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240VDc supply

bigkim100

Apr 17, 2013
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Ok, I need to make a 3 individual 240v/6VDC power supplies for 3 military radios. They dont require much in the way of amperage, and dont require regulation (military stuff is VERY forgiving).
So if I have 2-1000uf capacitors smoothing the 240vdc supply after a full wave rectifier, should I place a 1ohm resistor across each of the electrolytic capacitors to make certain that they actually do a good job of smoothing?
On a full wave bridge rectifier, do you think 2000uf will do the trick for smoothing??
PS, Im using a "BRUTE FORCE " supply (Transformer, Rectifier, Capacitors) rather than using an inverter, to keep stray noise from the supply
 

kellys_eye

Jun 25, 2010
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Rule of thumb is 1000uF per amp so 2000uF is overkill. You'd likely get away with 470uF (without knowing exactly what it is you're powering, this is a guess though).
 

bigkim100

Apr 17, 2013
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LOL...thats a friend of mine.
I have the Bc-453, BC_454, and R-25. I will probably get meore later, requiring more supplies
 

Harald Kapp

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Nov 17, 2011
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should I place a 1ohm resistor across each of the electrolytic
Definitely no!
With 240 V across and 1 Ohm, the power dissipated will be 57 kW.
Or do you mean in series with the caps? Useless as teh resultig corner frequency of the filter is around 160 Hz.
Usually no series resistor is used unless one needs to limit inrush current. In that case 1 Ohm is probably not enough.
 

AnalogKid

Jun 10, 2015
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Without knowing the output voltage and peak load current, nothing can be calculated. Does random guessing actually help you? Any particular reason you are keeping all of the design requirements a secret?

Which Specification(s) do your supplies have to meet? In the US military, the army, navy, and air force each have their own MIL-STD(s) for power systems.

ak
 

crutschow

May 7, 2021
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Unless the power input to the radio is internally isolated, you need a supply isolated with a transformer from the mains.
Otherwise be sure your accidental death insurance is in order. :eek:
 

kellys_eye

Jun 25, 2010
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The OP could be referring to a conventional pi-style DC filter (C-L-C) with the L sometimes replaced with R as per 'usual' tube receiver circuits. Such circuits are very forgiving for ripple and the C part is commonly as low as 32uF, the receiver current usually being of the order of 10's (perhaps up to 100) mA (peak audio). Certainly capacitance in the 1,000's is well over the top! The 6V part will be for tube heaters and not require anything at all in the way of smoothing - in fact they will work with AC as they usually do.
 
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