Maker Pro
Maker Pro

how to separate ground potential

S

Saul Bernstein

Jan 1, 1970
0
Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the fact
that the absolute potential values don't matter, one could say that the 2 kV
are virtually my ground potential. The problem arises by reason of the power
supply. I have to power my board with 5 V and for the mains adapter ground
is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

Thank you

Saul
 
B

Bob Myers

Jan 1, 1970
0
Saul Bernstein said:
Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the
fact that the absolute potential values don't matter, one could say that
the 2 kV are virtually my ground potential. The problem arises by reason
of the power supply. I have to power my board with 5 V and for the mains
adapter ground is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

Sure. Feed it AC and use an isolation transformer. Might have
to get one special-made to withstand that sort of potential
difference. Watch for safety regs. Rectify/regulate on-board.

Bob M.
 
I

IanM

Jan 1, 1970
0
Saul said:
Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the fact
that the absolute potential values don't matter, one could say that the 2 kV
are virtually my ground potential. The problem arises by reason of the power
supply. I have to power my board with 5 V and for the mains adapter ground
is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

Thank you

Saul
Nobody wants to touch this query because if you dont know HV stuff
pretty well, you *will* be incapable of safely implementing any
suggestions.

The idea of using a pluggable adaptor is EXTREMELY DANGEROUS as any
fault could lead to having 4 KV on the plug pins.

Its in the category: Make your will, pay for a funeral plan but dont
bother with life insurance because they wont pay out for suicide.

BUY IN an isolated PSU rated for sufficiently more than your working
voltage, Ground the case to the same ground as the HV source with a
BOLTED on cable (not removable without tools). Have all the high voltage
wiring hooked up by a qualified HV technician and you *may* stay out of
that pine box. *DONT* order anything you haven't cleared with the
technician.

Alternatively why not consider battery power? A SLA battery and a
regulator could easily power most microcontroller circuits for a day's
running then you'd shut down, isolate your circuit, unplug the battery
and recharge it overnight with an off the shelf charger. No more risky
than the rest of your board if the battery is in the same enclosure.

If you need to transfer data, use fibre optic cable or any sort of
wireless link.

If this is an academic project you've just been given for ****s sake
consult with your tutor, the senior departmental technician and the
Prof. You *may* need another project if you are asking this sort of
question here (sci.electronics.basics) and you want to pass the course.
 
W

Wim Lewis

Jan 1, 1970
0
I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. [....]

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

The easy way to do this is probably to use an isolated DC-DC converter.
A few kV of isolation is typical; I'm sure you can find ones with
higher ratings if needed. If you do not have any circuitry whose ground
potential needs to be at 0V then you can use an isolated switching power
supply to go from mains current to a floating 5V output (this would
be cheaper than a non-isolated supply followed by an isolated
converter). The transformer in many power supply designs provides
this kind of isolation "for free".
 
L

legg

Jan 1, 1970
0
Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the fact
that the absolute potential values don't matter, one could say that the 2 kV
are virtually my ground potential. The problem arises by reason of the power
supply. I have to power my board with 5 V and for the mains adapter ground
is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

You haven't indicated the voltage and power requirement for this
housekeeping supply.

At lower power levels, some simple self-constructed solutions are
possible.

RL
 
P

Phil Allison

Jan 1, 1970
0
"Wim Lewis"
The easy way to do this is probably to use an isolated DC-DC converter.
A few kV of isolation is typical; I'm sure you can find ones with
higher ratings if needed.


** One of these might be suitable, if all you need is 1 watt.

http://www.xppower.com/pdfs/SF_IV.pdf

Farnell have them for around $10.

Ground the 5 volt input side ( for human safety ) and install it INSIDE
the HV device.


If you do not have any circuitry whose ground
potential needs to be at 0V then you can use an isolated switching power
supply to go from mains current to a floating 5V output (this would
be cheaper than a non-isolated supply followed by an isolated
converter). The transformer in many power supply designs provides
this kind of isolation "for free".


