Resistors: Parallel vs Series best heat dissapation - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 01:52:00 am
content: Give all resistors are the same, what would be the best configuration for heat dissipation, series or parallel?

author: BradC
author_rank: Super Contributor
timestamp: November 11, 2021, 02:04:53 am
content: Given all resistors are the same, in series they'll dissipate less heat because there will be less current. Then again, if "best" implies dissipating more heat then put them in parallel. My I-ching calculator says "a suffusion of yellow"

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 02:27:01 am
content: Quote from: BradC on November 11, 2021, 02:04:53 amI should have said same resistance also, so same current. So, yes, R will be different, but what I meant is that the R value will be the same in either parallel or series.Ex:Two 12R resistors in parallel or two 3R resistors in series.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: November 11, 2021, 02:28:40 am
content: Seeing as how the resistor(s) in question in a given circuit must do a particular job, no matter how you arrange it, they, as a group, must drop a given voltage, V, and pass a given current, I, and therefore must dissipate a given power, P, then it follows that that much power must be dissipated by the bunch no matter how you arrange them. So if they are n resistors in series then they each must dissipate P/n Watts. If they are in parallel then they must each dissipate P/n Watts, too.Power-wise, it doesn't matter how you arrange them. But there may be a another conclusion when the voltage across each is considered.

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 03:18:02 am
content: Quote from: basinstreetdesign on November 11, 2021, 02:28:40 amI was reading about different voltages is series, but I'm not worried much about that. mainly, it was heat, and finally, something that makes intuitive sense in electricity--total heat is total heat - regardless of series or parallel. So, makes sense. Thanks.

author: Brumby
author_rank: Unknown
timestamp: November 11, 2021, 03:33:28 am
content: Quote from: DW1961 on November 11, 2021, 03:18:02 amYes - total heat dissipated in two packages of the same type will be the same, for the examples given.Be a little wary about getting too comfortable with things that seem to make "intuitive sense" as that can be risky. However, that risk will diminish the more you get familiar with things (.... which usually involves releasing some magic smoke along the way.**)(** It's a rite of passage )

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 05:23:15 am
content: Quote from: Brumby on November 11, 2021, 03:33:28 amDoes releasing the magic smoke from my brand new motherboard count, because that's how I ended up here -- lol?Seriously, though, I've learned so much, just casually, from doing stuff and using this board, in just a year.My next task is to somehow get a scope and learn how to use it so I can test things like power supplies. I need to see the ripple.

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 06:12:29 am
content: Quote from: Brumby on November 11, 2021, 03:33:28 amWhat happens to heat for each resistor if the resistors are different R values

author: james_s
author_rank: Super Contributor
timestamp: November 11, 2021, 07:48:48 am
content: Quote from: DW1961 on November 11, 2021, 06:12:29 amThe current will be different, so the power dissipated will be different, leading to the amount of heat being different. You might check out some of the resistor puzzles that are commonly encountered in EE courses. If you learn how to use Ohm's law and familiarize yourself with Kirchoff's law you can easily calculate any sane arrangement of resistors can the power dissipated by each one.

author: CaptDon
author_rank: Super Contributor
timestamp: November 11, 2021, 01:56:01 pm
content: Seen Ohm's Law lately? That will give you the answers you are looking for, especially the Ohm's Law wheel that is divided into 4 quadrants with E,I,R and P. You can calculate every imaginable scenario without ever killing yourself or burning up a resistor with trial and error.

author: TimFox
author_rank: Super Contributor
timestamp: November 11, 2021, 02:50:50 pm
content: This question must be answered quantitatively.In general, if the total voltage and current for two cases are the same (i.e., the total resistance from end to end is the same), and the resistors that make up each network all have the same resistance and package, and the number of resistors in each network is the same, then the actual individual resistor values in the two networks may well be different, but the total power dissipation is the same. Therefore, with equal numbers of resistors in the two cases, the power dissipation per resistor will be the same.For example, five 10 ohm resistors in series (50 ohms total) compared with five 250 ohm resistors in parallel (also 50 ohms).

author: Jwillis
author_rank: Super Contributor
timestamp: November 11, 2021, 06:27:03 pm
content: Given a specified voltage and two resistors of equal value .Voltage = 12Resistor =6P=V*IP=V2/RP=I2*RSeriesSeries resistance is R = R1+R2....P=122/ (6+6) P=12WThe current through the circuit is 1AThe power dissipated by Resistor 1 is 6 wattsThe power dissipated by Resistor 2 is 6 wattsThe total power dissipated is 12 wattsParallelParallel Resistance 1/R = 1/R1+1/R2.... OR R=R1*R2/R1+ R2P=122/ (1/ (1/6 + 1/6) P=48W or P=122/ (6*6 / 6+6) P=48The current through the circuit is 4AThe power dissipated by Resistor 1 is 24 wattsThe power dissipated by Resistor 2 is 24 wattsThe total power dissipated is 48 wattsGiven a specified Voltage and two equivalent resistors . In Parallel the resistors dissipate 4 times more power than the same resistors in a series circuit .

