[Emc-users] ESR testing [Was: Cute little machine]

[Erik Christiansen]

On an old thread; 08.05.15 05:29, Mark Wendt wrote:
> I bought a little transistor/cap tester kit from Banggood a while back, 

Having followed suit, I was disappointed today to find a new/old-stock
great fat 10,000 uF electrolytic giving an ESR reading of 0.8 ohm.
Being, at least philosophically, Scottish, I thought I'd give reforming
the dielectric a go. (My method is just to put the multimeter on ohms
range, to apply a low voltage at low current. Mine emits + on the
negative terminal in ohms mode, so reverse connection of the leads is
needed.)

When I came back later, the needle had crept up to full scale on ohms x 1,
and after briefly shorting with a screwdriver, just in case, retesting
gave an ESR of 0.03 ohms.

I don't know how typical that improvement might be, but it does show
that a capacitor oughtn't be ruled out at first glance.

Erik

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Re: [Emc-users] ESR testing [Was: Cute little machine]

[Mark Wendt]

On Thu, Sep 17, 2015 at 5:09 AM, Erik Christiansen
 wrote:
> On an old thread; 08.05.15 05:29, Mark Wendt wrote:
>> I bought a little transistor/cap tester kit from Banggood a while back,
>
> Having followed suit, I was disappointed today to find a new/old-stock
> great fat 10,000 uF electrolytic giving an ESR reading of 0.8 ohm.
> Being, at least philosophically, Scottish, I thought I'd give reforming
> the dielectric a go. (My method is just to put the multimeter on ohms
> range, to apply a low voltage at low current. Mine emits + on the
> negative terminal in ohms mode, so reverse connection of the leads is
> needed.)
>
> When I came back later, the needle had crept up to full scale on ohms x 1,
> and after briefly shorting with a screwdriver, just in case, retesting
> gave an ESR of 0.03 ohms.
>
> I don't know how typical that improvement might be, but it does show
> that a capacitor oughtn't be ruled out at first glance.
>
> Erik

I haven't checked my transistor/cap tester against a real ESR meter I
have for my bench, so I don't know how accurate it is at that.  My
electronics stuff is all packed up right now, waiting to be put in the
moving van, so I won't have a chance to play for a while.

We close on October 15th (hopefully), and then I put Washington DC in
the rear view mirror.

Mark



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Re: [Emc-users] ESR testing [Was: Cute little machine]

[Erik Christiansen]

On 17.09.15 05:54, Mark Wendt wrote:
> I haven't checked my transistor/cap tester against a real ESR meter I
> have for my bench, so I don't know how accurate it is at that.  My
> electronics stuff is all packed up right now, waiting to be put in the
> moving van, so I won't have a chance to play for a while.

For a quick reality check, I just wired a 1 ohm wirewound power resistor
in series with the cap. Now it reads 1.2 ohms. With resistor tolerance
and inductance, that's not too far off. Adding instead, a 0.02 ohm 1%
non-wirewound, the reading jumps from 0.05 to 0.17 ohm. My lead clips
are not making zero ohm connections. Just the leads and resistor reads
0.1 ohms. And yet it repeatedly gives 0.03 to 0.05 ohms for the
capacitor ESR.

There's no elaborate precision analogue circuitry in the thing, so we
can't hope for more than an approximate result. For me, it is enough
that it discriminates between 0.8 ohms and 0.05, and whether that 0.05
is really 0.03 or 0.07 is no biggie.

> We close on October 15th (hopefully), and then I put Washington DC in
> the rear view mirror.

That's the strongest reaction I've yet heard to the prospect of "The
Donald" maybe heading into town after the incumbent leaves.

Erik

-- 
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Aussie farmer: "I need my head read if I want to continue farming"
- Chris Rule cartoon in the Weekly Times, 05.08.15

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Re: [Emc-users] ESR testing [Was: Cute little machine]

[Gene Heskett]

On Thursday 17 September 2015 05:09:07 Erik Christiansen wrote:

> On an old thread; 08.05.15 05:29, Mark Wendt wrote:
> > I bought a little transistor/cap tester kit from Banggood a while
> > back,
>
> Having followed suit, I was disappointed today to find a new/old-stock
> great fat 10,000 uF electrolytic giving an ESR reading of 0.8 ohm.
> Being, at least philosophically, Scottish, I thought I'd give
> reforming the dielectric a go. (My method is just to put the
> multimeter on ohms range, to apply a low voltage at low current. Mine
> emits + on the negative terminal in ohms mode, so reverse connection
> of the leads is needed.)
>
> When I came back later, the needle had crept up to full scale on ohms
> x 1, and after briefly shorting with a screwdriver, just in case,
> retesting gave an ESR of 0.03 ohms.
>
> I don't know how typical that improvement might be, but it does show
> that a capacitor oughtn't be ruled out at first glance.
>
> Erik
>
And as a CET, and an old hand at that, thats a capacitor that would go in 
the bin Erik.  And its not open for discussion around my workbench.

