Current and voltage reqs for electrophoresis power supply

[Avery louie]

What kind of voltages / max currents do you generally run your gels at?  I am designing a power supply.

--A

[Dakota]

Dedicated gel power supply would be sweet!

I think 120V at 250mA is pretty common

[Sebastian S. Cocioba]

I run a small gibco horizon setup with an old power supply at 25v and some low amperage (analog readout) for 3hrs. I need a new system :P

Sebastian S Cocioba

CEO & Founder

New York Botanics, LLC

Sent via Mobile E-Mail 

On Dec 8, 2012, at 2:53 PM, Dakota <dko...@gmail.com> wrote:

Dedicated gel power supply would be sweet!

I think 120V at 250mA is pretty common

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[Avery louie]

Jeez.  Yea.

To spill the beans on my current plan (I will have schematics/parts avalible for discussion later), I am working on a cheap, high quality diybio gel supply.  Will it get done? Hopefully.  Will it have a sweet lasered box? Probably.  It may not be totally adjustable though, that is Tbd.

--A

[Avery louie]

Thanks for the replies by the way.  I appreciate it.

[Jeswin]

I run at fixed current, 75V for 20-25 minutes (fresh, and larger gels)
and 50V for 35-45 minutes(older gels that were stored in 4C before
using).

I noticed that too much heat can cause bubbles to form in some gels
which makes it harder to see faint bands.

[Nathan McCorkle]

On Sat, Dec 8, 2012 at 5:27 PM, Jeswin <phill...@gmail.com> wrote:

I run at fixed current, 75V for 20-25 minutes (fresh, and larger gels)
and 50V for 35-45 minutes(older gels that were stored in 4C before
using).

you mention fixed current, but then quote voltage specs. That would mean you control for gel resistance everytime you make a gel.

Controlling for resistance would probably be more precise for getting even gel results between batches, rather just adding X grams or Y ml of electrolyte/buffer stock powder or solution, you would simply measure the resistance of the warm gel solution and titrate/drop in buffer stock until you reach your target. 

I reckon a multimeter with a bult-in ohmmeter is cheaper than a decigram/centigram scale (1/10th gram, 1/100th).

[John Griessen]

On 12/08/2012 08:47 PM, Nathan McCorkle wrote:
> That would mean you control for gel resistance everytime you make a gel.

Sounds like a good way, and suggests a combo power supply and meter
to hook up to your gel trays. That would defeat safety interlocks though.
So maybe all you want is some meter leads that adapt an ordinary Fluke meter
to the safety HV leads that connect to a gel tray.

Or... removing the lid throws a switch that puts the system in meter mode
and stops any high voltage going out...

[Nathan McCorkle]

John, it looks like the best power supply would be something like this AC to DC converter which  (with a 1:1 transformer for mains isolation)

http://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/

or a boost converter (but I'm not sure how to vary it):

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

How would you increase the max current to a bit more, in case 100mA isn't enough? (for the first link)

On Sat, Dec 8, 2012 at 7:38 PM, John Griessen <jo...@industromatic.com> wrote:

d suggests a combo power supply and meter
to hook up to your gel trays.  That would defeat s

--
-Nathan

[Patrik D'haeseleer]

This little hack works quite well as a electrophoresis power supply:

http://www.science-projects.com/PowerSupply.htm

Essentially, it's just a 110V dimmer switch from a hardware store, plus a rectifier. Add a 1:1 transformer to be just a little less horribly unsafe, and voltage and mA readouts, and you'd have a pretty functional DIY power supply.

Of course, you'll never be able to produce anything higher than 110V DC this way (220V in Europe), but I managed to pick up some 2:1 travel mains voltage converters for a few bucks each, which I should be able to turn around to produce up to 220V DC from the 110V AC US mains voltage.

[Pieter]

Right now I just click 8 9V batteries in series. Does the job quite well, but the batteries get a bit hot after a while.

Looking forward to your device Avery!

[John Griessen]

On 12/08/2012 09:56 PM, Nathan McCorkle wrote:
> John, it looks like the best power supply would be something like this AC to DC converter which (with a 1:1 transformer for mains
> isolation)
> http://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/
>
> or a boost converter (but I'm not sure how to vary it):
> http://en.wikipedia.org/wiki/Boost_converter
>
> How would you increase the max current to a bit more, in case 100mA isn't enough? (for the first link)

That circuit is what is called a rectifier followed by a regulator. Better for not wasting power,
more power out per size (and expense) of parts used is a switching power supply.

To be safe and convenient one would copy many of the features of a Feathervolt 3000.
It will regulate the voltage out with a readout to tell you what that is, and have a max power limit
that will shut it down. In another mode, it regulates current to a constant value, ( for when
the resistance of the gel changes during the run). And it even has a mode where power
delivered is held constant. It has a knob for selecting modes, then a knob for setting level.

Feathervolt 3000's are obsolete and not made now -- too many parts, high costs, no automation features.
Nowadays it is easy to have a text window or graphic window for readout.
Maybe a strip chart function would be good in an electrophoresis supply?

I think it's important to use physical safety interlocks and circuit breakers.

And for usability timers and end of run detectors to shut it off, and if it has a
computer in it already, why not ports for controlling it by ethernet
and/or USB? (I like ethernet better, but...)

