Club 80-90 Forums

Could anyone have a look at the fairly simple Zig CF8 circuit diagram on this post and give some input on what the zenner and SCR are doing in the earthy side of the bridge rectifier please (I should know, but it's got me scratching my head )

Replies on that post please, not on this one

Thanks Ghost. Very kind of you to get me an answer. Plus others may learn too. That's what I like about these forums - we can delve into our passion and personally, I find knowing the principles helps immensely. Plus it's good for the wallet although my local garage would probably disagree with my motives!

Bubble Meister wrote:find knowing the principles helps immensely

Ooo, I just hate not understanding stuff (which is one reason I want to get the hook on this CF8 circuit). Plus, when I can look at a circuit diagram and fully understand what is doing what and why, especially radio circuits, understanding RF intermediate frequencies n stuff, I find it very rewarding. Same with chemistry (and cooking for that matter) E D I T = Oh and gardening. Oh and Astronomy I could go on, in fact I often do

What does puzzle me is folks who look at an engine say, and have no clue at all about pistons, crankshafts, camshafts etc. In some ways they have the benefit of not feeling the need to fill their heads with it all. I often think my head needs a clean out of useless files, then a defrag

A defrag is probably very appropriate. I have a head full of van interior design, internal power distribution, and headlining adhesive research.
Also I'm soon to start my own bright zinc plating experiments! The van is like the final master piece of all my research!

I've always taken a simple approach to complex questions (as best I can) without sounding patronising. The downside of that is my articles in the WIKI (and I have a whole newspaper to finish on my desk today) and posts, tend to be longer than I'd like, just to make things clear and easy enough to follow. On the other hand I get frequent PMs thanking me for taking the trouble so perhaps its the way forward.

Never assume the person you're talking to is an expert, or indeed a novice. A lot of 'experts' are armchair novices and a lot of 'novices' often have good and useful points to make.

You're right though, theres much to be said for bilissful ignorance at times.

CovKid wrote:I've always taken a simple approach to complex questions (as best I can) without sounding patronising

Which is summat I learned a long time ago when dealing with customers when talking about technical stuff, especially computers. Being a smart a*** never impresses a customer.



Aside = A good while ago (~35 years) I worked for a Hi-Fi shop. During staff training we were asked to stand up, each in turn, and explain, as if we were talking to a customer, what the then new Dolby C noise reduction did.

Most of the staff started to explain that the Doldy C system split the overall frequency response, of around 50Hz to 20kHz, into several separate bandwidths, then it compressed each one separately during recording. Then on playback, the separate audio bands were de-compressed so that the frequencies individual dynamic rage was preserved but the noise threshold resulting from the compression and de-compression was reduced.

I stood up and said "The new Dolby C system results in less hiss from your tapes"

I got a pat on the back

ok... i'll have a go,when the bridge rectifier is powered the 5.1volt zenner switches the scr on so the negative side of the bridge is connected to battery negative.
I think its a safety switch so you don't get 250volts on the primary of the transformer if you leave the Zig switches in the wrong position!!

So can the SCR work in reverse? I ask as it's wired in reverse with the anode on the negative side (earth) and the cathode on the positive side (wired to the rectifier side).
I thought the Zener broke down at 5.1v in reverse flow but worked normally in the normal path (ie as it's wired in - from the positive side to the negative side). My understanding was that the chassis would have to be 5.1v higher than the rectifier output before reverse flow occurred.

Hmm.what voltage have you got on the scr[with respect to battery negative ]
ps,all the scr/zenner stuff happens when you first switch it on..very fast!!

Protection against connecting the battery backwards?

OK, seeing as how you lot have ignored this bit :-

ghost123uk wrote:Replies on that post please, not on this one

I have decided to post the diagram here



Tis very odd and you ^^^ are right, the SCR and Zenner are the wrong way around but even if they weren't it still wouldn't make sense. I wonder if the diagram is erroneously drawn, it wouldn't be the first time, but it's unlikely.

@ marlinowner:- reverse battery protection, nah, the way the SCR is, it would conduct if you put the battery on the wrong way around.

Suggestion, as there are now two places were this conversation is going on, may I respectfully suggest we revert back to the other (main) thread HERE or things will get complicated and confused

But,but,but! at switch on the zenner will have a negative voltage* supplied through the resistor.
*With respect to battery negative.
Oh! bugger I still posted in the wrong place!

I copied it over

Still writing it though, so ang on