F5 increased capacitance

[JOHNNYCR100]

Hi Boys, may I ask a newbie question?

When in china I can get a 300V/A 220 v primary /2 x 18 volt output secondary transformer, however my mains input where I live is 240v, so to get 2 x 18 volts output on the transformer, what input voltage input should I select? (Bearing in mind my input is 240v not 220 v) should I select a lower secondary to get 18 v out or vica versa? (or wont it matter?)

I am interested to ask since I was looking at some mondorf mlytic caps from hi fi collective (2 x 47,000 uF per channel) at a nice price (around 12 UKP each) but there only rated at 25volts DC (+20% extra on the spec) my PSU PCB only has room for 2 caps per channel hence the fetish for the 47,000 Uf caps--or -are there better cap recommendations ???

see link: http://www.hificollective.co.uk/components/mcap_mlytic_si.html

Am i sailing to close to the wind here, or is the on load voltage low enough to be safe within the cap max tollrence

Thanks boys--blowed if i know!

regards

Johnny

 

[KatieandDad]

I wouldn't risk using a 220V transformer at 240V, it might well overheat.

But to answer your question all you need to do is find the Np ; Ns ratio.

220 / 18 = 12.2

So at 240V you should get 240 / 12.2 = 19.7V.

To get 18V you would need to find a 18 x 220/240 = 16.5V transformer.

 

[JOHNNYCR100]

Thanks Katieanddad, looks like i wont be getting a cheeop Chineest Tx, ill save and get the Amtek (or piltron if rich?)

Thank you for the easy to understand explenation sir🙄

Any one idears on the Cap issused raised here?

cheers

Johny

 

[AudioSan]

go for 35V caps. and use the 220V transformers. that is no problem.
and i would get another PSU Board, that can hold minimum 4 caps and can be used With CRC/CLC filter, bleader resistor and bypass caps.

 

[JOHNNYCR100]

Thanks Audiosan, I have the Paul Danuals PSU board with only 2 cap per PCB, wish i had the option of say 4 x 22,000 uf- that would be easyer- Mundorf look good but i think others have used Panasonics to good effect?

cheers
Johnny

 

[AudioSan]

do you mean peter daniels?
those Boards are single rail. so you ned 2 of them. 1 for +rail and 1 for -rail. so then you have for 4 caps, bleader resistor, CRC/CLC and bypass caps. if you want seperate PSU for each ch, then you need 4 PSU Boards.

 

[JOHNNYCR100]

Hi Again Audiosan,

Thanks for the reply to my inept questions, yes I read the circuit diagram again, now i understand!, think i got confused!! but as i am building monoblocks i do indeed require another set of PCBS.

But at least i can get a set of 4 (per channel) of 22,000 UF caps in with decent voltage ratings (35v) - it may be a good idea to reconsider and get 2 x DIY universal PCBS? for a monoblock configuration?
Any how thanks Audiosan-i now "get it"- keep em coming .

Best regards
Johnny

(PS- Paul Daniels was a Magician who worked for the BBC IN THE 1980S-- what was i thinking??)

😛