Re: [DIYbio] A simple and cheap >100V DIY electrophoresis power supply

On Fri, Jul 5, 2013 at 6:28 AM, Simon Quellen Field <sfield@scitoys.com> wrote:
> I like your point about the current limiting resistor.
> LED nightlights that plug into the wall use small capacitors to limit the
> current.
> But I suspect that method will have the same problem.
> To get the current you want in the gel, which has its own resistance, you
> would need a low enough output impedance on the power supply, and that is
> always going to be more than you'd want to touch.
>
> For beginners and hobbyists, running small gels that don't require stiff
> power supplies can make it easier to use a safer power supply.
>
> Saying "don't touch the wires" is great. Making it difficult to touch the
> wires is better.

Thank you, I think this is more on the way to build a reasonably safe
device. Live is a risky, and we should focus on the real risks, not
the superstitious ones.

> I write books about building scientific instruments, and many of my readers
> are middle school kids doing science fair projects. From the email I get, it
> is obvious that many of them don't read the text, they try to build things
> by looking at the pictures. Telling them not to touch the wires is like
> handing them a chainsaw and telling them not to let the tree fall on them.
>

That's a fine analogy. You could design a chainsaw that would prevent
the tree from falling on you buy turning it into a chainsaw tank. This
would look awesome, but seriously, just use common sense and safe
practice when cutting down trees.

