How did I blow the fuse in my multimeter?

[ric]

LEDs draw an insignificant amount of current.

LEDs, being diodes, draw *NO* current. They are connected *in series*
with a impedance limited voltage, and pass - in one direction - the
current that the series impedance dictates.

 

[Chaos Master]

mv /var/posts/Cyde Weys/[email protected] /dev/null:

So this multimeter can't even measure the current of a 9V battery?
Laaaame ... what about a AA battery?

You'd have to connect a load so you have current ,as in:

[view with fixed-width font, like Courier or Fixedsys]

------------------ ( MULTIMETER ) ------------
| |
--- _
--- 9V BATT | |
--- | | Resistor
| |_|
|______________________________________________|


[]s

--
Chaos Master® | "I'm going under,
Posting from Brazil! | drowning in you
ICQ: 126375906 | I'm falling forever,
ask for e-mail/MSN | I've got to break through"
---------------------. -- Evanescence, "Going Under"

 

[Andy Foster]

Raymond Sirois wrote:

LEDs, being diodes, draw *NO* current. They are connected *in series*
with a impedance limited voltage, and pass - in one direction - the
current that the series impedance dictates.

So, if I used an array of LEDs to power a solar cell, I could get infinite
free energy?

 

[half_pint]

LEDs, being diodes, draw *NO* current. They are connected *in series*
with a impedance limited voltage, and pass - in one direction - the
current that the series impedance dictates.

I am unsure what you mean by 'draw' current, however if you connect a led
across a battery with nothing to moderate the current you will probably
'blow' the LED.

I believe they are forward. biased in use as a light and so have negligible
resiatance.
(few ohms perhaps). I don't believe they are reversed biased as in a diode.
So I think it may be a little to dall them diodes, (eithetr that or I am
wrolng - lol)

If they drew no current your battery would last forever - which would be
cool.

Length explaination (sort of ) here.
http://www.chemistry.wustl.edu/~edu...odicProperties/MetalBonding/MetalBonding.html

 

[half_pint]

Testing the current from a battery is like testing the flow of water
from a tank.
It basically depends on the size of the hole.
An ammeter (the hole in this case) is designed to be a very 'big hole'
so it does not affect the flow of the current it is measuring.
Hence the fuse blew.

 

[half_pint]

I am unsure what you mean by 'draw' current, however if you connect a led
across a battery with nothing to moderate the current you will probably
'blow' the LED.

I believe they are forward. biased in use as a light and so have negligible
resiatance.
(few ohms perhaps). I don't believe they are reversed biased as in a diode.
So I think it may be a little to dall them diodes, (eithetr that or I am
wrolng - lol)

If they drew no current your battery would last forever - which would be
cool.

Length explaination (sort of ) here.
http://www.chemistry.wustl.edu/~edu...odicProperties/MetalBonding/MetalBonding.html

Wow I was sober when I posted that too
"dall them diodes, (eithetr that or I am wrolng - lol)"

 

[Trent©]

I blew the fuse on my Radio Shack multimeter recently. I was testing
the current across a 9V battery. I verified that it is just the fuse
that was blown by removing the fuse, shorting across the gap, and
verifying that the needle on the meter did indeed move on resistance
tests (no way am I gonna test anything other than ohms without a fuse,
hehehe).

Anyway, my multimeter has the following options on it: 15, 150, 1000
DCV, RX 1K(Ohms), OFF, 150mA DC, 1000, 150, 15 ACV. I believe I left
the battery attached to the leads when switching modes (is this bad?).
I did not go into any of the ACV modes.

So, can someone tell me how, with a 9V battery, I managed to blow a
315mA, 250V fuse? Thanks.

If yer shorting the resistance-test circuit...and then the meter is
moving...then you blew the resistance fuse.

If you blew the resistance fuse, that means you had it in resistance
mode when you checked the battery.

Having the meter in ohm mode when checking the battery current will
blow the fuse every time.

I think you'll find that the meter has 2 fuses inside.


Have a nice week...

Trent©

Follow Joan Rivers' example --- get pre-embalmed!

 

[ric]

So, if I used an array of LEDs to power a solar cell, I could get infinite
free energy?

Sure. Free except for the initial and replacement costs of the LEDS.
(They aren't very efficient operating in reverse. Kinda like a microphone
used as a speaker.)

 

[ric]

I am unsure what you mean by 'draw' current,

Like an IC, when placed in parallel with a voltage source, will "draw"
current. An LED is placed in series with a dropping resistor across
the voltage source. The current "drawn" is a function of the value of
the dropping resistor, and the forward voltage drop of the LED. The
current through the LED can vary widely depending on the value of the
resistor. The LED itself "draws" no current, like a normal diode "draws"
no current.

 

[kony]

Sure. Free except for the initial and replacement costs of the LEDS.
(They aren't very efficient operating in reverse. Kinda like a microphone
used as a speaker.)

Huh?

No free energy, it'd be a quite lossy.

 

[half_pint]

Like an IC, when placed in parallel with a voltage source, will "draw"
current. An LED is placed in series with a dropping resistor across
the voltage source. The current "drawn" is a function of the value of
the dropping resistor, and the forward voltage drop of the LED. The
current through the LED can vary widely depending on the value of the
resistor. The LED itself "draws" no current, like a normal diode "draws"
no current.

Your use of the word 'draw' is stupid, plenty of current passes through
the LED in the circuit, and because of its low resistance it will 'draw'
plenty diodes are desigm to draw plenty of current when forward biased.

