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

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.

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