Buying components online question

raymix

Hi, guys I am a little confused.
Trying to order some Radial 2A 250VAC Slow Blow fuses, 330R 1/2W and 33k 1/2W carbon resistors online.

Mouser requires 20EUR delivery charge, which is ridiculous.

ie.farnell requires minimum of 20EUR spent, but offers free delivery. Problem is, I'd be forced to buy something extra I don't even need to match the price required.

RS-Components is just simply overpriced, whole package of only 5 fuses + VAT + delivery comes down to around 18 EUR alone

cpcireland.farnell offers real good price for components, VAT+delivery comes down to around 10EUR only. However upon ordering they require Company name as mandatory instead of personal info. This greatly confuses me.
I've sent cpc an email asking about non-business customers, would it be fine to just fill in name/surname in company field.

What are your thoughts? Any better alternatives or Should I just go with CPC and fill in my full name in company field?

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Also a bit off-topic question - Does it matter if fuses are square or cylindrical? Datasheets are identical, sometimes square ones offers more max working temps, but that's about it. I am asking this because on certain websites cylindrical ones are out of stock, surprise, surprise.

whizbang

I detest those radials. While they are nice little space saving design, that fit nicely on a pcb, Easily soldering too.

But no visible way to tell if they are popped, usually hard to reach with meter probes, and quite often, if they are removable, the sockets are poor quality.

how many resistors are you looking for ?

raymix

Just 1 of each type, ordered metal oxide ones instead yesterday trough CPC, still waiting for them to withdraw money, probably tomorrow. Hopefully it works.

Space isn't the problem as it's monitor PSU I am fixing, but yeah, you need to get creative to test radial fuse without pulling out the board. 33k resistor has cosmetic damage due to glue while peeling protective shield off and 330R shows 0.05 Ohms, definitely shorted, probably reason why fuse got blown, rest of components are passing tests ok.

raymix

Got email from CPC, putting full name in Company field works. Order is on it's way.
Thought I'd report, since I didn't get a clear answer, maybe it will helps someone else with their decision. Simply put - CPC is cheapest way to go with for small orders, farnell is better at anything with value over 20EUR because of free delivery.

whizbang

Are you sure you are reading the 330R correctly.. shorted resistor:eek:

I imagine its meant to be 033R.

raymix

whizbang wrote: »

Are you sure you are reading the 330R correctly.. shorted resistor:eek:

I imagine its meant to be 033R.

Now that you mentioned it. I lifted resistor's leg further up and noticed another color band - black one. But that's just tolerance, I guess.

Also my apologies, i meant 00.5 not 0.05 ohms.

pics:
https://dl.dropboxusercontent.com/u/14423790/resistor_close.jpg
https://dl.dropboxusercontent.com/u/14423790/resistor_mm.jpg

Am I missing something? Sorry I am relatively new to this. I replaced caps for one monitor last week, figured i'd fix second monitor - replace blown fuse, rectifier, mosfet and both resistors close by, too. You can notice the burns in images... had to improvise and create new connections that got blown off by scratching off lacquer, applied little bit of flux and welded solder to it, basically creating new seatings.

here's pic showing how bad it is, lol:
https://dl.dropboxusercontent.com/u/14423790/board_blown.jpg

Please tell me I ordered correct resistors

Chet T16

That looks like 0.33 to me (orange orange silver gold)

raymix

I was under impression that 0.33 is for Kohms, translated to 330 Ohms. Yes, looks like it is 0.33 Ohm resistor, indeed. Well, crap...
Hopefully I can change order, maybe maplin will have those, but they never seem to have anything when you need it.

edit: weird, CPC doesn't have 0.33 trough hole resistors.

Chet T16

Does this link work?

http://cpcireland.farnell.com/jsp/search/browse.jsp?N=411+2006+215521+110062536&Ntk=gensearch&Ntt=resistor&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_CI&divisionLocale=en_CI&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=411+2006+215521&mm=1000194||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D411%2B2006%2B215521%26Ntk%3Dgensearch%26Ntt%3Dresistor%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_CI%26divisionLocale%3Den_CI%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D411%2B2006%2B215521

raymix

Hi, Chet, no, but it did give me chance to sort 4x 0.33 Ohm resistors (apparently called 0R33, did not know that!), but they are wirewound, does that make any difference?

