I will start presenting my observations about using this specific tool, by saying that every tool despite it price and performance ability, it does work as a teacher which helping you discover a new world.
In my surprise a simple battery testing application about testing Nimh 1.2V cells from Ansmann and Sanyo Eneloop, was enough so to understand that Ansmann white papers about their cells, containing a serious mistake regarding the condition of the cell which the user should perform a battery resistance (Impedance) measurement.
Sanyo - Panasonic gives the information that battery impedance test should be performed when battery is discharged at 1V and that the End-user will evaluate the condition of the cell by comparing the impedance of the specific cell model according to specifications’ sheet.
For example at that condition the HR-4UTGA cell type is expected to measure 40mOhm or less.
And additionally the ANSMANN 2850 digital cell type it is expected to measure 30 or less according to datasheet.
The mistake which ANSMANN did in their papers is their note that the cell should be evaluated only at full charge.
My own measurements’ shown that impedance evaluation when a cell is fully charged is meaningless when performed with low cost tools, which most users will attempt to buy.
For example the use of SM8124 meter which is capable measuring from the first mOhm at it first 20 Ohm range which is suggested for cells up to 2V max, shown as insufficient to do that correctly, because the impedance measurement of eight Nimh cells shown to be in the range of 5 to 10mOhm when the meter it self it straggles to maintain an perfect zero measurement even when it test leads are well in contact to its other.
The SM8124 which I received at 12C indoor temperature is able to measure with it test leads shorted together a 3 mOhm value instead of the expected zero.
This could be due calibration setting in another temperature than my indoor, but even so when you need to evaluate so small impedance values it does seems as a problem.
Naturally you may take your measurements’ and perform manual compensation when you gather all your measurement data over a paper sheet.
By combining all facts coming from my very first experiences, now I can safely conclude that a measurement when battery is discharged at suggested level makes more sense because the battery will have it max suggested impedance value and also because the meter will perform a safe measurement by measuring a higher value at it own measuring range, such a way of performing a measurement has much less influence regarding the parameter which called as measuring uncertainty.
The practical problem here is that in order to follow the correct advice regarding those conditions for a proper measurement, you do realize that you are missing the proper equipment which will properly discharge its one cell.
My very own original planning was to purchase one advanced charger-discharger with 14 channels and with impedance measurement, at a price range of 250EUR and I was ready to move in that direction but a sudden event influenced temporarily my cash flow and that plan and in now paused.
My alternative thought was to purchase this SM8124 instead, and now I am close to believe that this was a wrong decision especially regarding Nimh evaluation at it 2V lowest range.
The second range of SM8124 is up to 20V / 2 Ohm max, and is the suggested one for Li-Po and similar chemistry of battery cells, at that range my shorted leads measurement over it display is 003 mOhm ( 3mOhm) and definably this range seems as more trusted regarding the uncertainty of measurement factor.
The third and last range of SM8124 is up to 100V/ 200mOhm, by shorting the test leads I am getting over the display a measurement of 00.1 mOhm but the meter seems totally unstable about to retain this measurement at its and every time regarding shorted test leads connection, and therefore what I do see here is a extremely poor measuring stability.
In conclusion I will say that SM8124 is a meter which works as designed but definably it can hardly operate as expected due it budget build.
It would made more sense if the manufacturer was offering three separate models which its one should have a single range so to serve with higher stability it purpose.
SM8124 is not worthless but I can not recommend it either for serious work.
SM8124 build quality internally and externally is poor to average, my opinion is that I have here a product using parts worth 10$ max and it retail price is a game that eBay sellers are involved aiming the highest price due no competition at the current time.
Thankfully even my own experiment about getting this SM8124 it was limited to 39.9 USD range, and so it was not that costly either.
Below is a set of pictures of SM8124 and of my tests.
Topic: Battery Impedance Meter SM8124 mini review (Read 21864 times)
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