strategies for high voltage on PCB, wire terminals

[mw]

Is there a book or link that gives some hints on properly designing a pc
board so that it works well with ~100 VDC on the traces? I think that
having this high voltage on the pcb will cause a break down of the board
material (after several years). I want to prevent this. Is it as
simple as using large spaces between the traces? Using conformal
coating or varnish? Or is there a material other than FR4 fiberglass
that is available?

Also, I will want to attach a big transformer to the pcb and I know it
is bad to run wires directly into a pcb because the solder can be
brittle and this will cause the wires to be weak. It's also a hassle to
unsolder for repair (the traces get ruined due to solder gun heat). So
is there a terminal or "turret" like on tube amplifiers that can be used
to protect the pcb? Or maybe this is a lot of worry about nothing. But
I do want my power supply project to last for several years.

Any ideas for a simple wire terminal to save the pcb? I don't want to
use a connector because they can go bad after several years. Soldered
connections seem simpler and more robust for longevity.

 

[John Larkin]

Is there a book or link that gives some hints on properly designing a pc
board so that it works well with ~100 VDC on the traces? I think that
having this high voltage on the pcb will cause a break down of the board
material (after several years). I want to prevent this. Is it as
simple as using large spaces between the traces? Using conformal
coating or varnish? Or is there a material other than FR4 fiberglass
that is available?

100 is *not* high voltage! Just use reasonable spacing (50 mils should
be plenty) and coat it if you expect a lot of moisture. We do
kilovolts on FR4, uncoated.

Also, I will want to attach a big transformer to the pcb and I know it
is bad to run wires directly into a pcb because the solder can be
brittle and this will cause the wires to be weak. It's also a hassle to
unsolder for repair (the traces get ruined due to solder gun heat). So
is there a terminal or "turret" like on tube amplifiers that can be used
to protect the pcb? Or maybe this is a lot of worry about nothing. But
I do want my power supply project to last for several years.

Any ideas for a simple wire terminal to save the pcb? I don't want to
use a connector because they can go bad after several years. Soldered
connections seem simpler and more robust for longevity.

Molex-type (nylon shell, big fat crimp pins) connectors are fine. But
faston lugs are good, too. Solder the blade to the board and crimp a
push-on lug onto the tranny wire.


John

 

[Pooh Bear]

Is there a book or link that gives some hints on properly designing a pc
board so that it works well with ~100 VDC on the traces? I think that
having this high voltage on the pcb will cause a break down of the board
material (after several years). I want to prevent this. Is it as
simple as using large spaces between the traces? Using conformal
coating or varnish? Or is there a material other than FR4 fiberglass
that is available?

For recommended spacings check EN60065 ( or the original IEC ) Figure 10 .

That kind of voltage is no trouble at all unless you intend installing in a
condening climate. Even then - normal solder resist will provide modest
insulation on the surface.

I just did a pcb with those kind of voltages on it and I used 0.5mm between
traces ( good for around 150V IIRC )

Also, I will want to attach a big transformer to the pcb

That's generally a *bad* idea for many reasons.

and I know it
is bad to run wires directly into a pcb because the solder can be
brittle and this will cause the wires to be weak. It's also a hassle to
unsolder for repair (the traces get ruined due to solder gun heat). So
is there a terminal or "turret" like on tube amplifiers that can be used
to protect the pcb? Or maybe this is a lot of worry about nothing. But
I do want my power supply project to last for several years.

Use a pcb connector !

Any ideas for a simple wire terminal to save the pcb? I don't want to
use a connector because they can go bad after several years.

Uh ???? Not in my experience. Are you operating this in a corrosive
environment ?

Soldered connections seem simpler and more robust for longevity.

What *seems* may not actually *be*.


Graham

 

[Pooh Bear]

100 is *not* high voltage! Just use reasonable spacing (50 mils should
be plenty) and coat it if you expect a lot of moisture. We do
kilovolts on FR4, uncoated.

You do know that outside the USA 50 'mils' is verbal shorthand for 50 mm ?

I've never been able to work out why you guys call a thousandth of an inch a
*mil*. Over here its a thou, as in 'thousandth'.

And yet this absurd measurement is perpetuated in almost every pcb layout
package - since US suppliers know no better or want to impose their funny
quirks ? I dunno.

