$5 in-circuit ESR tester (junkbox cleanout) - Page 1
Forum section: electronics / projects

author: tocsa120ls
author_rank: Regular Contributor
timestamp: January 29, 2018, 06:03:33 am
content: Hiso, we had so far:* Jay_Diddy_B's 5-transistor ESR testerhttps://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/* Dave demoed the $7 component tester that does capacitor ESR testing on the side,* there are our Chinese overlords in the $40-50 category,https://www.aliexpress.com/item/2-in-1-Digital-Auto-ranging-Capacitor-ESR-Meter-Quality-Capacitance-Tester-Internal-Resistance-Measurement-with/32635955516.html* and at the other end of the scale, the big boyshttps://www.welectron.com/Keysight-U1733C-LCR-Meterfrom $400 up to... (I did not dare look)I have a junk box (who doesn't) with stuff that I sometimes tear down for parts. There are a handful CCFL driver boards, those awful plastic-y 5V wall-warts that everybody from PRC seems to give out, projects that failed to materialize, or did well below expectations. I recently bought a reel-to-reel deck that I will be restoring, and I thought, boy, 40-year old equipment, Japanese or not, will have dried out caps. Wonder if I could cobble together a cheap-as-dirt, handheld, in-circuit ESR meter? What do you think?This was the starting pile: a 5V USB "apple" (sure) wall adapter, and a battery tester. Last I checked both cost around $1.5.Pictured are the remains of another unit, as I, the dumbass I am, accidentally deleted the first couple of pictures I took.I removed the transformer from the power adapter, and the meter from the battery meter. Then I created a circuit on a breadboard, grabbed a used BC413 transistor from the used transistor tray, a TL061 OPA (schematic's wrong), some caps and resistors, three diodes and a potentiometer. Here is the schematic:The beautiful waveform of a blocking oscillator (the diode on the base of the transistor was necessary b/c the feedback winding of the transformer gave such a big negative impulse (like -6V) that the poor BC413 decided to turn off for good. If you get a 3MHz oscillation instead of ~20-30kHz, you have the feedback winding backwards. I tested it with the ubiquitous 2n2222, it works. Basically any NPN with a 100mA collector current _should_ do.You could also argue, that because the resulting waveform has a 6-700mVeff, the "in-circuit" aspect of this is gone (if you check the x40 amplification of the opamp, I was aiming around 200mVeff. I argue the circuit I'm going to use it in doesn't give a damn(Read: never imagined that little POS transformer to be this effective.)Here is the completed circuit on a veroboard, the basic calibration is to short the two leads (the one coming from the transformer and the another going into the OPA) and turn the pot until you are in the green. Power consumption is 3mA at 4.5V supply (3xAAA)And here it is hooked to a capacitor that came from the LED lamp that is the same type, age, usage, as the one that decided to explode on me a week ago. Connecting a 1R resistor across drops the meter in the yellow, and this cap is... well.Done, also, I finally used every one of those crappy leads I had laying around.Inspiration/original idea:http://ludens.cl/Electron/esr/esr.html

author: tigr
author_rank: Regular Contributor
timestamp: January 29, 2018, 09:18:49 pm
content: Why did not you use the classical scheme?

author: tocsa120ls
author_rank: Regular Contributor
timestamp: January 30, 2018, 09:35:16 pm
content: Quote from: tigr on January 29, 2018, 09:18:49 pmToo complexand I did this as a fun project to make space my junk box. And I like how dead simple / cheap it is. This was really a 2-hour project from start to finish.The next one won't be that quick

author: tigr
author_rank: Regular Contributor
timestamp: January 31, 2018, 09:47:39 am
content: Quote from: tocsa120ls on January 30, 2018, 09:35:16 pmThe whole complexity is 3 resistors. But you can get a higher frequency up to 100kHz and reduce the resistance of 10Ohm resistors by 10-20 times, which in turn makes it possible to stretch the scale near zero.