UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 1st Apr 2020, 5:11 pm   #1
ITAM805
Nonode
 
ITAM805's Avatar
 
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
Default Resistor power rating

Hi folks, does the team think this is a 1 or 2W?

many thanks
Attached Thumbnails
Click image for larger version

Name:	IMGP0418.jpg
Views:	223
Size:	51.8 KB
ID:	202004  
ITAM805 is offline  
Old 1st Apr 2020, 5:50 pm   #2
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: Resistor power rating

1W for me.
kalee20 is offline  
Old 1st Apr 2020, 6:16 pm   #3
ITAM805
Nonode
 
ITAM805's Avatar
 
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
Default Re: Resistor power rating

Thanks Kalee, that's what I suspected
ITAM805 is offline  
Old 1st Apr 2020, 6:39 pm   #4
RF Burn
Hexode
 
RF Burn's Avatar
 
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
Default Re: Resistor power rating

Modern resistors are amazingly small for their power dissipation capability these days . . . the laws of physics don't change so, for a given rating and element type, the smaller the resistor (hence it's surface area) the higher the permissible surface temperature is. That rules out doing any power dissipation/temperature tests!

To compound the problem, I have the following types of resistor in my stocks, the bodies of these are all about 12.5 (1/2") long:

2 Watt - RS 'Pro' CARBON Film 0.5% Body colour pink (YES - 2W!)
Neohm ROX2S Metal Oxide Film, 2W 5% Body colour Pinky-Brown Blue or Green
Wirewound type, manufacturer unknown.

1 Watt - Several older CARBON film types.

0.5 Watt - Few older CARBON types, up to 1970's manufacture

In my experience your resistors have the appearance of metal oxide types, in which case they could well be 2 Watt rated, but to be totally on the safe side I would say don't stress them beyond 1 Watt.

Adrian.
RF Burn is offline  
Old 1st Apr 2020, 7:31 pm   #5
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: Resistor power rating

Yes- I have to keep changing my expectations of how big a given power rating needs to be over the years. It can be very difficult now just to judge on appearances. I'd agree that it could well be 2W rated, I've recently been using PR02 resistors, just slightly smaller and more angular-bodied. However, I always feel that being cautious is cheap insurance on the small scale- if you're an OEM, you can save thousands by running close to the limit and by time the complaints come in, they're out of warranty (the art and science of thrifting...) but as a repairer, do you really want folk grumbling about you because you saved 10p on a resistor and something stopped working after a while?

I'd call it 1W and sleep easy!
turretslug is offline  
Old 1st Apr 2020, 10:22 pm   #6
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
Default Re: Resistor power rating

The wattage rating also depends on the temperature of the environment it is used in, the heat from adjacent components etc. and may be derated further for improved reliability.

Also if you've got say PVC insulated wiring touching the resistor, running it to modern surface temperature allowances will damage the insulation.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 1st Apr 2020, 10:55 pm   #7
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
Default Re: Resistor power rating

They could be wirewound, in whcih case they probably have a higher rating than if they were film resistors.
Maarten is offline  
Old 1st Apr 2020, 11:26 pm   #8
joebog1
Banned
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
Default Re: Resistor power rating

I would say that the pictured item is a metal glaze 2 watt resistor. I have many that are identical.

Joe
joebog1 is offline  
Old 1st Apr 2020, 11:51 pm   #9
ITAM805
Nonode
 
ITAM805's Avatar
 
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
Default Re: Resistor power rating

Maarten, I believe it's a metal film type.

I'll assume it's 1W which seems to be the consensus, thanks guys

crossed post Joe!
ITAM805 is offline  
Old 2nd Apr 2020, 1:27 am   #10
Terry_VK5TM
Nonode
 
Terry_VK5TM's Avatar
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
Default Re: Resistor power rating

12.5mm long (or 1/2" in proper measurements ) according to Vishay's data on several different modern resistor series, would be 2W.

But probably better to rate it as you have at 1W without confirmed make/manufacturer data.
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is offline  
Old 2nd Apr 2020, 7:14 am   #11
Craig Sawyers
Dekatron
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,942
Default Re: Resistor power rating

The max dissipation of any resistor, taken from a datasheet, is in free air. The big mistake is putting the resistor in hard contact to a circuit board. Even Tektronix have made that mistake from time to time.

At best it will discolour the board. At worst the resistor will burn out.

Space resistors being used close to their rated power rating off the board by a few mm at least.

Craig
Craig Sawyers is online now  
Old 2nd Apr 2020, 10:42 am   #12
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: Resistor power rating

^^ Wot he say ^^

Ceramic spacers (sometimes referred to as fish-spine beads) and tubes can be handy here, some manufacturers rivet tinned rolled copper tubes to PCBs and thread power resistors through them to maintain clearance. When possible, some put small holes in the PCB directly under and around hot components.
turretslug is offline  
Old 2nd Apr 2020, 11:40 am   #13
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
Default Re: Resistor power rating

Or put a small kink in each lead using fine nose pliers!
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 4th Apr 2020, 8:57 pm   #14
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Resistor power rating

They're about the size of PR02 resistors, which were good for 2W. But if you were planning on having them dissipating power continuously, you might want to limit that to 1W.

Resistors get hot, and all that's different about modern, smaller ones is they can withstand higher temperatures. The number of Watts you can transport through a square metre of surface area for 1 degree rise is the same as it ever was.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:42 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.