RoadTest: Cool Tools: ESR Meter, Capacitor
Evaluation Type: Test Equipment
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?:
What were the biggest problems encountered?: No issues, product works great for the intended application
This RoadTest was originally a blog about Cool Tools, but changed to a RoadTest. Originally, I had planned to make a few measurements with the device and write a short blog about the idea, but now that it is a RoadTest I planned a separate set of tests. Essentially, if I am going to give the device a rating, I feel as though it should be tested. This RoadTest is also late, for which I apologize; I was called into field operations for a month.
Figure 1 shows the PEAK atlas ESR meter. The first thing I noticed was how small it was. It’s not a bad thing – I’m just used to measurement gear being bigger. In fact, the more I used the device, the more I liked its size. The device has tones that play when you’re testing a capacitor. I never got the chance to hear the ‘bad ESR’ tone, but that could be seen as a good thing as I didn’t have a bad capacitor. On the right you can see the supplied alligator clips, which seem to have some sort of gold coating on them - probably for corrosion resistance.
Figure 1: PEAK Atlas ESR meter.
The alligator clips are connected via banana clips, which means you can remove them and put in your own set of probes. These connections are shown in Figure 2.
Figure 2: Banana plug connections on the meter.
To really show the size of the unit, here is a picture of me holding the meter while taking a measurement.
Figure 3: Holding the meter while taking a measurement.
I am a Research and Development Engineer, so I like data. First, I chose a bag of 22 uF capacitors I had lying around but did not have a part number. There were 93 capacitors in the bag and I was curious if I would get a Gaussian distribution if I measured them all … so I did. Figure 4 shows the measured distribution. The horizontal axis units are microfarads. Indeed, the distribution is Gaussian.
Figure 4: Capacitance distribution of 22 uF electrolytic capacitors. Horizontal units are microfarads.
The unit also measures ESR, hence the name ... ESR meter. So, Figure 5 shows the ESR distribution for the same set of measurements (horizontal units are ohms). It's an interesting plot, as the distribution seems to be bimodal. Bimodal distributions are usually explained by some interfering phenomenon - I wonder what would cause that in capacitor construction?
Figure 5: ESR values (ohms) for the same capacitors measured in Figure 4.
I had a bag of 39, 33 uF capacitors and tried the same experiment. Figure 6 shows the histogram for the capacitance, and Figure 7 shows the histogram for the ESR. The horizontal units are microfarads and ohms respectively.
Figure 6: Distribution for 33 uF capacitors. Horizontal units are microfarads.
Figure 7: ESR values (ohms) for the same capacitors measured in Figure 6.
Figure 8 & 9 shows the same graphs for a batch of 3.3 uF capacitors. Not great Gaussian distributions, but there is a resemblance.
Figure 8: Distribution for 3.3 uF capacitors. Horizontal units are microfarads.
Figure 9: ESR values (ohms) for the same capacitors measured in Figure 6.
At this point during testing I noticed a trend in the data I was taking, so I decided to measure the same capacitor repeatedly and see what the data looks like. Figure 10 shows the trend I had observed, which is a decreasing capacitance. Also note, the ESR had an increasing trend. I'm very curious what could be causing this.
Figure 10: 33 uF capacitor repeatedly measured (uF vs measurement number).
In a rather frank summary, the meter is good and I like it. If anyone has some insight into the cause of the distribution ‘anomalies’ I’d love for you to comment below.
Very good test report.
I wonder if you are leaving a residual charge on the capacitors after each test.
Did you short the leads together before the start of each test to make sure you were at empty charge…
As far as I know, these meters do their best to discharge the capacitor after testing and usually test using an AC signal of sorts.
I suspect what you might be seeing is a combination of temperature coefficient…
Nice Roadtest review. In addition to the temperature drift of the component, the instrument may also be experiencing some drift due to the repeated measurements. You could repeat your readings, with a…
Could the meter be sensitive to it's battery voltage? Continuous measurements may cause the battery voltage to drop too low for accurate readings, but still appear to work. Could you try an external power supply?
Can you compare the measurements in Fig. 10 with similar measurements done with an high class instrument?
In case the 2nd set of measurements gives constant results you could check what happens interlacing the 2 measurementes,supposing that the fancy instrument does not affect the capacitor values that should verify if the ESR70 does.
It is more a curiosity than an hint.
Interesting - I didn't think of that - it could indeed be a case of dielectric absorption (https://en.wikipedia.org/wiki/Dielectric_absorption) as you mentioned.
I tried the same experiment with an ESR meter that I have and I did see a slight downward tendency for the first several tests. I wonder if it might be related to the ability of electrolytics to self heal by creating an insulating surface on the plates. This would in effect create more of a dielectric layer and decrease the capacitance. I tried putting full voltage on the cap and letting it sit for a while to see if it would stabilize. This seemed to help a little but the conclusion was not definitive.
Nice Roadtest review. In addition to the temperature drift of the component, the instrument may also be experiencing some drift due to the repeated measurements. You could repeat your readings, with a delay between each reading to see if the drift diminishes (i.e. the instrument equilibrates in the delay).