Re: [DIYbio] Current and voltage reqs for electrophoresis power supply

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.

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