A simple and cheap >100V DIY electrophoresis power supply

[Josiah Zayner]

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

[Avery louie]

Nice gel!

An upgrade to this is to use a light dimmer for voltage control.  Iirc, these kinds of solutions are sketchy because they I are not isolated from the mains, making it a bit hazardous.

Something like a switching power converter is safer and relatively cheap (40 bucks).

--A

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[Josiah Zayner]

I don't know if that is really a problem.
If you mean isolating from large current draws the bridge rectifier has a 1A max draw.
If you mean for something else it would not be very difficult or expensive(> $1.00) to add in two wire wrapped toroids to use as inductors to isolate from the mains.

It is a good idea though and I can totally throw that in. Thanks!

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[Patrik D'haeseleer]

Here's an older article that does exactly that: dimmer + fuse + rectifier = 120VDC variable power supply for $20:

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

As you mentioned, this is horribly unsafe, but it does work. One upgrade would be to add an isolation transformer. Or better: get a 110->220V travel transformer (or a 220->110V one, and reverse it), so you get isolation from the mains *and* voltages up to 22VDC.

Patrik

[Josiah Zayner]

Cool other people have also thought of this so I know that it should be really usable.

The 120V-> 220V converter is a good idea! Connect that to a higher voltage bridge rectifier and a voltage divider output like 175V run your gels in 20 minutes for like $15 or $20.

Is this still unsafe even with the 1A load limit?
I mean obviously it is unsafe not being enclosed.

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[Avery louie]

The question is how long it takes before failing, and how many amps to gets to before failure.  Someone with more knowledge should weigh in on this, but 1A is probably dangerous at 120v.  It is tricky to say, because it depends on how you come in contact with it.

Ohms law says that V=IR.  You load is the resistance of your gel, which at 120v draws less than 1A.  The problem is if you get wet and touch it, and have a lower resistance, and draw more amps.  If the chip takes too long to burn out, you are toast.

According to the datasheet the fuse time is about 8.5 ms with a maximum draw of 50A.  Ouch.  It also looks like it can survive 10 cycles (1/6 sec) at 25A.

Its the amps that kill you, which is why low voltages are generally considered 'safe' - it is hard to draw much current with only 5v of potential.

It is probably fine, but definitely build at your own risk!

--A

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[Nathan McCorkle]

The danger isn't only because it's AC and has potentially a ton of current should the circuit be shorted... the danger is that when using AC there are a ton of grounding opportunities in most/any room of a building, meaning more opportunities to accidentally short the already dangerous circuit. Think the metal water faucet, it's a ground, the metal screw on the plastic light switch cover could work (if the paint is scratched a bit), etc, etc...

Adding a transformer decouples the circuit electrically via a magnetic coupling. This means all the unnoticed ground connections in a room aren't dangerous if you are touching it along with a hot wire from your shortable circuit.

From wikipedia 'Electric Shock':

"

A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC. At around 10 milliamperes, AC current passing through the arm of a 68 kg (150 lb) human can cause powerful muscle contractions; the victim is unable to voluntarily control muscles and cannot release an electrified object.^[2] This is known as the "let go threshold" and is a criterion for shock hazard in electrical regulations.

The current may, if it is high enough, cause tissue damage or fibrillation which leads to cardiac arrest; more than 30 mA^[3] of AC (rms, 60 Hz) or 300 – 500 mA of DC can cause fibrillation

"

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--
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[Nathan McCorkle]

There's also this simple circuit by JCline that adds a few voltage doublers:
88proof.com/synthetic_biology/blog/archives/303

--
-Nathan

[Cory Tobin]

> Is this still unsafe even with the 1A load limit?
> I mean obviously it is unsafe not being enclosed.

Unless there is an air gap this thing is pretty dangerous. If you
want something cheap and safe, check out this:
http://wiki.biohackers.la/Cheap_Power_Supply It will only put out 60V
but that is plenty if you have a small gel box.

Or just get a few 9V batteries and hook them in series. I have got
about 8.5 hours out of 7 9V batteries powering a 15cm gel box with
TAE.

-cory

[John Griessen]

On 07/03/2013 03:56 PM, Josiah Zayner wrote:
> Is this still unsafe even with the 1A load limit?
> I mean obviously it is unsafe not being enclosed.

The safety part of wanting an isolation transformer
is about being able to have some part of the thing
grounded to building safety ground.

Usually the grounded part is a metal box around the
power converter parts -- the rectifiers in your case.
The purpose of that is in case of accidental failure
inside the box and current going to the box, (safety ground), then a GFI breaker trips.
And even without a breaker trip, fire causing sparks are all within the box.

Once you get volts output, it's good to let that float
relative to the building ground so one terminal could be accidentally
connected to the lab sink, for instance, without sparks and destruction,
and the lab sink would stay grounded and near zero volts -- probably -- unless
it's installed with plastic piping and no good connection to earth ground...
The current standards of plumbing are to use insulating plastics for
water supply and drains. Or if you are lucky the little temporary surge of current when touching
something grounded will trip a GFI on the power circuit for the supply.



