strategies for high voltage on PCB, wire terminals

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

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

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

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.

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

Use a pcb connector !

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

What *seems* may not actually *be*.

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.

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

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

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

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.

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

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.

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

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.

Thanks.

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

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.

Hardly.

My first pcb layouts were taped up 34 yrs ago.

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

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

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

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

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

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

Best regards, 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

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. ;-)