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Thread: Simple guide to using a DMM for measurements

  1. #121
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by njet212 View Post
    I did things just like on your picture. I'm bit confused, if i'm doing thing just like your pic, I'm I measuring volt battery or current draw?
    That way you measure the current draw only, but not at a specific voltage. The voltage you measure before or after, on the battery, is without load and will be considerable higher than when you measured the current draw (especially when we are talking about the Preon ReVo at high).

    When doing this kind of current measurement it is best to use a fresh (or freshly charged) battery and then only specify battery type, not voltage.
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    Default Re: Simple guide to using a DMM for measurements

    Thanks for the answer HKJ, appreciate that!

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    Default Re: Simple guide to using a DMM for measurements

    Great work & thread
    "Now they will know why they are afraid of the dark. Now they learn why they fear the night."-Thulsa Doom PAYPAL FEE CALCULATOR; list of lights.

  4. #124
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    Default Re: Simple guide to using a DMM for measurements

    HKJ, last time was asking about how do you measure standby current on a flashlight and you did answer it already. But today i tried to look at it again but i realized your post was missing.

    Would you mind to explain it again ? the flashlight i'm going to measure is New Jetbeam RRT-0 Infinite Variable Brightness version. I was wondering how much is the standby current because it's suck all the juice on my AW RCR123 just only in a week !!


    Thanks

  5. #125
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by njet212 View Post
    HKJ, last time was asking about how do you measure standby current on a flashlight and you did answer it already. But today i tried to look at it again but i realized your post was missing.

    Would you mind to explain it again ? the flashlight i'm going to measure is New Jetbeam RRT-0 Infinite Variable Brightness version. I was wondering how much is the standby current because it's suck all the juice on my AW RCR123 just only in a week !!
    That light is supposed to have a real on/off switch, i.e. no current draw when switched off on the tail switch. If you want to measure the current draw with the ring in off position, you can just use the "Current consumption" chapter, but you will need to use the "mA" socket, not the "A" socket.
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  6. #126
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    Default Re: Simple guide to using a DMM for measurements

    Thanks for your answer HKJ

  7. #127

    Default Re: Simple guide to using a DMM for measurements

    HKJ,

    Many thanks for posting this. It is extremely helpul and beautifully illustrated and explained.

    Brightnorm

  8. #128
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    Default Re: Simple guide to using a DMM for measurements

    Added a "High current measurement" showing how to use a clamp meter.
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  9. #129
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    Default Re: Simple guide to using a DMM for measurements

    Very nice ! And clearly illustrated, thx for this thread.

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    Default Re: Simple guide to using a DMM for measurements

    I have a cheap Velleman DVM92 multimeter.


    Specs are:


    3 ˝ digit ( maximum display 1999 )
    Accuracy DC voltage +/- 0,5% of rgd +/- 1 digit
    Accuracy DC current 20mA +/- 0,8% of rgd +/- 1 digit
    Accuracy DC current 200mA +/- 1,2% of rgd +/- 1 digit
    Accuracy DC current 20A +/- 2% of rgd +/- 5 digits


    Is the DMM accurate enough for measuring flashlight batteries , or will you recomend me buying a better one.

  11. #131
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by Viking View Post
    3 ˝ digit ( maximum display 1999 )
    Accuracy DC voltage +/- 0,5% of rgd +/- 1 digit

    Is the DMM accurate enough for measuring flashlight batteries , or will you recomend me buying a better one.
    For LiIon batteries the charge voltage is usual 4.2 volt +/- 0.05 volt, as long as you batteries does not read above 4.2 volt on you DMM they are below 4.25 volt (According to the DMM specification below 4.23 volt).
    Most chargers will be more than good enough and you do not need to check the batteries each time you take them off the charger.
    Where it is important to check batteries is when you run them down, many LiIon batteries can get dangerous if you discharge them to low, to check this does not require much precision from the meter. If the battery measures below 2.5 to 3 volt (After they have rested some time), there is a risk they may explode when charged. This is a cumulative effect, each time they get discharged to much the risk for explosion during any subsequent charge will increase slightly.

    Batteries that show 0 volt on the meter might not be discharged to much, it is probably the protection that is tripped. If you charger can reset a protection (See my charger reviews), give the cell a second in the charger, then take it out and check the voltage again. If the charger cannot reset protection you need to wire it parallel with another LiIon cell for a second.

    And if you DMM's reading suddenly are a bit beside the expected values, you probably need to replace the battery in the meter.
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    Thumbs up Re: Simple guide to using a DMM for measurements

    Thanks for the answer

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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by HKJ View Post


    The tailcap is removed from the flashlight and the meter is substituted for that connection, i.e. one probe pin is placed on the battery and the other probe pin is placed on the battery tube, where there is some bare metal. Placing the probe pin on anodized metal will not work.
    As can be seen, the two meters do not agree on the value. That is because the current draw is not really DC, but drawn in very fast pulses, the meters does not sum this the same way. This is only a problem on some flashlights.
    Hello HKJ,
    have you ever tested the resistance of the probe leads of the cheap DMM?
    I got a Best DT9205A today to compare it too a good multimeter. The DT9205A is not very accurate but usable but the probe leads are crap, their resistance is far too high. I measured 0.46 ohms - ten times the value of some probe leads from another meter and more than 50 times the value of a pair of short leads with banana plugs on both ends.
    I don't think that fast pulses cause the wrong reading but the voltage drop across the probe leads makes the regulated light draw a higher current.
    Of course the effect of the high probe lead resistance gets worse with pulsed currents.

