to your equation, VxV/R , the watt rating is .9 watts with 100K resistors. (300 x 300 / 100,00)

If I use a 220K resistor the watt rating is .4 watts. This would make it compatible for the radioshack resistors.

Would this work?

Please help,

George
 
George L. said:
sorry nigel,
Also, radioshack only has 1/2 watt resistor, could I in some way, combine those to make a 1 or 2 watt resistor.

Thanks,

George

George,
Nigel is being conserative by suggesting four 1/2 W resistors and I agree. So I suggest that you use 390k resistors. Buy 12.

In other words, each resistor in Nigel's diagram is four 390k resistors connected in parallel. 4 in parallel will give you just under 100k (ie. 390/4) and at 1/2 W each gives you a max power dissipation of 4 W.

Len
 
But resistors also have some variations like capacitors. So should one not use preset potentiometers?

If I have followed this thread correctly, the resistors are meant to form a potential divider to compensate the potential divider formed by the capacitors. And the resistors are bypass resistors, to bypass the extra potential developed.

Am I correct?
 
ljcox said:
4 in parallel.....and at 1/2 W each gives you a max power dissipation of 4 W.

:D

lord loh. said:
But resistors also have some variations like capacitors. So should one not use preset potentiometers?

No, it is not required. Resistor tolerance is many times smaller than that of electrolytic capacitor and usually is quite sufficient to balance out the voltage variations.
 
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