what's wrong with my Multi-meter?

[pounder]

hey guys..for some reason when I check tailcap readings my MM is way too high..for my solarforce L2p with R2 drop-in it reads 5.40 amps when i'm on the 10a setting..it does this with all my lights also..ultrafire a30b is 3.35 amps...these are ridiculous readings and I don't know what is up..i've changed the batteries to brand new ones and the readings prevail..all the voltage readings are accurate, but the tailcap readings are off..

am I stuck buying a new MM? or is there a scientific reason why these readings are the way they are?

many thanks..

 

[qwertyydude]

Broken is all I can think of. What model DMM is it?

 

[march.brown]

Borrow one from a friend and put the two in series (on DC current) ... They should display the same readings.

Put the two meters in parallel (on DC volts) to check the voltage of a battery too , just to see if yours is OK on volts.
.

 

[45/70]

You might try installing a new battery in the meter. Some DMM's can come up with some pretty bizarre readings when the battery voltage is low.

Dave

 

[datiLED]

You might try installing a new battery in the meter. Some DMM's can come up with some pretty bizarre readings when the battery voltage is low.

Dave

+1

I have had some problems with my meter when the batteries were low. After replacing the batteries, normal function returned.

 

[Th232]

Since you said you already changed the batteries to new ones, double check that the positive lead is plugged in to the correct socket?

Is this a brand new multimeter or one that you've been using for some time and has only now started showing this problem?

 

[pounder]

yeah the battery was replaced and showed the same readings..I know mine gave really weird readings when the battery was dying..this is a new issue..it used to read correct tailcap readings..1.2 on the l2p..

red is in the right socket..it's a older motomaster DMM from canadian tire..very little use on it and the amperage is the only thing that went funky on it..the voltages are all correct..4.2v on charged lithiums and shows 3.xx as they discharge..

I guess i'll end up looking for a sale on a new DMM..thanks for the help

 

[45/70]

Sorry. I missed that you had changed the batteries :candle:

That was just the first thing I thought of when I read your post, as I've had this happen before. Is it possible that your "new" cells aren't really all that new? Probably not.

Dave

 

[mattheww50]

hey guys..for some reason when I check tailcap readings my MM is way too high..for my solarforce L2p with R2 drop-in it reads 5.40 amps when i'm on the 10a setting..it does this with all my lights also..ultrafire a30b is 3.35 amps...these are ridiculous readings and I don't know what is up..i've changed the batteries to brand new ones and the readings prevail..all the voltage readings are accurate, but the tailcap readings are off..

am I stuck buying a new MM? or is there a scientific reason why these readings are the way they are?

many thanks..

On Amps what you are really reading is the voltage across a shunt inside the meter.
Most meters I have used have a separate connection for the 10amp range. Make sure the test leads are in fact connected to the common and the 10 amp connection.

So either the shunt resistance is a lot higher than it should be, or you are using the wong connection. If the shunt resistance is high, make sure that the fuse inside isn't damaged.
(The 10amp connection is also usually fused separately).
The 10amp shunt probably has a resistance on the order of .1 ohms. You might ohm out the 10 amp to common resistance when the meter is on the 10amp scale. If it is more than a small fraction of an ohm, there is a problem.

 

[Mr Happy]

Another possibility is that the lamp is not drawing pure DC from the battery, but is drawing pulses with a funny waveform as needed by the boost driver. Ordinary multimeters are calibrated for DC and may fail to read oscillating waveforms accurately.

To get a better reading you might try to rig up a circuit like this:

The reservoir capacitor will bypass the oscillating wave forms and result in a much smoother current being demanded of the battery.

 

[pounder]

On Amps what you are really reading is the voltage across a shunt inside the meter.
Most meters I have used have a separate connection for the 10amp range. Make sure the test leads are in fact connected to the common and the 10 amp connection.

So either the shunt resistance is a lot higher than it should be, or you are using the wong connection. If the shunt resistance is high, make sure that the fuse inside isn't damaged.
(The 10amp connection is also usually fused separately).
The 10amp shunt probably has a resistance on the order of .1 ohms. You might ohm out the 10 amp to common resistance when the meter is on the 10amp scale. If it is more than a small fraction of an ohm, there is a problem.

the 10a says "unfused" next to it..and you were right about the shunt (piece of steel bridging the 2 lead areas?) i just touched it and now the meter works great..meaures 1.49-1.5 amp for my l2p..don't know what is up with that other than the shunt might have had a charge in it? and I grounded it by touching it? not a real wizz with DMM's, but it works more accurately now that I touched the shunt..

many thanks to all who chimed in!

 

[Mr Happy]

i just touched it and now the meter works great..meaures 1.49-1.5 amp for my l2p..don't know what is up with that other than the shunt might have had a charge in it? and I grounded it by touching it? not a real wizz with DMM's, but it works more accurately now that I touched the shunt..

It sounds like the shunt was making bad electrical contact at either end (bad joint? oxidation?) and when you touched it you joggled it, making a temporary improvement. You will either need to fix it permanently or buy a new meter, or your current readings will continue to be unreliable.

