[Open_electroporator] recommendations after John Griessen's lame pulser design ideas

NeonJohn jgd at neon-john.com
Wed Mar 19 20:03:40 UTC 2014



On 03/19/2014 11:08 AM, John Griessen wrote:
> On 03/18/2014 07:45 PM, TQ Hirsch wrote:
>> world's only programamble waveform (not just programmable pulse)
>> electroporator.
> 
> How would you make it low noise though?  HV and square pulses ==> radio
> waves.
> 
> The reason for keeping it simple in generating
> smooth rise and fall pulses is too keep radiated emissions down and
> because that's
> all anyone has used experimentally so far, and how would the bugs tell
> the difference?

Dang, you're quick to jump to conclusions.  And arbitrary waveform
generator makes whatever waveform you want.  Perfect sine waves.  Ripply
DC.  Straight DC.  Whatever.

Another reason to go with an Arb generator is that you don't know what
the effects of waveform have on what you're trying to achieve.  I know
that waveform has a HUGE difference with TENS.

> The the trigger pulse is
> safely isolated from the deadly HV,
> and the optical signals and DC power go through tiny  holes, letting
> tiny amounts of RF energy out.

Ummm, the kind of voltage and current that's been discussed so far
certainly isn't deadly.  Maybe make you hurt yourself but not deadly.
> 
> I imagine an electroporator box with a slide out safety insulating
> section for cuvette
> that is 2cm x 7cm x 11cm of machined white plastic -- the Faraday cage
> needs to be out of sight under that.
> A hand wound 20:1 transformer will fit easily in that envelope.  Hand
> winding means it can be made of
> silicone insulated HV wire, and so be part of the isolation

Way overboard.  We wind our induction heater transformers, which serve
as the life safety barrier for the machine, using sleeved enameled Litz
wire.  (Litz wire is not necessary in this application.) Two layers of
fish paper go between the primary and secondary with a layer of
non-adhesive fiberglass tape in between. The secondary is wound with
large sleeved Litz wire.  Then the transformer is VPI'd in 100% solids
dielectric epoxy varnish and baked.

The siliconized fiberglass sleeving has a 3000 volt rating by itself.
It, the fiberglass tape and the fish paper soak up the epoxy varnish to
acquire even more dielectric strength.

The resulting transformer shows infinite resistance between primary and
secondary at 2500 volts using a digital megger.  Every transformer is
tested for a 2 minute withstand.  Random samples are pulled and
subjected to 5kV overnight (12 hours).  It must pass no current after
that soak.

As important, the transformer only has about 10pF of capacitance between
the primary and secondary.  Inter-winding capacitance lets AC "leakage"
through even when the dielectric is perfect so I designed the
transformer for minimal capacitance, both inter-winding and
winding-to-ground.

> 
> Using a flyback inductor or transformer gives you a huge low noise
> advantage over using
> a HV switch.  The switch is on the low side of the transformer, or
> between the inductor and
> ground.  You can add snubber components to shape the pulse to be not so
> fast/hard edged,
> (which is an RF generator), and you keep the voltage down at the
> switching transistors
> if a transformer is used.  That makes parts cost less and having bigger
> safety margin possible.

I suggest two things.  1) get yourself a spectrum analyzer and gain some
experience and 2) call the FCC to find out what Type classification this
device falls under.  I suspect that it falls under Type 18 like our
induction heater does.

Type 18 is for devices that are not intentional radiators but as an
inherent characteristic of their function do radiate.  The levels are
unregulated.  All we have to do with our induction heaters is put a
blurb on the nameplate that it conforms to Type 18.  No testing necessary.

If you're worried about radiated energy affecting other instruments,
then I suggest you get that spectrum analyzer and prowl around an
existing lab.  You'll find a whole mish-mash of hash.  AAS and MS are
the worst.  Instruments with servos and steppers are right up there.

My approach to the output would be to have the arb waveform generator
drive a Class D digital amplifier to the requisite voltage.  I'd run the
carrier at about 400kHz (at least 10 times the highest frequency output
desired).  The carrier is removed from the output by a simple 1 pole LC
filter.

I designed and built my 100 watt/channel Class D stereo amp (on a PCB
about the size of a playing card) so I'm quite familiar with this
technology.  There are single chip solutions.

If the result is a high voltage arbitrary waveform generator then it
would have many applications other than just electroporation.  If the
goal is to imitate TAPR and form a non-profit to sell gadgets then this
would be the way to go.

John


-- 
John DeArmond
Tellico Plains, Occupied TN
http://www.fluxeon.com      <-- THE source for induction heaters
http://www.neon-john.com    <-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77
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