** Even if you find such a well insulated PSU, the problem is in having 3
or 4 kV to ground on the cable coming out from it - that must not be left
around for folk to touch !!!!

So, the PSU must be fitted INSIDE the device to be powered and the AC power
fed in.



...... Phil
 
P

Paul Keinanen

Jan 1, 1970
0
You haven't indicated the voltage and power requirement for this
housekeeping supply.

At lower power levels, some simple self-constructed solutions are
possible.

At very low power levels, just send optical power up on an optical
fiber and the data down on an other fiber.

This system is used on some high voltage measurement instruments
hanging on an overhead high voltage line.

Paul
 
I

IanM

Jan 1, 1970
0
Paul said:
At very low power levels, just send optical power up on an optical
fiber and the data down on an other fiber.

This system is used on some high voltage measurement instruments
hanging on an overhead high voltage line.

Paul
Thats an interesting technique I've been hearing a little about lately.

Whats state of the art for power over fiber? How big a laser does one
need for how many mW at the remote end? Got any good links?

Thanks.

Ian.
 
P

Paul Keinanen

Jan 1, 1970
0
Thats an interesting technique I've been hearing a little about lately.

Whats state of the art for power over fiber? How big a laser does one
need for how many mW at the remote end? Got any good links?

Do a Google search such as

"optically powered" "current transformer"

should give some useful links.

For instance
http://homepage.ufp.pt/alobo/page8/page5/files/IEEE PPT Conf2001_2.pdf
describe a 300 mW laser at 810 nm and a photocell efficiency of 40 %,
so you would get about 100 mW of usable DC power for the sensor and
the optical transmitter to send back the information.

Paul
 
S

Saul Bernstein

Jan 1, 1970
0
Hi,

thanks for your kind answers so far. To answer your question: The PCB won't
be connected to anything other than the 4kV and the 220V mains.

Saul
 
I

IanM

Jan 1, 1970
0
Paul said:
Do a Google search such as

"optically powered" "current transformer"

should give some useful links.

For instance
http://homepage.ufp.pt/alobo/page8/page5/files/IEEE PPT Conf2001_2.pdf
describe a 300 mW laser at 810 nm and a photocell efficiency of 40 %,
so you would get about 100 mW of usable DC power for the sensor and
the optical transmitter to send back the information.

Paul

Thanks Paul.

6V (open circuit) GaAs photovoltaic diode. It looks like there would be
no particular problem getting 15 mA at 3.3 V for a microcontroller or
whatever. I suspect that it would be out of the price range of the
average hobbyist but if one is building Van Der Graph generators or
similar it might be justifiable.

Its a far cry from two minature PM DC motors coupled shaft to shaft with
a couple of feet of Perspex rod in between :)

Ian.
 
C

CBFalconer

Jan 1, 1970
0
Saul said:
thanks for your kind answers so far. To answer your question:
The PCB won't be connected to anything other than the 4kV and
the 220V mains.

Please do not top-post. Your answer belongs after (or intermixed
with) the quoted material to which you reply, after snipping all
irrelevant material. See the following links:

<http://www.catb.org/~esr/faqs/smart-questions.html>
<http://www.caliburn.nl/topposting.html>
<http://www.netmeister.org/news/learn2quote.html>
<http://cfaj.freeshell.org/google/> (taming google)
<http://members.fortunecity.com/nnqweb/> (newusers)
 
M

MooseFET

Jan 1, 1970
0
Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the fact
that the absolute potential values don't matter, one could say that the 2kV
are virtually my ground potential. The problem arises by reason of the power
supply. I have to power my board with 5 V and for the mains adapter ground
is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?


How about a battery?

At low powers and bad efficiencies, transformers to handle a 4KV
isolation is fairly easy. At bigger power levels or efficiencies
above 50% it gets harder fast.

What does this PCB have to do? How much power etc?

Does the PCB live inside a shield?

