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PICList Thread
'Isolation Methods'
1996\12\12@001619 by Dave Mullenix

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>> > What's about a light source (light-bulb connected to AC) and some
>> > solar-cells ?  :-)
>
>Now for my own wacky idea: microwaves!  Use old uwave oven magnetron,
>transmit down waveguide (or between parabolic reflectors for that
>megavolt isolation), receive in 1/4 wave antenna and rectify using a
>swag of hot carrier diodes.
>
>Back to reality, another way of obtaining galvanically isolated supply
>is with piezoelectric 'transformers'.

Let's not forget the dynamotor: an ac motor driving a DC generator.  For
extra isolation, use a rubber belt to connect the two.

And has anybody tried an AC fan driving a windmill connected to a DC generator?

Or an AC powered Gerbil running in a wheel connected to a DC motor?

1996\12\12@013119 by John Payson

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> >Back to reality, another way of obtaining galvanically isolated supply
> >is with piezoelectric 'transformers'.
>
> Let's not forget the dynamotor: an ac motor driving a DC generator.  For
> extra isolation, use a rubber belt to connect the two.
>
> And has anybody tried an AC fan driving a windmill connected to a DC
generator?
>
> Or an AC powered Gerbil running in a wheel connected to a DC motor?

While your latter suggestions are getting a bit silly, the use of a motor/
generator setup was indeed common in some applications, especially before
the invention of good rectifiers.  In particular, many pipe organs circa
1950 or so used a motor/generator to produce the DC for the solenoids (the
same motor also provided the wind for the pipes).  Given that a decent-sized
motor was needed anyway (for the air supply) and that there weren't any good
technologies for producing 24v DC at moderate current, this was not a bad
method (interestingly, I was once practicing on such an organ when there was
a brief power failure.  The power supply switch is, I think, a latching relay
and so I was able to play through the power failure without interruption but
the organ quit about ten seconds after the power came back on!  It was only
then than I realized I had to push the "on" button again to restart the thing.

1996\12\12@021137 by Kalle Pihlajasaari

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Hi,

> > Let's not forget the dynamotor: an ac motor driving a DC generator.  For
> > extra isolation, use a rubber belt to connect the two.
>
> While your latter suggestions are getting a bit silly, the use of a motor/
> generator setup was indeed common in some applications, especially before
> the invention of good rectifiers.  In particular, many pipe organs circa

Often the Dynamotor was used in applications that worked from DC to AC.

These days our PICs and logic want low voltage DC and batteries come to
out aid, in them days there were only thermionic devices which
popularly needed some 100 .. 300V DC to work.  Dynamotors were used
in a lot of battery powered applications to step up typically 1.5V or
6V drycell batteries to 115V or 230V AC to drive mains apliances without
modification.

What was used in High voltage circuits where only low voltages were
available in DC such as in cars was another device called a vibrator
which was a can about 1" dia and 2" long that had what was mostly a
relay that would be made to cut its own power on energising so it
would buzz, mass added to the armature allowed the resonant mode of
vibration to be adjusted to 50, 60 or 400 Hz (or what you wanted
even a few kHz) and the vibrator would have some extra contacts that
could be used in a push-pull arrangement to drive a transformer with
alternating polarity.  This could be used to transform power or
signals and was how the earliest Chopper-Stabilised amplifiers
used to work at real low levels without drift as the signal was
converted to AC, then synchronously rectified (optional) that
would leave you with performance close to what we get out of a
cheap OP-AMP these days.

Cheers     *<<<-|
--
Kalle Pihlajasaari   spam_OUTkalleTakeThisOuTspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\12@032235 by John Payson

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> What was used in High voltage circuits where only low voltages were
> available in DC such as in cars was another device called a vibrator
> which was a can about 1" dia and 2" long that had what was mostly a
> relay that would be made to cut its own power on energising so it
> would buzz, mass added to the armature allowed the resonant mode of
> vibration to be adjusted to 50, 60 or 400 Hz (or what you wanted
> even a few kHz) and the vibrator would have some extra contacts that
> could be used in a push-pull arrangement to drive a transformer with
> alternating polarity.

