Searching \ for '[ee] A/C 120VAC traces on PCBs' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/pcbs.htm?key=pcb
Search entire site for: 'A/C 120VAC traces on PCBs'.

Exact match. Not showing close matches.
PICList Thread
'[ee] A/C 120VAC traces on PCBs'
2005\12\16@174848 by M Graff

flavicon
face
I've mentioned this in passing before, but hoped to get more advice as
this is my first highish-current A/C device.

I've designed a board that uses TRIACs to control A/C, probably at 120
VAC.  Since there are no outlets on this device, I opted to run only one
leg of the A/C on the board.  IMHO, this SHOULD reduce chances of Bad
Stuff happening, as a short on the A/C traces should only force a
circuit on.

I'm not putting fuses on the PCB either, as the case these are mounted
in will have a fuse.  Is this likely to cause any problems?  My
conscious tells me I should fuse the inputs and outputs on the PCB, but
my mind tells me I should be fine with an external breaker, once again
because a short across the A/C lines cannot be between AC-line and
AC-neutral.  The outputs are also on breakers to limit the current to 5
A/output.

The minimum trace width on this thing is about .250 inches wide, with
2oz copper, so my quick lookup of this means I should have no problems
with the 5 A/circuit, with 15 A max per set of four outputs I need.

Should this be acceptable for a small number of these devices, not mass
production?

--Michael

2005\12\17@120009 by Jesse Lackey

flavicon
face
Hummm... I'm sure more knowledgeable people on piclist will chime in,
but as far as shorts and fuses ... what if a grounded metal object
contacts the pcb?  kerpow.  Or one of the AC devices fails as a short?
Are triacs guaranteed to fail open-circuit?

Personally, fuses are cheap and relatively small, why not use them.

Something I built with solid-state relays (optoisolated triacs) for AC:
http://www.celestialaudio.com/dmx_relay/index.html

The digikey part# for the fuses and fuse holder aren't on the page,
email me and I'll look them up if you'd like.  It took a little while to
find a suitable fuse (readily available, small, 15A, and holders rated
for 15A as well).

2 Oz copper is a good idea.

Good luck!
J


M Graff wrote:
{Quote hidden}

2005\12\17@122725 by M Graff

flavicon
face
Jesse Lackey wrote:
> Hummm... I'm sure more knowledgeable people on piclist will chime in,
> but as far as shorts and fuses ... what if a grounded metal object
> contacts the pcb?  kerpow.  Or one of the AC devices fails as a short?
> Are triacs guaranteed to fail open-circuit?

If a triac fails closed circuit, all it means is the power for that
circuit is on.  I only have one leg of the A/C on this board.

> Personally, fuses are cheap and relatively small, why not use them.

Because an internal fuse requires someone to open up the case, rather
than pressing the externally pressable breaker button.

I think I'll add a fuse on the input to limit the current across the
traces to something I know they are safe for, but not fure each output
to guarantee its limit.  I'll recommend the user add a breaker per
output channel to limit to a safe value, or limit the input to be a max
per-channel safe value.

--Michael

2005\12\17@134131 by Spehro Pefhany

picon face
At 04:48 PM 12/16/2005 -0600, you wrote:
>I've mentioned this in passing before, but hoped to get more advice as
>this is my first highish-current A/C device.
>
>I've designed a board that uses TRIACs to control A/C, probably at 120
>VAC.  Since there are no outlets on this device, I opted to run only one
>leg of the A/C on the board.  IMHO, this SHOULD reduce chances of Bad
>Stuff happening, as a short on the A/C traces should only force a circuit on.
>
>I'm not putting fuses on the PCB either, as the case these are mounted in
>will have a fuse.  Is this likely to cause any problems?  My conscious
>tells me I should fuse the inputs and outputs on the PCB, but my mind
>tells me I should be fine with an external breaker, once again because a
>short across the A/C lines cannot be between AC-line and AC-neutral.  The
>outputs are also on breakers to limit the current to 5 A/output.

A typical glass or ceramic tubular fuse will protect the traces, but not
the semiconductors.

A typical breaker will protect the wiring, but not the traces because they
allow very
high surges for more than enough time to vaporize your traces.

Is the AC line polarized? A ground fault could take out either half of the
circuit
if the plug isn't polarized or if the outlet is wired wrong. If you keep the
neutral half the circuit off the PCB (in relatively thick wires- like in
the line
cord or bigger) you should be able to get away with a single glass fuse in
the hot
(fusing the neutral is not kosher).

>The minimum trace width on this thing is about .250 inches wide, with 2oz
>copper, so my quick lookup of this means I should have no problems with
>the 5 A/circuit, with 15 A max per set of four outputs I need.

Are you sure you actually have 2oz copper? Is the 0.25" for the common line or
for the 5A circuits?

>Should this be acceptable for a small number of these devices, not mass
>production?
>
>--Michael

Watch the clearances, especially to ground and double especially to anything
a user might touch. You can get away with less in the US/Canada in some cases,
but creepage (clearance over a surface) of 8mm+ is good to have. If the
board could have condensation or other moisture on the surface, you'll need
more distance and probably conformal coating or even slots machined into the
board. Avoid having any floating metal in the housing etc.
Nothing connected to the AC line should be possible to touch, or should
be possible to come into contact with anything that can be touched. If in
doubt, have someone knowledgeable look it over (perhaps in mock-up form)
before you have boards made.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\12\17@162608 by Peter
picon face

On this theme, what is the list's opinion on *inexpensive* thermal fuses
?

