[Open_electroporator] engineering is balance of cost and performance (was: switching PS parts)

[Nathan McCorkle]

Cool, thanks. Yeah I figured I might be way off, since it said for fax
application! I spent a good day or two readig 'The Art of Electronics'
a month or so ago, I even did some of the example math problems, maybe
I'll do that again this week. I was focusing then on diodes and
filters I think, maybe I'll see what it's got regarding high-voltage
or transients or pulses or boost circuits.

The author of the MOSFET electroporator responded to my e-mail asking
about his capacitor size and source, compared to the size of the
microwave cap that was only 1uF (when he used 5uF):
"
>Thanks for the email and interest in my previous work. You are correct
>that the capacitor in the picture is likely not the final one that I
>used for 3kV 5uF as I did go through several prototypes. I looked at my
>thesis and subsequent paper on the subject and could not find the part
>number but was not successful. I've provided links (below) to three
>student theses that continued work in the same area after I left, maybe
>they will have the part number or a picture of it. I recall the
>capacitor looking like a small metal can about the size of a pop can
>(but more rectangular). Putting several capacitors in parallel is a
>solution although there should be a place to purchase them. I was
>fortunate that there were many for me to chose from in my high voltage
>lab but do recall having difficulty searching online for them (and did
>so again now). One company that you may look into is General Atomics, I
>emailed them but never got a response at the time. They may also have
>restrictions on selling certain high energy devices outside of the U.S.

>Wish I could be more help, good luck

>http://www.ga.com/capacitors

>More theses on the subject (could also look at papers from these folks
>as well):

>Rina Baba
>http://uwspace.uwaterloo.ca/handle/10012/4970

>Mohammad Moonesan
>http://uwspace.uwaterloo.ca/handle/10012/6298

>Alex Yatong Yu
>http://uwspace.uwaterloo.ca/handle/10012/4815

>Yuseph Montasser
>http://uwspace.uwaterloo.ca/handle/10012/2895
"


then I responded:
"
I'm wondering if I could use a cheap $7 7kV boost converter power
module with a 100 MOhm and 20 MOhm resistors to load it current-wise
and drop the voltage to below 2kV for charging some microwave
capacitors (2.1kV, 1uF, $2.50 in packs of 20 from China), then pulsing
it to a cuvette with some parallel MOSFETs like you had.

Someone else said this wouldn't be practical, am I missing something
obvious (I'm not an EE)?
"

and his reply:
"
> I don't know if there is a short cut here or not but I think the boost
> converter will be very low current (if you boost the voltage and the
> power remains constant the current will decrease proportionally) and as
> a result the charging time of the capacitor will likely be on the order
> of 1 second, this will limit your pulse repetition rate. Also, the
> discharging may also be affect (ie slower ...I need to think about this
> more) and its possible that a fast discharging square wave pulse will
> become a slow exponentially decaying pulse with a long tail. If you can
> live with these effects that I would agree that the price is right.
"

I didn't respond after that, but from my experience with E.coli (and
some yeast and lactobacilli papers I read) 1 pulse is all you need per
sample, /once/ you figure out what the right settings are... field
strength, length of pulse, shape of pulse... (though changing the
length seems like it can substitute for using a worse/less-efficient
shape).

I have this old electroporation chamber that has a micrometer with a
geared-down knob for adjusting the electrode distance. Problem with it
is cleaning/sterilizing, or maybe that you can't quickly do multiple
sequential different samples (since cleaning time isn't an issue with
pre-sterile disposable cuvettes). The disposable cuvettes are
cleanable and reusable, but I they're a harder plastic which seems
like polycarbonate, which isn't autoclavable.

Here's a pic of a disposable:
http://www.westburg.eu/uploads/fckconnector/ec35c491-8e4f-4f15-95ae-6360dec4695a


On Sun, Nov 10, 2013 at 11:18 AM, John Griessen <john at industromatic.com> wrote:
> On 11/10/2013 05:10 AM, Nathan McCorkle wrote:
>>
>> How about this, it seems like plenty of inductance, is stocked on
>> digikey for ~$3, says 'Dielectric Strength (P/S)' is 6.5kVDC,
>
>
> It says line matching...  it might not have much copper and so not much
> current handling,
> and the magnetic material too.   it takes some looking at specs and knowing
> what you want...
>
> before you can choose.
>
> I can't spend time on it right now...  shopping for a complete thing aimed
> at the purpose is
> quicker and what I've done in finding some Chinese suppliers of flyback
> transformer/inductors.
> That has some specifying before buying also, but mostly for deciding how
> small and low
> cost it can be.
>
> If you want to make something, a HV flyback from any junk CRT will do, but
> then
> how do you duplicate it to sell?  This discussion is about developing low
> cost to sell, not DIY
> from junk pile parts, right?
>
> Look how cheap these are -- $1.8+shipping:
> http://www.alibaba.com/product-gs/357136589/FLYBACK_TRANSFORMER.html
>
> Those two knobs on its side mean it even has some passive parts integrated
> adjustable
> R's and some capacitance...   Question is what volt range can it do, and is
> there
> a smaller one for just 2kV instead of 7 or 12 kV?    No time to ask right
> now.
> It will have a dielectric strength of insulation in the many tens of kV,
> so it can operate for years at something like 7kV.  It also has design
> features on all
> exposed surfaces for HV and how that attracts dust and then the dust and
> moisture can
> break down, arc and burn.  The line matching function of the above part has
> none of that
> design -- its  6.5kVDC "strength" is just there to protect against
> occasional surges
> from lightning strikes.
>
>  what
>> does P/S mean?
>
> Searched.  Can't find except a mention of P-S in another datasheet.
> Volts /distance is Dielectric Strength definition.  P/S or P - S don't
> match.
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-- 
-Nathan
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