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From: Franc Zabkar on 9 Dec 2008 19:45
On Wed, 10 Dec 2008 11:41:45 +1100, Franc Zabkar
<fzabkar(a)iinternode.on.net> put finger to keyboard and composed:

>Having said that, I can't follow the current path. It appears to flow
>into the transformer's centre tap and then out via either end of the
>primary winding. It must then flow through the "transistors" into the
>"oscillator" because the side paths are blocked by reverse biased
>diodes. But the remaining terminal for the oscillator is also blocked
>by diodes ...

Sorry, I didn't read bud's post properly. It appears that he has
already come to the same conclusion.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
From: Ross Herbert on 10 Dec 2008 03:54
On Tue, 9 Dec 2008 08:24:37 -0800, DaveC <me(a)bogusdomain.net> wrote:

:> repost to
:> de.sci.electronics
:
:Thanks.


Your query seems to have the contibutors on de.sci.ing.elektrotechnik just as
baffled as the rest of us here Dave....
From: Dave W on 10 Dec 2008 08:44
The transformer feeds a block with a triangle symbol, so my hypothesis
is that this represents "rectifier" and it's a full-wave bridge,
especially as it says 42V= (42VDC) underneath. The block on the left
with three inputs at the top could be a three-phase rectifier, and the
small blocks with three terminals could be silicon controlled
rectifiers. Your mystery block must be something which flips into one
of two positions.

Dave W
From: Eeyore on 13 Dec 2008 06:07


DaveC wrote:

> This is a partial wiring diagram for an early 80's (West) German guillotine
> paper cutter:

That's a perfectly normal Euro standard symbol for a transformer.

The thing with an arrow it feeds is obviously a bridge rectifier which makes me
wonder if the arrow symbol thingies with 3 connections might be SCRs.

But the rest is extremely odd.

The ?? might be a panel mounted SPCO switch.

And yes, the clutch is in black because it's inductive.

Graham

From: daestrom on 13 Dec 2008 13:38
DaveC wrote:
> This is a partial wiring diagram for an early 80's (West) German
> guillotine paper cutter:
>
> <http://freefilehosting.net/show/42l0i>
>
> The goal of this circuit is to energize an electromagnetic clutch
> coil (m27) that takes rotational energy from a flywheel to do a task
> (bring down the knife blade). This circuit is currently not working.
>
> This machine has no ICs. There are some monolithic rectifier bridges
> and discrete transistors (the common symbol for which I cannot find
> *one* in the diagram), and plenty of passives.
>
> The transformer (m) primary center tap is connected to 24vdc. Do I
> interpret this correctly that the primary is run by a switched dc
> voltage? (This on a machine that runs on 3-phase 245vac.) Why?
>
> I can say from experience that other machines of this same
> manufacturer use a voltage derived directly from the 3-phase input to
> drive the electromagnetic clutch. Why use a switched voltage, I
> cannot understand.
>
> Is the triangle within a square symbol some sort of odd
> representation of a transistor? And the "arrow thing" that feeds
> them? Ideas?
>

The rectangle with double-headed arrow *might* be a center-tapped
inductor/choke. If the two items underneath it that you marked
'transistors?' are actually SCR's, then a center-tapped inductor could be
used to commutate them. When one fires, the sudden rush of current through
that half of the inductor produces enough induction to stop/reverse the
current through the other side and commutate (shut-off) the other SCR. In a
slightly different form this sort of circuit used to be used in power
inverters.

So the two SCR's would pulse each end of the center-tapped primary of the
transformer. But I'm not sure of the rest since it looks like +24V is
feeding the choke/SCR and the center-tap of the transformer primary is also
+24V. Where does match-mark 'A' go off to?

daestrom

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