  14. #134
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by Tohuwabohu View Post
    Hello HKJ,
    have you ever tested the resistance of the probe leads of the cheap DMM?
    I got a Best DT9205A today to compare it too a good multimeter. The DT9205A is not very accurate but usable but the probe leads are crap, their resistance is far too high. I measured 0.46 ohms - ten times the value of some probe leads from another meter and more than 50 times the value of a pair of short leads with banana plugs on both ends.
    I don't think that fast pulses cause the wrong reading but the voltage drop across the probe leads makes the regulated light draw a higher current.
    Of course the effect of the high probe lead resistance gets worse with pulsed currents.
    The test leads is probable part of the reason.

    I have been testing some leads, switches and dmm's:
    JetBeam M2S Tailcap 70 mohm
    ThruNite TN11 Tailcap 85 mohm
    4Sevens Quark X AA2 Tailcap 82 mohm
    Fluke 289 10A range 33 mohm
    Fluke 189 10A range 55 mohm
    Fluke 179 10A range 35 mohm
    Vichy VC99 20A range 48 mohm
    Best DT9205A 20A range 18 mohm
    Fluke test lead (x1) 38 mohm
    Fluke test lead (x1) 51 mohm
    No name test lead (x1) 257 mohm
    No name 10A test lead (x1) 22 mohm

    Doing a test with 10A current and measuring the voltage from test probe tip to test probe tip:

    10A Tot. Res
    Fluke 289 + Fluke test lead 1.02 volt 102 mohm
    Fluke 189 + Fluke test lead 1.16 volt 116 mohm
    Fluke 179 + Fluke test lead 0.97 volt 97 mohm
    Best DT9205A + No name 10A test lead 0.59 volt 59 mohm
    The connection resistance from test probe tip to current source is not included.
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  15. #135
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    Default Re: Simple guide to using a DMM for measurements

    so the ZTS battery tester (the one that supports 3.7V li-ions) can do protected cells fine?
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  16. #136
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by tobrien View Post
    so the ZTS battery tester (the one that supports 3.7V li-ions) can do protected cells fine?
    Yes, there is no difference between a protected and unprotected cell in this regards.
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by HKJ View Post
    Yes, there is no difference between a protected and unprotected cell in this regards.
    oh okay, thank you! I had been misinformed in the past that the protection circuits kept those cells from being accurately tested by the pulse load.
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  18. #138
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    Default Re: Simple guide to using a DMM for measurements

    I see that many of you ask why some multimeters do not display zero.
    For TrueRMS meters this is normal. They will not display zero, it's about how the processor makes the measurement.
    On Flukes seen here: 87, 179, 189, etc, calibration manual tells you which value is the calibration check on each scale. Eg: a Fluke 189 that has 5.0000 on it's input and reads between 4.9997 and 5.0023 then it's in spec. Next value is ten times the first one, in this case 50V and 500V DC.
    Good probes are below 0.1ohms each. Cheap chinese one are higher than that.
    Measurement of very low resistance can be done conveniently with an AC ohmmeter, or ESR meter.

  19. #139
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    Default Re: Simple guide to using a DMM for measurements

    I want to check the open voltage of my battery charger, and I think this is what you call it when its plugged in and no battery installed. [Sorry, not much electrical knowledge]
    My charger is labled at 4.2V output. Do I simply plug it in and attach each DMM probe [auto range set to AC V?] to the pos. and neg. sides of one channel?
    When I did the above I get a reading of .027V?? on the auto range setting.

    Does this make sence?

  20. #140
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    Default Re: Simple guide to using a DMM for measurements

    My DMM set on DC reads 4.87v off my WF-139 charger.

  21. #141
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by loquutis79 View Post
    I want to check the open voltage of my battery charger, and I think this is what you call it when its plugged in and no battery installed. [Sorry, not much electrical knowledge]
    My charger is labled at 4.2V output. Do I simply plug it in and attach each DMM probe [auto range set to AC V?] to the pos. and neg. sides of one channel?
    When I did the above I get a reading of .027V?? on the auto range setting.

    Does this make sence?
    Evert thing except the AC V part makes sense, try using DC V.

    But the open voltage does not say much about anything, the charger is electronically controlled and the open voltage might be above or below 4.2 volt, depending on how the electronic does the controlling.
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  22. #142
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    Default Re: Simple guide to using a DMM for measurements

    That makes more sence now. Told you I know little about electrical stuff :], but willing to learn.

