DIY power source for electrophoresis chambers?

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Avery Ashley

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Feb 18, 2013, 8:55:36 AM2/18/13
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I'm extremely dense when it comes to electrical devices and how they work. I need a power source for my electrophoresis chamber, but even used ones on ebay seem too much to justify. Is there a safe way of using a battery or otherwise creating a makeshift power source relatively cheaply?
If I understand the process correctly, one only needs to polarize the water in the chamber creating a positive and negative side, but to what degree? How "polarized" does it need to be? I hope my lack of knowledge in electrical terms doesn't make this question too hard to understand. 
Thanks for taking a look.

Cory Tobin

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Feb 18, 2013, 3:18:58 PM2/18/13
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> I'm extremely dense when it comes to electrical devices and how they work. I
> need a power source for my electrophoresis chamber, but even used ones on
> ebay seem too much to justify. Is there a safe way of using a battery or
> otherwise creating a makeshift power source relatively cheaply?

You can hook a bunch of 9V batteries in series like this
http://wiki.biohackers.la/File:9v_series.jpg Then you just need to
figure out how to hook the terminals up to your gel box. If you're
only planning on running a few gels this is a very inexpensive method.
Higher operating cost but lower up-front investment than a power
supply.

If you don't mind a little assembly there is this:
http://wiki.biohackers.la/Cheap_Power_Supply Requires a small amount
of soldering. You could probably get away without soldering if you
want to leave out the power switch.


> If I understand the process correctly, one only needs to polarize the water
> in the chamber creating a positive and negative side, but to what degree?
> How "polarized" does it need to be? I hope my lack of knowledge in
> electrical terms doesn't make this question too hard to understand.
> Thanks for taking a look.

I've run gels as low as 20V before. You might be able to go lower but
my power supply bottomed out at 20. Typically small-ish gels are run
around 100V. The higher the voltage you use the faster the DNA moves.

-cory

Avery louie

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Feb 18, 2013, 4:05:07 PM2/18/13
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The most elegant solution I have seen so far: http://www.science-projects.com/PowerSupply.htm

You can make it at home depot.  Dont zap yourself.

--A


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Brian Degger

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Feb 18, 2013, 4:35:29 PM2/18/13
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Not so good for the continent/eu, 220-240 v rectified coming out of science-projects.com
Remember, mains electricity is one of the most dangerous things you will encounter in a lab!
Be very careful.
Love the LA biohackers version, will probably make one myself :)

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Conner Berthold

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Feb 18, 2013, 4:43:01 PM2/18/13
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Wow! That is the simplest design I've ever seen.

If you wanted something that was DC-DC, take a look at this design. It has a 12-15V input, and 15-220V output @ 50mA.

Avery Ashley

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Feb 18, 2013, 4:47:32 PM2/18/13
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Wow thanks for all the tips. This looks much easier than I was expecting. That never happens!

Cory Tobin

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Feb 18, 2013, 5:02:07 PM2/18/13
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I would caution against building the device described on
science-projects.com for 3 reasons:

1) It's non-isolated so it's very unsafe. Non-isolated mains current
is potentially lethal.

2) It's non-isolated so it's very unsafe. Non-isolated mains current
is potentially lethal.

3) The output is rectified but not smoothed
(http://www.paleoelectronics.com/blog/wp-content/uploads/2011/03/800px-Smoothed_ripple.svg_.png)
and I'm not sure how well the electrophoresis will work with that
rectified voltage.


-cory

Avery Ashley

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Feb 18, 2013, 5:10:45 PM2/18/13
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I was planning on trying http://www.science-projects.com/PowerSupply.htm
Dumb question, but If I wear heavy duty rubber gloves I'm safe, right?

Cory Tobin

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Feb 18, 2013, 5:35:23 PM2/18/13
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> I was planning on trying http://www.science-projects.com/PowerSupply.htm
> Dumb question, but If I wear heavy duty rubber gloves I'm safe, right?

If you don't know the answer to that question then you shouldn't be
building non-isolated power supplies.

Saving 10 bucks isn't worth risking your life. You can build the one
on the biohackers.la wiki for like $25-30. It uses a standard
wall-wart AC adapter which includes a transformer so you're isolated
from the mains current.

