Regular resistor VS sense resistor

Ohm's Law is mostly used to select current sensing resistors.

Pick the most stable one, like the current sense resistor.

"Kris Krieger"

** The fact there IS a circuit plus YOU know its purpose gives you the other info.

... Phil

Pick a resistor that can handle the power, this usually turns out to be a 'Current Sense Resistor' or "Current shunt" if its more than a watt or 2. They are more stable over temperature. But if thats not important in your circuit then a metal film at the proper rating would do.

Cheers

"Martin Riddle" wrote in news:5ORek.322$jS4.114@trnddc07:

OK, that helps, thanks!

- Kris

Sjouke Burry wrote in news:487be423$0$6026$ snipped-for-privacy@text.nova.planet.nl:

THat's helpfult, thanks!

- Kris

Here's some wacky examples:

1 ohm 100W 1% To-247 Thick Film

-20/+80 ppm/C Digi Part MP9100-1.00F-ND Costs $11.88Can !! About the same US.

How about a 1000W edgewound resistor

+/-500ppm/C +/-10% tolerance It's $113.39Can

Maybe a Digi-Key Part Number RMC1/2011%R-ND RES TF 0.050W 1 OHM 1% 0201 ±300ppm/°C That one is 0.6mm x 0.3mm. You might need a microscope.

And then there's that resistive wire I've seen in power supplies.

If you're flying blind, go for the most stable low inductive resistor you can get,afford,without huge mins and doesn't use an outrageous amount of board space. And perhaps get the regular resistors too to try out for fun.

D from BC British Columbia Canada

Not at all - that's exactly how it's done.

Well, one ohm gives you one volt per amp, so it has to dissipate V * I watts - if you're sensing 5 amps, which is 5v across a 1 ohm resistor, that's 25 watts!

And, the precision of your measurement will depend on the precision of the resistor.

Good Luck! Rich

D from BC wrote in news: snipped-for-privacy@4ax.com:

THe example circuits I'm looking at are fairly low power; the battery charging circuit, for example, shows Input as "9VDC", tho' the battery charging IC will run on between 4.5 and 16.5Vbut doesn't mention input amperage (as gfar as I can tell at least) although it evidently outputs

1.07A - the input I'm looking at (from the power-boosting example circuit) outputs 5V at 500mA (?10 Watts?). So does that mean that I need resistors that are rated for 10W, or less wattage, or more wattage?

I realize these are probably "kindergarten" questions, but I'm trying to educate myself and have barely gotten tfrom a crawl to a walk ;)

Thanks!

- Kris

You need to know what sort of current will be passing thru the resistor. From there, you can determine the power rating of the resistor. It's overkill (size, cost) to use a 100W resistor if you only need a 0.1W rated unit.

-- Mark

Rich Grise wrote in news: snipped-for-privacy@example.net:

OH! OK, cool, thanks - I guess the only limiter there is the Ohm value in the circuit, and the Ohm vlaues available in current-sensing resistors (they don't seem to go over 10 Ohms).

Thanks ;) I'm teaching myself, so, although I've been reading a lot of resources, thre are still some basic questions that they leave out, so I appreciate teh info :)

- Kris

qrk wrote in news: snipped-for-privacy@4ax.com:

Yeah, some of these example circuits (my "learning tools") are not clear when ti coems to certian details - I assume that their typical readers know a whole lot more than I do ;) and re much more adept than I at figuring things out, but it'd be nice tohave some of the simpler things noted ;)

Thanks!

- Kris

I had the pleasure of servicing an electrically powered boat out in the boonies of Muskoka. I needed to measure the current draw from car batteries, so I cut a bunch of stove wire to short lengths and crimped them together with good terminals at each end to make a high watt .1 or .01 resistor, it worked well. The problem is to solve for a 100 amp draw without too much of a voltage drop, so a 0.01 ohm scoffs

1V, and 100W. Anyway, it's fairly easy to make a short length of Nichrome wire cable, economically. Ken

"Ken S. Tucker" wrote in news: snipped-for-privacy@e39g2000hsf.googlegroups.com:

REminds me of that old TV show, "McGiver" , where the guy would end up in various sitations and have to come up with all sorts of inventive devices, using only his wits and maybe a Swiss Army knife ;) Personally, I could do without the plot, and just go with the "if you're in this situation, here are some ways to get out" part ;)

500 mA at 5V is 2.5 watts. (Watts = Current times Voltage) You need a resistor than can safely dissipate that 2.5 watts, and you should provide a generous safety margin. So a 5 watt resistor would be a good choice, and 5 watts is a standard wattage. You could use a bigger wattage, but there is not much benefit.

Ed

MacGuyver.

You might try Survivorman or Man vs. Nature, on Discovery.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Tim Williams" wrote in news:XKdfk.59$m92.1 @newsfe02.lga:

Yeah, I watch those, esp. the latter (IIRC that's the one with Bear Grylls ).

Although I'd admittedly woeful with things electronic (which is why I have so many simplistic questions re: my over-complex attempted projuect ), I'm interested in things mechanical, esp. ancient engineering, since it's at the root fo modern engineering and presents a sort of "back to basics", or perhaps more accurately "back it inventive thinking" apporach.

Sometimes "how it's made" is interesting, although it tends to skip over a lot. "How To" shows and websites tend to be things I enjoy ;)

It' snto just the mechanics, tho', it's also fascinating to me because I'm interested in how the brain works, the process of how people come up with ideas. Or for that matter, animals, such as teh Green Herons in Florida who learned to use bait to amke it easier to catch fish.

Thre are too many fascinating things in the universe - I need a lot more time and a much bigger brain

- Kris

ehsjr wrote in news:U8bfk.25$0p1.2@trndny08:

Oh, OK! The "safety margin" is an excellent bit and is a good 80% of what I needed to know, thanks :) ((The infor from other folks re" sense resistors is also excellent.))

I can now revise my approach (and my parts spreadsheet).

Thanks again!

- Kris