For real safety of a HV supply, both output terminals need to
be in insulated and inside of interlocked covers
so the power turns off and goes to zero in a flash when covers are opened.

An isolation transformer won't save you from frying, it just lets one
rectifier output float when its other terminal is connected to building ground
or any DC voltage relative to building ground.

"1A is probably dangerous at 120v"

should be "120 Watts is plenty to start a fire", and,

"1A is deadly at any voltage if arm to arm". It depends a lot on how sweaty and salty you are.

At voltages like 200VAC the chances are very good to go above the few milliamps arm to arm
that cause your heart to go random because it's enough to get past the resistance of dry skin.

[Jonathan Cline]

Do not build the suggested circuit which runs directly from AC wall jack.  The article should be taken off your blog in my opinion similarly to suggesting that people should use EtBr at home (which also should just not be done).


Search the archives for my description of a simple current-limited power supply for electrophoresis at 220V.  The description is as follows. Total cost about $22-$25 from components bought online, no electronics knowledge required, some soldering is required.   Uses a 120V AC to 12V DC cigarette lighter adapter, then a 60W, 12VDC to 220V AC automobile inverter (EU version, for 220VAC), an EU wall plug (to plug into the EU automobile inverter), a bridge rectifier, and a filtering capacitor.   That yields 220VDC, current limited to 1A.  

Don't forget that AC voltage is listed as RMS so the actual peaks are higher (1.4x).

It would be possible to put all this together on a custom circuit board, overall though not really worth the effort since the inverter uses a switching power supply internally which would require some tuning to get right.  It would be a good project for an undergrad EE as a class project though, for ex. in a Power Systems class.


## Jonathan Cline
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[Josiah Zayner]

So from what I am understanding from what everyone is saying (Thanks for the comments) is that if I cover the circuit in a box to allow a  ground and add in inductors to isolate it from the AC it should be fine?

Most all power supplies have the final DC output at > 100VDC and a couple hundred milliamps so that should not be an issue only with this device.

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[Jonathan Cline]

No you won't be fine.  You need to add 2 fuses and PTC at a minimum.  And even then it is about as good an idea as playing with EtBr in your kitchen, i.e. not a good idea at all.

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[Josiah Zayner]

I still don't understand why it would then still be a bad idea. Maybe you could email me off list to discuss more in depth.

Josiah.Zayner [at] gmail

[Simon Quellen Field]

Let's look at what is needed for electrophoresis, and what is reasonably safe.

Current is what moves things through the gel. The more current, the faster things move.

Current is also what heats the gel. Too much current, and the gel falls apart, but even before that the results may be compromised.

Current is also what kills people.

"http://hypertextbook.com/facts/2000/JackHsu.shtml"

It seems that 60 milliamperes is an upper limit for safety, but 15 milliamperes might be enough that you lose the ability to let go of the electrode. 10 milliamperes is painful.

I have seen mentions of common electrophoresis currents in the range of 20ma to 41ma. I have also seen higher currents used but presumably we want the lowest that is effective so we can remain as safe as possible while getting the job done.

Electric fences pulse the current, so that if you touch the fence, it hurts, but you can then let go. This seems like a good safety measure to add to a home-brew power supply if we are using more than 15 ma.

It is not hard to use transformers to isolate the power supply from ground. That is good practice. Add a ground fault circuit interrupter (your lab should have one anyway, like kitchens and bathrooms do).

If you have a voltage of 220 volts, a 15 k ohm resistor will ensure you don't go above 15 milliamps. For 120 volts, use 8k ohms. This is the maximum short circuit current before the power goes through the gel -- i.e. what you would feel if you grabbed both electrodes. This means our amateur power supply would limit the size of the gel we could run, and increase the time it took for the run, in the name of safety.

Measure the current going through your gel when you do a successful run. Then calculate the resistance you need in order to cut that in half (Ohm's Law), and do another run, probably for twice the amount of time. Continue reducing the current until it is below 15 ma, or until you no longer get a good run, or until the time it takes to do a run is out of the question. That will give us some data to use in deciding whether the idea of a safe electrophoresis power supply is possible( it may not be). There are no safe shotguns or chainsaws, but some people still keep them in their homes.

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[Josiah Zayner]

The electrophoresis power supply in my lab runs at hundreds of milliamps so I feel comfortable using at least that much.

I don't think this is about what can kill you because my laptop power supply outputs ~ the same amount of wattage 90W.
I Googled "death by laptop power supply" and couldn't find anything.

I assume that sticking my right finger one plug and my left in the other plug of this power supply would not be a good idea. But otherwise how can one really hurt themselves with this? Isn't what people are saying the same for anything? for a wall socket and any power supply and many types of electronics?

I don't know if I would suggest people use EtBr at home but thousands or hundreds of thousands of professional Scientists have used it consistently for tens of years and there is not a cancer epidemic amongst us.

Gel green is $200 for 4L at 3x. For 50mL gels that's 250 gels. or $0.8 per gel
Ethidium bromide is $55 for 10mL 1% bottle. I usually add 2uL to a 50mL gel. That's 5000 gels at $0.01 a gel
That's almost 100 fold cheaper. I would use it at home if I could afford a nice UV-illuminator. Instead I use methylene blue which is super cheap but also super awful resolution-wise.

