Is my DMM broken (cannot read current)?

Hi, I just bought a cheap DMM (Elenco M-1000C), and I believe that the low-range current reader is broken.

The DMM has a 10A plug, which seems to work properly (it shows reasonable results in high-current circuits). However, switching to the mA plug doesn't seem to work at all. It always shows me 0mA when I'm expecting 9mA (the range is set to 20mA).

Also, when I use the 10A plug, a LED of my circuit lights up when I make the contact. It doesn't with the 20mA range.

Am I doing something wrong with the low-range current reader? I really think the DMM is not functionning properly, but I would like to know what you guys think.

Martin

Reply to
Martin Cote
Loading thread data ...

If you are lucky, there is an internal fuse in series with the low current ranges, to protect the current shunt resistor from being blown up if you connect the current measuring leads across a voltage source or anything that can drive much more than full scale current through the resistor. If you are less lucky, the resistor itself, acts as the fuse, and that range is destroyed.

Reply to
John Popelish

"Martin Cote"

** Even the cheapest DMMs have a fuse for the 200mA range.

Open it up and have a look - expect to see a 20 x 5mm, 0.5 A fuse.

........ Phil

Reply to
Phil Allison

You are probably right. I have a $2.99 meter (Are there any cheaper than that?) and it has that fuse replacement information on the back.

Reply to
John Popelish

That's right. I'll replace it an see how it goes.

Thanks, Martin

Reply to
Martin Cote

Also, all the current measuring ranges (and resistance, and diode- check, etc) are basically a short circuit. If you touch the meter leads to the wrong place for even a fraction of a second with the selector set to that, you will be replacing that fuse again.

And be ESPECIALLY careful with the leads plugged into the 10 amp socket, thats an unfused piece of wire connected internally to the sockets ... hook that up to the wrong thing, and you will be making big sparks, blowing breakers, or setting wiring on fire. For the 10 amp socket, it doesn't matter what the selector switch is set to, with the leads plugged into that socket, the leads form a direct short.

So make SURE the setting is correct BEFORE you hook up the meter. (and buy the fuses in a bulk pack ... cause sometimes one forgets ...)

John alluded to this, but I just thought I'd make it blindingly obvious.

Martin Bakalorz

Reply to
Martin

How much trouble could it have been for the manufacturers to add a 10A fuse to the 10A input...?

I guess that's what the home circuit breakers are for...

Thanks for the info

Michael

Reply to
mrdarrett

** A fair bit, actually.

** No way on earth.

Simple, cheap DMMs ( ie intended for hobbyists ) are not safe to use on AC mains wiring.

They should *never* be used by an electrician - for example.

Only DMMs which carry a safety category rating are safe to use around high voltage and high energy circuits like the AC supply.

They all have things like shrouded plugs on the leads, fused high current ranges ( using special fuses that cost more than a cheap DMM) and no access to the battery compartment without a tool.

....... Phil

Reply to
Phil Allison

"Martin"

** Totally false.

Those ranges are usually high impedance and protected against overvoltage accidents.

** Not true with the vast majority of DMMs.

........ Phil

Reply to
Phil Allison

protected against fires maybe,

I gave my meter 600V of B+ while on the 10VAC range while reaching towards the filament terminals, this and bent the needle against the stop and took out the diodes and a few resistors, the fuse survived intact.

I eventually got the needle straightened out and balanced again.

Bye. Jasen

Reply to
Jasen

"Jasen"

** Follow the f****ng topic !!!!!!!

You donkey c*ck sucking, 2 yo kiddie f****ng,

pile of autistic KIWI EXCRETA

Reply to
Phil Allison

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.