Resistor values in a simple parallel circuit - Page 1
Forum section: electronics / beginners

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 01:37:31 pm
content: This was just a simple learning circuit with 3 resistors in parallel connected to a 6V lantern battery. Wires were checked for accuracy compare to diagram. The only thing is the experiment called for values between 1K and 100K but we had a 1K, a 220 Ohm and a 470K in the circuit. I didn't think it mattered but as soon as it was connected to battery the 220 started smoking. So I'm wondering if the reason for 1k-100K values were necessary for some kind of compatibility?I wound up replacing the 470K with a 22K and the circuit worked. Maybe it was just a bad resistor.Edit: Sorry, I am enlarging the diagram but when attaching it doesn't seem to enlarge.

author: rstofer
author_rank: Super Contributor
timestamp: August 16, 2016, 01:58:52 pm
content: Power in Watts = Voltage Squared divided by ResistanceP = 36 / 220 or 0.16 Watts - somewhat more than an 1/8th Watt resistor could handle.What wattage resistor did you use?

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 02:02:41 pm
content: Quote from: rstofer on August 16, 2016, 01:58:52 pmOoops, sorry I left that out, but 1/4 Watt resistors.

author: Audioguru
author_rank: Super Contributor
timestamp: August 16, 2016, 03:27:29 pm
content: I think your 220 ohms resistor was actually 22 ohms. Then it dissipated 6V squared/22 ohms= 1.64W.The color stripes on cheap resistors makes brown and black look the same, and red and orange, and blue and green.The resistors are in parallel so are each is connected to the same battery. Their resistances do not affect each other.

author: rstofer
author_rank: Super Contributor
timestamp: August 16, 2016, 06:35:47 pm
content: I have completely given up on color codes. Between dubious colors on the device and a defect in color vision, I decided long ago to just use a meter. Always!

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 07:00:39 pm
content: Quote from: Audioguru on August 16, 2016, 03:27:29 pmI think that makes the most sense. My son was measuring so it's possible we didn't write down the correct range. However it's a good reminder to do P calculations prior.

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 07:01:46 pm
content: Quote from: rstofer on August 16, 2016, 06:35:47 pmAgree with using the meter. I'm blind as a batso it requires a magnifying glass for me. Just easier to grab the meter.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2016, 07:41:12 pm
content: Quote from: Stuartambient on August 16, 2016, 01:37:31 pmBecause you didn't enlarge the actual image. All you did was put a lot of blank space around it. I've cropped it and shrunk it and it looks better.The tiny image below the post, is just a preview. Click on it to see the full-sized image.

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 10:30:36 pm
content: Quote from: Hero999 on August 16, 2016, 07:41:12 pmMaybe it was my screen but it appeared in my edited (MS Paint) that it was enlarging. I should have cropped. Thanks!

author: karoru
author_rank: Regular Contributor
timestamp: August 16, 2016, 10:48:27 pm
content: Quote from: rstofer on August 16, 2016, 01:58:52 pmIf 1/8 W THT resistor started smoke emission after exceeding its power rating by 35 mW for few minutes (especially in thermally nice environment like single element on breadboard) I'd probably reconsider getting any more parts from that supplier/manufacturer.

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 11:41:08 pm
content: Quote from: karoru on August 16, 2016, 10:48:27 pmI think we figured out here that it was in fact a 22 Ohm, not 220 as originally intended. Put it at 1.66 Watts on 1/4 watt.

author: karoru
author_rank: Regular Contributor
timestamp: August 16, 2016, 11:42:35 pm
content: Quote from: Stuartambient on August 16, 2016, 11:41:08 pmFair enough:) I was considering original reasoning and math, to be clear, so author of thread wouldn't think that this kind of overload will kill any resistor instantly with bonus fireworks.

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 16, 2016, 11:51:42 pm
content: Quote from: karoru on August 16, 2016, 11:42:35 pmI appreciate it. The resistors were cheap (Banggood's) but for playing around they are fine. Smoking resistors are alright. Added a little excitement to the experiment. Exploding caps might not be so good

author: Brumby
author_rank: Unknown
timestamp: August 17, 2016, 12:22:03 am
content: You haven't really been properly initiated if you haven't let out some of that magic smoke....

author: Stuartambient
author_rank: Regular Contributor
timestamp: August 17, 2016, 12:46:22 am
content: Quote from: Brumby on August 17, 2016, 12:22:03 amWhich component gives off the best fireworks without starting a fire, at least before I can react?

author: karoru
author_rank: Regular Contributor
timestamp: August 17, 2016, 01:16:56 am
content: It depends how good are you with atypical odors.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 17, 2016, 04:11:11 am
content: Quote from: Stuartambient on August 17, 2016, 12:46:22 amSmall electrolytic capacitors can explode like little rockets, ejecting the innards in a long ribbon. You don't want to be standing right over the top of one when it goes!Tantalum caps explode nicely too, as do mosfets.

author: Brumby
author_rank: Unknown
timestamp: August 17, 2016, 05:04:05 am
content: I had a MOV across the mains fail once.That was .... 'exciting'.