    OK, now I get 4.2 from both channels.

    Just trying to learn as much as I can, and like to re produce some of the tests I see here on the site. While waiting for a Pila charger for my 18650's I am using an Ultrafire WF139 [don't throw anything at me!], and as there are so many negitive posts I want to check things out where I can.


    Thanks for the supper fast replies from you both. Now I can tell the wife that its not just me who spends weekend mornings reading about flashlight stuff.

  23. #143
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    Default Re: Simple guide to using a DMM for measurements

    So what I did next was to check voltage during testing. I did the tin foil at both ends of the 18650 while in the charger and attached the DMM leads to each side.
    As I knew the batteries were fully charged just last night, minus a bit of playing on turbo after that, I knew that it should not take long to light up the green lights on the WF139.
    So I watched for the few minutes until the light changed and what I saw was the following:
    1st -red light = charging. 4.21V-4.24V during this stage.
    2nd-green light = full charge. DMM jumped right to 4.59V
    I left it on only for a couple of minutes and then pulled the plug.
    Results = hurry up with the Pila charger order??
    Or did I miss something here also. It that an viable test?

  24. #144
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by loquutis79 View Post
    2nd-green light = full charge. DMM jumped right to 4.59V
    I left it on only for a couple of minutes and then pulled the plug.
    Results = hurry up with the Pila charger order??
    Or did I miss something here also. It that an viable test?
    Do not worry to much about the voltage, that was because the over charge protection in the battery tripped. The charger would have stopped soon enough if it had not tripped. The "problem" with the WF-139 is that it measures the voltage with the current turned off and that means it goes above 4.2 volt with the current on (The current on/off is to fast to reliable measure with a DMM).

    I had the same happen when I tested the WF-139.
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  25. #145

    Default Re: Simple guide to using a DMM for measurements

    Hi HKJ, can you recommend a Fluke DMM mainly to test and check batterries voltages and Mah?

  26. #146
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    Default Re: Simple guide to using a DMM for measurements

    A DMM isn't any use for measuring mAh (battery capacity), unless you use it to make repeated measurements of cell voltage as a cell or battery is discharged at a known current.
    Last edited by uk_caver; 01-20-2013 at 09:56 AM.

  27. #147
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by rjking View Post
    Hi HKJ, can you recommend a Fluke DMM mainly to test and check batterries voltages and Mah?
    Measuring mAh is not something you can just do with a DMM, a hobby charger is much better for it.

    I often use a Fluke 179 DMM for various tasks, but for just checking batteries it is way to expensive, a Fluke 115 would do for that.
    The 115 has a 6000 scale, i.e. you will get battery voltage with 3 decimal digits, but the DMM is missing the low current ranges and cannot be used to measure low modes current draw and standby current with.
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  28. #148

    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by uk_caver View Post
    A DMM isn't any use for measuring mAh (battery capacity), unless you use it to make repeated measurements of cell voltage as a cell or battery is discharged at a known current.
    Quote Originally Posted by HKJ View Post
    Measuring mAh is not something you can just do with a DMM, a hobby charger is much better for it.

    I often use a Fluke 179 DMM for various tasks, but for just checking batteries it is way to expensive, a Fluke 115 would do for that.
    The 115 has a 6000 scale, i.e. you will get battery voltage with 3 decimal digits, but the DMM is missing the low current ranges and cannot be used to measure low modes current draw and standby current with.
    Oh okay. So the only way I can make sure that i'm putting 2 x CR 123 or 2 x 18650 with similar capacity level is by checking on their voltage then, is that correct? Man, that Fluke 115 is way too expensive. Thought, there's something half the cost.

  29. #149
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    Default Re: Simple guide to using a DMM for measurements

    Quote Originally Posted by rjking View Post
    Oh okay. So the only way I can make sure that i'm putting 2 x CR 123 or 2 x 18650 with similar capacity level is by checking on their voltage then, is that correct?
    Yes.

    Quote Originally Posted by rjking View Post
    Man, that Fluke 115 is way too expensive. Thought, there's something half the cost.
    Fluke is rather expensive.
    For checking batteries just about any cheap DMM can be used, but many cheap DMM's shows a wrong value when the batteries are running low.
    If you want something more than a cheap DMM, then a good DMM for the price is UNI-T UT61E.

    You can also get a "cheap" Fluke (17B), but it is only sold in China (You can find it on Ebay). It looks like a decent DMM.
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  30. #150
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    Default Re: Simple guide to using a DMM for measurements

    So, I've read your guide, but I'm none the wiser.

    Nothing at all to do with the guide, it's me - I need to read things over and over again before it sinks in.

    I'm not very savvy with electronics either but if I read it a few times and keep referring back to it when needed then I'm sure I'll be ok.

    My multimeter came with a little booklet but only gives specs and isn't a guide to how to use it.

    I've only ever used it to measure that voltage is present but now I can refer to your guide, I'll be able to use it correctly.

    Many thanks.

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