There was a recent discussion in a stem cell thread saying that there should be no working with mammalian cell culture because it could be hazardous.

What are DIYBio people allowed to do these days?

I thought this was a cool little hack that costs ideally a couple bucks, I tested it thoroughly and think it would help alot of people out, it has helped me out but I guess people will only die from using it.

I guess I will try harder and hopefully no one will suggest my next hack or experiment will kill someone. :)

And Jonathan, no I will not take that blog post off the internet, that really cracked me up though. I mean on a scale of 0 to 9 this is probably a 1 or 2. I mean have you ever browsed the instructables website? heh

Thanks again everyone for the feedback though. I think I learned that it is good to keep other people's safety in mind.

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[Jonathan Cline]

It's nice to know you'd use EtBr at home. That's a good data point for
certain people.

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[Simon Quellen Field]

Understanding Ohm's Law is key to understanding electronics in general, and this topic in particular. I assume you know it well, but some others on the list might not, so a short review might be in order.

The current in a circuit is the voltage divided by the resistance.

If I wanted 10 ma to go through my body, from one thumb to the other, I would first need to know what the resistance was between my thumbs. So I take my multimeter, set it to Ohms, lick my thumbs, and hold the leads. Depending on how hard I press on the leads, I get between 100,000 and 150,000 ohms. Try this yourself to get the value for your body.

Now we have the resistance, and we know the current we want, so we solve for the voltage needed to provide that current. 10 milliamperes times 100,000 ohms is 1,000 volts.

That's for filtered DC.

With AC or pulsating DC, we have the problem of capacitance at the junction between the skin and the electrode. The dry skin acts like a dielectric, leaving the electrode and the salty water under the skin as the plates of the capacitor. This dramatically lowers the resistance of the body, into the single k ohms range. This is why grabbing a 120 volts AC in your hand makes it impossible to let go -- 15 milliamperes or more are causing the muscles in your hand and arm to contract involuntarily.

Given that an 8 pack of 9 volt batteries costs about $20 and can be clipped together in series to provide 76.8 volts in a DIY-friendly, no soldering required fashion, we might look into how well that works for electrophoresis. I's still add a current-limiting resistor in series though. That 8 pack will last about 50 hours at the 10 ma rate, or 25 hours at a 20 ma rate.

You could spring for rechargeable batteries if that became an issue.

In my country, you won't get into legal trouble telling kids how much fun it is to French kiss light sockets. But that doesn't make it a good idea. If you add an isolation transformer, a current-limiting resistor, perhaps a filtering capacitor, and recommend that the device only be plugged into a GFCI socket, you might not get angry parents threatening wrongful death lawsuits. Making it difficult to touch any of the metal parts (like using a plastic drawer to slide the gel into contact with the electrodes that are protected by a plastic cover) might prevent you from suddenly throwing the device through a window when you brush against it accidentally.

You built a nice device, and it works. But when a middle school kid builds the same device for his science fair project, will he be as careful as you were? At least mention the risks, and ways to mitigate them.

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[Jonathan Cline]

One critical point about dealing with AC is that in a failure case, the circuit may not blow to create an open circuit.  There's a smaller probability esp with a bridge (~5% ?) that the circuit will fail as a short.  Thus creating a direct wire to the source of the AC.

On 7/4/13 2:59 PM, Simon Quellen Field wrote:

In my country, you won't get into legal trouble telling kids how much fun it is to French kiss light sockets. But that doesn't make it a good idea.

 

Well said.   Also it's disappointing to see this from a univ student where just walking over to another building to talk to some EE power systems guys and get the scoop (and an earful) first hand.   There are many older published articles on exactly the circuit suggested with similar caveats to everything said here tho obviously no homework was done, plus disregard for MSDS, that's what I think is the real bummer.   diybio is supposed to be self policing to avoid possible future government regulation and I think we just got told "shove it I'm gonna do what I want".

[Josiah Zayner]

Jonathan
I don't understand why you are continously trying to disparage me?
I did search online and there is not much info on using a voltage rectifier directly as a power source like I do in the circuit. I assume because it is pulsating DC and people would tend to not want to use pulsating DC?
The link Patrik posted(I think it was Patrik) has an almost identical circuit to mine except it has a single fuse and the website is meant for high school students it looks like? So I guess I am not the only one.

University of Chicago despite being one of the most prestigious schools in the world does not have any engineering departments.

There is no disregard for MSDS. Search online. Ethidium Bromide disposal is not regulated by the EPA. Most states do not have regulations regarding it's disposal either.

I am sure Ethidium Bromide is mutagenic if  inhaled in high quantities or consumed in large quantities or placed it on the skin in high quantities. I have worked with Ethidium Bromide for ~10 years and I can't recall it ever even touching my skin... I wear gloves as when working with it as I assume most people wear gloves when doing lab work especially with potentially hazardous chemicals? Again, it would seem only logical that if Ethidium Bromide was so dangerous there would be an outbreak of cancer amongst professional Scientists but there is not...

