I have a resistor that shorted out, the colors dont make sense to me

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
This resistor is on my bug zapper and it shorted out causing the capacitor to pop its top I have the capacitors I just can't figure out this resistor so I can buy a new one, I am new to repairing circuitry so please forgive my idiocy, I don't have a lot of testing tools or measuring things yet, I am a civil engineer by trade but wanted to try my hand at the electrical side as well
20220719_211628.jpg
 

MrChips

Joined Oct 2, 2009
26,789
Welcome to AAC!

How do you know that it is a resistor and that it is bad?
The designation is F1 which would suggest that it is a fuse.

Can you show us photos of the whole board, top and bottom side?
 

MrChips

Joined Oct 2, 2009
26,789
Thanks for the very sharp photos.
I will look over these at a later time and I or someone else will get back with some answers.

Edit: Having a quick look I can see that it is in series with the black wire. Hence it is a fuse.
I would suggest replacing the two large orange electrolytic capacitors and replacing the burnt resistor with a fuse.
What is the power source powering the device?
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
Thanks for the very sharp photos.
I will look over these at a later time and I or someone else will get back with some answers.

Edit: Having a quick look I can see that it is in series with the black wire. Hence it is a fuse.
I would suggest replacing the two large orange electrolytic capacitors and replacing the burnt resistor with a fuse.
What is the power source powering the device?
It just plugs into a regular 120v outlet 20 amp circuit, if it helps it is a 6000v Black Flag Bug Zapper
 

MrChips

Joined Oct 2, 2009
26,789
Here is what I can see from the photos.

This device is directly powered from 120VAC line voltage without an isolation power transformer.
Not too long ago discussion of such circuits was prohibited on AAC forums because of concerns of health and safety.
Recently that restriction has been lifted. BE FOREWARNED.

The resistor labelled as F1 was intended to be a fuse. It got charred because something else in the circuit was drawing too much current.

The two orange capacitors are visible stressed as seen from the bulging tops. These could have been the initial cause of the fault causing the burnt resistor. If the resistor is still measuring as a short this is not unexpected. It got hot but not hot enough to go open circuit.

I can see capacitor C2 is 10μF/250V. I am going to say that 250V is too low for this application. 120VAC rectified becomes 170VDC.
I would like to replace that with a voltage higher than 250V rating.

I cannot see the markings on the other capacitor. I can barely see 50V. Whatever you read, increase that for a greater safety margin.

Replace the resistor F1 with a suitable fuse once we can determine the power requirements of the zapper. This should be clearly marked on the outside of the case.

Edit: I am going to guess that a 0.5A fuse would be adequate to allow 60W max power consumption.
I would use a 20mm fuse mounted on fuse clips.

1658287895375.png
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
Here is what I can see from the photos.

This device is directly powered from 120VAC line voltage without an isolation power transformer.
Not too long ago discussion of such circuits was prohibited on AAC forums because of concerns of health and safety.
Recently that restriction has been lifted. BE FOREWARNED.

The resistor labelled as F1 was intended to be a fuse. It got charred because something else in the circuit was drawing too much current.

The two orange capacitors are visible stressed as seen from the bulging tops. These could have been the initial cause of the fault causing the burnt resistor. If the resistor is still measuring as a short this is not unexpected. It got hot but not hot enough to go open circuit.

I can see capacitor C2 is 10μF/250V. I am going to say that 250V is too low for this application. 120VAC rectified becomes 170VDC.
I would like to replace that with a voltage higher than 250V rating.

I cannot see the markings on the other capacitor. I can barely see 50V. Whatever you read, increase that for a greater safety margin.

Replace the resistor F1 with a suitable fuse once we can determine the power requirements of the zapper. This should be clearly marked on the outside of the case.

Edit: I am going to guess that a 0.5A fuse would be adequate to allow 60W max power consumption.
Yes the two orange capacitors are the same rating 16582878166211633451107379164187.jpg
 

MrChips

Joined Oct 2, 2009
26,789
FYI, since you are new to this field, notice the Y pattern on the top of the orange capacitors.

