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Oscillator coil with common wires?
Oscillator coil with common wires?
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Old 9th July 2019, 04:46 PM   #1
PhantomBox is offline PhantomBox  Venezuela
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Default Oscillator coil with common wires?

Hi.
I want build an ESR meter from scratch.
I came across a tutorial on
Simple ESR Meter Circuit | Homemade Circuit Projects
where it says that "The transformer is built over any ferrite ring, using any thin magnet wire with the shown number of turns". (20 turns on one side and 5 turns on the other).
I took out an induction coil from a scrapped computer PSU, unturned the wires from the ferrite ring and put them back on with the indicated number of turns. Then I checked it for continuity and both coils were shorted. The isolating enamel had broken off the wire somewhere...
Then I went the easiest way and pulled to wires from a balanced cable (like the ones used in i.e. audio consoles) and wrapped these around the ferrite ring. I haven't installed this "component" into the circuit, yet.
Would it work?
Is it possible to paint the original copper wire (the one with broken off isolation) with fingernail lacquer?

Thanks for you replies.
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Old 9th July 2019, 04:50 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by PhantomBox View Post
I took out an induction coil from a scrapped computer PSU, unturned the wires
from the ferrite ring and put them back on with the indicated number of turns.
Then I checked it for continuity and both coils were shorted.
You can just use standard insulated wire instead.
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Old 9th July 2019, 05:07 PM   #3
PhantomBox is offline PhantomBox  Venezuela
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Thanks a lot for the tip.
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Old 9th July 2019, 08:34 PM   #4
Elvee is offline Elvee  Belgium
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The advice Rayma gave you is good, if you want to go on with this particular project.
The information given on that site is, let's say, weak: the first circuit will definitely not work, and you will be lucky if the one with the opamp does: operating a 741 on 5V is asking for trouble, and the statement "any ferrite ring will work" seems optimistic.

I can understand that you have difficulties sourcing components, but if possible, you should look for a better, more deterministic alternative.
I think that equally cheap, yet half-workable alternatives exist.
None will actually measure the ESR, but the magnitude of the impedance should be sufficient for basic troubleshooting purposes
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Old 9th July 2019, 08:46 PM   #5
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by PhantomBox View Post
"The transformer is built over any ferrite ring, using any thin magnet wire with the shown number of turns". (20 turns on one side and 5 turns on the other).
I took out an induction coil from a scrapped computer PSU, unturned the wires from the ferrite ring and put them back on with the indicated number of turns. Then I checked it for continuity and both coils were shorted.
OF COURSE they will read "shorted".
Resistance of such a short piece of wire (10cm or less) is, say, 0.01 ohm or so.

ANY wire that short will measure the same, no matter what the insulation.


Quote:
The isolating enamel had broken off the wire somewhere...
No it has not

EDIT:

Just checked the ESR meter project.

It has gross errors which make me doubt its effectiveness or even that it works at all.

such as:

Click the image to open in full size.

It rectifies 12VAC, applies the resultant DC voltage to capacitor and (tries to) measure DC current through it

Of course, capacitor will charge to peak voltage and stay there; so an initial (quite high but very short) current peak, then nothing.
Ok, maybe a few uA loss.
How/Why would that give any ESR indication at all is beyond me.

The application circuit
Click the image to open in full size.
does slightly better (at least in theory) by applying "high frequency audio" to capacitor and measuring current through it , as voltage developed across a 10 ohm resistor.

Nice in theory, terrible implementation:

* waveform is unknown, although being a relaxation oscillator (sort of) waveform is guaranteed to be wonky.
* voltage is also known, but because of the inductive load I expect somewhat high peaks, definitely higher than 5V, at least unloaded.
* oscillator drives capacitor straight up; not sure it will keep oscillating under such a heavy load (tens of ohms)
* the meter rectifier is wrong, as is it´s a half wave rectifier and the second diode does nothing.
Unidirectional current will charge .1uF capacitor to some peak voltage and stay there, being slooowly discharged by the meter.
Second diode should be moved to the left of the first one, so we have a full wave doubler/rectifier.

A minor matter: describing the Op Amp as:
Quote:
An opamp can also be seen attached with the above low voltage high frequency feed and is configured as a current amplifier.
while it actually is an inverting voltage amplifier.

Oh well
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Last edited by JMFahey; 9th July 2019 at 09:16 PM.
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Old 9th July 2019, 09:22 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by Elvee View Post
the first circuit will definitely not work, and you will be lucky if the one
with the opamp does: operating a 741 on 5V is asking for trouble
The 741 is rated for 20V minimum, not 5V. I would use a 5V op amp.
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Old 9th July 2019, 11:04 PM   #7
ubergeeknz is offline ubergeeknz  New Zealand
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Quote:
Originally Posted by Elvee View Post
operating a 741 on 5V is asking for trouble
Operating a 741 full stop is asking for trouble Oscillator coil with common wires?
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Old 9th July 2019, 11:55 PM   #8
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by rayma View Post
The 741 is rated for 20V minimum, not 5V. I would use a 5V op amp.
741 Op Amps were for decades the mainstay for 9V battery operated pedals (as in MXR Distortion Plus , Phasers, Equalizers, and countless others) .
Click the image to open in full size.
Maybe an "undocumented feature" but valid and widely known (and used).
That said, 5V operation IS way too low.
But don´t worry , clearly circuit designer never ever built, let alone tested it
Quote:
Operating a 741 full stop is asking for trouble
Only a geek would think that.
Oh .... wait !!!!

You should read some Audio History: 741 was a Godsend when it appeared.
Usable everywhere, specially in Instrumentation but so flexible that it could also be used in Audio,although not specifically designed for it.

Of course, the simplest Mathematical operation is multiplying by a fixed number, and in the Audio realm it means "amplification"; the most trivial application.

Real Pro Audio stuff was designed around it, from complex Graphic and Parametric equalizers to BBC issued Power amplifiers (HH amps) to Mic Preamps to you-name-it .

Of course, and that was to be expected, Technology advanced and it was surpassed by others ,,, many years later that is.

As of the application shown above, 47X amplification to drive a meter, it´s way more than adequate.
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Old 10th July 2019, 12:37 AM   #9
ubergeeknz is offline ubergeeknz  New Zealand
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Quote:
Originally Posted by JMFahey View Post



Only a geek would think that.

Oh .... wait !!!!



You should read some Audio History: 741 was a Godsend when it appeared.
Oh sure and I played with them back in the 80s since it's what I had on hand... But they have problems and there are much better opamps available these days. Sure if a 741 is all you can lay hands on, it might do. But why suffer when there are much better options cheaply and easily available...
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Old 10th July 2019, 03:49 AM   #10
PhantomBox is offline PhantomBox  Venezuela
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The 741 is not the only opamp I have on hand. I also have several NE5534, OPA134, TL071, 2003P (all sigle opamps). Which one would you suggest?
When I first saw the 5V in order to operate an LM741, it sounded funny to me, too.
I could rise the voltage to 9VDC, but I have no clue as to what to consider, either in the circuit as well as the ESR calculations goes.
What if I use the original copper wire that I took of the ferrite ring and apply some thick nail polish? That is the next best thing I have on hand for this purpose.
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