Anything else you want to attack me about?

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[Alexey Zaytsev]

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.

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[Jonathan Cline]

Maybe explain why you're taking this personally.  What I see is a lack of simple homework.  Basically your page is suggesting something as unsafe as using a hair dryer while taking a bath in a bathtub  - common sense not to do it, right?   It's a free country, do what you like, I guess.

A good paper on this topic is:

Analytical Biochemistry, Volume 137, Issue 1, 15 February 1984, Pages 156-160, An economic “power supply” using a diode for agarose and polyacrylamide gel electrophoresis, Y. Kadokami, K. Takao and K. Saigo

Quoted is a quick discussion I found with simple web search in a couple mins from 1997 -- interesting that this article below has a similar opinion to mine, why might that be? --   "" These cheap, simple designs are hardly novel and certainly not even worth paying anyone to get a circuit diagram.  ... No one who has any knowledge of/respect for electricity would use a stupid, cheap, live output "power supply".  ""    I have a hard time believing you chose the bridge etc of your circuit but didn't run into any of the related information regarding why direct connection to AC without fuses is bad, so why did you chose to ignore it, is the better question, and now feel personally attacked by those pointing it's drawbacks?

Didn't find anything online?  How long did you look?  Did you look in the journal Electrophoresis?  What search terms did you use?  Ask your PI?   Ever wonder why you didn't find anyone else using such a "simple and cheap" circuit?    It's all been re-hashed before even on this list, which you could also search quite easily in the search bar or with a link like this one https://www.google.com/search?q=electrophoresis+power+diybio
 or here http://www.google.com/search?q=Open+Gel+Box+2.0+Power+Supply
 or here http://openwetware.org/wiki/Talk:DIYbio:Notebook/Open_Gel_Box_2.0/Power_Supply
 or here http://www.google.com/search?q=Simple+power+supply
 or here http://www.eleccircuit.com/transformerless-ac-to-dc-power-supply-circuits/
 or here http://www.electroschematics.com/3752/transformer-less-power-supply/
  note the disclaimer "Caution! Circuit is lethal since it carries high volt AC. Do not touch or test when connected to Mains. Enclose in a shock proof case."
but you wouldn't be enclosing it in a shock proof case, because that's impossible, as the gel box is part of the circuit and directly accessible.


I'll just quote the entire article below
 
--quote --

Simple power supply

David F. Spencer dspencer at is.dal.ca
Mon Sep 22 14:36:19 EST 1997

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---

In article <5vub4d$d5v at cpca3.uea.ac.uk>, AndrewLeech at see.sig.for.email
(Andrew Leech) wrote:

> In article <5v74tp$qdi at news.cuny.edu>, kang at msvax.mssm.edu says...
> >
> >Dear colleagues;
> >
> >I recently developed new power supply which is totaly different from the
convent
> >ional one in that it does not use the core and coil and condenser for
transformi
> >ng AC to DC. Instead I used bridge diode just to change the AC to
directional pu
> >lse current. 
> 
> It's been done. We have a gel electrophoresis system called "Mupid-2", made
> by Cosmo Bio Co Ltd of Tokyo, Japan.
> Although the circuit diagram is not given in the manual, its characteristics
> are almost exactly the same as yours, and it does say "no transformer is
> used"...

And the Mupid is an extremely dangerous rig.  We have a Mupid (not a
Mupid-2) in the lab that I would never use and I have warned those who use
it that this design is nothing short of idiotic.  I just verified what I
already knew and that is that the negative output (in the case of the setup
we have, labelled 'BLK') is at full line voltage (here 115-120 AC) with
reference to any ground (in the UK, "earth") and that means air or gas
taps, sinks and faucets, and the metal cases of essentially any electrical
lab equipment which is grounded, in other words virtually everything sold
in the past 20 years in North America.  The current output of this "power
supply" would be more than enough to kill.

These cheap, simple designs are hardly novel and certainly not even worth
paying anyone to get a circuit diagram.  In 1964 the journal Ann. N. Y.
Acad. Sci. (vol. 121) devoted a whole issue to the then very young field of
polyacrylamide gel electrophoresis. In an article by Baruch J. Davis there
are presented two designs for power supplies, and one labelled "Simple 150
volt supply" is a circuit diagram obvious to anyone with any electronics
knowledge, a bridge rectifier (full wave) with a filter capacitor and a
couple of resistors on the line side of the diodes. It is called a 150
volt, 1 ampere power supply; 1000 mA should allow a fairly effective
electrocution.  Of course such cheap "power supplies" don't have any meters
because they are more expensive than transformers.

> >I made the beta version of this apparatus and wanat to sell with 40 dollars.
> 
> You might want to check it hasn't been patented first.
> 
> Then,
> In article <wqIErKAYO6F0Ewki at genesys.demon.co.uk>, duncan at genesys.demon.co.uk 
> says...
> >
> >This would be 'illegal' in the UK/EEC due to lack of safety and would
> >not be allowed to be sold. If one of the rectifiers fails short circuit
> >you can get full mains AC on the output with lethal consequences.  With
> >no current limiting this would kill. Given that a transformer and
> >condenser are literally only a few dollars surely it makes sense to use
> >that route?