-cory

Avery louie

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Feb 18, 2013, 5:36:34 PM2/18/13
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not really.  It could easily short through any other part of your body.

Mains isolation and smoothing are not a bad idea, especially the mains isolation part.  That should be easy though- just grab a transformer and boom! Isolated (as far as I know- cory, whats your take on this).

Smoothing is probably less of a big deal.

--A

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Cory Tobin

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Feb 18, 2013, 5:49:00 PM2/18/13
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> Mains isolation and smoothing are not a bad idea, especially the mains
> isolation part. That should be easy though- just grab a transformer and
> boom! Isolated (as far as I know- cory, whats your take on this).

Not sure. I will defer to a trained electrical engineer.


> Smoothing is probably less of a big deal.

Yeah, I have no idea if it will work. I'd imagine it *will* work (you
can get pulsed power supplies for specialized electrophoresis methods)
but I've never tried so I make no guarantees.

-cory

Nathan McCorkle

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Feb 18, 2013, 6:24:39 PM2/18/13
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On Mon, Feb 18, 2013 at 2:10 PM, Avery Ashley
<avery...@rams.sccnc.edu> wrote:
> I was planning on trying http://www.science-projects.com/PowerSupply.htm
> Dumb question, but If I wear heavy duty rubber gloves I'm safe, right?

If you think that route is OK for you, the next better thing /could/
be a Variac, it would provide isolation /and/ voltage variation.

On amazon.com they have a 3 Amp version for ~$70 with shipping, which
for being new is OK. A 1:1 AC transformer seems like it would be a lot
cheaper, but they don't turn up for me on google with prices :(

--
-Nathan

Nathan McCorkle

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Feb 18, 2013, 6:40:32 PM2/18/13
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basically the more voltage, the more current, the more heat is
generated. Heat can melt your gel, it also causes band broadening.
Electrophoresing too slowly causes band broadening due to longer time
for diffusion to occur. There is an optimum speed, it is dependent on
gel/buffer composition, fragment length, and resolution
desired/required. The resistance depends on the gel/buffer composition
and 3D size. Combining all the equations together to find the
optimization is, I believe, the Van Deemter equation (or some modified
version of it).

here's an explanation from chromatography, gel electrophoresis is a
bit different but still pretty similar
http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/chrom1.htm
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Mac

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Feb 18, 2013, 8:58:03 PM2/18/13
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Hey. I don't know your specs, but I suspect the folks around here are
making it more complicated than it needs to be. Just take the power
supply out of an old PC strip the wires.

http://en.wikipedia.org/wiki/ATX_power_supply

Does this make sense?

John Griessen

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Feb 18, 2013, 10:53:04 PM2/18/13
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On 02/18/2013 03:47 PM, Avery Ashley wrote:
> This looks much easier than I was expecting. That never happens!

I'd stick with switch mode power supplies from batteries for safety,
since they
1. Don't have a long cord to trip on
2. If you keep it close to the gel box, and/or use an interlock to
connect power only when the lid is on, you keep Volts away from your body.

But they still can make enough Volts to electrocute you, so keep it in mind
when handling the wires, electrodes for electrophoresis.

John Griessen

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Feb 18, 2013, 10:55:35 PM2/18/13
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On 02/18/2013 04:10 PM, Avery Ashley wrote:
> I wear heavy duty rubber gloves I'm safe, right?

With a strong Volt source like the house power, you could still kill yourself
by accident with just a cut in your glove and salty water or agarose completing
the circuit to defibrillate your heart

John Griessen

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Feb 18, 2013, 10:59:04 PM2/18/13
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On 02/18/2013 07:58 PM, Mac wrote:
> Just take the power supply out of an old PC strip the wires.

You only get 24 Volts from that. 100 Volts or more might be optimum.
The way to make it safe is interlocks on cable ends with bare metal and
on the gel box lid. That means more complexity, but is needed if you're
not patient enough to study the safety issues and work around dangerous
voltage carefully.

Avery louie

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Feb 18, 2013, 11:09:08 PM2/18/13
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you can probably boost convert one of the higher power voltages from an ATX supply to electrophoresis voltages.

