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 Short Circuit Detector and disaster prevention.
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 Return to top of page · Post #: 1 · Written at 3:33:54 PM on 29 January 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 867

Wow guys this very simple device which I made up according to directions from my technician is briliant for detecting short circuits and preventing disasters such as the meltdown I had with the Hotpoint Radio in tech advice.

It consists of 3 * 60 watt globes with the first one wired ( active ) directly to the active connector on the bulb socket and active again going out of the neutral side of the socket and directly to the active side of a switchless power socket. The earth and Neutral going directly to the socket. Then the other 2 bulb sockets hooked up in parallel.

The guy showed me on my own radio how well it works by putting a dead short on the on off switch , The bulbs will glow brightly if there is a short or nothing at all if things are fine . Its absolutely brilliant ( forgive my pun lol ).

Short Circuit Detector
Short Circuit Detector


 
 Return to top of page · Post #: 2 · Written at 11:12:08 PM on 29 January 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 3919

Known mostly as a dim bulb tester -- the bulb is goes dim if there is no short and remains bright if there is a short.

The total (incandescent) bulb wattage should be greater than the rated wattage of the radio under test by around 2 times.

I think you have one wired in series? (Not shown in your diagram.)

When using multiple bulbs, you can get fancy and switch them progressively in or out of circuit to vary the total wattage.


 
 Return to top of page · Post #: 3 · Written at 10:22:22 AM on 30 January 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 867

No that is actually the correct wiring diagram. The fellow who drew it up actually cut his teeth on valve radios and that is the diagram I used to build it. You only need two bulbs but I opted for three. As I said if your radio is ok then no bulbs light up ( not dim ) and if there is a short then they are bright.


 
 Return to top of page · Post #: 4 · Written at 5:33:56 PM on 30 January 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 3919

Depends on inrush current of the set/equipment under test. This will vary, depending on design of the load. Some will draw significant current briefly, and then settle down to the rated wattage once valves are operating and capacitors are charged up.


 
 Return to top of page · Post #: 5 · Written at 8:05:52 PM on 30 January 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 867

Ok I have a question . He has this operating with a isolation transformer and a variac . Does it Matter which one is in the power point first or can it be any which way. I have not asked him yet but will.


 
 Return to top of page · Post #: 6 · Written at 8:16:31 PM on 30 January 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 3919

The role of an isolation transformer is to remove the link to earth, which exists at the meter board where usually the neutral link is physically joined to the earth rod. The transformer therefore makes the mains on the secondary side "float" above earth so that anybody connected to earth does not complete a 240 volt circuit through their body.

The transformer ratio is 1:1, 240V in, 240V out, but you need to be aware of its current handing capacity in order not to overload it. Radios are usually light current loads, so you don't need a large transformer.

So, first comes the isolation transformer, and then other stuff such as a variac.

(I should add, that a variac, being by design an autotransformer, provides no isolation at all.)


 
 Return to top of page · Post #: 7 · Written at 8:46:54 PM on 30 January 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 867

So I am guessing that it should be isolating transformer then the Dim Bulb Tester and then the Variac because I'm assuming the Bulbs may not like the input being varied. Just putting the queery out there.


 
 Return to top of page · Post #: 8 · Written at 8:56:05 PM on 30 January 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 3919

Voltage-wise, bulbs don't mind anything as long as it's not above their rated voltage. You can bring a bulb from off to full on via a variac, just like a domestic light dimmer (except that they use triacs).


 
 Return to top of page · Post #: 9 · Written at 9:38:53 PM on 30 January 2016.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 4322

Standard light globes are a purely resistive load. You can dim them pretty much any way you want. Baretters, that are used in many Australian AC/DC sets are pretty much a 60-75 watt light globe and were a cheap and reasonably reliable way of limiting current flow.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Brad.

A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 10 · Written at 12:10:55 AM on 31 January 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 867

Ah of cause I did not think of the light dimmer situation now that makes things a little clearer.


 
 Return to top of page · Post #: 11 · Written at 2:39:00 AM on 16 February 2016.
Art's Gravatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

The light bulb is an old trick, the poor man’s variac.
You can use it to be nice to radios by winding them up gently over 5 or 10 minutes if you want to,
and then also taking time to turn them off. Also, valve radios will happily run at a Voltage
significantly lower than mains, but each radio is too different for a figure.

I was going to bolt a pair of isolation step down formers together in reverse for a “double insurance former”,
then a variac and meters, but it didn’t make sense for the isolation formers to be present in daily use.
The radio next to me is grounded again independently (stake in the Earth) as part of it’s antenna.
Brad might know if there’s a consequence re-referencing it to ground that way, and ever touching the active.
I suspect there would be, and the isolation former defeated the purpose of the RCD.

You can’t go wrong if you buy a good nylon driver, then there’s just no reason to ever deliberately touch one live is there?


 
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