surge suppressor

If you need to have your protection closer to 24, you can either use a zener diode with a thyristor, or a zener diode with a hefty power transistor darlington. The solutions make sure the input fuse blows, but the first solution only recovers after power removal, the second one recovers when the

Don't forget a fast blow fuse. That way when the MOV's fail, they will just blow the fuse and not explode.

Geoff.

I need to build a surge suppressor to go on the input of an alarm circuit. The circuit operates at 24.0 VDC. This is a two wire input with an end of line resistor. I pulled an AC line toroid off an old RCA TV and plan to connect it in series with my alarm circuit. Across the other side of the toroid I plan to connect two 33.0 V MOV's in series, with the center of the two connected to chassis, (building) ground. This combination on the other side of the toroid will then be connected to the alarm input. Additionally across the alarm input will also be connected a 1.0 uf capacitor. My theory is: a transient first sees the inductor which by nature resists a change in voltage. Next come the series MOV's which should direct everything above 24.0 V between each side of the line and ground, to ground. And finally will be the cap which will hopefully take care of whatever is left. I know that there are commercially available filters on the market but I would really appreciate any thoughts on my idea. Thanks, Lenny

----uuuuuu----,________________ | l M l Line |,,,,, __l__ To alarm panel input in | | ____ M GND l | l -----uuuuuu----'_________l,______

=A0 =A0l

larm panel input

=A0 =A0l

The input is aimply a DC voltage of about 15 volts. This is a 24 volt power limited circuit which has a supervision resistor at the end of the line. If the line opens the voltage will approach 24 volts and the system will see a fault but not an alarm. If the line is shorted or brought very close to zero volts the system will indicate an alarm. A fuse would seem to make sense but it is not permitted. It sounds crazy but there must be repeatability so circuit integrity cannot be compromised by an open fuse. By the same token on opto isolator cannot be used either because it circumvents the direct connection between the alarm initiating devices and the input to the panel. It makes for a frustrating endeavor trying to deal with the realities of the situation while staying within the guidelines of the original design. Lenny.

On Tue, 8 Jul 2008 13:09:00 -0700 (PDT), " snipped-for-privacy@yahoo.com" put finger to keyboard and composed:

Your ASCII art is barely understandable. You need to use a fixed width font.

- Franc Zabkar

It's readable if you think back to the 'ladder logic' days. I can read it fine uuu = inductor, M = caps, (unless it means "surgistor"). There's only so much you can do on an ASCII terminal. Bill Baka

=A0 =A0l

=A0 l

o alarm panel input

___

=A0 =A0l

The M's are MOV's the uuuu's are inductors and the cap is to the right.Lenny

On Sat, 12 Jul 2008 09:12:54 -0700, Bill put finger to keyboard and composed:

I don't have a problem with the OP's choice of letters and symbols. The problem is that the characters don't appear in their intended columns. To see what I mean, paste this message text into your word processor and select a fixed pitch font such as Courier New. Then change the font to a variable pitch type. I find that Tahoma (Western) or Britannica Bold give me the best rendering of the OP's drawing.

Now select a variable pitch font, start a new line, and type ten spaces followed by a period. Then start a new line and type ten 8s, followed by a new line and ten underscores, new line, and ten dashes, etc. Now do the same for a fixed pitch font.

- Franc Zabkar

That's one of today's problems, started my M$ and their zillion fonts for windows.

Oh Franc, Let him have some fun. At least he isn't that Curtis Brown jerk/troll. Bill Baka