 

[bearman]

Your use of the word 'draw' is stupid, plenty of current passes through
the LED in the circuit, and because of its low resistance it will 'draw'
plenty diodes are desigm to draw plenty of current when forward biased.

Exactly right. If the LED did not "draw" current, they wouldn't emit light.
Just put an LED across a car battery (or any battery, actually) in the
foward-biased direction and see how the current flows.

Bearman

 

[ric]

Huh?

No free energy, it'd be a quite lossy.

Shine a light in a LED, and you *DO* get a voltage out! Yes, free energy
(minus the cost of the LEDs, as mentioned.) Yes, very inefficient, but
they *DO* put out a voltage. Note that no mention was made as to how many
LEDs would be needed to provide useful power.

 

[ric]

Your use of the word 'draw' is stupid, plenty of current passes through
the LED in the circuit, and because of its low resistance it will 'draw'
plenty diodes are desigm to draw plenty of current when forward biased.

A piece of wire will pass plenty of current, but it in itself "draws"
no current. Same with a LED or a diode. They pass current in one
direction, but "draw" none themselves. [BTW, current draw is a standard
electric term.]

The only thing "stupid" in this thread is your input. (Awaiting your
normal expletive filled response.)

 

[ric]

Exactly right. If the LED did not "draw" current, they wouldn't emit light.

Incorrect. LEDs do not "draw" current. They pass current. The amount
of current passed through an LED is totally the function of the dropping
resistor in series with the LED. It could be 2 mA or 40 mA depending on
the value of the resistor. If the LED itself "drew" current, the amount
of current would not be dependent on the dropping resistor.

Just put an LED across a car battery (or any battery, actually) in the
foward-biased direction and see how the current flows.

Same with a standard piece of wire, but no one claims that a piece of
wire draws current.

The poster who brought up the "LED current draw" said that LEDs draw
very little current. Kinda flys in the face of your "LED across a
battery" scenario.

 

[bearman]

light.

Incorrect. LEDs do not "draw" current. They pass current. The amount
of current passed through an LED is totally the function of the dropping
resistor in series with the LED. It could be 2 mA or 40 mA depending on
the value of the resistor. If the LED itself "drew" current, the amount
of current would not be dependent on the dropping resistor.


Same with a standard piece of wire, but no one claims that a piece of
wire draws current.

The poster who brought up the "LED current draw" said that LEDs draw
very little current. Kinda flys in the face of your "LED across a
battery" scenario.

Maybe I was too subtle for you. I thought the quotes around "draw" would
tell you something.

Lighten up! <grin>

Bearman

 

[half_pint]

light.

Incorrect. LEDs do not "draw" current. They pass current. The amount
of current passed through an LED is totally the function of the dropping
resistor in series with the LED. Nope.
It could be 2 mA or 40 mA depending on
the value of the resistor. If the LED itself "drew" current, the amount
of current would not be dependent on the dropping resistor.

The current depends on the combined resistance, the LED has a small
resistance, say 1 ohm and the series resistor has say 500 ohms.
You will be hard pushed to measure the extra 0.2% resistance if indeed it
is that large.
You are at the limits of most multimeters there.

Same with a standard piece of wire, but no one claims that a piece of
wire draws current.

The poster who brought up the "LED current draw" said that LEDs draw
very little current. Kinda flys in the face of your "LED across a
battery" scenario.

The LED would probably melt if it had to draw say 12 or maybe 50 amps.

 

[half_pint]

Your use of the word 'draw' is stupid, plenty of current passes through
the LED in the circuit, and because of its low resistance it will 'draw'
plenty diodes are desigm to draw plenty of current when forward biased.

A piece of wire will pass plenty of current, but it in itself "draws"
no current. Same with a LED or a diode. They pass current in one
direction, but "draw" none themselves. [BTW, current draw is a standard
electric term.]

The only thing "stupid" in this thread is your input. (Awaiting your
normal expletive filled response.)

Sorry about the use of stupid, i meant incorrect, everyone makes mistakes
and it dont mean your stupid.
My opologies.

I am in a good mood so no ecxpletives :O)

 

[Raymond Sirois]

LEDs, being diodes, draw *NO* current. They are connected *in series*
with a impedance limited voltage, and pass - in one direction - the
current that the series impedance dictates.

There IS a VERY small voltage drop across a diode, as a result, there
is a small amount of impedance. The power supply will see this as a
load and therefore there will be current applied to the diode...
never speak in absolutes. As I said, LEDs draw an INSIGNIFICANT
amount of current...

Raymond Sirois
SysOp: The Lost Chord BBS
607-733-5745
telnet://thelostchord.dns2go.com:6000

 

[ric]

There IS a VERY small voltage drop across a diode, as a result, there
is a small amount of impedance. The power supply will see this as a
load and therefore there will be current applied to the diode...
never speak in absolutes. As I said, LEDs draw an INSIGNIFICANT
amount of current...

You can lead a horse to water....

An LED connected through a 50 ohm resistor to a 5v source will pass
about [(5v - 1.5v)/50] amps, or about 70 mA. That same LED connected
through a 500 ohm resistor to that same 5v source will pass about
[(5v - 1.5v)/500] amps, or about 7 mA. So what is the current "draw"
for this LED? The RESISTOR controls how much current flows through
the LED. If the resistor was just 5 ohms, the current through the LED
would be 700 mA (for a short period.) How do these facts jive with
your statement that "LEDs draw an INSIGNIFICANT amount of current" ??
They draw none. Just like any diode, they pass the forward current
presented to them.