Lowering B+ in PS

[h00hbt]

Hi all

What would be the best way to lower the B+ in the PS. I have an excessive 30-40V overall. Im pushing 520V into first caps rated max 500V.




Cheers

[Rod Coleman]

If you can get a GZ37, these will drop at least 20V more than a GZ34. Watch out for extra heater current though!

A better way is to configure the PS to quasi- choke input. Remove the electrolytics at C1 [cap after rectifier] and replace with MKP [stacked] polypropylene. Panasonic box type for preference. Use PSUDii to find the value of the MKP: 1uF to 5uF are good starting points.

Cheap motor run MKPs sound horrible IME. Stacked MKP are cheap and 630V rated, and sound fine.

[h00hbt]

Originally Posted by Rod Coleman

A better way is to configure the PS to quasi- choke input. Remove the electrolytics at C1 [cap after rectifier] and replace with MKP [stacked] polypropylene. Panasonic box type for preference. Use PSUDii to find the value of the MKP: 1uF to 5uF are good starting points.

Hi Rod

Yes, I have been reading up and this might be the way to do it. Pity I don´t know how to use the PSUDII or I would have.....

Thanks

[Rod Coleman]

What's your Load Current?

[SY]

Try using a buck winding on the primary- a 12.6V filament transformer will work. That will be the most efficient way to do it rather than burn up heat in a higher rectifier drop or series resistors. It will also drop the heater voltages, but not by much- if you drop 30V out of 520, your 5V heater will drop to about 4.7V. That could work in your favor as well.

[h00hbt]

Originally Posted by Rod Coleman

What's your Load Current?

Rod

I have 390VAC, 0,5A, 18 OHM

Cheers

[h00hbt]

This maybe a stupid question but why wouldn´t a 600V 30uf cap and resistor after the rectifier and keep whats already there in the PS work?


Cheers

[Rod Coleman]

It work work fine.
You can make 33uF or so by using 100uF/400V electrolytic (Panasonic HA or HB or TSUP, Nichicon KX). Use three in series like you have two in series now, with 220K 1W resitor across each one, to keep the voltage balanced in each one.

Or you could use a quality MKP of 30uF/630V. I use and enjoy the AMPOHM [LCR] MKP series

AMPOHM WOUND PRODUCTS|FP-CA-10-AU|CAPACITOR, AUDIO, 10UF, 630VDC | Farnell United Kingdom

[Rod Coleman]

O, and the second capacitor, if that is seeing more than 500V, would need to be made from 1000uF/400V x2, and 150K 3W across each. That may be found to be somewhat expensive, though, in which case, reducing C1 to a 10uF 630V MKP may be a better solution.

[h00hbt]

Originally Posted by Rod Coleman

It work work fine.
You can make 33uF or so by using 100uF/400V electrolytic (Panasonic HA or HB or TSUP, Nichicon KX). Use three in series like you have two in series now, with 220K 1W resitor across each one, to keep the voltage balanced in each one.

Or you could use a quality MKP of 30uF/630V. I use and enjoy the AMPOHM [LCR] MKP series

AMPOHM WOUND PRODUCTS|FP-CA-10-AU|CAPACITOR, AUDIO, 10UF, 630VDC | Farnell United Kingdom

Rod

Oh shoot, I thought I had 30uf but checking now they are 50uf/600V. So I guess these won´t work?



I was thinking of something like this. 1st cap 50uf/600V and then a resistor.



Cheers