This type of design would never meet standards in either the US or Canada
nor I'm sure in any western European country.  Given that electrophoresis
setups are used with conductive water solutions and that there is
frequently liquid spilled around the gel setup (which can leak as well) and
you've got the makings of a disaster.  And don't be lulled into any false
sense of security that there must be a component failure to cause a
problem; even in a full wave rectifier the output is only one diode from
the input, and the voltage drop across a silicon diode is only about 1.5
volts.  What you get hit with is a pulsed DC rather than a true AC but that
will give you a nasty bite none the less.

Indeed the cost of a basic transformer is trivial, even a simple 120 volt
to 120 volt .5 amp isolation transformer. Be warned though that variable
autotransformers (in the US and Canada sold under the names Variac and
PowerStat) have one line as a straight feed through and thus are not fully
isolated.

> I wasn't in the lab when it arrived, so where it came from...? Anyway it
> is well fused and has a cutout switch in the gel tank to stop you frying
> yourself.

Fuses protect electronic circuits not humans; a 250/500 mA fuse is totally
irrelevant when you are the load on the circuit.

> Ironically though, because the mains supply in the UK is 230V, it has to
> be supplied from a small step-down transformer, so it is isolated.

So they sell this cheap setup with a stepdown transfomer for use in Europe
where the line voltages are 205-250?  That's brilliant marketing, having an
external transformer worth more than the standard power supply.

> Personally I don't like it - but that may be because the gel trays are
> rather small and fiddly for cutting out bands, and of course you only have
> "slow" and "fast".

No one who has any knowledge of/respect for electricity would use a stupid,
cheap, live output "power supply". What amazes me is that we don't hear
about lab personnel being killed by such treacherous setups.

Dave Spencer

-- 
David F. Spencer, PhD
Dept. Of Biochemistry
Dalhousie University
Halifax, Nova Scotia
Canada

dspencer at is.dal.ca
dspencer at rsu.biochem.dal.ca



-- end quote --

[Alexey Zaytsev]

Ok, I've actually looked at the original article.
Don't ever build anything this way. The comment "You can step this
down using a voltage divider in the output of your circuit" is just
stupid, you can't, sorry, Europe. But add a switch and a fuse, build
it a lot less flimsy, put it in a plastic case, and it's not all that
much unsafer then a commercial power supply.

[Jonathan Cline]

On 7/4/13 4:10 PM, Alexey Zaytsev wrote:
> They take the theoretical worst case scenario and run it as
> something that's sure to happen.

You can do anything you like, supposedly. If you've been thru any lab
safety class then you know there's many things which are recommended not
to do. Does it mean they'll all occur - no - they are best practices.
I wouldn't use a bunsen burner in a small closet without any ventilation
for example yet you might insist that you want to - whatever - that
doesn't make it a good practice or allow any justification that "oh,
it's okay! I do it all the time!". I wouldn't add agar to water and put
in a microwave unattended to boil for several mins and then remove
immediately. You know why, right? Yet this discussion has begun to
split hairs, about what is and isn't safe, even if all the information
is freely available with a little looking around. There are a lot of
things which are common sense after basic education of what not to do.
Should we have a long discussion about thousands of them or suggest
people to do a little bit of basic homework first. I suggest the
latter. Especially if the former has already failed to yield much other
than stubborn answer-backs. Do we want some newbie to get hurt and
their parents call the regulators and then talk of regulation starts up
again? Um, no way. Should bad ideas be kept on a web page for others
to similarly try bad practices? I suggest not. You mention GMO
scares, well, that just shows how paranoid the public and/or regulators
can be related to anything mildly scientific looking, yet still you'd
like to stick to less-great practices which might add safety risk? Not
a great idea.

On 7/4/13 4:42 PM, Alexey Zaytsev wrote:
> Ok, I've actually looked at the original article.
> Don't ever build anything this way.

How many votes will go this way, I wonder. ;-D LOL!

> But add a switch and a fuse, build
> it a lot less flimsy, put it in a plastic case,

2 fuses and a PTC at least and it's still not a good idea as I suggested
before. Putting it in a case is still not that safe since the buffer
on the table is always a part of the electric circuit.

> and it's not all that
> much unsafer then a commercial power supply.
>

Guaranteed that the commercial supply will have current limiting. Or it
couldn't be sold commercially, period. A Zener is a simple method of
current limiting but may not be cheap, a feedback circuit is better. At
which point, building the circuit homebrew to save time and money is
questionable, although it still has great educational value.

[Alexey Zaytsev]

1) Fuses don't change anything here, they are to protect your wiring,
not yourself.
2) Current limit makes no sense regarding safety here. The current
that runs through the gel is much higher than the current that would
ever run through a person who's grabbed the electrodes, as the
resistance of the gel is much lower. A commercial power supply won't
shut down if you grab both electrodes as well.

