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'Creepage, clearance and track width'
2009\09\10@094759 by olin piclist

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Philip Pemberton wrote:
> What I need to know is:
>   - How thick these tracks need to be to carry 1650W

Track width requirement doesn't come from power, it comes from current.

It seems most tables on the net show the temperature rise as a function of
current and width, but not the resistance or voltage drop or some other way
to compute the same thing.  Advanced Circuits has (did about a year ago at
least) a calculator that does give you all these things.  If I remember
right, their web site is http://www.4pcb.com.


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2009\09\10@133658 by Philip Pemberton

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Olin Lathrop wrote:
> Track width requirement doesn't come from power, it comes from current.

Well, that makes sense... Ohm's Law in action.

> It seems most tables on the net show the temperature rise as a function of
> current and width, but not the resistance or voltage drop or some other way
> to compute the same thing.  Advanced Circuits has (did about a year ago at
> least) a calculator that does give you all these things.  If I remember
> right, their web site is http://www.4pcb.com.

Yep - Tips and Tools ==> trace width calculator, which links to
circuitcalculator.com.

For 10A, 1oz copper, and a rise of 10C, that's coming up with 283 mils.
That seems fairly sane... but may make it difficult to wire up the
terminal block connectors I was intending to use:

  Input voltage is 240V AC RMS, or 1.414*240=339.41V peak. Round that
to 340 to make the math easier.

  Per Art of Electronics page 841, "a good rule is 5 volts per mil".
Let's run with that. 340/5=68mils minimum clearance (i.e. the distance
from the centre of track1 to the centre of track2, minus half the width
of track1, minus half the width of track2). Rounding this up to 70mil
clearance...

  Working backwards, to keep a 70mil clearance with a pin pitch of 200
mils, that means each track will be about 130 mils wide, at most. With
1oz copper and 10C temperature rise, that's ~5.75A at most...

So it looks like I'll be using one pair of terminal blocks for each L
contact, one pair for each N. I get the feeling a bag of 25 connectors
might not go as far as I'd originally thought.

Oh well, at least I have a reasonable idea what I'm doing now... :)

Thanks,
--
Phil.
spam_OUTpiclistTakeThisOuTspamphilpem.me.uk
http://www.philpem.me.uk/

2009\09\10@135717 by peter green

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Philip Pemberton wrote:
> Olin Lathrop wrote:
>  
>> Track width requirement doesn't come from power, it comes from current.
>>    
>
> Well, that makes sense... Ohm's Law in action.
>
>  
>> It seems most tables on the net show the temperature rise as a function of
>> current and width, but not the resistance or voltage drop or some other way
>> to compute the same thing.  Advanced Circuits has (did about a year ago at
>> least) a calculator that does give you all these things.  If I remember
>> right, their web site is http://www.4pcb.com.
>>    
>
> Yep - Tips and Tools ==> trace width calculator, which links to
> circuitcalculator.com.
>
> For 10A, 1oz copper, and a rise of 10C, that's coming up with 283 mils.
>  
Do you really need the rise that low?
{Quote hidden}

If you are only dealing with a pair of terminals the pads don't have to
go in the middle of the tracks.
> With
> 1oz copper and 10C temperature rise, that's ~5.75A at most...
>  
but if you allow a 20C temperature rise it's presumably about double
that. Can your really not afford a 20C rise?

2009\09\10@144300 by Geo

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Philip Pemberton wrote:

>    Working backwards, to keep a 70mil clearance with a pin pitch of 200
> mils, that means each track will be about 130 mils wide, at most. With
> 1oz copper and 10C temperature rise, that's ~5.75A at most...

Can you lay out that part of the pcb with tracks running on both sides
(1/2 the width).

George Smith



2009\09\10@152418 by Philip Pemberton

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Geo wrote:
> Philip Pemberton wrote:
>
>>    Working backwards, to keep a 70mil clearance with a pin pitch of 200
>> mils, that means each track will be about 130 mils wide, at most. With
>> 1oz copper and 10C temperature rise, that's ~5.75A at most...
>
> Can you lay out that part of the pcb with tracks running on both sides
> (1/2 the width).

