Trace separation

I building a level converter with a bunch of optical isolators. The conversion is to and from 130 VDC to 5 VDC/3.3VDC. So, a number of traces on my PCB will have the 130 VDC (low current, only 10’s of ma’s). What would be a good trace separation for these traces. I would like to have as much as possible, but at the same time do not want a monster board. Actually, since there are so many of these high voltage traces, some of them will be wired between pads. Thanks for the help, Mike.

Generally I don’t like to do question a posters design motives, but… :wink:

If it is so low amperage why bring potential problems to the board level? My printer, my laptop, some of my TV’s all use wall warts. It also makes a fix easier if one side or the other of the voltage has a problem.

That said I did a quick search and found calculators. Some of seem to be concerned with layer separation also.

What I’m doing is connecting my 1959 Friden flexowriter to my DEC PDP8E computer. Problem is the Friden uses 130 VDC logic and is non ASCII. So I made a circuit (wirewarpped) that does this conversion with a Raspberry PI. Since the curcuit is functional, I thought I’d try and make a PCB out of this circuit. Thanks for the reference,Mike

I totally missed the DC part of the 130V. Sorry. Opps. :wink:

OMG. Sweet memories. The first real computer I worked with was a PDP8 (1970). Wire core memory and all…

What does this mean:

I have a vision of a 2.54mm pitch DIP IC with 130Vdc tracks routed between it’s pins.
There are norms and websites that post guidelines about PCB track spacing for different voltage levels. This forum just reminded me I wanted to post the same link as hermit already did. The minimum is apparently around 200V/mm, but this assumes clean PCB’s. Mains voltage on PCB’s requires a creepage distance of 8mm as a safety precaution. It also depends on the sort of damage done wen “accidents” happen. Will it just change the state of some relay that results in a mis typed character, or will irreplaceable old vintage IC’s release their magic smoke?

Maybe an “hybrid” approach is more suitable. Put most of the footprints and tracks on the PCB, and then use insulated wires for the 130Vdc wiring. An easy way to do this, is to design a 4 layer PCB, and then dedicate a PCB layer as a presentation of your air wires. Make sure to use big fat via’s so you have pads to solder your wires to.

You can of course also order a real 4 layer PCB. When you put 130Vdc wires on internal layers there is no need at all to increase the clearance. 0.2mm will be plenty. It’s only the places where the PCB is exposed to dirt and contamination that the clearance has to be increased.

Which lead to the document below. It’s a quite big list of computers existing in 1966, combined with some articles. There is even an description of what an operating system is, and why it would be useful to use one on a computer :slight_smile:

if your question regards the crafts part with Kicad: I use the B+FMask layers to draw isolation gaps. After manufacturing they are still visible if you look through the pcb against the window. In photo the isolation gap is shown dark green. This gap is helpfull at placing the components and must not cross by any traces. If you need to cross, the design is wrong and needs additionl components like optocouples, Relais or DC/DC converters to bridge the isolation gap.

If your question regards the design part, its usefull to have minimum 1mm/100Volt. If your design allows, take more or consider “bottle-neck” lines for partitionally thinner gaps under some components.

IPC-2221 is the goto for creepage distances and kicad’s calculator includes this.
I am assuming this is sea level so the two of most concern are

  1. B2
  2. A6

This however only considers a pollution degree 2. Personally I would add as much as I can, possibly slot the card and consider some form of coating (hot glue for instance)

1 Like

Paul, in my attempt to keep the PCB as small as possible, I’m having trouble with some of the traces crossing the board. So, I have decided that I would use wire for some of the 130 VDC traces. Instead of a trace between certain parts I would place a pad near each part and simply install a wire (with the appropriate insulation). This is only my second PCB that I have made. Mike

Neat article. I have forgotten about those old Brainiac kits that were available in the stone age.

Janvi, After reading some internet info, I have decided to use 40 volts/mm. My experience with building pcb is limited. I’ll give what you have mentioned a try. Thanks, Mike

40v/mm is way conservative.
40V/mil is more like it.

I’m sorry, I mis typed. I meant 40 volts/mil, MIke

FWIW, I’ve used 40v/mil for boards that can see up to 480V, and have not had a failure in normal operation. The limiting factor is generally the pin-pin spacing on the DIN connectors.

Of course, a lighting strike will cause an arc, but that would happen with even a grossly over-designed board.

40 volts/mile?

And indeed, if you design a PCB with 40v/mile and guesstimate the voltage of a lightning strike at 300kV, then you will get quite a big PCB and it’s also likely to be hit by multiple lightning strikes.

Well, this is just for my use. I suppose I can live with lightning. The Friden/PDP8E will be unplugged most of the time. It is not as if these machines are being used a lot. The wire wrapped board works just fine and I have not had any problems with flash over or lightning.
Actually, right now I’m having trouble routing the traces on this rather small board (4in x 4in). I have 36 resistors, of which half have to be 1/2 watt and the rest 1/4 watt. Those take up quite a bit of the board space. I also have 9 transistors and six IC’s. I’m attempting to get this all on a two sided board. So far I have gone through 5 iterations of the layout and still run into problems. Mike

That does not sound excessive for a 100x100mm PCB, unless those IC’s are big like DIP40. You also have not mentioned connectors, and those can take up a significant amount of space too.

Footprint placement is an extremely important step in PCB design. It’s easily the difference between an easy to route PCB or an impossible PCB. Allowing for wires can significantly ease the pcb design too.
I’m always curious, can you post a screenshot of this PCB?

Well, I’m getting an education, as my Dad would say. I’m using a 22 pin edge connector (22 pins on each side of the PCB). Things that have cleared the way so to speak have been rearranging the parts, looking for smaller footprints, rotating the parts, rearranging the pins on the connectors. I’m getting closer. It’s kinda fun, like a puzzle, but so far I’m still losing, but have not given up. I have only done a handful of PCB’s. All the early ones were small and simple. This one is a little more difficult. I’m sure that you experienced guys could whip this out pretty quick. I need plenty of breaks in that I’m getting old and can not see as well as I did. Thanks for the help, Mike

There is nothing difficult about a PCB for a “clean” 130Vdc. CRT TVs had plenty of circuitry at these levels.
What matters is keeping your 130V signals away from the low voltage circuits at the connectors, to allow a logical component placement.
Your typical optoisolator is rated to withstand 3 kV for surviving dirty AC power

Well… at long last, I got all the traces and footprints onto the PCB. Had to use a dozen or so ‘via’s’. My general approach was to group footprints together according to their relative electrical connection. Then view the rats nest. At the beginning I had many twists or air wire crossings. I figured that these had to be minimized. Thought a process of rotating and re positioning footprints of the parts and the connector pads the majority of the crossings were eliminated. The remainder were resolved using vias. Although I have the connections correct ( the error checker says I good ). Next I want to ‘straighten out’ the PCB, add some labeling and move some of the part labels so I will be able to see them. Lastly I want to recheck my schematic to be sure everything is OK. Should I check anything else? Thanks for the help, Mike