Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > General Electronics Technical Discussion
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 06-13-2022, 05:36 PM   #1
littlejohn
New Member
 
Join Date: Mar 2022
City & State: Chatham Ontario
My Country: Canada
I'm a: Knowledge Seeker
Posts: 5
Default resistors in parallel ?

I need a 1.5 k 2watt resistor , can I use 2 1 watt resistors in parallel for testing purposes while waiting for a 2 watt to arrive?
littlejohn is offline   Reply With Quote
Old 06-13-2022, 06:06 PM   #2
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,645
Default Re: resistors in parallel ?

You can use two 3k ohm resistor @ 1 watt in parallel to get 1.5k @ 2 watt that you are looking for
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
sam_sam_sam is offline   Reply With Quote
Old 06-13-2022, 09:15 PM   #3
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 7,200
Default Re: resistors in parallel ?

And two 750Ω 1W resistors in series would also result in a 1.5KΩ 2W resistance.
eccerr0r is offline   Reply With Quote
Old 06-14-2022, 12:44 AM   #4
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,645
Default Re: resistors in parallel ?

Quote:
Originally Posted by eccerr0r View Post
And two 750Ω 1W resistors in series would also result in a 1.5KΩ 2W resistance.
Are you sure about this because I thought that if one was 1 watt total because it would just add more resistance but I could be wrong
sam_sam_sam is offline   Reply With Quote
Old 06-14-2022, 07:18 AM   #5
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 7,200
Default Re: resistors in parallel ?

Do the math.

BTW, should always do the math. You can even do funny things with nonmatching resistors but yeah it gets complicated when they don't match as the power dissipated will be different if resistances are different.

Last edited by eccerr0r; 06-14-2022 at 07:21 AM..
eccerr0r is offline   Reply With Quote
Old 06-14-2022, 03:35 PM   #6
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,617
Default Re: resistors in parallel ?

The heat to be dissipated would be shared over two parts, each one dissipates a ratio of the value a single part would. Regardless of whether the two are in series or parallel.
50-50 split so 1W each using two 750Ω series or 3kΩ parts parallel.
If you used a 2.2kΩ and 4.7kΩ in parallel, each see about 1.36W and 0.64W - the same ratio as their resistances.
redwire is offline   Reply With Quote
Old 06-16-2022, 04:22 PM   #7
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 7,200
Default Re: resistors in parallel ?

Then you'll need a 1.5W 2k2 resistor which rounds up to 2W, and why not buy a 3k 2W resistor to begin with
With dissimilar resistors, probably only for last resort or if you have other values to burn... I was trying to do this with a 10R 2W and a 40R 10W in series for a 50R load, now need to calculate the system max sustained wattage... Then realize that inductance in the pair was too high for VHF frequencies...
eccerr0r is offline   Reply With Quote
Old 07-13-2022, 04:33 AM   #8
EasyGoing1
Shock Therapist
 
EasyGoing1's Avatar
 
Join Date: Sep 2016
City & State: Victorville, CA
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hardcore Geek
Posts: 805
Default Re: resistors in parallel ?

Quote:
Originally Posted by eccerr0r View Post
Do the math.

BTW, should always do the math. You can even do funny things with nonmatching resistors but yeah it gets complicated when they don't match as the power dissipated will be different if resistances are different.
Here's the math if anyone is interested or ever will be interested ...



What I find particularly interesting about this thought exercise, is that like sam, my knee-jerk reaction to the statement was to pause and question it. And I think that is because we are used to thinking about net values - where resistors are concerned anyways - differently depending on whether the resistors are in series or parallel ... so I think naturally the brain wants to continue that pattern of thought even if the value in question is wattage dissipation. Which as it turns out, does not care if the resistors are in series or parallel, wattage dissipation adds up linearly.
__________________

Last edited by EasyGoing1; 07-13-2022 at 05:26 AM..
EasyGoing1 is offline   Reply With Quote
Old 07-13-2022, 07:53 AM   #9
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 7,200
Default Re: resistors in parallel ?

I think the main reason to answer the way sam did is he was thinking about batteries and considering amps and not watts.

two 12V 1Ah batteries in series will give you 24V but still only 1Ah.

Now the rhetorical question: if you change the question to two 12V 1Wh batteries in series, how many watt hours do you get out of the system?
eccerr0r is offline   Reply With Quote
Old 07-14-2022, 02:31 PM   #10
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,645
Default Re: resistors in parallel ?