Peter

2005\12\17@164633 by Spehro Pefhany

picon face
At 11:26 PM 12/17/2005 +0200, you wrote:

>On this theme, what is the list's opinion on *inexpensive* thermal fuses ?
>
>Peter

The type used in many appliances (they open permanently when subjected to
excessive temperature) seem to be fine. What's your concern?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\12\17@170908 by Peter

picon face


On Sat, 17 Dec 2005, Peter wrote:

> On this theme, what is the list's opinion on *inexpensive* thermal fuses ?

Continuing on this theme, polyfuse type protection:

http://www.electronicproducts.com/ShowPage.asp?SECTION=3700&PRIMID=&FileName=marray1.mar2003

I am already using varistors for Tyco but I cannot find the PPTCs they
use for primary protection easily. Has anyone seen these (I can only
find PPTCs to 60V, I need 300V) ?

thanks,
Peter

2005\12\17@175034 by Spehro Pefhany

picon face
At 12:09 AM 12/18/2005 +0200, you wrote:


>On Sat, 17 Dec 2005, Peter wrote:
>
>>On this theme, what is the list's opinion on *inexpensive* thermal fuses ?
>
>Continuing on this theme, polyfuse type protection:
>
>http://www.electronicproducts.com/ShowPage.asp?SECTION=3700&PRIMID=&FileName=marray1.mar2003
>
>I am already using varistors for Tyco but I cannot find the PPTCs they use
>for primary protection easily. Has anyone seen these (I can only find
>PPTCs to 60V, I need 300V) ?
>
>thanks,
>Peter

There are some rated at 600V, but beware, their interrupting capacity is
EXTREMELY limited, a sad joke really.

They are NOT suitable for general use on mains circuits.

An inexpensive 1.25" 3AG glass fuse is typically rated for at least 10,000A
interrupting capacity at 125VAC.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\12\17@183355 by William Chops Westfield

face picon face

>>  fuses are cheap and relatively small

Fuses are HUGE, especially if you want to use common replaceable types.
get depressed every time I try to "harden" one of my PCB designs by
adding fuses...

BillW

2005\12\17@194117 by Xiaofan Chen

face picon face
On 12/18/05, William Chops Westfield <.....westfwKILLspamspam.....mac.com> wrote:
>
> >>  fuses are cheap and relatively small
>
> Fuses are HUGE, especially if you want to use common replaceable types.
> get depressed every time I try to "harden" one of my PCB designs by
> adding fuses...

Fuses are really HUGE but I have to put it in for UL approval. ;-(
Of couse big and samll are always relative to the board size. ;-)
I was using three fuses for one EEx ia product (Intrinsic Safety product
used in explosive environment) and the brand of the fuses to choose for
Ex use was really limited for PTB approval. But it is of course necessary
to put them in so that extra reliability/safety can be achieved.

Regards,
Xiaofan

2005\12\17@212723 by Harold Hallikainen

face picon face
I haven't read this whole thread yet, but I try to avoid fuses in my
products. As pointed out they are big. They also nuisance trip. When the
line current is low enough, I've designed in PTC thermistors for
overcurrent protection. BC Components has a series of them rated at
260VAC. I believe they are a UL recognized component. Our test lab has
listed our products as compliant with UL508 when we use these parts.

The other pain with line voltage on a circuit board is creepage distances.
It's real hard to run any traces when you need to leave so much space
between them!

Harold


{Quote hidden}

> -

2005\12\18@151804 by Peter

picon face

On Sat, 17 Dec 2005, Spehro Pefhany wrote:

> At 11:26 PM 12/17/2005 +0200, you wrote:
>
>> On this theme, what is the list's opinion on *inexpensive* thermal fuses ?
>>
>> Peter
>
> The type used in many appliances (they open permanently when subjected to
> excessive temperature) seem to be fine. What's your concern?

Assembly on printed circuit board by soldering (by careless personnel).
One too long/too close soldering and you have an oopsed product. I would
also like it to be able to take 15A. The ones used in heftier appliances
seem to be right (ex: microwave oven etc). These are bimetal type afaik.

Peter

2005\12\18@152207 by Peter

picon face

On Sat, 17 Dec 2005, Spehro Pefhany wrote:

>> www.electronicproducts.com/ShowPage.asp?SECTION=3700&PRIMID=&FileName=marray1.mar2003
>>
>> I am already using varistors for Tyco but I cannot find the PPTCs they use
>> for primary protection easily. Has anyone seen these (I can only find PPTCs
>> to 60V, I need 300V) ?
>>
> There are some rated at 600V, but beware, their interrupting capacity is
> EXTREMELY limited, a sad joke really.
>
> They are NOT suitable for general use on mains circuits.

Contrary to what the article above says ?

> An inexpensive 1.25" 3AG glass fuse is typically rated for at least 10,000A
> interrupting capacity at 125VAC.

I know but I want fire/overheating protection.

Peter

2005\12\19@095338 by alan smith

picon face
The biggest issue with fuses....is replacement.  I have used PICO fuses for years, generally they never blow, just there...in case....
 
 If you feel like the fuse may blow, and the board is hard to get to replace, then just the simple AGC 1-1/4 with an external holder.  If the board is going to be in a moist enviroment, then decide....is this a throw away ?  Should you pot the assembly?  Maybe a combination...pot the assembly but stick a couple of sockets out of it for the fuse.  It all depends on the application, and if you think a fuse will blow.  Generally, I have found that a fuse will blow if they wire it up wrong...the first time....and after that, they generally never blow UNLESS something really bad happens....and thats what its there for.


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

More... (looser matching)
- Last day of these posts
- In 2005 , 2006 only
- Today
- New search...