> I don't want Josiah to feel picked-upon or disrespected. We want people to
> perform the service he has. But someone mentioned DIYBio self-policing, and
> this is how we do it -- by pointing out how something can be done more
> safely.
>
> It should not be difficult to put the hot contacts in a box that you can't
> get your hands into.
> You would them put the gel in the box, and then put something under the gel
> so that it lifted into the contacts.
>
> But using a transformer to isolate from the mains ground is still a good
> idea, as is a ground fault circuit interrupter socket (they are only a
> couple of bucks). A safety interlock, so that the power can't come on until
> the lid is closed is another cheap and easy safety measure. But just assume
> that someone is going to try washing it in the sink while it is plugged in,
> and that's what the GFCI is for.
>
> We can't fix stupidity or carelessness, but we can do a little more to make
> it less likely to be fatal.
>
> -----
> Get a free science project every week! "http://scitoys.com/newsletter.html"
>
>
>
> On Thu, Jul 4, 2013 at 4:10 PM, Alexey Zaytsev <alexey.zaytsev@gmail.com>
> wrote:
>>
>> Guys, sorry to intervene, but just 2 cents from someone who's studies
>> at a university that's got "Electrotechnical" in its name.
>>
>> This whole discussion reminds me of the argument from the anti-GMO
>> crowd. They take the theoretical worst case scenario and run it as
>> something that's sure to happen.
>> Just don't grab the damn wires. Isolating the output from the input is
>> a good idea and allows you to grab individual wires while being
>> grounded, but it's not a hard requirement. You should just know that
>> the device you've built is not fool-proof, and handle it with care.
>> And while it's not absolutely impossible, you are very, very unlikely
>> to die even from 380v ac, let alone 100-something volts dc.
>>
>> Btw, the current limiting resistor is a terrible idea. From a quick
>> google search, it seems that the electrophoresis requires currents in
>> the range of tens of milliamps, hundreds for bigger gels. So it's just
>> not going to work. Even if we assume that it would require, say, 5ma,
>> and you limit the current to 10ma with a resistor, it means that 2/3
>> of the voltage will drop on the resistor, and you would need a circuit
>> that can output 300+ volts, which does not look like it's making it
>> any safer.
>>
>>
>> On Wed, Jul 3, 2013 at 7:58 PM, Josiah Zayner <josiah.zayner@gmail.com>
>> wrote:
>> > Using a bridge rectifier($0.30) one can basically use AC mains voltage
>> > to
>> > run your gel electrophoresis. You can buy all the components for under
>> > $5.
>> > I tested it out and it works great. Can run a really good looking gel in
>> > around 30 minutes.
>> >
>> > I made a blog post here about it:
>> >
>> > http://doitourselfscience.blogspot.com/2013/07/a-cheap-simple-diy-electrophoresis.html
>> >
>> >
>> > Any questions let me know.
>> >
>> >
>> > Josiah Zayner
>> >
>> > --
>> > -- You received this message because you are subscribed to the Google
>> > Groups
>> > DIYbio group. To post to this group, send email to
>> > diybio@googlegroups.com.
>> > To unsubscribe from this group, send email to
>> > diybio+unsubscribe@googlegroups.com. For more options, visit this group
>> > at
>> > https://groups.google.com/d/forum/diybio?hl=en
>> > Learn more at www.diybio.org
>> > ---
>> > You received this message because you are subscribed to the Google
>> > Groups
>> > "DIYbio" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an
>> > email to diybio+unsubscribe@googlegroups.com.
>> > To post to this group, send email to diybio@googlegroups.com.
>> > Visit this group at http://groups.google.com/group/diybio.
>> > To view this discussion on the web visit
>> >
>> > https://groups.google.com/d/msgid/diybio/91b49cd4-e25a-4001-9843-ca09ae50773f%40googlegroups.com.
>> > For more options, visit https://groups.google.com/groups/opt_out.
>> >
>> >
>>
>> --
>> -- You received this message because you are subscribed to the Google
>> Groups DIYbio group. To post to this group, send email to
>> diybio@googlegroups.com. To unsubscribe from this group, send email to
>> diybio+unsubscribe@googlegroups.com. For more options, visit this group at
>> https://groups.google.com/d/forum/diybio?hl=en
>> Learn more at www.diybio.org
>> ---
>> You received this message because you are subscribed to the Google Groups
>> "DIYbio" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to diybio+unsubscribe@googlegroups.com.
>> To post to this group, send email to diybio@googlegroups.com.
>> Visit this group at http://groups.google.com/group/diybio.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/diybio/CAB9v_DHRZi%2BP3%3DsWckHzF6V4Cb%2BkEz61w36wpuA2sUEqvochxA%40mail.gmail.com.
>>
>> For more options, visit https://groups.google.com/groups/opt_out.
>>
>>
>
> --
> -- You received this message because you are subscribed to the Google Groups
> DIYbio group. To post to this group, send email to diybio@googlegroups.com.
> To unsubscribe from this group, send email to
> diybio+unsubscribe@googlegroups.com. For more options, visit this group at
> https://groups.google.com/d/forum/diybio?hl=en
> Learn more at www.diybio.org
> ---
> You received this message because you are subscribed to the Google Groups
> "DIYbio" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to diybio+unsubscribe@googlegroups.com.
> To post to this group, send email to diybio@googlegroups.com.
> Visit this group at http://groups.google.com/group/diybio.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/diybio/CAA0yOM7tWZ2T8h5uTETuph8qHw27KAeo-Wubq-ws%2BNzWohk4QQ%40mail.gmail.com.
>
> For more options, visit https://groups.google.com/groups/opt_out.
>
>

--
-- You received this message because you are subscribed to the Google Groups DIYbio group. To post to this group, send email to diybio@googlegroups.com. To unsubscribe from this group, send email to diybio+unsubscribe@googlegroups.com. For more options, visit this group at https://groups.google.com/d/forum/diybio?hl=en
Learn more at www.diybio.org
---
You received this message because you are subscribed to the Google Groups "DIYbio" group.
To unsubscribe from this group and stop receiving emails from it, send an email to diybio+unsubscribe@googlegroups.com.
To post to this group, send email to diybio@googlegroups.com.
Visit this group at http://groups.google.com/group/diybio.
To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/CAB9v_DGTVFX2VnN1kymHLyjfRp8ovLy9EmoJW3j0pQBbeysW7Q%40mail.gmail.com.
For more options, visit https://groups.google.com/groups/opt_out.