Quote:
Originally Posted by eccerr0r View Post
I think the main reason to answer the way sam did is he was thinking about batteries and considering amps and not watts.

two 12V 1Ah batteries in series will give you 24V but still only 1Ah
This is what I was thinking about but after I saw the math that EasyGoing did it cleared up the confusion about this thanks to both of you
sam_sam_sam is offline   Reply With Quote
Old 07-14-2022, 02:35 PM   #11
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,645
Default Re: resistors in parallel ?

Quote:
Originally Posted by eccerr0r View Post
Now the rhetorical question: if you change the question to two 12V 1Wh batteries in series, how many watt hours do you get out of the system?
I will run this test and give you a definite answer to this question over the weekend by doing an actual test I think I know the answer to this question but I want to know for sure that I am right because I have a way to do this test
sam_sam_sam is offline   Reply With Quote
Old 07-14-2022, 02:46 PM   #12
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,617
Default Re: resistors in parallel ?

It's the difference between power and energy. Resistors are only concerned with power they dissipate, regardless of the time, how long they've been doing it.
Batteries are limited - if each battery has X watt-hours of energy, then two batteries gives you... well 2X. The energy available just adds up.
redwire is offline   Reply With Quote
Old 07-14-2022, 03:08 PM   #13
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 3,273
Default Re: resistors in parallel ?

Quote:
Originally Posted by redwire View Post
Batteries are limited - if each battery has X watt-hours of energy, then two batteries gives you... well 2X. The energy available just adds up.
only if in parallel . otherwise its the same as the lowest value .
resistors in series are the wattage of the lowest wattage one .
example .. 2 watts and 1 watts in series = 1 watt .

Last edited by petehall347; 07-14-2022 at 03:11 PM..
petehall347 is offline   Reply With Quote
Old 07-14-2022, 04:00 PM   #14
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,617
Default Re: resistors in parallel ?

In parallel you get double the Ah, in series you get double the voltage. So two batteries will always give the energy of... well... two batteries. Not one.
Where is the confusion on this I wonder.
redwire is offline   Reply With Quote
Old 07-14-2022, 06:00 PM   #15
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 7,200
Default Re: resistors in parallel ?

in this case power and energy don't really matter, just take a fixed amount of time and the math works out.

This confusion is because some people equate amps (or amp hours) with, or as a proxy for watts (or watt hours), and then extrapolate to resistors, leading to improper conclusions.
eccerr0r is offline   Reply With Quote
Old 07-16-2022, 03:32 AM   #16
EasyGoing1
Shock Therapist
 
EasyGoing1's Avatar
 
Join Date: Sep 2016
City & State: Victorville, CA
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hardcore Geek
Posts: 805
Default Re: resistors in parallel ?

Quote:
Originally Posted by petehall347 View Post
only if in parallel . otherwise its the same as the lowest value .
resistors in series are the wattage of the lowest wattage one .
example .. 2 watts and 1 watts in series = 1 watt .
I can't help but notice that this is similar to capacitors ... parallel ADDS values and series become some ratio of the total ... though this makes sense since a battery is just a pre-charged capacitor I suppose ... mathematically speaking ... or at least in some loose way they are.
EasyGoing1 is offline   Reply With Quote
Old 07-16-2022, 03:37 AM   #17
EasyGoing1
Shock Therapist
 
EasyGoing1's Avatar
 
Join Date: Sep 2016
City & State: Victorville, CA
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hardcore Geek
Posts: 805
Default Re: resistors in parallel ?

Quote:
Originally Posted by eccerr0r View Post
in this case power and energy don't really matter, just take a fixed amount of time and the math works out.

This confusion is because some people equate amps (or amp hours) with, or as a proxy for watts (or watt hours), and then extrapolate to resistors, leading to improper conclusions.
I struggle with these MAh ratings on these batteries ... so for example, a battery is rated at being capable of sustaining 3,000 MAh ... which says to me that it can continuously provide 3 amps for an hour ... but that never seems to be the observed reality ... in any specific case from what I remember back when I was trying to make sense of all that stuff.

I wanted to make an arduino based LiIon charger at one point and I specifically remember struggling with the actual HOW in calculating how many MAh were going into the battery as it charged.
EasyGoing1 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2022
Powered by vBulletin ®
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 09:41 AM.
Did you find this forum helpful?