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 06:34:47 pm
content: Quote from: CaptDon on November 11, 2021, 01:56:01 pmOr maybe just use this?https://eepower.com/tools/power-dissipation-calculator/#

author: Jwillis
author_rank: Super Contributor
timestamp: November 11, 2021, 06:42:33 pm
content: I like to practice the math myself . Just personal preference .Or this onePower Dissipation Calculator

author: DW1961
author_rank: Frequent Contributor
timestamp: November 11, 2021, 10:54:00 pm
content: Quote from: Jwillis on November 11, 2021, 06:42:33 pmYeah I understand that. I use to do the same thing, but since I have always sucked at math, and when I needed to do fast calculations throughout the day for percentages, I started using a percent calc or my on screen normal calc. I'm never going to find math fun and I'm never going to be good at it, so I decided to just not worry about it anymore, especially at my age. That, and the calcs never make mistakes. Thanks for the links.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2021, 12:13:23 am
content: I'm not a math whiz either but Ohms law isn't exactly advanced mathematics, it's like 7th grade algebra. Math is such a fundamental part of engineering that it's very difficult to do much of anything without at least a basic understanding of math.

author: DW1961
author_rank: Frequent Contributor
timestamp: November 12, 2021, 06:22:41 am
content: Quote from: james_s on November 12, 2021, 12:13:23 amI can do applied math and basic algebra, I just don't like doing it.If I can use a percent calculator or other converters, I do that now.

author: magic
author_rank: Super Contributor
timestamp: November 12, 2021, 05:27:37 pm
content: Parallel:- voltage is equal on both- current mismatch in % is same as resistance difference in %Series:- current is equal in both- voltage mismatch in % is same as resistance difference in %Drawn your own conclusions

author: TimFox
author_rank: Super Contributor
timestamp: November 12, 2021, 05:35:38 pm
content: The other difference is failure: resistors tend to fail open-circuit.In the series connection, one failure causes an overall open circuit, but no further failures of the other resistors in the string.In the parallel connection, one failure will increase the overall resistance and decrease the total current, but the current will remain the same in the other resistors (assuming a constant voltage across the network), so no further failures should ensue.Of course, the effect of the total open circuit (series) or fractional increase in resistance and decrease in current (parallel) may affect the rest of the system.

author: DW1961
author_rank: Frequent Contributor
timestamp: November 13, 2021, 09:41:05 pm
content: Quote from: TimFox on November 12, 2021, 05:35:38 pmHey Tim. Always thanks! Yes, I read about the failure types series vs parallel. It's just a set of resistors for a dummy load, so I don't care about that much.

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2021, 09:44:57 pm
content: Quote from: DW1961 on November 13, 2021, 09:41:05 pmGiven a choice, I would use a series connection, since you can be sure the current in each resistor will be the same. With the parallel connection, you may need to be careful about the wiring: not so much a problem at DC with high resistance values.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 14, 2021, 01:15:02 am
content: anyone ever bunched up 20 200 ohm 1/4 watt resistors to go into a motor before? =)

author: tkamiya
author_rank: Super Contributor
timestamp: November 16, 2021, 07:03:40 am
content: If total ohm values are the same, theoretically, series or parallel doesn't matter. They both dissipate same amount of heat. But if you have n number of registers, you won't always be connecting all parallel or serial. There are all sorts of series-parallel connections as well. The total dissipation will depend on total ohmic value, but maximum allowed dissipation will change. You'll have to follow the ohms law and calculate each and every permutations of them.This question is little too vague to answer directly.By the way.... I have been dissapointed with electronics components from Amazon lately. There are too many defective components. Quality and accuracy will vary greatly not only from make to make but from piece to piece. Best to take advertised dissipation with gran of salt. Many of them are too optimistic. If it says 100 watts, I wouldn't apply any more than half that, no matter how big the heat sink might be.