Graham

 

[John Larkin]

You do know that outside the USA 50 'mils' is verbal shorthand for 50 mm ?

50 mm would work at 100 volts, too.

I've never been able to work out why you guys call a thousandth of an inch a
*mil*. Over here its a thou, as in 'thousandth'.

Thou means thousand here. "Thou" is shorthand for $1000. We have so
much money we need words like that.

And yet this absurd measurement

How is "mil" any more absurd than "thou"? It sure sounds nicer.

is perpetuated in almost every pcb layout
package - since US suppliers know no better or want to impose their funny
quirks ?

300 million people don't have quirks. 300 million people make the
rules.

I dunno.

The suppliers are mostly American and their customer base is mostly
American. So does it follow that they should favor the conventions of
(whatever tiny country you care to name)?

John

 

[Ban]

You do know that outside the USA 50 'mils' is verbal shorthand for 50
mm ?

I've never been able to work out why you guys call a thousandth of an
inch a *mil*. Over here its a thou, as in 'thousandth'.

And yet this absurd measurement is perpetuated in almost every pcb
layout package - since US suppliers know no better or want to impose
their funny quirks ? I dunno.

Graham

Seems you are only short time in the business. Nobody will mix up mils with
mm, even the German software Eagle has that by default for the drill
diameter.

 

[mw]

For recommended spacings check EN60065 ( or the original IEC ) Figure 10 .

That kind of voltage is no trouble at all unless you intend installing in a
condening climate. Even then - normal solder resist will provide modest
insulation on the surface.

I just did a pcb with those kind of voltages on it and I used 0.5mm between
traces ( good for around 150V IIRC )

That all sounds reasonable to me. I will put spacing of 100 mil (2.5mm)
between the spaces where it's easy to do it. I have plenty of room.
I won't be soldering the transformer such that it is supported by the
board. It is one of the kind that comes with flying leads.

That's generally a *bad* idea for many reasons.

Yeah. I can't disagree, but the board will need power.

Use a pcb connector !




Uh ???? Not in my experience. Are you operating this in a corrosive
environment ?

The environment is potential corrosive / condensive. Plus there is
vibration, including likely shock from mishandling mishandling by the
customer (expected falls to the floor... "accidents"). And of course it
will be getting shipped during delivery. All this is tough on
connection points.

What *seems* may not actually *be*.

I agree that it's possible to implement good ideas badly, or
misinterpret the problems and waste effort.

 

[mw]

100 is *not* high voltage! Just use reasonable spacing (50 mils should
be plenty) and coat it if you expect a lot of moisture. We do
kilovolts on FR4, uncoated.

I'll probably go with .100" (2.5 cm) spacing where it is easy to do. I
want a little overdesign in this, just to remove uncertainty.

Molex-type (nylon shell, big fat crimp pins) connectors are fine. But
faston lugs are good, too. Solder the blade to the board and crimp a
push-on lug onto the tranny wire.

I'll take a look at them. I'm still a leaning a little toward the
soldered connections, for simplicity in tough long life use.

Thanks.

 

[Adrian Tuddenham]

Is there a book or link that gives some hints on properly designing a pc
board so that it works well with ~100 VDC on the traces? I think that
having this high voltage on the pcb will cause a break down of the board
material (after several years). I want to prevent this. Is it as
simple as using large spaces between the traces? Using conformal
coating or varnish? Or is there a material other than FR4 fiberglass
that is available?

I have come across laminated boards where moisture found its way into
the board material and caused HV to turn up in unexpected places, but I
don't think there is much risk of this happening with modern board
material.

 

[Bob Eldred]

You do know that outside the USA 50 'mils' is verbal shorthand for 50 mm ?

I've never been able to work out why you guys call a thousandth of an inch a
*mil*. Over here its a thou, as in 'thousandth'.

And yet this absurd measurement is perpetuated in almost every pcb layout
package - since US suppliers know no better or want to impose their funny
quirks ? I dunno.

Graham

A mil is a thousanth of anything like milli..meter milli.. liter. The mill
as an abbreviation comes from the decimal inch system which is like the
metric system based on the inch instead of the meter. There is nothing magic
about meters in fact in many ways they are an inconvienient length. Even
more confusing is the use of the word "tenth" in the US system. A tenth is
a 10th of a mil or a 10 thousanth of an inch, 0.0001 in, 2.5 microns. I
myself prefer the femto-light-year. It's a measurement that's much easier to
visualize (sic). Sometimes we use furlongs also.
Bob

 

[John Larkin]

I'll probably go with .100" (2.5 cm) spacing where it is easy to do. I
want a little overdesign in this, just to remove uncertainty.