Let me explain the common sense behind the regulations that require a
power supply to have the output decoupled from the input. Suppose you
have a 12v power supply. It's totally safe to grab the electrodes with
bare hands, so most people won't see it as a problem. Until they grab
an electrode and some grounded object, at which point they connect
themselves between the phase wire and the ground. Boom.

In case of a 100+v power supply, you should not grab the electrodes in
the first place, so the fact that you should not grab both an
electrode and a grounded object does not add that much risk.

I think the parallel between anti-GMO and this case is correct, people
tend to overestimate unfamiliar risks.

And one thing that that's related to safety that I've missed. The
switch should disconnect _both_ wires.

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[Jonathan Cline]

Current limiting is more for fire prevention than human safety in my
suggestion. The power supply is basically boiling the buffer slowly.
As it heats up the buffer, the resistance of the gel decreases as it
melts, which increases the current, and so on - until the gel becomes
solution again and resistance is so low that current overloads the
bridge and the bridge starts to smoke. If the bridge burns into a short
or etc, then things will get hot really fast. Then the duct tape will
catch on fire and the case if any will melt. And so on.. This could
all happen without the main's circuit breaker tripping (@ 15A or @
30A). Even GFCI would not be protection in this case.

## Jonathan Cline
## jcl...@ieee.org
## Mobile: +1-805-617-0223
########################

[Simon Quellen Field]

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.

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.

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.

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[Alexey Zaytsev]

On Fri, Jul 5, 2013 at 4:05 AM, Jonathan Cline <jcl...@ieee.org> wrote:
> Current limiting is more for fire prevention than human safety in my
> suggestion. The power supply is basically boiling the buffer slowly.
> As it heats up the buffer, the resistance of the gel decreases as it
> melts, which increases the current, and so on - until the gel becomes
> solution again and resistance is so low that current overloads the
> bridge and the bridge starts to smoke. If the bridge burns into a short
> or etc, then things will get hot really fast. Then the duct tape will
> catch on fire and the case if any will melt. And so on.. This could
> all happen without the main's circuit breaker tripping (@ 15A or @
> 30A). Even GFCI would not be protection in this case.

Why would you install a 30A fuse? That's an assload of current, such
fuse is more appropriate for a small apartment.
For this application, a 0.5A fuse looks more appropriate. The
rectifier from the article is rated up to 1A, so just choose something
lower then that.

>
> ## Jonathan Cline
> ## jcl...@ieee.org
> ## Mobile: +1-805-617-0223
> ########################
>
>
>
> On 7/4/13 5:36 PM, Alexey Zaytsev wrote:
>> 1) Fuses don't change anything here, they are to protect your wiring,
>> not yourself.
>> 2) Current limit makes no sense regarding safety here. The current
>> that runs through the gel is much higher than the current that would
>> ever run through a person who's grabbed the electrodes,
>

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[Alexey Zaytsev]

On Fri, Jul 5, 2013 at 6:28 AM, Simon Quellen Field <sfi...@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.

> https://groups.google.com/d/msgid/diybio/CAA0yOM7tWZ2T8h5uTETuph8qHw27KAeo-Wubq-ws%2BNzWohk4QQ%40mail.gmail.com.

[Cathal Garvey]

<snip>

> There is no disregard for MSDS. Search online. Ethidium Bromide
> disposal is not regulated by the EPA. Most states do not have
> regulations regarding it's disposal either.

It is regulated in some other *countries* though, meaning that even if
we all accept that it's not as dangerous as commonly thought, we're
better off suggesting alternative gel dye methods as "community
standards" that we can expect to be equally applicable to all. Those
with a need for higher gel resolution can upgrade to something more
effective later on.

> I am sure Ethidium Bromide is mutagenic if inhaled in high
> quantities or consumed in large quantities or placed it on the skin
> in high quantities. I have worked with Ethidium Bromide for ~10 years
> and I can't recall it ever even touching my skin... I wear gloves as
> when working with it as I assume most people wear gloves when doing
> lab work especially with potentially hazardous chemicals? Again, it
> would seem only logical that if Ethidium Bromide was so dangerous
> there would be an outbreak of cancer amongst professional Scientists
> but there is not...

We've actually had discussions intermittantly about the safety or lack
of regarding EtBr, and I've seen others off-list between
old-as-the-hills molecular biologists.

Also, there's this:
https://en.wikipedia.org/wiki/Ethidium_bromide#Health_risks

It does appear that, while EtBr is highly mutagenic in the Ames test
when treated with liver homogenate, there's little evidence that it has
the same level of mutagenicity in humans under normal circumstances.
The studies mentioned in the Wikipedia article do not appear to study
teratogenicity, so the safest option would be to assume it is a mild
to moderate teratogen, given its very mixed reputation: avoid exposure
months before making babies (either gender) or while pregnant.

However, all that said, EtBr is still regulated in some countries, I
think. I don't know whether it was law or merely policy, but EtBr had
to be handled by a waste disposal specialist in Ireland in my local
University. We had special decanters with activated charcoal teabags to
collect post-gel EtBr waste, and the "teabags" were sent for disposal.