3W 100V
7W 200V
2W 50V
4W 100V

This is super confusing.

Chet T16

0R33 is 0.33. They don't use the decimal point as it is small enough to be missed off print pcb silkscreens and schematics.

Any of those listed will be fine, hard to judge from the pic but i'd say the existing one is only 2W

whizbang

The Silver band on the resistor is multiplier value (0.01). gold here is tolerance (5%)

PR32 looks like a current sense resistor, wirewound will be ok.

If they are used as the snubbing components, then wirewound is not good. (R4)
(you should change C4 as well)

raymix

Components arrived. What do you guys think? Is that 0.33 Ohm resistor in picture dead or fine?

whizbang

Yep, its fine.

A lot of what destroys PSU's like these are transient/switching noise spikes. The other resistor in the pic appears to be the snubbing components, which control these noise spikes. So all these components are important.( D6, R4,C4 in the other pic)

raymix

Hi, thanks for all your help guys. Monitor is up and running.
https://dl.dropboxusercontent.com/u/14423790/8.jpg

I left those resistors untouched.
Could you explain what C4 actually does? Does it act similar to an inductor coil?

I had to replace D6, because it was shorted, letting same signal both ways. I also left the old R4 in there. The metal oxide resistors I ordered were almost 2-3 times smaller.. can't figure out what these grey giants are made of... carbon film? Or size doesn't matter? Must be a reason they uses these instead and it's not the price, because they cost an arm and a leg in maplin.

Funny story, after blowing up second fuse (before this delivery), I didn't bother to test AC part of components, apparently bridge rectifier (4a 600V max) got blown to peace, instantly blowing up third fuse. Luckly i had an old laptop adapter lying around, borrowed rectifier from it and it worked. Altho it was skinnier in depth, but datasheet said 4A 800V, rest of stuff was the same, so close enough. Or is this dangerous?

whizbang

No issue with the rectifier. 4A is plenty.

Leakage inductance is that tiny bit of inductance that lives in wires, pcb traces, component leads, etc. In a SMPS its mainly the transformer.
When the FET turns off, It works the same as a switch that cuts off the current in the (Leakage)inductor. - this causes the voltage to shoot up, as the inductor tries to maintain the current.
This voltage spike can be massive, if nothing is done to control it, and will certainly do damage to the FET among others.
A big resistor would keep it down, but thats wasting power the rest of the time. So use a diode to only pass the spike into the resistor, and a capacitor in parallel will soak up the initial spike.
BUT all of these components have to act very fast, so be careful of the diode, cap has to be good quality, and lastly a wirewound resistor has its own inductance, so that will definitely not help.

It looks to me like these ccts have a weakness in the snubbing, as the diode was shorted. See if you can get a better (faster) diode, and maybe double the value of C4 to be sure .

raymix

That's one hell of an explanation. Thank you, I thought that one of resistors was underlying reason for blown diode, but it's just my lack of knowledge. This is good to know.
I've got Panasonic FM series caps for this board, replaced completely all of them.

Keplar240B

I needed a couple of dozen resistors to finish off a project and
could not be bother going on line as I happened to be passing by Maplins, I know they are rip off but I said surely a few resistors will be cheap so I dropped in, 0.65 cent a resistor.
walked out before the red mist descended.

Yurp! I have one 5 mins walk away and I loath giving them money. I don't have to anyways unless I'm impatient. I'm in the UK these days and RS will ship me one £0.01 resistor, next day by courier if ordered before lunchtime. No minimum order, no shipping charges better stock too.

...I'm off to the Aldi tomorrow to get me 2 more component cases...I'm running out of wall to put them on though..:D

ShRT

Ditto - the cheapest hdmi cable in the local one was €50!!
Even PC World don't have the cheek to charge more than a tenner for their "basic" one

1.49 in Dealz :-)

Here's another shining example

Maplin PV

Fair price PV