--A



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Patrik D'haeseleer

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Feb 19, 2013, 3:23:28 AM2/19/13
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Apparently, the non-smoothened output is not a problem for electrophoresis. But yes, that dimmer + rectifier hack is horribly unsafe. Other than that, great hack though!

You can make things a bit safer by adding a 1:1 transformer. Or even better (for people in the US), a 110 -> 220 travel transformer, so you get to voltages above 110V! I managed to pick up two 220 -> 110 travel transformers for a few bucks each that I'm thinking of using for this purpose. Should be just a matter of swapping the plugs around. Of course, you'd also like to add other niceties such as Volt and Amp meters etc.

Another important resource to look at: the Open Gel Box folksa couple of years back came up with some good de novo specs and designs:

http://openwetware.org/wiki/DIYbio:Notebook/Open_Gel_Box_2.0/Power_Supply

Patrik

Cathal Garvey

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Feb 19, 2013, 6:00:15 AM2/19/13
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Oh, you'd be lucky if it de-fibrillated you. More likely you get knocked
into ventricular fibrillation if your heart isn't literally burned by
the current.

The LA biohackers solution looks really good. I'd go with that one. If
you feel like having a faster gel run, make two and run them in series
(unless someone feels that'd blow up?), but 120V might actually be a bit
*too* strong..

Cathal Garvey

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Feb 19, 2013, 6:02:36 AM2/19/13
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Based on prior wrangling with ATX supplies to get higher voltages (in
this case trying to run in series), it'd probably work, but not before
you pull your hair out trying to bypass the overcurrent/leak protections
many of them have built in.

As I recall, to get one of the PSUs to power up, we had to wire a bulb
into the motherboard portion of the supply, or it would declare
shenanigans and shut down.

On 19/02/13 04:09, Avery louie wrote:
> you can probably boost convert one of the higher power voltages from an
> ATX supply to electrophoresis voltages.
>
> --A
>
> On Mon, Feb 18, 2013 at 10:59 PM, John Griessen <jo...@industromatic.com
> <mailto:jo...@industromatic.com>> wrote:
>
> On 02/18/2013 07:58 PM, Mac wrote:
>
> Just take the power supply out of an old PC strip the wires.
>
>
> You only get 24 Volts from that. 100 Volts or more might be optimum.
> The way to make it safe is interlocks on cable ends with bare metal and
> on the gel box lid. That means more complexity, but is needed if you're
> not patient enough to study the safety issues and work around dangerous
> voltage carefully.
>
>
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Avery louie

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Feb 19, 2013, 7:31:07 AM2/19/13
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yea, there is a load sense pin.  Just put a paper clip in there and it will go all day- it differs on atx and dell psus, so I dont remember exactly what pins to short.

--A

jlund256

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Feb 19, 2013, 12:17:54 PM2/19/13
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As the other replies mention, lower voltage is OK.  I routinely run genomic DNA digests at high voltage when I need results quickly, and turn it down to 15v - 20v to run overnight.  Time and voltage are roughly proportional--1/2 the voltage, twice the time.  One other thing--very small dna, say 500 bp or smaller, will noticeably start to diffuse during long runs, turning from a sharp band to a diffuse band.  In a run of several hours, or overnight, this is apparent.
 
Jim Lund

Jonathan Cline

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Mar 2, 2013, 5:22:15 PM3/2/13
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Hi all,
I posted about my power supply before, I'll post plans once I reproduce it in the carlsbad lab.  I guess make it an instructable in addition to openwetware page since that's maybe the best way to get it out there.  Some brief notes,

a) I don't think the "hi voltage nixie" supply will work.  It is not high enough current.  Compare to bio protocols and this should be the conclusion.

b) plugging directly into the wall is a really bad idea, although there are published journal articles about this (ummm what? yes peer-review/editors are that silly).

c) using an AC transformer is costly and heavy and bulky and doesn't provide the below point by itself,

d) the power supply should have current limiter in addition to thermal shutoff.  Easy to add to the design and much safer.

For home/kitchen use it's best to plug into a GFCI outlet too...


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