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Short Circuit Tool

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3 years 7 months ago - 3 years 7 months ago #42071 by Tutti57
Short Circuit Tool was created by Tutti57
I was in a electrical class l
last year and the instructor gave us these parts and a diagram to build this tool that you put in place of the fuse that keeps blowing. It lights up while the short is present so you can isolate it or do wiggle tests. The problem is that I lost the diagram and don't remember how to build it, ha. I remember you were supposed to get those GTC fuse things so you had a good way to plug it into the fuse place and add long wires to it so you can bring it in the car with you if needed. He also said that the yellow things were important but I don't know what they are. Some kind of capacitor I suspect, with xx30 UF400 on them. Does anyone have an idea of what I'm talking about here? I'm working on a short to ground now and thought this would be helpful.



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Last edit: 3 years 7 months ago by Tutti57.

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3 years 7 months ago #42074 by juergen.scholl
Replied by juergen.scholl on topic Short Circuit Tool
Not exactly what you are asking for but you'll find these on Amazon and you can build your gear; the company is general technologies corp. Or just blow a fuse and solder some wire and a socket to it...


An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
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3 years 7 months ago #42077 by Matt T
Replied by Matt T on topic Short Circuit Tool
Testing for shorted wiring, with the load off/unplugged, you can just use a test lamp, without any electronics, in place of the fuse. And the lamp automagically limits the current so you don't have to worry about melting the harness unless you use a very large lamp.

If the load is small enough, relative to the lamp, this also works with the load plugged in. My 100W test light will flow a 2A current without significant volt drop.

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3 years 7 months ago #42078 by Tyler
Replied by Tyler on topic Short Circuit Tool
Those yellow doodads sure look like PTC fuses:

www.aliexpress.com/item/32328262898.html

It's a pretty good idea for short circuit testing, especially combined with some kind of bulb to visually let you know if the fuse is open/closed/in the process of opening/whatever.

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3 years 7 months ago #42081 by Matt T
Replied by Matt T on topic Short Circuit Tool

Tyler wrote: Those yellow doodads sure look like PTC fuses:

It's a pretty good idea for short circuit testing, especially combined with some kind of bulb to visually let you know if the fuse is open/closed/in the process of opening/whatever.


Good find. Wiring the PTC fuse and the lamp in parallel should make the lamp light when the fuse opens, so long as there is a path to ground on the load side.

Found a data sheet for these things. Looks like they take a while to trip, and also take time to reset. Good idea in theory but might not respond fast enough for wiggle testing??

www.littelfuse.com/~/media/electronics/d...rf_datasheet.pdf.pdf

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3 years 7 months ago #42088 by Tutti57
Replied by Tutti57 on topic Re:Short Circuit Tool
Ah, yes. That's what they were. I'm going to try to track down the instructors email address and ask for more info. I'm not sure if he mentioned the wiggle test specifically but I remember it being good for breaking off legs of the circuit.

I got a chance to look at the car again today at work and found the short. I used a little different method than I have in the past. I pulled the fuse and used my power probe lights and sound to help find it. Power leg in the socket was power and the other side should have been nothing but was showing ground. At first it was a constant short so I turned the annoying sound off and watch for the green light to go off during the wiggle test. Then it changed to there not being a short so I turned the sound back on so it would make it when it came back. It worked well.

For those interested, it was a 2017 Rogue. Complaint was low oil pressure/shut off engine warning came on and engine turned off and wouldn't restart. It was short to ground on a TCM power wire. There is a golf ball sized harness that runs up along the left side of the valve cover and curves back around it. The harness rubs on a bolt there.

Nissan Technician

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3 years 7 months ago #42097 by Tyler
Replied by Tyler on topic Re:Short Circuit Tool
Nice. B) I'll keep my eyes open for that one.

Didn't know newer Nissan products would shut the engine off in response to a perceived low oil pressure condition...

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3 years 7 months ago #42113 by Tutti57
Replied by Tutti57 on topic Re:Short Circuit Tool
I've wanted to look into that too. I'm not sure if that's what turned it off. After that fuse blew, it wouldn't start. I've seen this a few times where it doesn't know if it's in park without the TCM and won't start. I've started them with my power probe on the starter in those cases so I'm not sure if it would shut off right when it happens or not.

Nissan Technician

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3 years 7 months ago #42114 by Matt T
Replied by Matt T on topic Re:Short Circuit Tool
Good thinking using the PP as a short finder.

Regards the "low oil pressure" I guess that was transmission oil pressure. Or have nissan powered the engine pressure transducer/switch from the TCM?

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3 years 7 months ago #42115 by Tyler
Replied by Tyler on topic Re:Short Circuit Tool

Matt T wrote: Good thinking using the PP as a short finder.


I'm sitting here at home, and I can hear that Power Probe singing 'GROUNDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD' :angry: :lol:

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3 years 6 months ago #42793 by Hardtopdr2
Replied by Hardtopdr2 on topic Re:Short Circuit Tool
I was thinking beep beep beep beep of the ect tester lol lol powed probe 4 kit has saved me a few times..

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3 years 4 months ago #44201 by Tutti57
Replied by Tutti57 on topic Re:Short Circuit Tool
I found the diagram! But, I don't understand how this would work in parallel with the bulb?


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3 years 4 months ago #44202 by Matt T
Replied by Matt T on topic Re:Short Circuit Tool

Tutti57 wrote: I found the diagram! But, I don't understand how this would work in parallel with the bulb?


With the e-fuse closed the circuit is basically like this:

Power > e-fuse > Load > Ground. Voltage drop is mostly across the load so the bulb in parallel with the e-fuse isn't lit.

When a short opens the e-fuse the circuit changes to this:

Power > bulb > Ground. The bulb limits short circuit current and lights up to let you know the e-fuse has opened.

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3 years 4 months ago #44206 by Tutti57
Replied by Tutti57 on topic Re:Short Circuit Tool
Ok, I think I've got it. It's still ohm's law in action of course. I thought when I was reading about these fuses that their resistance increases when they heat up, PTC thermistors. So if you have say a 4ohm bulb in parallel with a 4ohm resister, and a 12v source, you have 2 ohms of total resistance. Current increases with more branches and voltage stays the same in each branch. What changes is current. So a short would heat up that fuse and increase it's resistance and decrease total current flow enough to turn off the bulb.

Is that right?

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3 years 4 months ago #44210 by Matt T
Replied by Matt T on topic Re:Short Circuit Tool
Guess it's time to break out the crayons :silly:

The indicator lamp is 5W and the load lamp is 55W in the following example. I've used hot resistances for them calculated from wattage. And I'm using the specs for a 10A e-fuse from the datasheet I linked earlier in the thread.

Here's the circuit under normal operation. The e-fuse and indicator lamp are the first resistance in a series resistance circuit with the load lamp being the second resistance.



Now with the circuit shorted to ground you've got system voltage across both the indicator lamp and the e-fuse. Lights the lamp and trips the e-fuse. Total current limited to less than 1 amp.



This is the tripped circuit with the short removed. Most of the volt drop is still across the indicator lamp and e-fuse. Indicator is still lit which is why I questioned how useful this device will be in the real world.

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1 year 4 months ago - 1 year 3 months ago #58970 by amadjan22
Replied by amadjan22 on topic Re:Short Circuit Tool
You can check short circuits through millimeter which is best way to get your issue solution Reviewreview
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Last edit: 1 year 3 months ago by amadjan22. Reason: words error
The following user(s) said Thank You: jrgreene1968

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