1658288680928.png


This is a relief pressure valve on the capacitor casing. You will notice a brown stain already erupting from the top of C2.
When the capacitor is starting to breakdown from being overstressed the internal electrolyte will begin to boil away. Without a weak spot built in on the top of the capacitor to vent the excess pressure the can would explode in a very dramatic fashion.

Don't be afraid to ask for clarification if there is something you wish explained.
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
FYI, since you are new to this field, notice the Y pattern on the top of the orange capacitors.

View attachment 271843


This is a relief pressure valve on the capacitor casing. You will notice a brown stain already erupting from the top of C2.
When the capacitor is starting to breakdown from being overstressed the internal electrolyte will begin to boil away. Without a weak spot built in on the top of the capacitor to vent the excess pressure the can would explode in a very dramatic fashion.

Don't be afraid to ask for clarification if there is something you wish explained.
I forgot to ask what size capacitors should I put in would 10uf 350v be enough or to much? Or not enough and I did find the fuses and holder
 

Ya’akov

Joined Jan 27, 2019
6,260
This resistor is on my bug zapper and it shorted out…
Welcome to AAC. Good to have you around, I hope we inspire you to continue your electronics exploration and visit regularly.

Just for the record, that fusible resistor should fail open. If it is shorted (~0Ω) something is wrong. If it is open, with no continuity, then it didn’t “short our” and you need to be careful with casual use in technical contexts.

It also led you to the conclusion the fusible resistor was the cause, but they are designed to be an effect.

Not a big deal but in technical areas words often have very precise meanings and using them without precision is that much more misleading to others and ourselves.
 

Ian0

Joined Aug 7, 2020
5,819
3.9Ω fusible resistor.
I think I’ll revise that.
It’s a ordinary 3.9Ω metal oxide resistor used as a fusible resistor, because ordinary metal oxide resistors are cheaper. Proper fusible resistors don’t get a big burn mark when they fail.
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
Welcome to AAC. Good to have you around, I hope we inspire you to continue your electronics exploration and visit regularly.

Just for the record, that fusible resistor should fail open. If it is shorted (~0Ω) something is wrong. If it is open, with no continuity, then it didn’t “short our” and you need to be careful with casual use in technical contexts.

It also led you to the conclusion the fusible resistor was the cause, but they are designed to be an effect.

Not a big deal but in technical areas words often have very precise meanings and using them without precision is that much more misleading to others and ourselves.
Oh OK I will work on the proper wording, and I will see if it has continuity
 

Ya’akov

Joined Jan 27, 2019
6,260
Oh OK I will work on the proper wording, and I will see if it has continuity
I find that technical terms can encapsulated a lot of information and when you think in them you can more quickly understand the problem. But to be clear it wasn’t a chastisement, it was intended as a heads up to be picky about what technical terms mean. Rather than learning them from context looking them up so you don’t have a misimpression.

By the way, a fusible resistor is resistor designed to heat up as too much current is drawn by the circuit it is supplying until it eventually overheats and opens. It is like a very slow blow fuse.
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
I find that technical terms can encapsulated a lot of information and when you think in them you can more quickly understand the problem. But to be clear it wasn’t a chastisement, it was intended as a heads up to be picky about what technical terms mean. Rather than learning them from context looking them up so you don’t have a misimpression.

By the way, a fusible resistor is resistor designed to heat up as too much current is drawn by the circuit it is supplying until it eventually overheats and opens. It is like a very slow blow fuse.
I appreciate the help very much, I don't like sounding like the "new guy" even though I am very new to circuitry, I really appreciate everyone's help
 

Thread Starter

Rob Wenzel

Joined Jul 19, 2022
9
I appreciate the help very much, I don't like sounding like the "new guy" even though I am very new to circuitry, I really appreciate everyone's help
I just wanted to let you know I fixed my bug zapper I used 2, 350 10uf capacitors and a 0.5 amp fuse, it works good now
 
Top