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#4660638 - 02/09/18 07:45 AM The percentage on a resistor...
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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.
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#4660655 - 02/09/18 08:03 AM Re: The percentage on a resistor... [Re: daves66nova]
Trav Offline


Registered: 11/20/06
Posts: 18892
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#4660660 - 02/09/18 08:07 AM Re: The percentage on a resistor... [Re: daves66nova]
Fitter30 Offline


Registered: 05/05/13
Posts: 101
Loc: Peace valley, Missouri
1% is a closer tolerance that 10% so it should be closer to .1 ohm but being such a low resistance you might not tell without out a very good meter

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#4660670 - 02/09/18 08:20 AM Re: The percentage on a resistor... [Re: daves66nova]
SR5 Offline


Registered: 07/07/15
Posts: 4465
Loc: Down Under
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.
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#4660672 - 02/09/18 08:24 AM Re: The percentage on a resistor... [Re: daves66nova]
Donald Offline


Registered: 03/21/04
Posts: 20457
Loc: Upstate NY
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.
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#4660686 - 02/09/18 08:40 AM Re: The percentage on a resistor... [Re: daves66nova]
Quattro Pete Offline


Registered: 10/30/02
Posts: 35866
Loc: Great Lakes
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.
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#4660741 - 02/09/18 09:30 AM Re: The percentage on a resistor... [Re: daves66nova]
Kestas Online   content



Registered: 06/04/02
Posts: 12333
Loc: The Motor City
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.

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#4660774 - 02/09/18 09:54 AM Re: The percentage on a resistor... [Re: daves66nova]
mk378 Offline


Registered: 09/27/15
Posts: 1420
Loc: USA
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.

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#4660904 - 02/09/18 11:50 AM Re: The percentage on a resistor... [Re: daves66nova]
Papa Bear Offline


Registered: 08/11/05
Posts: 7050
Loc: Leamington, ON, Canada ..... r...
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?
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#4660930 - 02/09/18 12:22 PM Re: The percentage on a resistor... [Re: daves66nova]
supton Online   content


Registered: 11/09/08
Posts: 11974
Loc: NH
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


Edited by supton (02/09/18 12:24 PM)
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#4660934 - 02/09/18 12:24 PM Re: The percentage on a resistor... [Re: daves66nova]
Win Offline


Registered: 02/05/03
Posts: 4448
Loc: Arkansas
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.
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#4660937 - 02/09/18 12:26 PM Re: The percentage on a resistor... [Re: Win]
supton Online   content


Registered: 11/09/08
Posts: 11974
Loc: NH
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.
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#4660942 - 02/09/18 12:30 PM Re: The percentage on a resistor... [Re: Kestas]
Win Offline


Registered: 02/05/03
Posts: 4448
Loc: Arkansas
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.
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#4660943 - 02/09/18 12:30 PM Re: The percentage on a resistor... [Re: supton]
Win Offline


Registered: 02/05/03
Posts: 4448
Loc: Arkansas
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.
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#4660945 - 02/09/18 12:32 PM Re: The percentage on a resistor... [Re: daves66nova]
supton Online   content


Registered: 11/09/08
Posts: 11974
Loc: NH
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.
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