My fried multimeter

[Ziddik]

today i fried my multimeter!! I dont knw what the problem is! I was set it to 20V In DC range and was measuring the output of 7805 which is powered by a 12v 5amps transformer suddenly the 250ma internal fuse of the meter is blown and the meter turned off itself! I changed the fuse but the meter never turned ON!!.. Any idea? I touched On the very very bad (looks like an IC) looking ic (surface mounted Ic? Lol) and it was getting hot.. Got a pic of it and i may buy a new one soon so i think i must know some more rules when using a digital multimeter,

 

[crutschow]

Did you accidentally have the probes plugged into the current input instead of the voltage input on the multimeter or have it set to measure current instead of voltage? That could fry the meter.

If not, then it sounds like the IC just failed for unknown reasons.

 

[transistor495]

You told you're gonna power the meter using power supply unit instead of 9V PP3 battery, may be you fried it because of this?

I was gonna advice you like just buy a 9V PP3 NiMH rechargeable (@ Rs 300) type instead of that.

RIP meter..

 

[Ziddik]

Did you accidentally have the probes plugged into the current input instead of the voltage input on the multimeter or have it set to measure current instead of voltage? That could fry the meter.

If not, then it sounds like the IC just failed for unknown reasons.

nope, everything was set correctly dunno what happend! BTW i have a doubt that increasing current in a circuit would fry them? For example i got a circuit which will work with 5vDC and 300mA current, so what will happen if i gave 5vDC and 1 or 5 amperes to the circuit? Will it fry?!!!

 

[crutschow]

If you connect a meter set to the current range directly to a power supply, it will short the supply and can damage the meter.

Did you try to power the meter from an external supply as transistor495 stated? That could certainly fry the meter if the external supply and the supply you were measuring had the same ground..

 

[Ziddik]

You told

no.. I was using the meter from a regulated 9v powersupply for a very long time!! Nd it would work just fine.. The problem might be something else! Something strange!! Why is that 10A jack in multimeter? Should i plugg the red probe into 10A Jack when measure voltage with more current? I mean when measure only voltage not current!

 

[Ziddik]

If you connect a meter set to the current range directly to a power supply, it will short the supply and can damage the meter.

Did you try to power the meter from an external supply as transistor495 stated? That could certainly fry the meter if the external supply and the supply you were measuring had the same ground..

u got it very correct!! I measured the same current maybe the same 'GND'! but if it was the problem why should the fuse and meter fry together instead of only fuse?..

 

[crutschow]

The 10A input is strictly for measuring current up to 10A, not voltage. It has a very low resistance shunt and will short a power supply. That's why it's labeled with "Amps".

The likely reason it blew both the circuit and the meter, is that the meter supply common goes directly to the chip which apparently provide a path through the meter chip and the supply you were measuring, blowing both the fuse and the chip. Most meters require an isolated power source for proper operation. You learned this the hard way. Hope it wasn't an expensive meter.

 

[JimB]

today i fried my multimeter!! I dont knw what the problem is! ...
... so i think i must know some more rules when using a digital multimeter,

**broken link removed**

Oh dear!, not so chirpy with the smart comments and silly images now, are we?

JimB

 

[Brevor]

its -MASTECH- made in india

You put it out of it's misery.

 

[Ziddik]

it wasn't that expensive, it costd me 280.INR ($6) and bought 6 months ago, There are even cheap chinese multimeters in market, starts from $2.50.., i must buy a cheap one

 

[Ziddik]

there is a large chinese super market here in our town everything is inexpensive here.. U will get a chinese made mobilephone only for $20! But u cant use net or use applications on it, only for music,call,camera,videos,bluetooth,Radio and some built in games **broken link removed** but its cool and cheap **broken link removed**

 

[carbonzit]

That's my advice: get the cheap ones. At your stage of learning, they'll be plenty good enough. (As I said, that's what I use for a DMM, a Harbor Freight (Chinese) $3 one. I also use old-school analog VOMs, which I actually prefer for a lot of work; much easier to see the relative quantity being measured without having to interpret a bunch of digits.)

 

[Ziddik]

Oh dear!, not so chirpy with the smart comments and silly images now, are we?

JimB

i am not very chirpy now because my meter fried!

 

[Ziddik]

sometimes cheap things last much longer than expensive one.. Maybe with our luck

 

[crutschow]

For 99% of typical applications, the cheap multimeters work fine. And if you blow one, it's not a big loss.

 

[Ziddik]

i have a doubt that increasing current in a circuit would fry them? For example i got a circuit which will work with 5vDC and 300mA current, so what will happen if i gave 5vDC and 1 or 5 amperes to the circuit? Will it fry?

 

[ericgibbs]

i have a doubt that increasing current in a circuit would fry them? For example i got a circuit which will work with 5vDC and 300mA current, so what will happen if i gave 5vDC and 1 or 5 amperes to the circuit? Will it fry?

A voltmeter is able to measure a voltage OK, whatever the current rating of the power rail.

Make sure that the voltage range of the meter is correctly set before taking a voltage measurement.

 

[Reloadron]

i have a doubt that increasing current in a circuit would fry them? For example i got a circuit which will work with 5vDC and 300mA current, so what will happen if i gave 5vDC and 1 or 5 amperes to the circuit? Will it fry?

A circuit rated for 5 volts @ .3 amp will draw just that. It matters not what the supply is capable of. The common example is a car's battery. The battery (supply) is capable of delivering hundreds of amps. However, the accessories on the car's system only draw the current they need at their rated voltage.

When using a voltmeter to measure voltage it is placed across the load, when measuring current with a current meter it is placed in series with the load. Note how the ammeter and voltmeter are configured in the attached illustration.

Ron

 

[MrAl]

Hi,

This reminded me of a funny story i think is worth repeating. It's not really funny though.

Long time ago in the dead of winter my car wouldnt start early morning because the battery was getting old and needed replacement. I took the battery out and brought it in the house for charging. I decided to measure the voltage as it was charging, and bang! Blew out my hundred dollar multi function meter. The meter was set for amps and i forgot to change it back to volts. I usually dont make this kind of mistake but i was in a hurry and got a little too hasty. Needless to say i was very sad about that.

Later that day i checked the meter and everything was still working, except for the amps. It would not measure amps anymore. No reading on any current scale even though everything else worked just fine. I was happy that at least the other functions worked as this was a pretty nice meter, not a common run of the mill 20 dollar meter by any means.
So next i checked the fuse, and it looked good but i replaced it anyway. Still no current measurements. I was very disappointed but i was at least happy that the meter still worked for voltage and frequency and so on. I used the meter this way for some 10 years after that.

Some 10 years later, i was talking with a friend and the subject of meters came up and their display connections. For some reason i decided to take the meter apart so i could inspect the meter display connections to see how they did it in this decent grade meter as opposed to the cheaper 20 dollar meters. I took it apart carefully and checked the display and lo and behold, i found another friggin fuse! The fuse was hiding under a shield so it wasnt obvious even with the meter apart, but because i was inspecting the meter so carefully looking from the side i was able to spot it. All i could think of was, "Wow". The manual said nothing about this secondary fuse so i was a bit upset about that.

Anyway, changing that second fuse and suddenly the current functions all came back into perfect working state. I checked for burnt resistors too but they all looked good and the calibration seemed fine.

What's amazing is that because the manual said nothing about that second fuse i was using the meter for 10 years without knowing i could fix the current functions simply by taking the meter apart and finding that other fuse and replacing it. Not a good manual for sure.