How did I blow the fuse in my multimeter?

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.

Cyde Weys wrote:

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

A 9v battery will easily put out more than 315mA.

ric wrote:

> Cyde Weys wrote:
>
>
>> So, can someone tell me how, with a 9V battery, I managed to blow a
>>315mA, 250V fuse? Thanks.
>
>
> A 9v battery will easily put out more than 315mA.

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

On Fri, 21 May 2004 07:33:34 GMT, Cyde Weys <vze23tnc@verizon.net>
wrote:

>>> So, can someone tell me how, with a 9V battery,
>>> I managed to blow a 315mA, 250V fuse? Thanks.
>>
>> A 9v battery will easily put out more than 315mA.
>
> So this multimeter can't even measure the current of a 9V battery?
> Laaaame ... what about a AA battery?

Did you put the meter in "ampere mode" across the battery?
Never do that! That's a big beginner misstake.

Cyde Weys schreef:
> I blew the fuse on my Radio Shack multimeter recently. I was
> testing the current across a 9V battery.

When you say "across" , do you mean that you connected the black lead to
the minus of the battery and the red lead to the plus of the battery? If
so, this is not the correct way te messure the current, how ever it is
the correct way to messure the voltage. Mistakes are easely made.


>
> Anyway, my multimeter has the following options on it: 15, 150, 1000
> DCV, RX 1K(Ohms), OFF, 150mA DC, 1000, 150, 15 ACV.

The way i read this, your meter only supports current messuring
up to 150mA DC. So 315mA from the battery is enough to blow the fuse.
The rest of the ranges are used for resistor messuring and voltage AC
and DC voltages

Succes
Chris

Christiaan van Bladel wrote:

> Cyde Weys schreef:
>
>> I blew the fuse on my Radio Shack multimeter recently. I was
>> testing the current across a 9V battery.
>
>
> When you say "across" , do you mean that you connected the black lead to
> the minus of the battery and the red lead to the plus of the battery? If
> so, this is not the correct way te messure the current, how ever it is
> the correct way to messure the voltage. Mistakes are easely made.

So what is the correct way to measure current?

>> Anyway, my multimeter has the following options on it: 15, 150,
>> 1000 DCV, RX 1K(Ohms), OFF, 150mA DC, 1000, 150, 15 ACV.
>
>
> The way i read this, your meter only supports current messuring
> up to 150mA DC. So 315mA from the battery is enough to blow the fuse.
> The rest of the ranges are used for resistor messuring and voltage AC
> and DC voltages

Yeah, that must be what I did. I must've had it in current measuring
and put it across the 9V battery and fried the fuse. Oh well. What is
the mA option for? Obviously it doesn't work directly across battery
leads ... is it for putting into a circuit that has resistance? I.e.
you could measure the current being drawn by an LED, but it won't work
if you just put it across the battery?

On Fri, 21 May 2004 10:22:05 GMT, Cyde Weys <vze23tnc@verizon.net>
wrote:

> > When you say "across" , do you mean that you connected the black lead to
> > the minus of the battery and the red lead to the plus of the battery? If
> > so, this is not the correct way te messure the current, how ever it is
> > the correct way to messure the voltage. Mistakes are easely made.
>
> So what is the correct way to measure current?

You can't measure current in a battery.
You can measure current a load takes from a battery.

Cyde Weys wrote:
> Christiaan van Bladel wrote:
>
>> Cyde Weys schreef:
>>
>>> I blew the fuse on my Radio Shack multimeter recently. I was
>>> testing the current across a 9V battery.
>>
>>
>> When you say "across" , do you mean that you connected the black
>> lead to the minus of the battery and the red lead to the plus of the
>> battery? If so, this is not the correct way te messure the current,
>> how ever it is the correct way to messure the voltage. Mistakes are
>> easely made.
>
> So what is the correct way to measure current?
>
>>> Anyway, my multimeter has the following options on it: 15, 150,
>>> 1000 DCV, RX 1K(Ohms), OFF, 150mA DC, 1000, 150, 15 ACV.
>>
>>
>> The way i read this, your meter only supports current messuring
>> up to 150mA DC. So 315mA from the battery is enough to blow the fuse.
>> The rest of the ranges are used for resistor messuring and voltage AC
>> and DC voltages
>
> Yeah, that must be what I did. I must've had it in current measuring
> and put it across the 9V battery and fried the fuse. Oh well. What
> is the mA option for? Obviously it doesn't work directly across
> battery leads ... is it for putting into a circuit that has
> resistance? I.e. you could measure the current being drawn by an
> LED, but it won't work if you just put it across the battery?


Imagine a simple circuit with a battery source and a resistor. Each leg of
the resistor is connected to the battery; one to the +ve side, one to
the -ve side. To measure voltage across (in parallel) the resistor aka load,
place the meter in DC voltage mode. Place the black probe to the the -ve
side of the load, red probe to the +ve side. Take a reading. That's the
procedure for voltage.
A voltmeter can be thought of as a resistor with an infinitely high internal
resistance.

Imagine the same circuit, a battery and a resistor. To measure current, the
ammeter must be in _series_ with the load. Set the meter to measure DC
current. Current will flow _through_ the meter, as if it is another resistor
in the circuit. In fact, it will be just that, a very low resistance. Open
the circuit by lifting the -ve leg. Connect the red probe to the now open
leg of the resistor. Connect the black probe to the -ve terminal of the
battery. The circuit is now closed. Current will flow. Take the current
measurement.

Voltage|in parallel|voltmeter like a 10G Ohm resistor.

Current|in series|ammeter is like a .1 Ohm resistor.

On Fri, 21 May 2004 07:33:34 GMT, Cyde Weys <vze23tnc@verizon.net> wrote:

>ric wrote:
>
>> Cyde Weys wrote:
>>
>>
>>> So, can someone tell me how, with a 9V battery, I managed to blow a
>>>315mA, 250V fuse? Thanks.
>>
>>
>> A 9v battery will easily put out more than 315mA.
>
>So this multimeter can't even measure the current of a 9V battery?
>Laaaame ... what about a AA battery?

What purpose is there in measuring current of a 9V battery? You want to
see if it's adequate for jump-starting a car?

Current consumed by a device is limited by that device, while current from
a shorted battery is limited only by the battey's internal resistance, so
from a small battery you may be looking at dozens of amps, and potentially
a vented battery (some call that "exploding") if left shorted.

No, you can't measure current of a AA battery either, except in circuit,
device it's to be powering.

"Cyde Weys" <vze23tnc@verizon.net> wrote in message
news:_Hfrc.7295$dq4.1638@nwrddc01.gnilink.net...
> 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.

Sounds to me like you tried to test a huge current.
Current=voltage/resistance so the only resistamce in the circuit
is the interlnal resistance of the battery (very small) and the resistance
of
the multimrter (neglible) so you qould have say 9/0.01 ie 90 Amps,
probably a lot more in reality.