Author Topic: What about home made (ESR) Meter ? (Read 69472 times)

Kiriakos-GR · « **on:** August 15, 2011, 11:26:25 pm »

I just found one video about a home made (ESR) Meter.

The web page about it is here.
http://ludens.cl/Electron/esr/esr.html

I am trying to understand if the idea about getting fooled from an damaged capacitor,
is still on, when we use the latest and greatest capacitor testers found on the most modern and expensive DMM ?

ejeffrey · « **Reply #1 on:** August 16, 2011, 08:50:56 am »

The most common form of degradation of electrolytic capacitor is by increasing series resistance. A capacitance meter doesn't measure this -- it measure only the reactive/capacitive part of the impedance. It isn't that the capacitance meter is malfunctioning or getting fooled, it just isn't measuring what you need to know. For a full measurement you want an LCR meter that can measure both the capacitance and the ESR/Q/dissipation factor (which are all equivalent) at a selectable frequency. A simple ESR meter is a lot easier to build and is effective at identifying bad devices.

Balaur · « **Reply #2 on:** August 16, 2011, 02:02:14 pm »

Quote from: Kiriakos-GR on August 15, 2011, 11:26:25 pm

The web page about it is here.
http://ludens.cl/Electron/esr/esr.html

I am trying to understand if the idea about getting fooled from an damaged capacitor,
is still on, when we use the latest and greatest capacitor testers found on the most modern and expensive DMM ?

Yassou Kiriakos,

This is exactly the same schematics I've used myself. When I'll get home I'll put a picture eventually.

I've replaced the internal board of a 8 euros analog multimeter with my board while taking care of re-using the selector button for on/off; measured the indications while using a series of low-value resistors and changed the original scale with a custom design (as shown) to be able to read accurately.

Works nicely enough for my needs and it was able to provide a surprisingly useful service.

One drawback of this particular implementation is that the working frequency is a fixed 50KHz, while a more sophisticated approach could be to use several choices up to 100KHz maybe.

Cheers,
Dan

Kiriakos-GR · « **Reply #3 on:** August 16, 2011, 10:00:13 pm »

Hi Balaur

Thanks for the picture about the analogue meter.
Yes the idea about the conversion of one cheap analogue multimeter looks fantastic smart !!

No way to use the body of my own analogue Metrawatt for a such a project, but I will find something in the way.

I would love to see all the details of your project, and mostly to see what version of transformer you had find for it.

Balaur · « **Reply #4 on:** August 16, 2011, 11:19:02 pm »

Hello Kiriakos,

Thank you for your interest.

Here are some details about my implementation.

I have found a Mastech M1015B in my local home improvement store for about 8 euros or so. The donor provided the shell, the microampere meter, the full-scale adjustment potentiometer and the selector knob.

I had tried to wound my own transformer but I didn't had enough of the correct wire gauge at hand. The transformer you see in the picture is retrieved as is from a defective computer switching supply. The turn ratio is a bit different and I had to modify the R8 value to avoid saturation.

The galvanometer is a 150uA or so. I've reused the original ohm adjust pot as a full-scale (0 ohm) pot.

The galvanometer display is made by myself. I've measured the deflection for a few resistor values (this is where your resistor box could have come in handy) and used the Galva software to design a new replacement panel that I've laminated and cut to size.

The PCB is a one-side job (with only two wires). The selector knob is used to power on/off the meter. I had to measure the size, the adjustment and selector positions to ensure the good fit. It worked out nicely in the end.

Power is provided by a 9v battery that fits in the original AA battery after some modding.

Cheers,
Dan

Kiriakos-GR · « **Reply #5 on:** August 17, 2011, 12:26:55 am »

Great work the least that I can say !!

What is the value of the C4 ?
And the C8 ? does not look clearly

w2aew · « **Reply #6 on:** August 17, 2011, 06:10:09 am »

For what it's worth - I also have a video of the ESR meter that I built several years ago. Here's the link. It's not as nice looking as the one at the head of this thread, but it works well...

Balaur · « **Reply #7 on:** August 17, 2011, 08:01:35 am »

Quote from: Kiriakos-GR on August 17, 2011, 12:26:55 am

Great work the least that I can say !!

What is the value of the C4 ?
And the C8 ? does not look clearly

Thanks!

C4 is a 10uF, C8 is a 100nF.

Cheers

ejeffrey · « **Reply #8 on:** August 17, 2011, 08:40:38 am »

Quote from: Balaur on August 16, 2011, 02:02:14 pm

One drawback of this particular implementation is that the working frequency is a fixed 50KHz, while a more sophisticated approach could be to use several choices up to 100KHz maybe.