The 31 Watts of the above crude supply is an OK power range for a lot of things
that aren't super speedy and cooking the gel so it melts... One could power
up to 60 Watts via power over ethernet connection alone, and keep all the "hot"
high voltages inside plastic boxes, and several of them plugged into ethernet,
and triggering other automation steps as they complete. Think of a system with
transparent trays and when done, take images, do image processing, report data
to someone's smart phone as images and charts and tables. All that could be done
without separate modules for supply volts at low cost, and with the high voltages
hidden as in the volts for a xenon flash tube in a camera. No one thinks of those
as a huge hazard -- they have KiloVolts inside though. It's not such a hazard
because there are no cables stretching across a lab bench with big potentials
in them.


An isolation transformer is helpful for avoiding volts on the metal chassis of
your instruments parked near the sink with its
faucets at a solid building safety ground voltage, but it doesn't
save you if you touch both leads of the supply when fiddling with the
conductive goo in a tray, does it?

No one has said they want more volts than the 155 VDC you get from rectifying USA wall outlet power.

Why does a Feathervolt 3000 go to 3KV? Who uses that? Not the salty ones, I guess.

[Jeswin]

On Sat, Dec 8, 2012 at 9:47 PM, Nathan McCorkle <nmz...@gmail.com> wrote:
> On Sat, Dec 8, 2012 at 5:27 PM, Jeswin <phill...@gmail.com> wrote:
>>
>> I run at fixed current, 75V for 20-25 minutes (fresh, and larger gels)
>> and 50V for 35-45 minutes(older gels that were stored in 4C before
>> using).
>
>
> you mention fixed current, but then quote voltage specs. That would mean you
> control for gel resistance everytime you make a gel.
>

Ack. I meant voltage fixed at 75 or 50 and let the current vary. My
gelbox is a simple affair. It's lets you choose 6 or 7 different
voltages to run at and lets you program the timer.

[Nathan McCorkle]

From what I've read constant current means constant migration speed, but as electrolysis occurs the resistance goes up and more heat is generated. Constant voltage means as resistance goes up due to electrolysis, current goes down and so does migration speed, but heat stays low.

[Sebastian S. Cocioba]

I know this may be overkill but would a PID controlled peltier work to control the heat generated from high current runs? Speed up gels and whatnot? Would we start delving into the land of agarose damage if the current is too high despite the relatively cool buffer? Lets say on top of the silly peltier we have a means of circulating the buffer also, could one make high speed gels like that? Just a thought.

Sebastian S Cocioba

CEO & Founder

New York Botanics, LLC

Sent via Mobile E-Mail 

[Patrik D'haeseleer]

Actually, I believe that depends on the gel. In a vertical gel, resistance can increase over time, as the more conductive ions get electrophoresed out of the gel. But in a horizontal gel, the gel resistance typically *drops* as it heats up. So if you run at constant voltage, when the gel heats up, the current will increase, creating more heating, etc. - a thermal runaway effect!

To be safe, you can run at constant wattage, which should guarantee constant heating.

[Avery louie]

Why does it drop?

Cooled rigs exist for more exotic applications.  I saw a few surplus ones somewhere.

--A

To view this discussion on the web visit https://groups.google.com/d/msg/diybio/-/sFy27ec-GYwJ.

[John Griessen]

On 12/10/2012 01:00 AM, Patrik D'haeseleer wrote:
> To be safe, you can run at constant wattage, which should guarantee constant heating.

That's a feature a supply I have does. Seems like a good thing for any open hardware supply
based on a microcontroller.

[John Griessen]

On 12/10/2012 04:52 AM, Avery louie wrote:
> Why does it drop?

I think of temperature as
electron mobility and diffusion in a liquid --> easier movement as temp rises.

But, in solid state material, electrons can move already through crystalline
pathways that get knocked around more
as temperature rises, so increasing resistance.

[Nathan McCorkle]

But the gel isn't a conductive crystal, it's a dielectric matrix. Current flows only because of the electrolyte.

On Mon, Dec 10, 2012 at 9:06 AM, John Griessen <jo...@industromatic.com> wrote:

te material, electrons can move already through crystalline
pathways that get knocked a

--
-Nathan

[Nathan McCorkle]

Still not sure, seems like Avery was asking why a horizontal gel vs vertical gel would have different resistive scenarios. Seems like in either case you're removing electrolytes via electrolysis, so resistance would increase due to less charge carriers in solution. Imagine the charge were people, the ions are taxi cabs. Getting to the airport from downtown has some ease/difficulty, when there are less taxis on the road it gets harder to catch a taxi, when there are more taxis on the road it is much easier to get to the airport.

I'm not sure why a vertical gel vs a horizontal gel would change the ending resistance, unless the two gels are not made the same (agarose vs polyacrylamide, totally different buffers)... I'm guessing the gels Patrik is mentioning have different buffering systems.

On Mon, Dec 10, 2012 at 11:02 AM, John Griessen <jo...@industromatic.com> wrote:

On 12/10/2012 12:20 PM, Nathan McCorkle wrote:

But the gel isn't a conductive crystal, it's a dielectric matrix. Current flows only because of the electrolyte.

On Mon, Dec 10, 2012 at 9:06 AM, John Griessen <jo...@industromatic.com <mailto:jo...@industromatic.com>> wrote:

    te material, electrons can move already through crystalline
    pathways that get knocked a

Reread what I said in context.

--
-Nathan