PSU/schottky diode rectified

JaredC79

Banned
2015-09-02 4:32 am
NJ
I am using 4 large Schottky diodes for rectification going into capacitor banks for both positive and negative rails. I am Nichicon FWs as the caps 12 per bank of a lower value and want to add a PI filter/CR arrangement. I know i need 4 10 ohm resistors if i don't want to use inductors and i don't. Do i use the resistors on the the opposite of the rail to ground (neg side of positive rail and then opposite) before and after the capacitor bank?
 

rayma

Member
2011-04-29 8:37 pm
Do i use the resistors on the the opposite of the rail to ground (neg side of positive rail and then opposite)
before and after the capacitor bank?

Since you have a single FWB rectifier to supply both rails, the R must be in series with each of the positive and negative rails,
between the capacitors, not in either of the ground rails.
 
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JaredC79

Banned
2015-09-02 4:32 am
NJ
Ok so each + and - gets a r prior to the beginning of the cap bank? I have a bunch of the schottskys and can do 2 fwbs if it makes a difference. Figured the resisters we to snub or ground the opposite on the rail so that faston connections only had 1 charge. I have slow blos set up before the input from the tranny and before the out of the + or - does the opposite of the rail need to be gounded out before the fuses and fastons?
 

rayma

Member
2011-04-29 8:37 pm
I'm sorry, the secondary are 55+/-. Center tap is grounded.

Ok, then you have two 55V secondaries in series, with the common connection grounded, giving +/- 78VDC outputs.
This allows a maximum output of 55Vrms, or 380W into 8 Ohms, with enough power supply and heat sink available.
If you use a CRC supply, the 10 Ohm resistors may need to be lower in value, or high in power rating.
The resistors must go in the positive and negative legs, not the grounds, with capacitors both before and after them.
 
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JaredC79

Banned
2015-09-02 4:32 am
NJ
I don't have the operating systems for it. I'm using 4 schottskys for a full wave bridge. V+ and negs to vas have slow blo fuses. Each pos and Neg have 12 2200uf nichicon golds. AC ins have slow blos also. There's an earth faston and amp ground faston on. I know the guy refered to it as a PI filter but doesn't look like one. It's a multi layer board so tracing it can be hard. The resistors are smd and look to be bridging the pos rails of the caps to the net rails of the caps. Seperating them in groups of 6. I would like to make something similar for testing purposes with different resistors and caps and see if there any tonal differences
 

JaredC79

Banned
2015-09-02 4:32 am
NJ
Rails I believe are 78 v specs recommend 80v snap in caps, I'm using radials and rather not glue and use a lot of solder - I went over incase I want to use duel dye mosfets and got the 100vs. I really want to make an identical board and change caps and resistors out and record the differences and AB them and see how much of a difference it is. Yea that is the correct value as the smd components are 4 r100 resistors. He refered to it as a PI filter set up but I after looking online I can't see anything similar from a schematic standpoint - it's a multi layer board so following the traces is impossible but looks like 2 resistors are used on each Pos and neg rail. But then again they can also be connected to the diodes.
 

rayma

Member
2011-04-29 8:37 pm
He refered to it as a PI filter set up but I after looking online I can't see anything similar from a schematic standpoint

A pi filter (in this case) means first a cap to ground, then a series R, and then another cap to ground.
If you draw it, the schematic sort of looks like the Greek letter pi.
https://en.wikipedia.org/wiki/Pi#/media/File:Matheon2.jpg

If the rails are 78V, then you'd want 100V rated parts for a reasonably long useful lifetime,
especially if they get hot. Using 105C caps instead of 85C caps will also give longer life.
 
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rayma

Member
2011-04-29 8:37 pm
It's a 55/55 toroid running 78v rails. I upgraded the caps to 100v. So we are good.
Just trying to figure out the topography and where the 4 resistors were installed.

Is this supply for two channels, or do you have one toroid per channel?
There are probably 2 paralleled 10 Ohm resistors in each +/- supply leg.
Do you know the wattage rating of the resistors?
 
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