Do resistors/diodes etc have to be exact with a custom build?  - Page 1
Forum section: electronics / beginners

author: Thedrunkenflea
author_rank: Contributor
timestamp: December 22, 2022, 10:44:18 am
content: Hello.Before i buy a bunch of resistors and stuff I was wondering how exact do they need to be?My power pack is asking for:Through Hole Resistor, 100 ohm, MCCFR0W4J Series, 250 mW, ± 5%, Axial Leaded, 250 VThrough Hole Resistor, 220 ohm, MCCFR0W4J Series, 250 mW, ± 5%, Axial Leaded, 250 VThrough Hole Resistor, 820 ohm, MCCFR0W8J Series, 125 mW, ± 5%, Axial Leaded, 200 VI can only seem to find exact ones in the USA which isnt ideal due to long delivery times for such small items.Am i over thinking this or will similar ratings be fine IE just need a 100ohm, 220ohm, and a 820ohm resistor?Amazon has all these but not exact.Thanks lads,Flea.

author: bidrohini
author_rank: Regular Contributor
timestamp: December 22, 2022, 11:19:07 am
content: What's the particular circuit that you're working on? I think the choices will depend on your application.

author: Thedrunkenflea
author_rank: Contributor
timestamp: December 22, 2022, 11:20:39 am
content: Hi im just enjoying working on magnetic type devices at the moment not for any practical use I find it interesting.This is the build I found.https://www.hackster.io/mircemk/simple-to-build-high-power-pemf-therapy-device-f38d46At most i might power it up with 12v 10amps - maybe go to 12v 17amps to stay within 20% safety/buffer.

author: Swainster
author_rank: Frequent Contributor
timestamp: December 22, 2022, 11:23:58 am
content: Those are bog standard 1/4W carbon film resistors - anything in the correct resistance and wattage should do.

author: Thedrunkenflea
author_rank: Contributor
timestamp: December 22, 2022, 11:25:42 am
content: oh good that makes it a lot easier for me to proceed with the project.thanks man.

author: themadhippy
author_rank: Super Contributor
timestamp: December 22, 2022, 12:56:00 pm
content: QuoteAnd the power rating ( wattage) can be bigger,although it may take up more space on the circuit board

author: tooki
author_rank: Super Contributor
timestamp: December 22, 2022, 09:37:30 pm
content: Quote from: Thedrunkenflea on December 22, 2022, 10:44:18 amDon’t buy electronic components on Amazon. Aside from Amazon having turned into an astoundingly scummy company, you’re likely just buying from the same vendors that sell on aliexpress for less.In the specific case of resistors, the ones on Ali, Amazon, eBay etc often have obnoxiously thin leads. Just buy from a real electronics distributor.If you need something in the middle, look at Tayda Electronics.

author: Thedrunkenflea
author_rank: Contributor
timestamp: December 23, 2022, 08:27:32 am
content: Quote from: tooki on December 22, 2022, 09:37:30 pmI got a few sites now for parts - farnell, and a few others. Been told repeatedly amazon and eBay will give me low quality parts. I got a few smaller companies too. I went past amazons main warehouse in my area it looks liek something out of a future movie where they control all the buying and selling. lmao

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 23, 2022, 10:41:16 pm
content: I bought a selection of 1% tolerance resistors on e bay. They are just fine and seem to be well within the 1%. Although 1% is not necessary for most of my applications, I think the price difference is so small I order 1% resistors when available.Sometimesthe thin lead resistors are easier to use.

author: Swainster
author_rank: Frequent Contributor
timestamp: December 27, 2022, 04:31:28 am
content: Just to add an another observation, I bought a set of 1% axial resistors from Aliexpress, branded Eiechip, and to be honest, 2% would be a safer description. That said, it's a perfectly usable set for prototyping. I'd be a bit worried about using them in repairs unless the load was quite light as I have no idea what their long term stability is like.

author: tooki
author_rank: Super Contributor
timestamp: December 27, 2022, 12:31:43 pm
content: That’s an interesting question. I have some eBay 1% resistors that are now probably 5-6 years old or so, but I don’t think I have any that have been in significant use since then, they’ve mostly been in protoboard experiments.

author: wasedadoc
author_rank: Super Contributor
timestamp: December 27, 2022, 01:20:47 pm
content: Quote from: Swainster on December 27, 2022, 04:31:28 amHow do you know that they are worse than 1%? What is the accuracy of whatever you used to meadure them?

author: Swainster
author_rank: Frequent Contributor
timestamp: December 27, 2022, 02:49:17 pm
content: I was using an in-cal Keithley 2010 in 4 wire mode, but I was mostly looking at the spread rather than the absolute values, as I haven't looked at how accurate a 2010 is for resistance.

author: tooki
author_rank: Super Contributor
timestamp: December 27, 2022, 03:56:24 pm
content: Quote from: Swainster on December 27, 2022, 02:49:17 pmWay,waybetter than 1%.https://download.tek.com/datasheet/2010.pdf

author: Terry Bites
author_rank: Super Contributor
timestamp: December 28, 2022, 07:08:07 am
content: It depends on the precsison you want in a particular circuit. If you're building down to a price on a hundred thousand units cost matters.For hobby/ protoyping use you might as well get yourself a pile of 1% E24 MFs. Muticomp brand are fine.Many of the big component houses will offer a "student account".Dont forget to ask for a competitive quote for your resistor kit.Stock more of common values. I'm sure there are stats on this kind of thing. Ask digikey what the sales stats are on popular E24 values.