If you want do that, I think it is better to implement a full LCR meter. A fixed frequency is sufficient to test the vast majority of electrolytic capacitors you will run across. Maybe a simple thing to do would be to put a potentiometer to set the frequency roughly, and you can just see if the ESR varies with frequency. At the low end, the capacitor's capacitance will start to affect the reading, and at the high end maybe the ESL will be a problem but there should be a very broad minimum for properly functioning capacitors.

With a proper LCR meter you can measure separately the ESR and C at any given frequency, so you can properly measure the low frequency behavior as well.

Kiriakos-GR · « **Reply #9 on:** August 17, 2011, 02:26:10 pm »

It looks that many started to use the word " frequency behavior "

and this had born in my head some extra question marks.

Questions :
The correct Frequency ( for testing )has to do with the type of the capacitor ? ( electrolytic tandalium ceramic )
OR
the high frequency ( 150KHz) can tell if the capacitor are totally healthy for usage in high ripple situations like Pulsing PSU ?

And the Chery in the pie

The one who does analogue TV repairs , does it have the same needs about the LCR testing Frequency,
with some one who does exclusively repairs on Pulsing PSU ?

Balaur · « **Reply #10 on:** August 17, 2011, 04:15:49 pm »

Ideally, any ESR readings at a given frequency should be corrected by removing the expected reactance, according to the cap value and the working frequency.

The kind of simple ESR meters that we are discussing rely on the assumption that the reactance of the cap is negligible wrt. the ESR at the current working frequency. To fulfill this expectation, the working frequency and the cap value should be high enough. Or, the operator could correct the value by using pre-computed tables or additional scales.
A more sophisticated approach should consists in measuring the cap value, computing the reactance and deducting the ESR.

As an example, a 10 uF cap @ 100 KHz frequency has a 0.159 Ohms reactance. Good ESR expectations for common aluminium caps are in the range of 0.1-5 Ohms.

Low ESR electrolytic caps (both aluminium and tantalum-based) are available. Ceramics have a very low ESR (<0.01).

The choice of the working frequency is indeed dependent of the required application. Electrolytic caps are usually used with low (<a few hundreds KHz) applications. A practical 100 KHz frequency for a ESR seems reasonable for most cases, including checking capacitors used in switching PSUs and TV repairs.

I would guess that a higher working frequency for measuring the ceramic capacitors could be useful in order to minimize the reactance. However, I haven't really seen very high frequency (i.e. >> 150 KHz) ESR meters.

Kiriakos-GR · « **Reply #11 on:** August 17, 2011, 05:45:17 pm »

Thanks Balaur

I will start working on this new project about making my own home made (ESR) Meter,
in few days from now, my bench space is currently occupied.

Due the fact that I am currently working on a B&O TV set, I had the chance to check about 60 electrolytic capacitors,
I discovered that the small ones like 0.47uF to 10uF, are the most " sensitive group " about indicating a damaged.
The Agilent DMM U1272 did a great work, and even if it rared at 10.000 uF it managed to measure up to 11.200 uF at easy.

One last general question , due the fact that I own one tone generator that it has a square wave output up to 25KHz,
is there any way, to work out with it , in combination with a DMM and get similar readings , like to was an dedicated ESR meter ?

ejeffrey · « **Reply #12 on:** August 17, 2011, 06:18:42 pm »

Just apply your tone generator and measure RMS voltage and current with two meters. Volts/amps = ohms.

alm · « **Reply #13 on:** August 17, 2011, 08:27:33 pm »

Watch the AC current bandwidth of your meter if you do this, it's often less than the AC voltage BW. Especially if you use a square wave, but if you measure current, you might as well use a sine. Putting a resistor in series seems like the obvious solution to me, but I haven't researched ESR meters. There's a fair bit of documentation about DIY ESR meters, some methods are more accurate than others.

ejeffrey · « **Reply #14 on:** August 17, 2011, 09:10:43 pm »

I happen to know that Kiriakos has a meter that will read out to 100 kHz on volts and amps

A series resistor is a good idea in any case. The tone generator is not designed to drive such a low impedance -- the capacitor is essentially a short circuit at this frequency. I don't know how small a series resistor you can get away with, it will depend on your tone generators output impedance. Probably either 600 ohm or 50 ohm. With 600 ohm the voltage drop across your capacitor will only be a few millivolts per ohm of ESR, which may limit your resolution. With a 50 ohm function generator you should have no problem.

alm · « **Reply #15 on:** August 17, 2011, 10:08:13 pm »

Quote from: ejeffrey on August 17, 2011, 09:10:43 pm

I happen to know that Kiriakos has a meter that will read out to 100 kHz on volts and amps

Which meter? Few handhelds have 100kHz ACI bandwidth.

