Good cheap multimeter?

[march.brown]

The dollar amount here is not the important thing. There's something about using such low quality stuff that's it's almost demeaning to the user. Some low dollar stuff is OK or even quite acceptable.

I guess that is the reason why some people buy expensive torches ... It is demeaning to be actually seen with a cheap torch ... I don't mind being demeaned (?) ... I don't have any expensive torches but I still have my immaculate (but very old) Avo Model 8 meter which still works perfectly ... I could even use it on my Li-Ions if I wanted to as the mirror scale makes it easy to read very accurately ... Checked against my five volt reference device , it is spot-on ... However it is so much easier to read my digital cheapie meters that the Avo is just left sitting on display in the study in its nice polished leather case ... The Avo 8 was a very expensive meter when it was bought for me about 37 years ago ... As I was working on electronics , I also had some Flukes for a few years ... The three Flukes all died and yet the old Avo 8 has carried on working as good as ever ... The Flukes were deemed to be beyond economic repair when in-fact it was only their display that had failed ... They had frequency measurement on them which was useful , but as I also carried a TMS and an SLMS with me that feature wasn't absolutely essential ... Luckily I wasn't paying for the Flukes ...

My ultra cheap Harbor-Freight lookalikes are absolutely spot on in their readings of my reference and that is all I need for my Li-Ion voltage readings ... If a meter starts reading low , I check its battery and if that is not the problem I will dispose of the meter ... So far , I have given away only one meter that was 30mV out on the 20V range when measuring the 5V reference ... It was given away to my Son-in-Law 'cos it was still OK for him to check bulbs , fuses and NiMh batteries with.

So, cheap meters are OK as long as you can trust their readings ... All meters , even the most expensive should be checked against a reference that is at least ten times better (preferably more) ... Nowadays , you can have your reference checked annually for just a few dollars plus postage if you really need the ultimate accuracy.
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[Jakpro]

You can find cheap Fluke 12's and 113's on the auction site.

 

[SemiMan]

You cannot possibly know that your Li-Ion batteries are fine without an accurate means of measuring the open-circuit battery voltage ... The state of charge of a Li-Ion can be easily checked by simply measuring its rested voltage ... There are tables available on CPF that will give you the Percentage Charge in the battery ... Obviously a reasonably accurate DMM is required , or a precision reference with which to check your meter.

No-one should put their faith implicitly on the charger alone ... That is irrespective of the make of the charger and its apparently good reviews ...

I use cheap meters but I know they are very accurate as I check them against a known high accuracy voltage reference device ... I check all my meters regularly and if one is not the same as the others , it is usually because the battery in the meter needs replacing ... If (or when) a meter is out of my limits , it is either thrown away or given to someone who doesn't need this degree of accuracy ... So far , I have only given away one cheap meter ...

My meters are all identical to the Harbor Freight cheapies and bought here in the UK for less than £5 each.
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Just because you can get an accurate voltage reading on one scale does not indicate that you can get accurate readings on all scales and all things you are reading. This has been my issue with cheap meters ... cheap switches and dials and flaky readings. I would certainly feel more comfortable with a cheap autoreading meter as there is less to go wrong.

Semiman

 

[TigerF]

I have a DT 830B Digital Multimeter, on sale at Fry's Electronics for probably $4.00-5.00 or so, a couple of years ago. It looks almost identical to the Harbor Freight multimeter. I haven't had problems with any leads breaking or anything like that. It's fine for simple measurements. I use it to perform simple diagnostics on my car, as well as check battery voltages. It runs on a single 9V battery. Like others said, set it on the 20V scale to check battery voltages. It's worked for me, so far...

 

[march.brown]

Just because you can get an accurate voltage reading on one scale does not indicate that you can get accurate readings on all scales and all things you are reading. This has been my issue with cheap meters ... cheap switches and dials and flaky readings. I would certainly feel more comfortable with a cheap autoreading meter as there is less to go wrong.

Semiman

My cheapie meters are normally only used for measurements on my torch batteries ... I use the twenty volt DC range for Li-Ions and the two volt DC range for NiMh cells ... The resistance ranges also get used on fuses , bulbs etc ... I can trust the reading on the twenty volt DC range as it is checked against my five volt reference device.