At low powers, the simplest design is to use an "air core" transformer
with the primary and secondaries tuned and loose coupling between then
because of the large clearance. The down side is that this tends to
radiate a lot of RF at your operating frequency.
 
P

Paul Keinanen

Jan 1, 1970
0
Its a far cry from two minature PM DC motors coupled shaft to shaft with
a couple of feet of Perspex rod in between :)

At least this mechanical system can be scaled to quite large power
levels :)
http://en.wikipedia.org/wiki/Lyon-Moutiers_DC_transmission_scheme

Other low power isolated power transmission systems include feeding
acoustic vibrations into an isolating rod or using radio frequency
power transmission (after all the isolation distance required is only
a few meters).

Paul
 
P

Paul E. Bennett

Jan 1, 1970
0
Saul said:
Hi,

I have to design a printed circuit board for a high-voltage
environment. Hence, the "ground potential" of the board has to be on 4
kV. Du to the fact that the absolute potential values don't matter, one
could say that the 2 kV are virtually my ground potential. The problem
arises by reason of the power supply. I have to power my board with 5 V
and for the mains adapter ground is really 0 V.

Can someone think of a possibility to supply my board with a mains
adapter (AC/DC 220V/5V) and translate between the two ground reference
potentials?

Thank you

Saul

Yes this sort of thing can be done but you really should know what you
are doing in the high voltage areas when doing projects like this. Some
of the systems I work with have rails of 132kV DC (in the MW region) and
this takes very special handling and checking from the design through
the implementation to maintenance planning before we build such systems.

As many of the professional engineers here who would know this stuff and
know of the dangers it is hardly surprising you are not getting much
help without knowing your level of experience. It is an area that is at
such a level that if you have to ask then you shouldn't be doing this
without adequate oversight and supervision. The professionals will want
to know that you have that in place and by asking here it is obvious
that you probably haven't and it would be criminal for them to offer a
solution.

--
********************************************************************
Paul E. Bennett...............<email://[email protected]>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************
 
W

whit3rd

Jan 1, 1970
0
I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV.

This is the same sort of problem as electron microscopes (and
even microwave ovens) have in driving the filament. The easy
solution is to box up a 6V battery and regulate down to 5V.
The commercial solution is a custom-made, tested, transformer
that safely holds off 4 kV. It's likely to be potted (embedded
in a blob of tar or silicone).

You don't want any of the 4kV parts outside a shielded and
interlocked enclosure, of course...
 
L

legg

Jan 1, 1970
0
At very low power levels, just send optical power up on an optical
fiber and the data down on an other fiber.

This system is used on some high voltage measurement instruments
hanging on an overhead high voltage line.
If the OP would care to respond with the actual requirements, we'd
know if this was a candidate.

RL
 
P

Paul Keinanen

Jan 1, 1970
0
There are neon signs all over the place, often within reach of drunks
........ ?

The output impedance and hence short circuit current of the HV supply
is also on issue. A 4 kV 1 mA should not be that dangerous :), unless
of course if there is a large (stray) capacitance at the power supply
output, which could store a significant charge, which could cause a
nasty electric shock flowing through your body. For instance the CRT
25 kV anode connection has quite a significant capacitance.

There are miniature neon signs within windows advertising a product,
in which the leads or connections could be touched. The short circuit
current is so small that it does not do any harm.

Other typical examples would be simple ionizer with about two dozen
rectifiers and capacitors in a voltage multiplier chain, fed directly
from the 230 V mains. You could touch the output of the chain, but of
course it is a good idea to have a 1 megaohm at the output to limit
the current in case of the extremely rare situation that _all_
rectifiers and capacitors would fail and you would have 230 V mains at
the other end of the resistor.

We do not know if the original poster is using such high impedance HV
source, but in that case using a high isolation transformer to feed
the 5 V side, the transformer stray capacitance (perhaps less than 10
pF) may feed 50/60 Hz hum into the HV line.

Paul
 
Top