Given its reputation, difficulty in acquisition in some places, dubious
legal standing, and the fact that you need UV to image (even seconds of
UV transillumination slash transformation/cloning efficiency rates), I'm
still in favour of alternatives like Sybr-Safe.

-Cathal

[Josiah Zayner]

I think most University disposal of EtBr(at least in the US) is self-policing, which is great. The less of a potential hazardous substance in the world the better.

I just found this journal article, no joke, about an internet mailing list(newsgroup) discussion about EtBr disposal from 1994, no joke.

https://docs.google.com/file/d/0B_R75gIJvkFUTTR6WDI0c1k2NVE/edit?usp=sharing

I am glad this issue has not been resolved since 1994 and no new arguments are being made, haha.

The whole "community standards" idea is interesting.

This next part is not meant to be about EtBr specifically
Who decides what should be a community standard? I assume someone would say "the community". Is there a vote? Do a few people just try and push what they think it should be?
In most mainstream Science there are only two things that are used to determine if something becomes akin to a "community standard".

1. Does it work.
2. Is it legal to work with.

To me Science is about doing Science. Maybe I am reckless. But deciding what chemical I think people should use for electrophoresis or as is apparent recently on this mailing list, what power supply people should use, seems bureaucratic. No one cares what chemical or power supply you are using if you are doing good Science.
No journal is going to say, "Well his Science is good but he used EtBr and a sketchy power supply and we don't want to promote that soooo we won't publish it."

I mean bureaucracy is why so many people I know want to leave mainstream Science and it seems to be rearing it's head here.

I hope we as a group are going to give people the most benefits in our doubts and do Scientific work and judge people's Scientific work instead of what and how they do it.

-Cathal

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[Cathal Garvey]

Ah, forgive me if I gave the wrong idea with the word "Standard". I'm
not advocating some sort of design-by-committee for DIYbio protocols,
just suggesting that if a n00b asks "how do I make my first gel?", we
suggest protocols that are:
A) As close to home as possible; methylene blue is a very easy dye to
get a hold of, even if it sucks somewhat
B) As safe and legally unencumbered as possible
C) As easy and user-friendly as possible

That's because, to me, when a person says "how do I run a gel?",
they're asking "How would someone who is totally new to this run a
gel?", whereas when someone asks "What's the best dye to use for high
sensitivity?", they mean just that, and answers can become more complex.

Not that you're wrong to use or recommend EtBr, though I would
*recommend* adding a responsible warning that its safety is under
decades-long dispute, some common methods for disposal (bleach!)
actually make it more toxic, and it may have legal encumbrance in some
areas.

[Eugen Leitl]

On Thu, Jul 04, 2013 at 01:57:47PM -0700, Jonathan Cline wrote:
> It's nice to know you'd use EtBr at home. That's a good data point for
> certain people.

What is the particular problem with EtBr? It's neither
VX nor plutonium.

[Jonathan Cline]

Circuit breaker is 15A or 30A.
The reading comprehension of this thread has apparently taken a dip, I
wonder if the weather is to blame.

## Jonathan Cline
## jcl...@ieee.org
## Mobile: +1-805-617-0223
########################

[Josiah Zayner]

Why are you being such an asshole to people?

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[Josiah Zayner]

I am sorry for calling you an asshole. There is no reason for me to say something such as that on this list.

What I meant to say is:
Why do you resort to personally attacking people?
Maybe you think the things you say are coming across as funny but to me they are not. Your attitude from the beginning was immediately aggressive telling me to take down the post, telling me/us to search for your post and not even commenting on what should be fixed. Then being sarcastic or demeaning towards me about the EtBr. Saying I should be smart enough to just walk across the street to the non-existent EE department. Saying I should have searched properly(I was searching for "rectifier power supply" on Google not "simple power supply" I honestly never would have even thought people would publish electrophoresis power supply designs in Journals so never even looked there). You were posting and specifically quoting parts of email threads to reference how I am stupid for doing what I am doing. Referring to people as having reading comprehensibility problems, perhaps including myself and also perhaps including non-native English speakers.

We are all here to learn or well I think most of us are. There is no need for that. Attacking people personal discourages them, especially when they are looking for feedback on something or trying to give feedback on something.

Criticism is great for Science personal attacks are not. I am sure I have been guilty of it before, I in fact just called you an asshole in this thread. Again, I am sorry for that. I don't really know who you are or your intentions. All I know is what I can take from my viewpoint on what you wrote. I will not post in this thread again. I just wanted to apologize for allowing my emotions to come out. Sadly, in the end I am only human.

On Friday, July 5, 2013 1:24:01 PM UTC-5, Josiah Zayner wrote:

Why are you being such an asshole to people?

On Fri, Jul 5, 2013 at 1:16 PM, Jonathan Cline <jcl...@ieee.org> wrote:

Circuit breaker is 15A or 30A.
The reading comprehension of this thread has apparently taken a dip, I
wonder if the weather is to blame.