I am perfectly happy with my meters and should they eventually fail , I will simply buy another ... I can take my five volt reference device to the shop and check the cheapie meter before I buy ... No problem ... The salespersons all seem very keen to see how their products perform.

 

[xul]

It's not obvious but you can use a wall oven and a 4-1/2 digit DVM to measure the short circuit current capability of your residential panel. Mine came in at 10,800A.

You can probably make any cheapie meter safer for mains work by putting a fuse in series with the meter with an interrupting current rating greater than your particular value.

The RCA Voltohmyst, a VTVM, used this method. It had two fuses in series which didn't make sense until you looked at the parts list.

 

[Flying Turtle]

I've also been using a Craftsman for a few years. I think I paid less than $20. They are often on sale and there is a large selection. Certainly good enough for voltage checks.

Geoff

 

[samgab]

Here's something interesting:
I just received a DMMCHECK precision 5.000V voltage reference in the mail today.
I tested the Entry level Fluke 17B versus one of the old cheapies I had lying around.
Here are the results:

So the cheap junkie one is more accurate (At 5 V) than the Fluke that I have been relying on!
Now I want to get a "PentaRef" so I can check the readings at different scales of DC Voltage.

Edit: I've adjusted the 17B now. The precision voltage reference is accurate, for those of eevblog who doubt:

 

[xul]

So the cheap junkie one is more accurate (At 5 V) than the Fluke that I have been relying on!

On average it shouldn't be but you'd have to check several meters of each kind to see how these two meters compare.

Does 5.00 +/- 0.04 v pass spec on the Fluke?
+/- 0.5% of 5v is .025v + 3 LSBs would give 4.98v + 3 LSBs.
The Fluke might be out of spec by 1 LSB.

 

[samgab]

On average it shouldn't be but you'd have to check several meters of each kind to see how these two meters compare.

Does 5.00 +/- 0.04 v pass spec on the Fluke?
+/- 0.5% of 5v is .025v + 3 LSBs would give 4.98v + 3 LSBs.
The Fluke might be out of spec by 1 LSB.

The rated accuracy spec for the Fluke 17B for DC Volts is .05% +3 counts Least Significant Digits.
So the spec for 5.00V would be (rounded) 4.95-5.06 V. So yes, it's within spec... Just.
(4.98-3LSD is 4.95.
5.03+3LSD is 5.06.)
See @6m 18S of the video onwards for explanation of the LSD counts...

 

[HKJ]

The rated accuracy spec for the Fluke 17B for DC Volts is .05% +3 counts Least Significant Digits.
So the spec for 5.00V would be (rounded) 4.95-5.06 V. So yes, it's within spec... Just.
(4.98-3LSD is 4.95.
5.03+3LSD is 5.06.)

That is the reason to get a DMM with 6000 reading (Like the one I posted before). The + count is 10 times less significant when measuring on LiIon.
The better Fluke meters does also have 6000 count.

 

[samgab]

That is the reason to get a DMM with 6000 reading (Like the one I posted before). The + count is 10 times less significant when measuring on LiIon.
The better Fluke meters does also have 6000 count.

Yes... What a shame the chemistry isn't fully charged at 3.95V I think a 6000 count is the way to go... Not necessarily more accurate, in percentage, but under 6V it has much better resolution.

 

[march.brown]

On average it shouldn't be but you'd have to check several meters of each kind to see how these two meters compare.

Does 5.00 +/- 0.04 v pass spec on the Fluke?
+/- 0.5% of 5v is .025v + 3 LSBs would give 4.98v + 3 LSBs.
The Fluke might be out of spec by 1 LSB.

It would be nice to have an extra digit in the display ... 4.98V could be out by plus or minus five millivolts ... So the actual reading on a better meter display could be anywhere between 4.975V and 4.985V ... I can't justify spending more money just to get that degree of accuracy even though I would like it ... So I make do with being possibly up to five millivolts out as well as the 0.5% and the 3LSBs ... Luckily the Li-Ions have a small ammount of latitude and mine always come off the charger at less than 4.25V.

I also check that my cheapie meters read 5.00V when checked against my five volt reference device ... I've been lucky so far and my meters are reading within five millivolts ... That's great for meters that cost well below £5.
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[xul]

I couldn't do anything right yesterday.
+/- 0.5% of 4.96v is .025v + 3 LSBs is .03 so you'd have 4.96 + .03 + .03 would give 5.02v so this meter is within spec. It also means about 2/3rds of the meters sold would read 4.96 +/- .03.