Did the things really need precisely-tuned AC, or did they just need high
voltage?  If the latter, I'd think just using a highly-inductive relay coil
would do the trick (since its flyback energy could go to hundreds of volts).
Any idea if people ever did such nasty things?

1996\12\12@085357 by Kalle Pihlajasaari

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face
Hi,

> Did the things really need precisely-tuned AC, or did they just need high
> voltage?  If the latter, I'd think just using a highly-inductive relay coil
> would do the trick (since its flyback energy could go to hundreds of volts).
> Any idea if people ever did such nasty things?

Probably.

Cheers     *<<<-|
--
Kalle Pihlajasaari   .....kalleKILLspamspam@spam@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\12@105045 by Martin McCormick

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       Don't forget the 750-millivolt thermocouples found on
gas water heaters and furnaces.  They deliver power for decades as long as
the flame from the pilot light hits the thermocouple.  If one had four or
five thermocouples in series, there would be enough voltage to run a PIC
and other low-current logic circuits.  I don't know the current generated by
such a thermocouple, but older gas furnaces did use them to generate the
control voltage that went through the thermostat to open the solenoid valve
and turn on the main burners.  If the gas went off or a draft through the
vent sucked out the pilot flame, another little valve lost power and closed
to prevent gas from escaping when the pilot was not lit.  While this was a
very inefficient way to generate electric power, it was a case of making good
use of what was already there and that is almost as good as getting something
for free.

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group

1996\12\12@134444 by )

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Dave Mullenix wrote:
>
>>> > What's about a light source (light-bulb connected to AC) and some
>>> > solar-cells ?  :-)
>>
>>Now for my own wacky idea: microwaves!  Use old uwave oven magnetron,
>>transmit down waveguide (or between parabolic reflectors for that
>>megavolt isolation), receive in 1/4 wave antenna and rectify using a
>>swag of hot carrier diodes.
>>
>>Back to reality, another way of obtaining galvanically isolated supply
>>is with piezoelectric 'transformers'.
>
>Let's not forget the dynamotor: an ac motor driving a DC generator.  For
>extra isolation, use a rubber belt to connect the two.
>
>And has anybody tried an AC fan driving a windmill connected to a DC
>generator?
>
>Or an AC powered Gerbil running in a wheel connected to a DC motor?

Anybody know the dielectric constant for a gerbil? ;-)

1996\12\13@024138 by nigelg

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In message  <199612120811.CAA18717spamKILLspamVenus.mcs.net> .....PICLISTKILLspamspam.....MITVMA.MIT.EDU writes:
> > What was used in High voltage circuits where only low voltages were
> > available in DC such as in cars was another device called a vibrator
> > which was a can about 1" dia and 2" long that had what was mostly a
> > relay that would be made to cut its own power on energising so it
> > would buzz, mass added to the armature allowed the resonant mode of
> > vibration to be adjusted to 50, 60 or 400 Hz (or what you wanted
> > even a few kHz) and the vibrator would have some extra contacts that
> > could be used in a push-pull arrangement to drive a transformer with
> > alternating polarity.
>
> Did the things really need precisely-tuned AC, or did they just need high
> voltage?  If the latter, I'd think just using a highly-inductive relay coil
> would do the trick (since its flyback energy could go to hundreds of volts).
> Any idea if people ever did such nasty things?

They just used the relay to generate an AC square wave which was fed into the
transformer which then supplied all the required voltages in the equipment.
Although I'm not THAT! old, I do remember seeing the odd car radio that used
vibrators, and we even used to keep them in stock for repairs. As you can
probably imagine, the power consumption was horrendous.

There were two basic types, syncronous and asyncronous, the asysncronous ones
needed a rectifer to provide the secondary DC HT supply, usually a metal type,
these were normally made of selenium and smell terribly when they fail. The
syncronous types didn't require a rectifier, they had yet another set of
contacts which reversed the secondary HT winding as the primary switched. This
gave the required DC output, and was even fullwave rectified.

Nigel.

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