Basic questions about electronic components

Hi

When formatting in Scientific, how can you keep the exponent constant and allow the decimal point to move? For example

If I have:

How do I ensure that Excel keeps the E to E-3 and adjust the decimal point?

Cheers

WayneL

The 1/4W resistors run twice as hot as the 1/2W resistors. If they don't run hotter than their rated temperature, it usually doesn't matter. In high precison circuits, where the temperature coefficient of the resistors becomes important, smaller temperature rises can still be embarrassing.

Provided that the capacitors aren't charged to more than 25V, you are pretty unlikely to see a difference. Most capacitor leakage currents are non-linear functions of the voltage across the capacitor, so you might see significantly higher leakage currents, and some capacitors show voltage-dependent capacitance, which would be worse in the 25V parts but these effects are rarely significant.

Probably not, but only an idiot would take the risk.

Finding mysterious bugs in scholar projects takes just as long as it does in professional projects. Scholars tend to think better, but they've had less practice in thinking about specific electronic circuits, so it tends to come out about the same. But see the comments I have published in Rev.Sci. Instrum. over the years (as A.W.Sloman).

Using off-specification components is a great way of producing mysterious bugs.

-- Bill Sloman, Nijmegen - Ph.D. in Physical Chemistry and experienced electronic engineer.

they work exactly the same in 99.99% of cases. In that one situation per 10,000, you might see a small increase in measurement errors

yes only if same type with same t_max. R max temps vary widely.

nothing. The 25v ones can take upto 25v, the 50vs upto 50v.

That I cant make sense of. I can think of no reason at all to avoid subbing a 25v cap with a 50v part in a school project. I've done it loads of times, and I'm not an iddi... iddy... damn I cant spell it.

NT

Bill, Jim Thompson is going to have a field day tearing you a new one for this! "Twice as hot"? At the same intrinsic power? I seriously doubt it - and what does "twice as hot" mean anyway? One runs at 315K and the other at 630K? ;-P

ObOnTopic: Has anyone ever measured the deg.C/W for those sizes, or is it such a widely published spec that I'm looking quite the idiot asking? %-}

Thanks! Rich

The junction temperature of the lower power resistor is likely to rise twiice as much - above ambient - if you dissipate the same power in the resistor.

The manufacturers data sheet usually give a thermal derating current, of permissible power dissipation versus ambient temperature, and you can work out the thermal resistance from the steepness of the sloping bit at the high temperature end. Analog freaks have to look at this sort of detail - guy s who do digital can spend an entire career without needing to know this.

So you've worked on 10,000 projects, and one went wrong? To have any minimal confidence that the true rate was close to 1 in 10,000, you'd want to have worked on 40,000 projects and seen four go wrong, from which you could infer a large sample rate in the range 4+/-2 .

Between different kinds of resistors - carbon film to metal oxide to metal film. Most labs use only one type for run-of-the-mill applications.

You lack imagination. Different voltage ratings can imply different non-linearities and different ESR's. If you survive long enough to get old and accumulate painful experience, you will learn that the universe is out to get you, and learn to deny it every opportunity you can manage.

Yabbut, what's "twice as hot?" I mentioned in another post, does that mean that if one's at, say, 313K, that the other one is at 626K? ;-)

But do NOT put a 25V cap in a 50V application, because it will blow up.

Six munce ago, I cutnt evn spel tecknishun, now I are one! ;-P

Cheers! Rich

^^^^

???

That's odd - my advice would be exactly the opposite.

(i.e., it's the denial that makes the universe look like it's out to get you.)

On 8 Jan 2006 10:36:58 -0800, snipped-for-privacy@yahoo.com wrote in Msg.

What do you think voltage and wattage ratings are for? What's your "project" -- an RC low-pass?

Think about it a bit yourself before hitting what you think is called "Google Groups" with such a question. Besides, there is a newsgroup called "sci.electronics.basics".

robert

the old F C or K question. Sometimes taken the wrong way I find!

thats what I thought. Until I found a 16v cap fitted backwards on a 23v supply, still working perfectly 20 years later. Must ave been lucky!

NT

...or seen 10,000 resistors on schematics

... or seen 100 projects and guesstimated how many of those Rs would influence measurement error.

Even working on 10,000 projects wouldnt tell you, as most of us tend to specialise in some area or other, so it wont be a random mix of projects. In fact they'd have to be especially small projects!

I must have been an exception then. Ditto TV designers. I've used c film, wirewound, lightbulbs, diodes, nichrome, probably others too.

I would normally treat the 2 things as separate, ESR and V rating. I'm not seeing how a V rating tells you when to use a low ESR part - or even avoid low ESR.

Are you saying you can deduce ESR requirement from V rating? I dont see it.

Ohh yes. Its always finding new ways. It only does it to annoy us, its nothing to do with inadequately conceived plans.

NT

You can't deduce ESR from voltage ratings, but a different voltage rating usually implies a difference in construction - a thicker layer of oxide or a thicker plastic film as the dielectric, which means a lower capacitance per unit area and longer paths through the capacitor

- which can imply a difference in the ESR.

All plans are inadequately conceived, based - as they are - on simplified models of reality.