Well that would appear to be a 10% tlrenmace with te briwn band being te temerature coefficient. The other bands dont make sense though.
looks like black orange white which is 039 with no multplier.
Oooh you modernist!
It will be whatever wattage is needed for the circuit. Presumably something has drawn a lot more current through it than it was rated for so replacing it will merely kill another unfortunate 0.39R component.
Resistors in properly designed circuits seldom burn out unless something else catastrophic has happened like a crowbar circuit across the PSU.
Its probably a current sense resistor.
Something will be reading the voltage across it to control the feedback.
1A current will give 0.39V and about 400mW power dissipation.It looks like a half watt resistor so I expect it to be something around there.
Without a circuit that's about all I can say.
Well it is from an Apple supply ;-)
I too think it's 0.39 or 0R39
and the black band is zero and probably there to itentify which end you use to start from 039 x 0.01 at 100ppm rather than 1s930
The only resistors I have with a first band as black are some zero ohm resistors which just have one black band.
A lecturer has asked me if I can buy some 10% (silver band) tolernace resistors
As !% and better resistors generally have 3 digit bands, the leading zero is probably to avoid having an even smaller negative index than silver.
In article <5854d3fa-5450-496e-9f5b-
Why does he want resistors with such a wide tolerance?
I haven't been responsible for ordering components regularly sine 1969 (!) and I didn't have a resistor with a tolerance worse than 5% in my entire stock even then.
Taking a qick look on-line to see what is available today:
or
L looked for 10% tolerance and only found 9 results - and they are all 2W at 8p ea!
Interestingly, in 1969 I wasc paying 16/- (80p) for 100 0.5W
5% resistors so a pretty comparable price despite all the rampant inflation in the intervening years!Given that all my resistors were carbon film and the modern ones are superior metal film, todays prices are a bargain!
Since it looks to be in good condition, measure it? That can give clue to what system they are using.
But it sounds typical Apple. Use any non standard thing they can everywhere. ;-)
Um, the other side is burnt. It?s fecked.
Tim
May I refer you to
That?s unusual, one side of a power resistor burnt and the other perfect.
You sure it wasn?t burnt by what it was next to ?
That's brilliant reasoning, and answers my puzzlement as to what it's for. I can't see any damage in the photo, but it would take say 2A to blow it up.
She asked me because part of a lab is to test and understand tolorencies and also the series of E values that are made for resistors although that was my idea. We also have to teach them the intricacies of power rating and what happens when these are exceeded. So in a lab it'd be nice to have these to test. I actually remmeber 20% which IIRC had a pink band, they were 2W and had a sticky waxy feel to them.
Obviously the problem is how do you really test a 5% resistor with meters that are only accurate to 1-2%. I've tested a few 5% and it is suprising how accurate they are I don't think I've found one that is more than 3% out, and there's no way I'm going through my boxes of 1000 per value :-<>
But don't forget this is a lecturer not someone that actually deals in such things in the real world. ;-)
Today we are running a lab titled Embeded Systems. Which uses a freescale development board the first part shows them how to connect a push switch to the GPIO and then an LED off that. The LED is shown in the diagram as connected to a 300 Ohm resistor the lecturer has even bothered to draw the resistor in place showing how to connect it up to a protoboard and the resistor with the colour code LtoR ! of Red Black Orange.
So I have 40 odd (very odd) students coming to me asking why I don't have any 300 ohm resistors.
One student was very proud of the fact of working out he could use 2 150R to make a 300R resistor, I did say he could use a 270R or a 330R and all that would do is change the brightness of the LED, I also said if he used the 330 then that would reduce the amount of current and help the world cut down on global warming and perhaps save trees too. I've stopped a couple of them walking off with 330K resistors, as they weren't sure of the relivance of the R & K after the digits But don't forget I'm not allowed to teach students, but I am allowed to and expected to impart my knowledge, which strangley enough doesn't warrent a salery scale increase.
This is what I buy
I have bought some 1% t 100R 1K 10K 100K a few 0.1% 1K , 10K and a 50R and a 1K of 0.01% for £15 each for demonstrating to any inquisitive student or academic.
We do have a LCR meter that can measure resitors to 0.1% accuracy but as it was £1,400 we only have one making it difficult for up to 50 students per session to use.
Yes and I'd need at least 50 of a few values and that is if students after using them didn't lose them, break them or eat them, which is why I've told the lecturer I don't keep 10% as they aren't really used/made in this millennium.
I heard that in 1979 a blue LED retailed at £30 ! I leave them out in the lab for students to help themselves same as the red, yellow, green and white versions in both 5mm and 3mm sizes.
yes I agree and why I don't really want students putting them back in draws if the leads are damaged as puting them back into our protoboards can and does damage the contacts in the protoboards which are £10 each ! we orered 100 protoboard for this year, hopefully most will survive and can be reused next year.
I thought an AK-47 was a sort of semi automatic gun and AK47 was a strain of marijuana :-)
OK. Although it would be difficult to measure a fraction of an ohm accurately anyway.
Wonder if the heat cooked some of the colours? Because I can't see any reason to start with a 0. Given resistors of less than 1 ohm ain't exactly rare.
But it does show why having international standards for such things may not be the bad idea many think it is.
It's 1%, so three bands for the numbers for consistency, I imagine.
Cheers
True, although my bench meter (in 4 wire mode) would do it OK.
I agree. 0 at the start is a bit peculiar, although I can't think of any other interpretation.
True. Thinking on, many sub ohm resistors are high current so have the actual value printed on them. At one time.
I would think it's perfectly possible. Film type resistors are often in the form of a spiral track on the body, and one part of a spiral can blow, making a small burnt hole in the paint.
He didn't say a small burnt hole tho and they don't usually fail like that when their power rating is exceeded.
Yes, in theory those spiral power resistors can be made bad and fail like that, but that is very rare indeed, particularly with the higher quality stuff like Apple gear.
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