Calculation current trough resistors

[danyCro]

Hi, can someone explain to me why my calculate are not the same in practice?

I bought a bunch of 1/4 resistors and found LED from USB Card Reader. It is red color in transparent glass.
Let say that LED is Vl=1.60 & I= 0.02 mA.

I tested on two different batteries and two multimeters.
My Goal would be 20 mA trough resistors.

Example 1)
Vs=9.10v
Vl=1.60
I= 0.02 A
R=372 (I used R400)

LED shine too bright, and it says that the current is over 200 mA. How is that possible? Do I mistake somewhere?

Example 2
Vs=2.70v (2x AAA)
Vl=1.60
I= 0.02 A
R=55 (used R400,again)

LED shine to bright, and its says that the current is 116 mA. That I use R55, will be worse.

Example 3
Vs=2.70v
Vl=1.60
I= 0.02 A

R=55 in calculation.
Finally, this time I found that 2K resistor gives me a goal of 19.5 mA!!
At same time LED voltage shows 1.62v, which corespond to mA.

For 9v battery it will be worse.

So what happened between R55 and R2000 ??

No too many videos who calculate resistors and then test current in practice.

[jim-p]

@danyCro

(I used R400

400 ohm thru hole resistors are quite unusual.
However a R400 SMD = 0.4 ohms

[sterretje]

Meter connected wrong?

To measure current, you need to connect red wire form the LED to the A of the meter and set you meter to one of the current ranges.

[danyCro]

Resistors are like it must be,I think
400 ohm (2x200 in my case).

[Dave_Lowther]

@danyCro

Let say that LED is Vl=1.60 & I= 0.02 mA.

In all the places where you say 0.02mA, I think you mean 0.02A or 20mA, not 0.02mA.

[jim-p]

See @sterretje comment about using the meter correctly

[danyCro]

Yes. I using it right.
See position at 5A and 200mA, om 9v battery

And 3v bellow pictures.

[danyCro]

@Dave_Lowther

In all the places where you say 0.02mA, I think you mean 0.02A or 20mA, not 0.02mA

Yes, sorry, you are right.
Like normal LED, 20 mA.

If calculate from behind.
If I got with 2000 ohms 19 amps, that means that source voltage must be over 30 volts. What is impossible.

[david_2018]

Can you show a view of the entire breadboard?

The top two pictures don't make sense. 0.01 on the 5A scale would be 10mA (or somewhere from 0.006A to 0.014A to allow for rounding). That should not be off scale on the 200mA scale. The internal meter connections for the 5A scale is a heavy ware between the 5A and GND terminals, with the meter measuring the voltage drop across that wire, so it seems unlikely that would add enough resistance to lower the current.

[danyCro]

On red multimeter, inside board, where 5A jack is, was disconnected. Don't know why. I solder them to make a bridge (because I thought that not show A messaure good).

But I can try test with black multimeter which have 10A.

[PaulRB]

@david_2018

Can you show a view of the entire breadboard?

@danyCro I see you are still carefully keeping half the breadboard out of the picture.

Have you replaced the batteries inside the multimeters? 80~130mA would burn out a small led in seconds.

[jim-p]

I think there are shorts in your breadboard. Can't think of any other logical explanation

[runaway_pancake]

Some ammeters aren't so good.
V1 + V2 + V3 = V_S
V1 / R1 = V2 / R2 = series current, circuit current

[EmilyJane]

@PaulRB

carefully keeping half the breadboard out of the picture.

Yes, @danyCro post a photo showing the entire breadboard.

[danyCro]

It is over 200 mA on 9 v battery But only for take pictures.

Other half? Hmmm That my other project (which @PaulRB know).

But don't worry, I disconnect all from x4 +/- rows, to not disturb of this test (after he asking for show it).

[kmin]

Make it simple. Just wire that led with single 470ohm resistor to 9V battery.
For expected 1.8V forward voltage it should draw ~15mA. And shine bright.
Then measure the current. If it doesn't match at all you have some problem with your multimeter.

[build_1971]

Something is hiding there!
Or you really shoukd worry...
2 broken multimeters...

[danyCro]

Ok. I showing a full board (before I start soldering).
Now with other multimeter. This one show 83 mA on 3v (40 mA lower then red one - 127 mA).

But still over my calculation.

Maybe is just a LED? If is from USB then maybe is little different.

Do you guys get good current result in practice after calculation?

@build_1971

2 broken multimeters.

Maybe. They are cheapest ones.
Red have normal big fuse, but black don't have fuse. Or is it some small chip.
But voltage show correct.

Why multimeter? LED shine to high on that two resistor. I see with eyes. On 2000 ohm glow like normal.

EDIT:
I was used now IR LED from my camera. Resistors 2x R200 really help to decrease light, but multimeter show still 120 mA.

[david_2018]

What does the black meter show when you measure the resistance of the resistor?

[PaulRB]

@danyCro

It is over 200 mA on 9 v battery But only for take pictures.

That is about 10x the max current of a small led. It would burn out while you take the picture. So I don't think that current reading can be true. Did you replace the multimeter batteries with fresh?