The fact that you shorted it while charged with only the meters volt or 
so charge, and "fixed" it, which punches thru the foil oxides and 
restores a good but temporary connection, making that cap look good 
again, also says it will be bad again quick enough to eat your warranty 
budget.

Making a good, very low resistance connection between the external 
terminal metal, normally made out of something solderable like copper, 
and the alu foils that make up the capacitors  "plates" is a high art 
form because the alu is so reactive with the oxygen in the air we 
breath.  Throw in that it is etched chemically to increase its surface 
area 10 to 50 fold over plain alu, which increases its capacitance by 
the same factor, and you can begin to imagine the difficulty in actually 
getting a "gas tight" joint between the terminal and the alu foils.  The 
lack of that says the ESR will rise to the failure point in a relatively 
short time.  In low power stuff, the circuit will just mis-behave.  In 
higher powered situations, the heating from the ESR will eventually blow 
the caps case top open, or causing bulging of it before.

When inspecting any circuit that uses electrolytic capacitors, seeing any 
of them with bulged tops, is grounds to warm up the iron & replace them.  
They have already failed in terms of their ESR.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] ESR testing [Was: Cute little machine]

[Mark Wendt]

On Thu, Sep 17, 2015 at 8:48 AM, Erik Christiansen
 wrote:
> On 17.09.15 05:54, Mark Wendt wrote:
>> I haven't checked my transistor/cap tester against a real ESR meter I
>> have for my bench, so I don't know how accurate it is at that.  My
>> electronics stuff is all packed up right now, waiting to be put in the
>> moving van, so I won't have a chance to play for a while.
>
> For a quick reality check, I just wired a 1 ohm wirewound power resistor
> in series with the cap. Now it reads 1.2 ohms. With resistor tolerance
> and inductance, that's not too far off. Adding instead, a 0.02 ohm 1%
> non-wirewound, the reading jumps from 0.05 to 0.17 ohm. My lead clips
> are not making zero ohm connections. Just the leads and resistor reads
> 0.1 ohms. And yet it repeatedly gives 0.03 to 0.05 ohms for the
> capacitor ESR.
>
> There's no elaborate precision analogue circuitry in the thing, so we
> can't hope for more than an approximate result. For me, it is enough
> that it discriminates between 0.8 ohms and 0.05, and whether that 0.05
> is really 0.03 or 0.07 is no biggie.

Yeah, I figured that.  I bought the thing mainly for the quick and
dirty transistor/diode checking.  If I really want to get into
profiling transistors or diodes, I've got a Tek 577 Curve Tracer to do
that.  I've mainly used the tester just to get decent capacitance
readings on the cap side of the house.  I've got a really good ESR
that I use to really check electrolytics.

>
>> We close on October 15th (hopefully), and then I put Washington DC in
>> the rear view mirror.
>
> That's the strongest reaction I've yet heard to the prospect of "The
> Donald" maybe heading into town after the incumbent leaves.
>
> Erik

Eh, he couldn't do any worse than the clowns that currently occupy DC.

Mark

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Re: [Emc-users] ESR testing [Was: Cute little machine]

[Erik Christiansen]

On 17.09.15 09:39, Gene Heskett wrote:
> On Thursday 17 September 2015 05:09:07 Erik Christiansen wrote:
> The fact that you shorted it while charged with only the meters volt or 
> so charge, and "fixed" it, which punches thru the foil oxides and 
> restores a good but temporary connection, making that cap look good 
> again, also says it will be bad again quick enough to eat your warranty 
> budget.

It is reforming the dielectric which was performed. It deteriorates
during prolonged disuse, and can be regenerated by applying a low
voltage at a modest current. Discharging the capacitor was merely to
avoid risk to the tester electronics afterwards, nothing else.

OK, a weak dielectric manifests primarily as increased leakage (shunt
resistance) and susceptibility to failure at less than full voltage,
suddenly applied. The effect on series resistance is harder to qualify.

> Making a good, very low resistance connection between the external 
> terminal metal, normally made out of something solderable like copper, 
> and the alu foils that make up the capacitors  "plates" is a high art 
> form because the alu is so reactive with the oxygen in the air we 
> breath.  Throw in that it is etched chemically to increase its surface 
> area 10 to 50 fold over plain alu, which increases its capacitance by 
> the same factor, and you can begin to imagine the difficulty in actually 
> getting a "gas tight" joint between the terminal and the alu foils.

Not a lot of imagination needed. The big aluminium electrolytics I've
examined over the years had plain aluminium strip which looked to be
welded to the etched plates (prior to etching, I expect.) and also to
the terminals.

In this case, the terminals are aluminium posts, internally threaded.
The internal terminal connection, presumably also welded, isn't going to
experience oxidation, I suggest.

In any event, the resistance of an unetched oxide layer on aluminium
ought not be overestimated. Whether the mechanism is electron tunnelling
or not, the massive current which flowed through two series oxide layers
on the outside terminals, with only a volt or two, confirms at high
current what an ohmmeter shows on placing two probes on an aluminium
surface - at least an order of magnitude less than my 0.02 ohm resistor.

Most of the ESR is in the electrolyte, AIUI.

Erik

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