# short circuit detector

Discussion in 'General Electronics Discussion' started by ratstar, Nov 2, 2020.

1. ### ratstar

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20
Aug 20, 2018
got another one for u dudes to gawk at the insane simplicity. =)

I replaced the picture for a better one, more descriptive and in voltage divider mode instead of current divider to save overloading the led.

Last edited: Nov 2, 2020
2. ### Harald KappModeratorModerator

12,454
2,984
Nov 17, 2011
What is your power supply going to be?
With only 1 Ω in series with the LED you'll need veeery tight regulation of that supply otherwise the LED will burn through quickly and your "detector" will show a permanent short circuit.

ratstar likes this.
3. ### ratstar

485
20
Aug 20, 2018
I think a 9v battery will do.
I can see u understand the circuit, because of what you said.

4. ### Harald KappModeratorModerator

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Nov 17, 2011
9 V to an LED with 1 Ω series resistor will result in ~7 A current.
Don't worry about draining the battery: The LED will burn through much quicker.

5. ### ratstar

485
20
Aug 20, 2018
but its 4.5 volts cause its in a voltage divider, and you can light an led off a battery with no resistor fine, with the volt reduction I think would be about safe.

6. ### Harald KappModeratorModerator

12,454
2,984
Nov 17, 2011
Before you edited your image there was only one 1 Ω resistor, you "secretly" added a second one.
Even with two 1 Ω resistors current through the LED will be ~ 3.5 A, still way too high.
Yes, once, for a few milliseconds.
Do not think, do the math -> no this won't work.

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7. ### ratstar

485
20
Aug 20, 2018
The second resistor, makes it a voltage divider, so only half the power of the battery hits the led. it should be safe. but i spose, I could be wrong...

The fact that the invention actually works is not as important as the led frying with the wrong resistance, is it.
U guys help keep my work safe from plagiarists, thankyou.

Last edited: Nov 3, 2020
8. ### AnalogKid

2,639
764
Jun 10, 2015
With this circuit, I don't think that's a problem.

ak

OBW0549 likes this.
9. ### ratstar

485
20
Aug 20, 2018
Why? it cant be because it doesnt work, because it does.
Is it because its so easy everyone already knows?

Have a look at this circuit on the internet-> (these guys dont know...)

https://www.instructables.com/Short-Circuit-Detector-Part-1/

Its overcomplicated, and I doubt it even works.
You guys are lucky you have me here to point out these things to you. (im sorry if it offends the ego a little tho...)

Last edited: Nov 3, 2020
10. ### Harald KappModeratorModerator

12,454
2,984
Nov 17, 2011
Are we? Or are you lucky to be still here?

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11. ### ratstar

485
20
Aug 20, 2018
If I count my blessings (albiet in an unavoidable circumstance.), I guess so.

Im just letting you guys know that a voltage divider is enough to detect short circuits. isnt that clever.

Last edited: Nov 3, 2020
12. ### Bluejets

5,615
1,188
Oct 5, 2014
Wally..??

Martaine2005 likes this.
13. ### ratstar

485
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Aug 20, 2018
So u think it isnt true?

14. ### Harald KappModeratorModerator

12,454
2,984
Nov 17, 2011
If you want to keep your "inventions" from being used by others then don't post here. This is a public forum, open for everyone to read.

ratstar likes this.
15. ### ratstar

485
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Aug 20, 2018
yes. sneaky business! =) u guys are an enigma to me.

16. ### AnalogKid

2,639
764
Jun 10, 2015
Do you mean 'anathema"?

ak

17. ### ratstar

485
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Aug 20, 2018
of course not, I love you guys. enigma as i meant, meant someone that is misunderstood by me.

18. ### AnalogKid

2,639
764
Jun 10, 2015
It will do something, but not something useful. In this circuit, the beeper is on constantly until the probes are connected to a resistance of something less than 10,000 to 100,000 ohms. At that point the transistors attempt to place a dead short across the battery to turn *off* the beeper.

It is clear from the schematic what the intent of the design was, but he got it wrong. BTW, this is to be expected from "Instructables". If you check the archives of this and other forum sites, you will find that many of his postings are wrong, and some are dangerous.

ak

ratstar likes this.
19. ### AnalogKid

2,639
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Jun 10, 2015
Only at the concept level. To us it isn't useful because of the strain it puts on the battery.

ak

ratstar likes this.
20. ### ratstar

485
20
Aug 20, 2018
Thats understandable. I wonder if that wasnt the case maybe thered be some way to turn finish it off into an ohmmeter but unfortunately doesnt work very well...

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