I'll take a look at them. I'm still a leaning a little toward the
soldered connections, for simplicity in tough long life use.

If you solder stranded wire to a board, some solder will wick up the
strands some distance and then stop. That point is a stress
concentrator; if the wire is vibrated or flexed, strands will break
there; try it. Mil-spec and NASA soldering discourage this and have
special anti-wicking tools and rules.

And if you don't use a good plated-through board, wire stress will
break pcb traces. Soldering big wires (or any wires, actually) to a
board is nasty.

John

 

[Pooh Bear]

Seems you are only short time in the business.

Hardly.

My first pcb layouts were taped up 34 yrs ago.

Nobody will mix up mils with
mm, even the German software Eagle has that by default for the drill
diameter.

You'll have fun finding inch sized drills in Germany ! Even when I did that
tape up 34 yrs back I never considered anything other than metric size drill
bits.

Graham

 

[Fred Abse]

A mil is a thousanth of anything like milli..meter milli.. liter

At one time, the Cyprus pound unit of currency was divided into 1000 Mils.

 

[keith]

At one time, the Cyprus pound unit of currency was divided into 1000 Mils.

The US dollar is often expressed in mills (one tenth cent) too, though
there is no currency in that denomination. ;-)

 

[John Larkin]

At one time, the Cyprus pound unit of currency was divided into 1000 Mils.

In the US, another meaning of mil is 1/10 of a cent, 1/1000 of a
dollar.

So a mil = $0.001

a thou = $1000


'Mil' can also refer to a tax rate of 0.1%. Local school taxes on real
estate is sometimes called "millage."

There are no 'mil' coins, and pennies are going out of style. Most
small stores commonly round off a penny or two in either direction,
and have little dishes where you can grab a stray penny, or donate
your excess. Yesterday at the Safeway in Kentfield, I was a penny
short of exact change and they let it go. The checker said "I'll just
overcharge the next customer" who was standing right there.

When I was in Russia (USSR, in those days) they'd make change only
approximately, in whatever mix of currencies happened to be handy.
When I'd buy something, I'd just hold out a fistfull of odd coins and
they'd fish around and take whatever looked right. Taxi drivers would
take anything that wasn't a rouble.


John

 

[Spehro Pefhany]

The US dollar is often expressed in mills (one tenth cent) too, though
there is no currency in that denomination. ;-)

Property taxes are determined by the "mill rate".

Usually small currency variations are expressed in "pips" - for
example, you might be able to get a 3-pip spread (0.03%) on a EUR/USD
forex transaction (that's dealing with electronic blips, not physical
currency, but the minimum size (one contract) is only ~100K ).


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

When I was in Russia (USSR, in those days) they'd make change only
approximately, in whatever mix of currencies happened to be handy.
When I'd buy something, I'd just hold out a fistfull of odd coins and
they'd fish around and take whatever looked right. Taxi drivers would
take anything that wasn't a rouble.

In USSR-era Eastern European duty-free shops they would give change
from hard currency notes in chocolate bars.


Best regards,
Spehro Pefhany

 

[Keith Williams]

In USSR-era Eastern European duty-free shops they would give change
from hard currency notes in chocolate bars.

The same thing happens in Canada. When one buys widgets with hard
currency (USD) they often return trinkets with pictures of waterfowl or
bears as "change". ;-)

 

[Spehro Pefhany]

The same thing happens in Canada. When one buys widgets with hard
currency (USD) they often return trinkets with pictures of waterfowl or
bears as "change". ;-)

I hope your definition of "hard" is more accurate in other domains.
;-)


Best regards,
Spehro Pefhany

 

[Keith Williams]

I hope your definition of "hard" is more accurate in other domains.
;-)

Well, your "duck" is still only worth three Washingtons and a
Jefferson. Which is up from a low of two Washingtons, a Roosevelt, and
three Lincolns, three or so years ago but still down from an Indian
squaw, thirty years ago. The looney change your shopkeepers give is
still a losing proposition. ;-)