Blown wire wound resistor

[halobender]

I have a blown wire wound resistor that I need to determine the value of. Sadly no schematics are available.

Physical size 5.77mm dia, 16.10mm len. Axial through hole. Flame retardant green.

Part of 12v 250ma circuit.

 

[gar]

171203-2016 EST

Inadequate information.

Why size it in mm? 1 mm is about 40/1000". The absolutely exact value is 25.4 mm/inch. Thus, it is about 0.25 " dia, and about 0.7" long. Probably it is not rated as high as 5 W.

Suppose you had 12 V 250 mA applied to this resistor that would be 3 W dissipation. A 2 W wire wound probably would not fail in an ambient temperature of 70 F with 3 W input.

What is the circuit, what does it do, and how does the resistor fit in? Do some circuit analysis. How can we have any idea what the resistance was based on your information?

12 V at 0.25 A would be 48 ohms. Rounded this would be 50 ohms, but why should we expect 12 V and 0.25 A would be applied to this resistor.

I found a 5 W Ohmite on a hollow core it is about 0.362" min dia, and 1.003" long. A 2 W carbon composition is 0.312" OD, and 0.7", and in about this same package size are wire wound rated about 3 1/4 W.

.

 

[halobender]

I will do my best. Hoping my photo doesn’t scale huge.

Anyhow looks like the 12v 3W .25A output from”U2” to “D1-“. Then as you see it feeds around through that whole area finally ending up at the pin circled in red at the top. Voltage at that pin should be 12v but not sure on current.

Again this was a wire wound, ceramic core, flame retardant coated resistor. Measurements are mm. D=5.77mm, L=16.10mm. This thing got retarded hot and blew up. You can see in the photo where it melted into the fuse mounting plastic.

 

[Besoeker]

171203-2016 EST

Inadequate information.

Why size it in mm? 1 mm is about 40/1000". The absolutely exact value is 25.4 mm/inch. Thus, it is about 0.25 " dia, and about 0.7" long. Probably it is not rated as high as 5 W.

Suppose you had 12 V 250 mA applied to this resistor that would be 3 W dissipation. A 2 W wire wound probably would not fail in an ambient temperature of 70 F with 3 W input.

What is the circuit, what does it do, and how does the resistor fit in? Do some circuit analysis. How can we have any idea what the resistance was based on your information?

12 V at 0.25 A would be 48 ohms. Rounded this would be 50 ohms, but why should we expect 12 V and 0.25 A would be applied to this resistor.

I found a 5 W Ohmite on a hollow core it is about 0.362" min dia, and 1.003" long. A 2 W carbon composition is 0.312" OD, and 0.7", and in about this same package size are wire wound rated about 3 1/4 W.

.

One might also quite reasonably ask why convert it to Imperial units? The "I" in SI is International. Unless you are in Burma or USA.................
And 12V and 3W are SI units.

 

[halobender]

https://goo.gl/AFKRzg

noticed the other photo was garbage. Not sure of a good image host.

 

[gar]

171203-2333 EST

Besoeker:

Because I grew up using English units, I think in terms of them, and most of my measuring instruments are inch based.

halobender:

Your second photo is much better, but not such that I could circuit trace what the resistor connects to.

You clearly have higher voltages on this board because of the labeling on the onboard DC power supply. Also because the power supply is labeled 250 mA on the output does not mean it would limit at this current. You are going to have to troubleshoot the board yourself.

Apply input power and see what you can trace with a voltmeter. Do you get 12 VDC out of the supply? Etc.

.

 

[Besoeker]

171203-2333 EST
Because I grew up using English units,

British units.
You guys need to understand the difference between British and English. I'm British but not English.

 

[junkhound]

I have a blown wire wound resistor that I need to determine the value of. Sadly no schematics are available.

Physical size 5.77mm dia, 16.10mm len. Axial through hole. Flame retardant green.

Part of 12v 250ma circuit.

Resistors just slow down the electrons - just solder in a piece of wire wound around a pencil, about the same size.. :ashamed1:

In a similar vein?
Oh, I have an old tube tv, it does not work, which part should I change, just the tube that is not glowing or the one that is really ot and bright red that has a big cap on the top.

 

[retirede]

Remember that a burnt resistor is normally a victim, not the culprit. You likely have more problems (failed semiconductor or capacitor). Maybe you already know that, but I thought worth mentioning.

 

[mivey]

British units.
You guys need to understand the difference between British and English. I'm British but not English.

Need to? Well, you are way over there and we are way over here so from a distance it all looks like one spot.

 

[halobender]

Resistors just slow down the electrons - just solder in a piece of wire wound around a pencil, about the same size.. :ashamed1:

In a similar vein?
Oh, I have an old tube tv, it does not work, which part should I change, just the tube that is not glowing or the one that is really ot and bright red that has a big cap on the top.

I understand what the purpose of a resistor is and would have no problem making my own wire wound. I however want to put a resistor if comparable value back in the circuit and hoped there might be someone that could offer some actual advice. Not. “Hey put a resistor in there, they are all the same.”