You mean just use a double sided board and run the same tracks on both
sides?

Yes but then I'd need to rig up some form of through plating (probably a
few dozen extra holes and a similar number of Harwin track pins) -- my
home PCB lab is double-sided capable, but not PTH capable.

Cheers,
--
Phil.
.....piclistKILLspamspam@spam@philpem.me.uk
http://www.philpem.me.uk/

2009\09\10@164340 by Geo

picon face
Philip Pemberton wrote:
> Geo wrote:

>> Can you lay out that part of the pcb with tracks running on both sides
>> (1/2 the width).
>
> You mean just use a double sided board and run the same tracks on both
> sides?
Yes - if you can use right angle connectors it is often possible to
solder the pins top and bottom  - otherwise just drill a hole and solder
a wire then trim it off to join the upper and lower layers. It may be
necessary to widen the track slightly from that "via" to the connector
or device pin (or bend the "via" wire over and solder it along the last
couple of mm.)

George Smith

2009\09\10@200555 by Philip Pemberton

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Geo wrote:
> Yes - if you can use right angle connectors it is often possible to
> solder the pins top and bottom

Problem is, all I've got in the way of connectors is:
  - a box full of 0.1in Molex KK connectors (the real ones, sourced
from Digikey -- good to 2A, 250V if memory serves). No R/A connectors,
all straight PCB and crimp-to-wire.
  - A couple of different sizes of PCB-mount terminal block. Again, not
R/A.
  - Some really weird FPC/FFC connectors for an LCD display.
  - Some even weirder FPC/FFC connectors. SMD, with a really nutty
voltage rating (15.3V or something like that -- yes the D/S lists the
point-three)
  - Maybe a couple of 8-way FCi Clincher connectors (which work
*really* nicely for the 0.1in-pitch print-head connectors on the Seiko
MTP printer modules)
  - A valve base. B12A or something like that, to fit a DG7/32 CRT.
I've got the CRT as well :)

> otherwise just drill a hole and solder
> a wire then trim it off to join the upper and lower layers.

A standard DIY wire-via then. Basically what the track pins are, but
somewhat less convenient.

> It may be
> necessary to widen the track slightly from that "via" to the connector
> or device pin (or bend the "via" wire over and solder it along the last
> couple of mm.)

Indeed.

Getting some 2oz board, or simply using more connectors may be an easier
solution (except if I want 2oz FR4 blanks, I have to special-order them).

Although a 10C temperature rise is pretty conservative -- I suspect the
board could survive a 20C rise at ~60C ambient (which is probably
roughly in line with the temperature in the box where the timer and
switches are mounted, while the oven is operating).

Hmm.

--
Phil.
piclistspamKILLspamphilpem.me.uk
http://www.philpem.me.uk/

2009\09\11@144342 by Peter Restall

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On Fri, 11 Sep 2009 01:05:50 +0100, Philip Pemberton wrote:

> Getting some 2oz board, or simply using more connectors may be an easier
> solution (except if I want 2oz FR4 blanks, I have to special-order them).

If you're in the UK then I would certainly recommend these people for PCB
supplies:

http://myworld.ebay.co.uk/lamargroup

Very cheap and very good service and quick delivery; at least they were
when I last bought from them (I stocked up about 6-9 months ago).

And have you tried Rapid Electronics (http://www.rapidonline.co.uk) for connectors
and things ?  They tend to be a lot cheaper than RS, Farnell, etc. and more
geared for low order quantities - but their product range is not as large.

Regards,

Pete Restall

2009\09\14@141717 by Gerhard Fiedler

picon face
Philip Pemberton wrote:

{Quote hidden}

These calculations are for a long track. You can go smaller on a short
piece of track. It will of course become hotter at the smaller piece,
but the larger copper around it will be able to dissipate some of the
additional energy. Possibly the connector helps, too.

Remember that the clearance is a voltage thing and needs to be there
always. But the width of the track is a question of dissipating the
energy, and as long as you can dissipate the energy, you can have
smaller and wider parts in the track.

Gerhard

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