E002 - Gigaohm Capacitor Leakage Tester - Design & Development
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- Опубликовано: 29 июн 2024
- This is my creation of a low voltage capacitor leakage tester circuit, with background info as well as schematics and function. Links to various sources of info are below. I used a tomtestkit channel as a reference to modify his build and do some further research and design mods.
RUclips - tomtestkit - TTT339 New DIY Capacitor Tester - • TTT339 New DIY Capacit...
Sprague TO-6A Capacitor Tester - bama.edebris.com/download/spr...
Sencore LC53 "Z" Meter - bama.edebris.com/download/sen...
Multisim.com ( Online SPICE tool ) - Schematic - www.multisim.com/content/qbFB...
0:00 Intro & Info
5:46 Excerpt from tomtestkit video
8:06 Thoughts on a more sensitive circuit design
11:59 Spice Modeling
20:07 Demo of Circuit
26:29 Testing some capacitors
36:44 Summary and thoughts on enclosure build 
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even non polarized caps have a ground pin. Great video, nice breadboarding work. Just subscribed. TY.
Thank you. Non-polarized caps, when made properly, should behave close to the same when the polarity is reversed, but yes, they do have a "outside foil" property to one lead that is usually best wired to the circuit's connection that is closest to the ground of a sensitive circuit (away from a tubes "grid", a transistors "base", or a MOSFET's "gate"), so it will be less likely to pick up added stray EMF radiation from other parts of that circuit or outside EMF bleed over.
Great work! may build it. Thanks
Thank you. Most of this video just elaborates the simplicity of building a circuit like this, which Tomtestkit found info for, and added to himself.
Interesting. I might experiment with a 50uA panel meter instead of a LED, and some trimpots (what/how/where to be determined) for calibration, to make a high resistance ohmmeter... BTW: @23:57 you mean 100 nanoamps, not picoamps.
Well, as far as the nano-pico, yes, I was off a few decimal's, like 3 of them. Using Multisim to check the current flow when connecting a 15G ohm resistive value to the third transistors base does give a LED indication with a picoamp current flow range, but not with the second transistors base connection. I'm going to play around with some other "indicator" config's as well, when I take a break from tinkering with other stuff. Thanks for the input!
Very interesting to see the simplicity of the test device. @220 hfe I see an amplification factor of 10,648,000 for the three transistors.
Maybe useful in a test probe for zero contact measurement.
Interesting
It is difficult with the circuit you designed to figure out that the current is because of capacitor charge or leakage resistor. To fix that you need to use an op amp to bring the stored voltage on the capacitor to the same level as the base of the transistor, using a voltage follower, then remove the the op amp and connect the capacitor to to the base of the transistor to see if there is a leakage.
Another way is to use Wheatstone bridge and compare a capacitor with a good capacitor of the same value using instrumentation amplifier.
The point of this build was, keeping it simple, low cost, low component count, and easy to build. Others have gone the route of using more components, and the device they made has a similar qualatative display and functionality to it. You can always "try your hand" at what you have suggested and share it with us as well.
Hi, thank for sharing. Do you think it's really necessary the 3 stages instead of the 2 used by the tomtestkit circuit? Basically you are getting more sensitivity in the test, isn't it?
It just increases sensitivity, if you feel that 2 transistors are sensitive enough, you can build it as you wish. Maybe using 2 transistors with a higher gain can change it to eliminate the need for a third one as well. I have found that, a lower level of leakage current/higher "parallel resistance", can be found adding the third transistor into the circuit. I had 2 - 4.7uF Tantalum caps ( 50+ years old, only had low level AC voltage applied to them) for a stereo amplifiers input coupling caps, (1 for each channel) and one indicated a leakage using the 3 transistor circuit that the other one did not have,, that did not appear with using 2 transistors. It just increases sensitivity,
this is similar to Mr. Carlsons lab's low voltage capacitor leakage tester.
Yes, as far as being a "qualitative" test device, without a calibrated indication of the actual resistance measurement it is connected to, it is. I am sure that the similarity ends there, as this requires fewer parts and effort to construct (and all of this info is and will be free), and I am hoping to construct this into a small box enclosure soon as well.
@@poormanselectronicsbench2021 i'm looking forward to see your finished capacitor leakage tester. here's a tip carlson's leakage tester would use 2N5088 or 2N5963 in darlington configuration.
@zim2493 Thanks! I will stick with what I have selected for parts, just enclose it in a box sized to hold a small board and 9V battery, of course.
Try it with with 2N2222's (the 2N3904 has 5x the leakage, don't use it).
Considering that, with "open circuit" leads, it is not creating enough leakage to light the LED, the 3904's's I used, which, are most likely counterfeit's ( I sourced them from amazon I believe), still work acceptably, AND, if for some reason they blow up due to hooking to a charged capacitor, they can be cheaply replaced as well. Anyone can feel free to modify this circuit as they choose though :) I just went the "low cost" route.