Kiriakos-GR · « **Reply #16 on:** August 17, 2011, 11:51:46 pm »

True I can do 100kHz on ACV, but only 2kHz at ACI .

I bet that my reply helped Alm to not had a hart attack .. LOL

Thanks for all the suggestions.

I will share my results as soon I run few tests.

Conrad Hoffman · « **Reply #17 on:** August 20, 2011, 04:12:50 am »

Just some armchair thoughts on the matter-

ESR meters are used on caps that fail, and that would mostly be electrolytics of a few uF and higher. Thus a fixed frequency of 50 or so kHz seems fine. Almost any cap one would be suspicious about would be essentially a short circuit at that frequency. For the service person an ESR meter makes a lot of sense.

That said I prefer a proper LCR meter, but not the common types built into DVMs and such. What I want is a proper LCR meter that will give me dissipation factor (DF) and Q (1/DF). Dissipation factor tells me how much energy I got back out for what I put in on each cycle.

Further, many commen meters use the series capacitance model, and that can totally mislead you with defective caps if you're not paying attention. A cap with high dissipation can give you an artificially high capacitance reading- the bad cap looks good. If the meter doesn't read dissipation, it's pretty much useless except for sorting parts by value.

When in doubt, the parallel capacitance model makes a lot more sense. You'll see high dissipation combined with a low capacitance reading, which is what you'd expect from a bad cap. There's nothing wrong with the series model or the meter, it's just how the math works.

I've got some useful capacitance utilities and articles on my site at http://www.conradhoffman.com

Kiriakos-GR · « **Reply #18 on:** October 04, 2011, 01:27:14 am »

Ok got my spare parts in hand, and even made a hand made transformer ,
about the transformer I did my best because I had to use used parts.

The ferrite transformers found in PC PSU, its almost impossible to open them up and rewired them.
Mostly because the ferrite are glued, and if you use force the ferrite breaks apart.
Even so I did all my hokes-pokes, and managed to open it up.

My first attempt will be to replicate the primary thread link.
Wish me luck.

eliocor · « **Reply #19 on:** October 04, 2011, 08:11:20 am »

Quote from: Kiriakos-GR on October 04, 2011, 01:27:14 am

[...] The ferrite transformers found in PC PSU, its almost impossible to open them up and rewired them.
Mostly because the ferrite are glued, and if you use force the ferrite breaks apart. [...]

Put your transformer in boiling water for some minutes: the two ferrite parts will separate easily.

firewalker · « **Reply #20 on:** October 04, 2011, 08:45:02 am »

Sometimes I use a solution of paint removal or acetone.

Alexander.

Quote from: eliocor on October 04, 2011, 08:11:20 am

Quote from: Kiriakos-GR on October 04, 2011, 01:27:14 am
[...] The ferrite transformers found in PC PSU, its almost impossible to open them up and rewired them.
Mostly because the ferrite are glued, and if you use force the ferrite breaks apart. [...]

Put your transformer in boiling water for some minutes: the two ferrite parts will separate easily.

Kiriakos-GR · « **Reply #21 on:** October 05, 2011, 12:36:33 pm »

Thanks for the tips, If my current transformer fails, I will need probably another one ...

In one piece.

BravoV · « **Reply #22 on:** October 06, 2011, 03:25:53 am »

I know you got all your components there, just want to share another version that is using 100KHz (this is more common freq) and the best part is "NO INDUCTOR"

, also it has an internal discharge diodes (DS1 and DS2) which I think is good enough for common caps when they're still charged.

Source - > http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/index.htm

Kiriakos-GR · « **Reply #23 on:** October 06, 2011, 04:30:49 am »

Have you built this one ?
Do you have test it ?

amspire · « **Reply #24 on:** October 06, 2011, 05:10:36 am »

Inspired by Kiriakos's post, I decided it was about time I made an ESR tester too.

I had seen the circuit from BravoV, but I decided on the transformer based approach as well. The bridge circuit needs the full 9V from the battery, and it draws a fair bit of current, so you would have to re-zero the meter every time the battery volts falls.

The transformer based circuit is a lot more efficient and stable. With the regulator, it looks like it doesn't need to be zero'ed more then once.

For the transformer, I took a ferrite toroid off a dead PC motherboard, and wound it. It is only about 15mm in diameter with about 420 turns on the primary, 20 on the secondary. Works great. I will run it at 100KHz, but the transformer could do 500KHz or more easily. Maybe I will have switchable frequencies.

I went and ordered a $10 multimeter that looks like it has a decent 50uA meter movement. I will build the ESR meter into it. It has a 9V battery holder. I will probably build the ESR circuit in the space the AA cell currently occupies.

Richard


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Author Topic: What about home made (ESR) Meter ? (Read 69472 times)

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