schematic for linear pelt psu

[hydrogen18]

KnightElite:most ppl commonly use "m" to represent microfarad. I'd like to see a 31000 megafarad("Mf") capacitor...

Grayson:I dont understand what you are trying to say. A 2000 microfarad capacitor is a 2000 microfarad. Now yes it is has a insulation rating. A 1000 volt 2000 mfd will not charge up to 1000 volts with a 12 voltinput if thats what you are thinking. If what you are trying to say is that most rectifiers have a higher voltage output under no load than their input that is true. But it will not be a situation of "better". If the voltage is too high the insulation will be pierced and will destroy the capacitor. Another interesting fact: some capacitors work better around their rated voltage. 2x 25000 microfarad 70 volt capacitors gave me poorer regulation that 2x 24000 40 volt capacitors gave me on my 20 volt psu(drops to about 13 under heavy load).

[Since87]

Originally posted by hydrogen18
Another interesting fact: some capacitors work better around their rated voltage. 2x 25000 microfarad 70 volt capacitors gave me poorer regulation that 2x 24000 40 volt capacitors gave me on my 20 volt psu(drops to about 13 under heavy load).

It is not the voltage rating that determines how well the capacitor filters the ripple. It is the Equivalent Series Resistance (ESR) of the cap. These are independent issues, and a higher voltage cap won't necessarily have a higher ESR.

[KnightElite]

Hydrogen18: Actually, MF is generally used in the capacitor industry to represent µF, while mF would be milliFarads. Just a note . Dunno why they don't just add a µ (ALT+0181) to their printers and do it correctly, but whatever.

I think that what Grayson is saying is to choose capacitors that are rated for slightly more voltage than you will need. I agree, running things at their max tolerance is not advisable for this (only for computer hardware ).

[hydrogen18]

Originally posted by KnightElite
Hydrogen18: Actually, MF is generally used in the capacitor industry to represent µF, while mF would be milliFarads. Just a note . Dunno why they don't just add a µ (ALT+0181) to their printers and do it correctly, but whatever.

I think that what Grayson is saying is to choose capacitors that are rated for slightly more voltage than you will need. I agree, running things at their max tolerance is not advisable for this (only for computer hardware ).

lol, we need some standards not involving symbols liek µ then it seems. so how would I symbolize megafarad(Although that is pretty unrealistic, but 1 farad capacitors were unrealistic until recently)

[mikoto]

I have a line on some old equip. Caps and such. This stuff comes from a tenant who can't pay rent and is willing to trade to defer some cost. I don't know how to tell if it is gonna be any good but I can pick and choose what I want from a fairly large selection. Probably 2k+ misc components total. Hope he has what I need. Some of the stuff is obviously pretty old and has just been sitting, warehoused, for quite a while. He builds outdoor speaker systems for churches. He has some pretty heavy duty things but plenty of finer equipment as well. Hopefully I can get more specifics as I select what I want. Would make the whole project cheaper.

In addition, this same guy has an old-school o-scope. I mean really old. Looks to be at least 20-25 years old, maybe older. What the hell do I know? Anyway, it is all analogue. Just dials and switches and stuff. No digital lcd displays or any of that cool stuff like I have seen on the new ones. Just a plain old o-scope. He is willing to part with it "cheap", or so he says. We haven't talked price yet. Any pointers on how to tell if it is worth anything? Or what would be a fair price? (assume it works) Perhaps I don't want an old one?

Kind of bogging down on a couple of points. Step-down transformers are so expensive as to make this whole project silly. Variacs are worse :P

Since87, pm about the variac?

thanks for all the info guys.