 

[gar]

171204-0849 EST

Besoeker:

From Wiki

The inch (abbreviation: in or ″) is a unit of length in the (British) imperial andUnited States customary systems of measurement now formally equal to  ¹⁄₃₆yard but usually understood as  ¹⁄₁₂ of a foot. Derived from the Roman uncia("twelfth"), inch is also sometimes used to translate related units in other measurement systems, usually understood as deriving from the width of thehuman thumb. Traditional standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as exactly 2.54 cm.

Here in the US I believe we usually refer to them as English not Imperial, but possibly we should call them Roman.

I am directly at least 1/4 English, 1/4 German, 1/32 Ottawa American, and in turn almost certainly 1/32 French, at least 1/16 Swedish, some Welch, and Norwegian. By the National Geographic from 10,000 to 50,000 years ago I have more English Isles, like about 60%.

.

 

[steve66]

So what is this?

Does it have a 120V input? If so, it might be the resistor in series with the rectifier and input filter capacitors.

If that is the case, its possible the rectifier or one of the input capacitors shorted out, frying the resistor.

Also, if that is what the resistor is for, its purpose is to limit the current that flows when the capacitors first charge up.

They are normally in the 0.3 to 1 ohm range, with the exact value not usually being too critical.

But that's all a big if....

 

[junkhound]

I understand what the purpose of a resistor is and would have no problem making my own wire wound. I however want to put a resistor if comparable value back in the circuit and hoped there might be someone that could offer some actual advice. Not. “Hey put a resistor in there, they are all the same.”

The reply was a jest in reply to a request that showed total lack of knowledge of circuits and component characteristics.

As bad as if an electrician said he replaced a black CB with another 'black' CB that fit the space so must be good since it is the same sie and color :roll:

Seriously, first you need to determine WHY that resistor failed, trace out the circuit and lookup the spec sheets for the ICs in the photo, etc. The IC spec sheets often show typical circuits as a starting place.
Somewht surprised one of the mods did not close this thread before it got started, but did turn into nice 'give and take' on SI, old metric, imperial, etc. comparisons.

 

[junkhound]

British units.
You guys need to understand the difference between British and English. I'm British but not English.

I know the Scots and Welsh sure don't like being called English.

Serious question, not a jest: What is your definition as to the difference? English being Saxon decent (or even Norman) vs Celtic or Danish DNA? Or is it all political now vs. heritage?

 

[Besoeker]

171204-0849 EST

Besoeker:

From Wiki
Here in the US I believe we usually refer to them as English not Imperial, but possibly we should call them Roman.

I am directly at least 1/4 English, 1/4 German, 1/32 Ottawa American, and in turn almost certainly 1/32 French, at least 1/16 Swedish, some Welch, and Norwegian. By the National Geographic from 10,000 to 50,000 years ago I have more English Isles, like about 60%.

.

My father is British from the outer Hebrides. Islands off the north west coast of Britain. Not English Isles.
He was British and fought Britain in WWII. In the Cameron Highlanders.

So please don't call us all English. And the Welsh (not Welch) would take great exception to that.
And the units are Imperial. Not English. Nor Roman. Our and your numbering system is, I believe, derived from Arabic.
Stroll on. In yards or metres as you please. But don't count me in as English.

 

[gar]

171205-0855 EST

Besoeker:

We don't have Chemists selling toothpaste and razors, rather they are called Drug Stores. But today our Drug Stores are more like a grocery store. And grocery stores today may have pharmacies.

I never hear Americans talk about Imperial units, they speak of English units.

You have many times said you are not English.

In Edinburgh do you still have an old railroad bridge made of curved steel plates riveted together?

In the US we spell it meter.

I spell it Welch see https://www.merriam-webster.com/dictionary/welch . It just flows easier.

.

 

[Little Bill]

Let's try and stay on topic here. For the most part, the OP question has been addressed. If it goes further "South" then it's time to say "done"!

 

[ggunn]

I understand what the purpose of a resistor is and would have no problem making my own wire wound. I however want to put a resistor if comparable value back in the circuit and hoped there might be someone that could offer some actual advice. Not. “Hey put a resistor in there, they are all the same.”

Even if you could find an exact match, as I am not the first to say, it would likely blow when you powered up the board. The blown resistor is most likely a symptom of the failure, not the root cause.

 

[Besoeker]

Even if you could find an exact match, as I am not the first to say, it would likely blow when you powered up the board. The blown resistor is most likely a symptom of the failure, not the root cause.

I agree with that. A circuit diagram would greatly help.
It looks like a switch mode power supply.

Maybe the OP should contact Mean Well. Or one of the electronic distributors. Here, both RS and Farnell stock their stuff. Maybe radio Shack might. Or a suitable equivalent.

http://www.meanwell.com/meanwell_products.html

It doesn't look like a PCB densely populated with expensive components. I'd be inclined to go down the road of discarding it and fitting a replacement unit.
Might seem like a bit of a waste but possibly more cost effective than the time taken to bottom out the actual fault.