In the video he, I think, showed +/- 1 mV and +/- 2 counts. This is not the same as +/- [1 mV + 2 counts], which I think is the correct statement.
In the first statement the LSB or LSD error could cancel out the mV error. I don't think that happens.

I did find it surprising how the meters displayed resolution as the voltage was increased. I've never had an occasion to discover this.

If he heard me speak he'd say I have a thick American accent [because I had a hard time understanding him in some places].

 

[Tommygun45]

Goodness, thanks for all the replies guys. Again, I was not saying that I 'know' that my batteries are in great shape, but they are all fairly new and I really dont use my lights that much to be honest. They have never been totally drained, and I have never left them on the Pila for extended periods of time, just until the light turns green.

That being said, this is the only application I have to use a multimeter. I was just kind of curious because of some strange behavior from the Pila. When I have two AW cells on there and one of them shows green, when I take it off the other one will switch to green as well. This happens each time I change cells on either side. If I put that cell that just turned green back on it will charge, sometimes for hours more. But other times its on my 16340's and I know they dont take long to charge, so it can be tricky. Having one of these things would just allow me to confirm that its in the proper voltage range.

Ill order up one now and see how it goes. Ill try to find the one for ~16 off amazon. Thanks guys

 

[samgab]

Cheap meters can be taken apart and adjusted using the trim pots if you have a precision reference to get source readings from:
It feels great to connect to a 5.000V source and see 5.00 on the display, or connect to a 1.0000 mA source and see 1.00 mA or 1000 μA. Good times.
Pix or it didn't happen:

To the OP, good on you for ordering a DMM... you will find it invaluable as you get more into li-ion chemistry etc. It's really an essential item.

I think a few things to look for, even in relatively cheap DMMs:
* Ceramic HRC (High Rupture Capacity) fuses - not glass.
* Fused at both Amps and mA.
* Good input overload protection, such as PTC thermistors and MOVs.
* Quality test probes, with quality rated leads.
* Build quality/plastics quality/soldering.
* Good positive dial. Not "mushy".
* Clear readable display, at most angles of view.
* Avoid silly gimmicks like transistor test functions.

 

[xul]

For accuracy, what is the smallest volt difference or percentage difference in batteries that is meaningful? Get a meter that reads 5x better than this.

For trends you only need ratio accuracy, not absolute accuracy.

 

[march.brown]

If you can check your meter against a voltage reference device , you will see how far out your meter is reading ... You can then correct any other readings taken on that meter range to get the absolute value ... I had one meter that was reading 40 millivolts high on the 20 volt range when checked against my five volt reference ... If I deducted 40mV on a five volt reading then it became five volts ... For four volt readings , I deducted 32mV to give the corrected reading ... I never thought about taking the back off to adjust the potentiometer ... I must remember that for the future.

As my other cheapie meters were reading spot-on , I gave that meter to my Son-in-Law as he didn't need a high degree of accuracy.

It would be very nice to read Li-Ion voltages with an accuracy of one millivolt , but in all fairness if you can get it within 10mV it is perfectly adequate ... I know that my meters all read my reference as 5.00V ... When I check a Li-Ion at 4.20V , the actual voltage can be up to 10mV out (probably less) ... Because of the number of LCD digits on the meter , mine will only read to ten millivolt divisions ... An extra digit would add quite a bit to the price ... For the cost of these meter , their accuracy is amazing ... I check my meters against the reference quite regularly (just in case) ... It only takes a couple of minutes as the reference is always kept at room temperature.
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[moderator007]

Since we are discuss adjusting cheap meters. I dont think I remember seeing A pot on my cheap harbor frieght DMM.
So has anybody attempted to try to adjust A HF DMM by changing resistors or installing a pot?
Or maybe even know which resistor affects the voltage reading. I have one out of three thats about .03v off.
I liked to see if I could correct it if possible.

 

[xul]

Post the meter schematic or the numbers off the top of any chips inside.

The trouble with cheap stuff is that it may drift with time or temperature or humidity even if you manage to get it to read exactly the true value at the moment.

That's another thing I learned from that video; determining your own calibration interval based on measurements over time.