## Jonathan Cline
## jcl...@ieee.org
## Mobile: +1-805-617-0223
########################

On 7/5/13 1:16 AM, Alexey Zaytsev wrote:
> On Fri, Jul 5, 2013 at 4:05 AM, Jonathan Cline <jcl...@ieee.org> wrote:

>> If the bridge burns into a short
>> or etc, then things will get hot really fast.  Then the duct tape will
>> catch on fire and the case if any will melt.  And so on..   This could
>> all happen without the main's circuit breaker tripping (@ 15A or @
>> 30A).  Even GFCI would not be protection in this case.
> Why would you install a 30A fuse? That's an assload of current, such
> fuse is more appropriate for a small apartment.
> For this application, a 0.5A fuse looks more appropriate. The
> rectifier from the article is rated up to 1A, so just choose something
> lower then that.
>
>

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[Jeswin]

On Friday, July 05, 2013 7:03:17 PM, Josiah Zayner wrote:
> What I meant to say is:
> Why do you resort to personally attacking people?

One, I didn't see this. It's just a discussion that got heated. I'm
much less competent than most here with circuits. Would I try to build
my own circuit using live current. No way. I can probably build a PC
PSU to Lab PSU.

Second, about EtBr. I hate working with it. I have to make sure the
hold my breath pouring gels. I don't want to breathe TAE buffer fumes,
much less EtBr. It will get all over your workbench from when you hold
the gels and off of your stained gloves. Outside of a dedicated home
lab space, I wouldn't suggest anyone work with it for DIY purposes.

PS Now I know why Eugen keeps writing to "bottom post" replies and
trim/edit the original replies. Everyone is going off on a different
tangent; no one has any idea what the previous guy wrote.

[Mega]

I heard that farmers use Ethidium Bromide intravenously to treat parasites in cows. Thus it can't be that dangerous.

A professor of mine always tells us, anything that stains DNA is dangerous. EthBromide, SybrGreen/Midori Green, they all are accumulated between the DNA strands, which may cause mutations.

> assume that sticking my right finger one plug and my left in the other plug of this power supply would not be a good idea.

The finger yes. just make sure the current does not run through your heart (don't touch it with two hands! or cross your hands while they touch)

[Cathal Garvey (Phone)]

Orally IIRC, not intravenous..

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[John Griessen]

On 07/04/2013 11:33 AM, Josiah Zayner wrote:
> Most all power supplies have the final DC output at > 100VDC and a couple hundred milliamps so that should not be an issue only
> with this device.

No, the safety problem is common to all that perform that way. It's a higher than safe power level.
So, it needs consideration in design, like insulated cabinet interlocks for both output wires.

On 07/04/2013 01:22 PM, Simon Quellen Field wrote:> Electric fences pulse the current, so that if you touch the fence, it hurts,

but you can then let go. This seems like a good
> safety measure to add to a home-brew power supply if we are using more than 15 ma.

And concepts like that...

"or until you no longer get a good run, or until the time it takes to do a run is out of the question. That will give us some data
to use in deciding whether the idea of a safe electrophoresis power supply is possible( it may not be). There are no safe shotguns
or chainsaws, but some people still keep them in their homes."

and decisions like keeping chainsaws around.

"The electrophoresis power supply in my lab runs at hundreds of milliamps so I feel comfortable using at least that much. "

Why? That sentence sounds like faith in brand names that will save one from electrocution. They won't.

And then again Alexey is right on target here:
On 07/04/2013 06:10 PM, Alexey Zaytsev wrote:> 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.

Josiah, you just don't sound very experienced with electricity and I want you to be careful.
Some of your descriptions are disconnected and inconsistent, thus, probably unsafe
experimenting going on. I like Alexey and Simon's style of suggestions best -- make it
less easy to make a mistake, but no need to go overboard.

[Andreas Sturm]

I once had a printer power supply that had 16V AND 32V DC at once... (strange thing, it had 3 wires. Btw, it died and I found no spare part below 42€)

If you can get such a power supply, that will be as cheap and safe as possible.

I remember we calculated how much Volts are dangerous for humans back in school... You need to know the value of resistance for the human body, and how much milliamps are dangerous... So U=I*R => 60V conservatively calculated.

32V is rougly 1/3 as 100V so you need the triple time, but are still perfectly safe.

Perhaps one could also find 50V or 55V power supplies?

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[Avery louie]

As someone mentioned, switching power supplies can be haf for about 20-40 bucks in the 50-98 volt region.

Not only are they cheap amd pre-assembled, they are also very efficient.

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[John Griessen]

On 07/10/2013 06:25 AM, Avery louie wrote:
> As someone mentioned, switching power supplies can be haf for about 20-40 bucks in the 50-98 volt region.
>
> Not only are they cheap amd pre-assembled, they are also very efficient.
>

And they are always isolated by their nature, (so you can ground either output lead to the sink without sparks),
so no extra parts on that recommendation.

[Avery louie]

Also did I mention they are adjustable?

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[Abizar Lakdawalla]

Old discussion, but I finally built an electrophoresis power supply similar in concept to Josh's idea. Details on the build at instructables.

https://www.instructables.com/id/DIY-Power-Supply-for-Gel-Electrophoresis/

[Otto Heringer]

Awesome documentation. Congratz!

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