Another possibility is a bad connection in your meter leads. Sometimes the banana plugs get coated with oils or oxidation and need a good clean, and the same inside the sockets.

 

[pounder]

It sounds like the shunt was making bad electrical contact at either end (bad joint? oxidation?) and when you touched it you joggled it, making a temporary improvement. You will either need to fix it permanently or buy a new meter, or your current readings will continue to be unreliable.

Another possibility is a bad connection in your meter leads. Sometimes the banana plugs get coated with oils or oxidation and need a good clean, and the same inside the sockets.

might have been that also..I did resecure the connection at the lead and give it a good twist..i'll keep an eye on it and see if it happens again..

 

[kaptain_zero]

Go over to the EEVBlog site and look for the video titled "Why Chinese Multimeters Suck" episode..... Pretty much sums up all the issues with CTC branded DMMs and a host of others too.

 

[pounder]

Go over to the EEVBlog site and look for the video titled "Why Chinese Multimeters Suck" episode..... Pretty much sums up all the issues with CTC branded DMMs and a host of others too.

CTC meaning Canadian tire? yeah a lot of things they come out with really blow..i've seen the horrors on their torque wrenches for rebuilding my scooter engines..cracked the cases of some engines because they are so far off the mark...

any other brands in Canada that I could get for under 50$? i'm not a rich man with kids and a wife etc...don't have the coin for a 300$ DMM....cheers

 

[kaptain_zero]

Dave on the EEVblog does do a $50 MultiMeter shootout if you'd care to check it out. Not too many survivors in that one, but there were a couple of acceptable ones. He also does a $100 meter shootout with meters ranging from around $80 up to $120 where he finds you're in the middle of the meat and potatoes meters, meaning each one is acceptable, for the most part, and it becomes more of a "depends on what you need" sort of thing, rather than what he, or anyone else for that matter, says is the best.

I was in the same boat as you, only I KNEW I was in a leaky boat with 2 CTC meters, and I did and do dabble in building my own electronics circuits. Being short of funds, I simply waited around until one of my Amateur Radio Tech buddies found a used, non working Professional grade meter that he picked up for chump change at a ham radio flea market. This particular unit had a battery go bad, leaked, needed cleaning and new cables, but that was it. It was an old Beckman DM800 and I ended up getting it from him for a measly $25. Mind you, it's not going to be as convenient as a new Agilent or Fluke, but the components it was made from were top quality and they are still very much in spec so I know I can rely on it (particularly seeing my buddy verified it against a recently certified lab instrument). Having two cheap meters and this older quality unit lets me keep track of the three... if one reads weird, I can check it against the other two... if they concur, I know it's fine, if they don't, then the odds are that 2 out of 3 will be correct and the third one out and by comparing them all, I can most likely figure out which of the three it is. With only 2 meters, I would never know which one started to drift......

So there's the long answer...... I suggest checking out Dave's video blogs on the $50 and $100 meters.... they are long videos, and he's a bit quirky and over enthusiastic, but he does get down to the nitty gritty and doesn't hold back on the punches. He's even come out swinging on behalf of one of the other board members who owned what he felt was a top notch meter, only to find out, that it has a weakness when it comes to GMS cell phones. This was only discovered when a tech happened to place his GSM cell phone next to the meter while doing something else, only to find it scrambled the firmware in the meter when he got a phone call!

Seeing you are in Canada, places like Active Electronics should be able to sell you a reasonable priced multimeter that isn't pure rubbish. Digi Key could also supply something I would think.... maybe check your local yellow pages for electronics supply companies, once you've decided on a unit or two and then do some comparison shopping. Extech will probably have what you are looking for, in your price range.... BK Precision would have something slightly more expensive but still close to what you are looking for... If you need to bide your time and save a bit, do so.... buying cheap meters will never get you ahead in the end.

Regards

Christian

 

[pounder]

Dave on the EEVblog does do a $50 MultiMeter shootout if you'd care to check it out. Not too many survivors in that one, but there were a couple of acceptable ones. He also does a $100 meter shootout with meters ranging from around $80 up to $120 where he finds you're in the middle of the meat and potatoes meters, meaning each one is acceptable, for the most part, and it becomes more of a "depends on what you need" sort of thing, rather than what he, or anyone else for that matter, says is the best.

I was in the same boat as you, only I KNEW I was in a leaky boat with 2 CTC meters, and I did and do dabble in building my own electronics circuits. Being short of funds, I simply waited around until one of my Amateur Radio Tech buddies found a used, non working Professional grade meter that he picked up for chump change at a ham radio flea market. This particular unit had a battery go bad, leaked, needed cleaning and new cables, but that was it. It was an old Beckman DM800 and I ended up getting it from him for a measly $25. Mind you, it's not going to be as convenient as a new Agilent or Fluke, but the components it was made from were top quality and they are still very much in spec so I know I can rely on it (particularly seeing my buddy verified it against a recently certified lab instrument). Having two cheap meters and this older quality unit lets me keep track of the three... if one reads weird, I can check it against the other two... if they concur, I know it's fine, if they don't, then the odds are that 2 out of 3 will be correct and the third one out and by comparing them all, I can most likely figure out which of the three it is. With only 2 meters, I would never know which one started to drift......

