Very handy indeed. The ones I bought were 3 pounds 99p, ($6us?) I have around 8. Soon after buying one, I thought I'd discovered that they have an overvoltage LED. However, the smell of burning FR4 soon made me realise otherwise.
It's amazing how many multimeters you can use when you have them free. I was just discharging a series string of Li-Ion batteries, to measure capacities. In the past I would have taken measurements every 5 minutes to ensure none had approached 3V.
Why bother, just hook up 5 of them, and glance over every once in a while.,
--
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---------------------------+-------------------------+--------------------------
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Dude, go back to school, Algebra 1. V=IR > I=V/R > R=V/I etc. The equation can be rearranged to any of the others by simple multiplication and division by whichever variable.
Tim
-- In the immortal words of Ned Flanders: "No foot longs!" Website @
How hot? One solution is P=EI, where power in watts is equal to the product of voltage and current. So the voltage drop across the resistor multiplied by the current in amps through the resistor will yield watts of heat created by the resistor. Now, if you know the composition of the resistor, you can look up the specific heat of the material and calculate how much energy it takes to change its temperature. You will need to know how many joules of energy have been applied. Calculate the joules by multiplying the time that the power was applied in seconds by the power in watts. Now look at the specific heat table and it will tell you how many joules per Kelvin it takes to raise the temperature. If you have any physics experience, it will be very simple.
Sir Charles W. Shults III: That is a good in depth, overly complicated, answer but not the one I was looking for..... obviously since the Tim Williams posting said ".And besides that, it measures actual in-circuit conditions, because a resistor is *supposed* to get hot, at least if it's doing its job..." ..... and since the overly discussed "2 meters and power supply" ohm meter method can overheat low-ohm resistors..... and the resistance of any resistor will vary with temperature..... I was wondering at what exact "hot" temperature the resistor should be at to make an accurate measurement..... LOL Obviously I am not looking for any kind of answer here....... I just think that this thread went bonkers when all the original poster wanted to do is, as Chuck Harris indicated in his reply post, show off his new found factoid.... however it seems clear that it may not be a very practical and convenient method as evidenced by the length and tone of the majority of the reply posts.
-- Best Regards, Daniel Sofie Electronics Supply & Repair
Thanks, I think. Well, for most applications, the variation does not really matter. But "overly complicated" is a relative thing. Without all those steps and facts, you can't really derive an answer at all. That is, unless somebody has made a chart like a nomograph where you pick out the resistor type and go to a table, start at the room temperature, drop a ruler across to a power value, and derive the reading from a scale.
But, But.. Doesn't the FR in FR4 mean flame resistant? If so, how could it burn? Char?
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I believe everyone on this newsgroup can isolate each of the terms algebraically. What is your point? What don't you agree with? What is incorrect? Be specific. Ratch
Excellent point. If you adjust the voltage (and current) to the same as the V (and current) in circuit, then your measurement reflects a more realistic value of resistance.
And another thought. If you are trying to ferret out an intermittent problem, then subjecting the resistor to similar V and I conditions found in the circuit can help make the problem appear, so it an be isolated to a certain component.
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----------------(from OED Mini-Dictionary)-----------------
PUNCTUATION - Apostrophe
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where there is no possessive sense, as in ~tea's are served here~;
(ii) there is no such word as ~her's, our's, their's, your's~.
Confusions: it's = it is or it has (not 'belonging to it'); correct
uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
but ~the dog wagged its tail~ (no apostrophe).
----------------(For the Apostrophe challenged)----------------
From a fully deputized officer of the Apostrophe Police!
I bought some batteries, but they weren't included,
so I had to buy them again.
-- Steven Wright
FOR SALE: Nice parachute: never opened - used once.
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I squared R hot, in watts or fraction thereof. And that value should be (somewhat) less than the maximum rating for that component.
You could be running just a few volts across a 1/8W resistor, and it may not feel so hot to the touch, but it may be running at or above its rated dissipation. And that's not cool, no pun intended. :-)
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----------------(For the Apostrophe challenged)---------------- From a fully deputized officer of the Apostrophe Police!
I bought some batteries, but they weren't included, so I had to buy them again.
-- Steven Wright
FOR SALE: Nice parachute: never opened - used once.
Whew! Sounds like an experiment in calorie whatever, with all the thermometer measurements, etc. Yeah, now I remember. It's called Cold Fusion!!
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----------------(from OED Mini-Dictionary)-----------------
PUNCTUATION - Apostrophe
Incorrect uses: (i) the apostrophe must not be used with a plural
where there is no possessive sense, as in ~tea's are served here~;
(ii) there is no such word as ~her's, our's, their's, your's~.
Confusions: it's = it is or it has (not 'belonging to it'); correct
uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
but ~the dog wagged its tail~ (no apostrophe).
----------------(For the Apostrophe challenged)----------------
From a fully deputized officer of the Apostrophe Police!
I bought some batteries, but they weren't included,
so I had to buy them again.
-- Steven Wright
FOR SALE: Nice parachute: never opened - used once.
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Well, if you think about it, doing cold fusion experiments will teach you everything you need to know about calorimetry and heat measurement! So even if the effect is never shown to yield any anomalous heat, you still got an education. Funny how pursuing even an odd question can teach you worlds.
Exactly. It is un-eff-ing believable how some people just love to snipe.
I wonder how many of the "snipers" ever had to brew a meter shunt? You can use the "Watson ohmmeter" for that - and, as another poster mentioned - toss your Fluke in the dustbin. :-)
YES!!!! I had a situation where I needed to continually and simultaneously monitor current and voltage into and out of a dc-dc converter with two outputs, while varying the loads and the input supply. Some asshole said he could do it with two meters - another "sniper" who obviously did not understand the word "simultaneously". Anyway, there's a catalog outfit named Harbor Freight, and they had multimeters on sale for $2.99 including the 9V battery. I bought 4 of them. As you correctly pointed out, it's amazing how many you can use at the same time when they are just sitting around waiting for use!
I think, for "practical" electronics, the "ohmic" and "non-ohmic" properties of resitance and its implication in the Ohm's Law equation is largely depreciated. All resistors are likely assumed ohmic except for specialty devices or applications, most of which deal with temperature and not voltage. Personally, I find the voltage-dependant-negative-coefficient resistances (such as carbon fiber) particularly interesting. :)
I was going to ask you to check out an image, but I can't find it... anyways it was a simple circuit I drew and simulated in proteus. It was a battery, a lightbulb, and an ohmmeter across the lamp. The lamp was lit and the resistance was 120 ohms...
Oh well it might have been funnier with the actual drawing. Man I need to get out more... :)
In article , snipped-for-privacy@Comcast.net mentioned...
I think the point of everyone here is that you're being pedantic, pointing out something that has no real relation to the topic being discussed.
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