Choosing resistor for indirect current test. Help!

[Deleted member 8382]

I was planning to buy some stuff for laser building and testing, and I found www.parts-express.com, wich seems to have good offers.

What power do a resistor for laser testing need to have and what tolerancy is acceptated. I found 1ohm at 5% toelrance with 1/2 watt, 1 watt, etc, I actually have no idea of what to choose.

Also

 

[Illuminum3415]

Re: Choosing resistor for indirect current test. H

well, your right with the 1 ohm, the wattage would have to be set where it can handle the maximum current draw of the laser....
Usually a shunt resistor is used to measure current too large for you to directly connect your ammeter/multimeter to, before going about looking/researching for resistors... do tell what sort of current are you trying to measure? 10ma? 100ma? 1A? 10A? 100A?

Common shunt resistor's usually have a common Accuracy of +/- 0.1%, 0.25% in North America and 0.5% in the rest of the World.

 

[Cyparagon]

Re: Choosing resistor for indirect current test. H

What are you running that exceeds 20A?

 

[691175002]

Re: Choosing resistor for indirect current test. H

I would recommend a tolerance closer to 1% or better. With 5% error in the resistor and perhaps a few percent in a cheap/uncalibrated multimeter you could conceivably be looking at 5-10% error. 117-143mA is a pretty wide range of uncertainty for powering a PHR diode.

 

[Deleted member 8382]

Re: Choosing resistor for indirect current test. H

my multimeter is good enough, but where to get a resistor with less than 5% tolerance? Remember I live in spain, parts-expres.com won't ship to me

Yours,
hallucynogenyc

 

[lasersbee]

Re: Choosing resistor for indirect current test. H

I was planning to buy some stuff for laser building and testing, and I found www.parts-express.com, wich seems to have good offers.

What power do a resistor for laser testing need to have and what tolerancy is acceptated. I found 1ohm at 5% toelrance with 1/2 watt, 1 watt, etc, I actually have no idea of what to choose.

Also

A resistor that has a tolerance of 5% is not necessarily 5% off... it is just a tolerance
percentage that the manufacturer guarantees will not be exceeded..

You can take a batch of 1 ohm 5% resistors and test them individually with your DMM...
Note the values and choose one from the middle range of values and you will have
a good chance to get one that is a lot better than 5% error ...
The bigger the sample lot... the closer to 1% or less you will get...

Jerry