So there's the long answer...... I suggest checking out Dave's video blogs on the $50 and $100 meters.... they are long videos, and he's a bit quirky and over enthusiastic, but he does get down to the nitty gritty and doesn't hold back on the punches. He's even come out swinging on behalf of one of the other board members who owned what he felt was a top notch meter, only to find out, that it has a weakness when it comes to GMS cell phones. This was only discovered when a tech happened to place his GSM cell phone next to the meter while doing something else, only to find it scrambled the firmware in the meter when he got a phone call!

Seeing you are in Canada, places like Active Electronics should be able to sell you a reasonable priced multimeter that isn't pure rubbish. Digi Key could also supply something I would think.... maybe check your local yellow pages for electronics supply companies, once you've decided on a unit or two and then do some comparison shopping. Extech will probably have what you are looking for, in your price range.... BK Precision would have something slightly more expensive but still close to what you are looking for... If you need to bide your time and save a bit, do so.... buying cheap meters will never get you ahead in the end.

Regards

Christian

thanks for that..a lot of information for sure..I guess I should just stay to "checking voltages of lithium batteries"...there isn't really anything I should check beyond these needs for the time being..I really don't know of a time when I would have a few hundred that wouldn't be better used on other things..checking currents of my flashlights "flashlights being a ridiculous obsession in the eyes of my wife" isn't high on the list..just wondered why this DMM was so off...now that it's fixed I think i'll keep it..

I appreciate the insight..many thanks to you guys..

 

[kaptain_zero]

thanks for that..a lot of information for sure..I guess I should just stay to "checking voltages of lithium batteries"...there isn't really anything I should check beyond these needs for the time being..

Just..... for the record...... and I DO have two Canadian Tire cheapo digital multimeters......... The simple (seemingly) act of checking the voltage of Lithium Ion batteries with such a multimeter doesn't tell you that much....... depending on what exactly it is, that you want to know. If you really want to know if it's 4.xx then you either need to get your Canadian Tire meter calibrated, or you need to buy a higher quality meter AND STILL have it checked on a regular basis!

Why do I say that, it's because my first CTC meter indicated that my charger was charging my batteries to 4.24v! Wow... that's dang near the top of what is acceptable, right?

Enter the second CTC multimeter..... again on sale, turns out it's the same dang meter I had before, except the color is different as well as some of the labels.... otherwise, electronically, mechanically.... it's the same darn meter, only made X years later..... I check the battery with this new meter (did I mention that I had to return one that failed in a matter of minutes?!?!?) and lo and behold, it reports that my charger is charging to 4.19v! Well, that's better.... but wait, the other meter, that has worked so well for me in the past 10+ years says it's 4.24v ?!?!

This is why you pay good money for a digital multimeter....... measurement confidence, the fact that you can actually TRUST what your meter is telling you.


Enter the third, old, grungy, rescued from h*ll, Professional Multi Meter that has seen better days. After cleaning, checking and calibrating + plus some serious arm twisting on my part to get the guy to sell it to me for $25 bucks, I check the same dang battery and it reads....... wait for it............. 4.20v.

After seeing that, I have the Tech ( we meet for coffee every Saturday morning at a local McDonalds for coffee) bring 2 more pro digital meters + his Lab meter that has been calibrated by verified sources and have him read the same battery with all of them. One of his DMMs reads the same as mine, the other is slightly off.... the Lab Meter agrees with my DMM and one of the DMM's he brought, the other pro meter is slightly off, by, if I recall correctly, 0.03v. The conclusion is that my Beckman, at 4.20 v reads dead nuts accurate (uhm.... today, who knows what it will read tomorrow?), my Chinese meter (old) reads 0.04v high and my new Chinese meter reads 0.01v low.

The moral of the story is.......... don't trust a single DMM, no matter how much it cost! If you want to know if something is at a 4v potential vs an item at 5v potential.... well, pretty much all the DMMs out there will do that with enough accuracy to be valid. When you get down to the 0.01v range........ it gets dicey at best..... The cheaper the meter, the less reliable the claims of accuracy from the manufacturer becomes.

I won't even get into low current measurement with DMMs..... even ones costing a thousand or more are not that accurate..... it takes a separate device, in addition to the DMM to take an accurate measurement. It relates to burden voltages.... if you don't know what that is, don't worry about it, if you do, you'll know what I mean. In the end, my entire purpose of this reply is to educate those who read this in the simple fact that just because you have purchased a $20 DMM, does not mean that what you see on the display, is what is actually going on. And worse yet, in the 0.01v range..... you might still have accuracy problems, even if you bought a new, high cost meter....... unless it comes with certified calibration docs and even then, they are only valid for a given time.

Regards

Kaptain" Even with three DMM's, I'm still looking for the cash to buy another meter" Zero

 

[pounder]

lol love the enthusiasm K zero...unfortunately my funds do not support my obsessive behaviour or I would be swimming in Ra clickies...hahaha :thumbsup:

 

[Notsure Fire]

I'd get a new one.