Component tester for varistors - Page 1
Forum section: electronics / testgear

author: Traceless
author_rank: Frequent Contributor
timestamp: January 09, 2023, 07:22:37 pm
content: Hey everyone, does anyone know if there is a component tester that can deal with varistors? I have one of those genecric el-cheapo-ones but it detects a capacitor instead of a varistor. Obviously for a varistor a voltage/resistance plot would be interesting, similar to what the Peak Atlas DCA75 Pro can do for transistors.

author: Greybeard
author_rank: Frequent Contributor
timestamp: January 09, 2023, 08:44:24 pm
content: For I-V plots you can use a curve tracer with suitable maximum test voltage, for example Tektronix 576/577/370...https://w140.com/tekwiki/#Curve_Tracershttps://vintagetek.org/curve-tracers/

author: Traceless
author_rank: Frequent Contributor
timestamp: January 09, 2023, 09:07:47 pm
content: Curve tracers are super interesting, ever since I saw them on Curious Marc's channel for the first time. For some reason they seem to have become "unfashionable". It seems they are no longer produced. I've looked around for used ones but they seem to be in pretty bad shape, super expensive or both. It would be nice if one could upgrade a modern DSO to operate as a curve tracer.

author: Ian.M
author_rank: Super Contributor
timestamp: January 09, 2023, 09:41:02 pm
content: Many DSOs make fairly lousy display devices for a curve tracer - for three terminal active components, one often needs to step one parameter to display a family of curves on the screen, which was reasonably simple to display on a CRO in XY mode, if each curve could be swept fast enough for phosphor persistence to eliminate flicker, but on a DSO the trace intensity is usually *NOT* related to the sweep speed so the fast retrace from the end of one curve to the start of the next becomes visible. *IF* the scope has a Z (intensity) input, the curve tracer can be designed to provide a blanking pulse to eliminate this problem, but DSOs with Z inputs are fairly rare and typically expensive.OTOH Arduinos are dirt cheap, and its fairly simple to hook a couple of DACs and >12 bit ADCs (with PGAs so they can range shift) to one. That also brings the benefit of being able to do low duty cycle pulsed measurements e.g. turn on for one ms in a second so the effect of self-heating of the device under test can be minimised, so if I was 'rolling my own' curve tracer and I wanted something better than the classic 'Octopus' type (orvariationsof it), I'd almost certainly go for an Arduino based one, logging to the bench PC for display and analysis.

author: Whitefoot
author_rank: Contributor
timestamp: January 09, 2023, 09:52:23 pm
content: A power supply which develops at least the breakdown voltage of the varistor is needed. Connect the varistor to the power supply thru a resistor to limit current. Connect a voltmeter across the varistor to measure when it reaches breakdown. Raise voltage carefully to avoid excessive current.An old capacitor tester which does leakage testing can be used. The varistor is essentially open until breakdown voltage is reached, then it begins to conduct which looks like leakage.

author: threephase
author_rank: Regular Contributor
timestamp: January 09, 2023, 10:56:06 pm
content: An insulation tester with a ramp function can be used to test a varistor.Keysight have now discontinued their 1450/1460 series that did this, but you may be able to get one second hand or old stock. This worked up to 1000V.There are other options at higher test voltage, but the prices obviously go up considerably.

author: DavidKo
author_rank: Frequent Contributor
timestamp: January 11, 2023, 06:26:47 am
content: In your case you can use the scope in X-Y mode. Use AC voltage on one axis and voltage from shunt resistor on another. You will need some current limitation, not to burn your varistor.Curve trace is an overkill for such a application and mostly useless these days, since mostly you want to have digital data and curve tracers uses the luminophore to "store" the information. You can use also SMU or PS+DMM driven from computer or by hand. For component testing like transistors 2 SMUs is equivalent solution and fully digital.I have found in the past the SW for Keithley 23X and 24XX that isfreeware for home use.