The percentage on a resistor...

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I need to get 0.1 Ohm, 10%, 1 Watt. Question is, is it better to have a 5% or even 1%? I need to get 2 of these for someone to repair a board.
 
The percentage is the error in the resistance value, or how close it is to it's nominal value. So yes a lower % is better.

Most regular resistors are 10% from memory.

Often there is a variable resistor in the circuit to do the fine tuning, so a higher % deviation from the ideal value may not be a big issue, as it can be tuned out later. Still I have found lower % resistors are almost always better made and of better overall quality.

If I needed a 10% resistor, them I would often spend a bit more and get a 5% one.
 
Originally Posted By: daves66nova
I need to get 0.1 Ohm, 10%, 1 Watt. Question is, is it better to have a 5% or even 1%? I need to get 2 of these for someone to repair a board.


The % is tolerance to the stated resistance. So a 1% is best.
 
Originally Posted By: daves66nova
I need to get 0.1 Ohm, 10%, 1 Watt. Question is, is it better to have a 5% or even 1%? I need to get 2 of these for someone to repair a board.

It depends on how close to 0.1 Ohm you need to be.

With a 10% tolerance, the actual resistance can be anything from 0.09 Ohm to 0.11 Ohm.
With a 1% tolerance, the actual resistance can be anything from 0.099 Ohm to 0.101 Ohm.
 
If the circuit originally called for a 10% tolerance resistor, spending more for tighter tolerance would be a waste of money. It's like buying premium fuel for a vehicle that specifies regular.

Why are the resistors being replaced? Did they burn up? If you want to upgrade resistors, go higher in wattage. 2 watts would be appropriate. I restore old radios and I exclusively buy 2W metal film resistors for replacement (which happen to be 5% tolerance). They don't cost much more than 1W, and the physical size of 2W resistors is about the same size as the carbon resistors they replace.
 
In some circuits a low ohm resistor is used as a fuse. This has several implications:

* Find out why it burnt, or the new one is going to do the same thing.
* Don't increase wattage.
* Use a fusible or "flame proof" resistor.
 
Originally Posted By: daves66nova
I need to get 0.1 Ohm, 10%, 1 Watt. Question is, is it better to have a 5% or even 1%? I need to get 2 of these for someone to repair a board.


Why do you need this resistor? What circuit is it in?
Why isn't the tech who is fixing the board getting the part(s)?
Is this a stereo amplifier you are working on?
 
Lower % is better. However, get the same type, or one better. Most 1%'s film types aren't rated for surge power; they seem to drift if abused. Carbon composition or other power types will take abuse better. I'd think 5% 1W metal film of some sort, maybe surge rated.

I do most of my shopping at Digikey; I assumed thro-hole and narrowed the search donw. Link

Edit: on the off-chance it's SMT: Link
 
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Is it being used for a precise voltage drop at a given current?

I would get a 1% resistor. They're only pennies more, if that.

You need special equipment or some other techniques to accurately measure resistance that low, so get the 1% part and hope for the best.
 
Originally Posted By: Win
Is it being used for a precise voltage drop at a given current?

I would get a 1% resistor. They're only pennies more, if that.

You need special equipment or some other techniques to accurately measure resistance that low, so get the 1% part and hope for the best.



His 1W requirement kinda points otherwise; yeah, one can do high power dividers but it's kinda rare to see that. At least I haven't come across that need.

If the circuit was properly designed and meant to be ok with 10% resistors, then I don't see a need to measure. Replace and move on.
 
Originally Posted By: Kestas
.... I restore old radios and I exclusively buy .... metal film resistors ....


They can be more inductive than carbon comp. Modern ones are pretty good, but it can still be an issue at VHF.
 
Originally Posted By: supton
Originally Posted By: Win
Is it being used for a precise voltage drop at a given current?

I would get a 1% resistor. They're only pennies more, if that.

You need special equipment or some other techniques to accurately measure resistance that low, so get the 1% part and hope for the best.



His 1W requirement kinda points otherwise; yeah, one can do high power dividers but it's kinda rare to see that. At least I haven't come across that need.

If the circuit was properly designed and meant to be ok with 10% resistors, then I don't see a need to measure. Replace and move on.


I was thinking of a meter shunt.
 
I could see meter, but why would it have used a 10%? I guess if there was a cal pot someplace.

Curious now what the application is.
 
5% will be fine. I'd measure the size of the old one, and look at the open space on the board; perhaps a 2W will work. Odds are though there isn't enough space. But measuring the old one will help with the selection of the new one.
 
Originally Posted By: daves66nova
Measure the size physically,not by resistance? The resistor is mounted vertically. So a 2 watt one is better?


Depends on what it's used for. Why did it fail?

I guess it goes without saying they the color bands have been correctly identified, and it is supposed to be 0.10, and not, 1 or 10, or something else ....
 
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