Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

PCB Current capacity??

50 views
Skip to first unread message

Fran...@cableone.net

unread,
Jan 19, 2003, 10:24:22 AM1/19/03
to
Hi guys,

I need to connect some fuses and relays and figured a home built PCB
would be the most simple.

Problem is the contacts side of the relay needs to be able to carry
about 25-30Amps. Can a PCB do that??

If so, how?

Thanks in advance.


--

Regards,
Frank R Firestone II

Brett

unread,
Jan 19, 2003, 12:26:34 PM1/19/03
to
see ultracad.com. check out their calculator selection.

I had it up and put in random values, well sort of. 5in length. 500mil trace
width. 2Oz thinkness. Current 30A.

solve for temp change: 67 degree C.

hrumph!

Brett

<Fran...@cableone.net> wrote in message
news:9ffl2v8ouuae05fkh...@4ax.com...

Spehro Pefhany

unread,
Jan 19, 2003, 1:04:18 PM1/19/03
to
On Sun, 19 Jan 2003 12:26:34 -0500, the renowned "Brett"
<tempa...@hostedscripts.com> wrote:

>see ultracad.com. check out their calculator selection.
>
>I had it up and put in random values, well sort of. 5in length. 500mil trace
>width. 2Oz thinkness. Current 30A.
>
>solve for temp change: 67 degree C.
>
>hrumph!

Are you sure you didn't select an internal trace by accident?

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Brett

unread,
Jan 19, 2003, 1:36:44 PM1/19/03
to
Yup you're right. That should be 19.7 C.

"Spehro Pefhany" <sp...@interlog.com> wrote in message
news:irpl2v4hv0uo8umhj...@4ax.com...

Jim Thompson

unread,
Jan 19, 2003, 1:36:10 PM1/19/03
to
On Sun, 19 Jan 2003 13:36:44 -0500,
"Brett" <tempa...@hostedscripts.com>,
In Newsgroup: sci.electronics.design,
Article: <b0eqh5$ogr0p$1...@ID-144300.news.dfncis.de>,
Entitled: "Re: PCB Current capacity??",
Wrote the following:

I've been known to solder a #14 on top of a track to handle big
currents. I've also been know to use real copper eyelets so I could
connect to large stranded wires, but the military frown on it as
"un-inspectable" ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

For proper E-mail replies SWAP "-" and "_"

I love to cook with wine. Sometimes I even put it in the food.

DG_1

unread,
Jan 19, 2003, 6:38:57 PM1/19/03
to
> about 25-30Amps. Can a PCB do that??
Sure it can. Here is how to calculate the PCB
trace current:

I = k * T^0.44 * A^0.725
where is:
I = max. trace current
k = derating constant (.024 for inner layer, 0.48 for outer)
T = maximum temperature rise above ambient (in deg. C)
A = cross sectional area in square mils
      as a product TW*CW where TW is trace width in mils
      and CW is coper wight in oz. (1oz = 1.44 mils)

Cherrs,
D.G.
 

Spehro Pefhany

unread,
Jan 19, 2003, 6:44:59 PM1/19/03
to
On Sun, 19 Jan 2003 13:36:44 -0500, the renowned "Brett"
<tempa...@hostedscripts.com> wrote:

>Yup you're right. That should be 19.7 C.

Does the difference (>3:1) between internal and external strike anyone
as being less than credible?

Mike Deblis

unread,
Jan 20, 2003, 6:11:31 AM1/20/03
to
Fran...@cableone.net wrote in message news:<9ffl2v8ouuae05fkh...@4ax.com>...
> Problem is the contacts side of the relay needs to be able to carry
> about 25-30Amps. Can a PCB do that??
>
> If so, how?

Try: http://www.nick01.demon.co.uk/TraceWidth.html

Mike

Fran...@cableone.net

unread,
Jan 20, 2003, 4:37:02 PM1/20/03
to
On Sun, 19 Jan 2003 23:38:57 GMT, "DG_1" <dga...@cox.net_NOSPAM>
wrote:

Thanks to all who responded, I am heartened by the prospect of using
PCB. It will sure make my life easier.

Thanks again.

Fran...@cableone.net

unread,
Jan 20, 2003, 4:39:40 PM1/20/03
to
On 20 Jan 2003 03:11:31 -0800, mde...@hotmail.com (Mike Deblis)
wrote:

>>Try: http://www.nick01.demon.co.uk/TraceWidth.html

Thanks Mike but that timed out several tries. Are you sure the link
still works??

robrk

unread,
Jan 20, 2003, 10:26:50 PM1/20/03
to Fran...@cableone.net
Worked for me....

qrk

unread,
Jan 21, 2003, 1:06:48 AM1/21/03
to

I like using solderwick to beef up traces. Easier to handle. Good way
to get rid of that crappy Chemwick.

-
Mark Chun
Santa Barbara, CA

Paul Burridge

unread,
Jan 21, 2003, 2:33:26 AM1/21/03
to
On Sun, 19 Jan 2003 23:38:57 GMT, "DG_1" <dga...@cox.net_NOSPAM>
opined thusly:

>> about 25-30Amps. Can a PCB do that??
>Sure it can. Here is how to calculate the PCB
>trace current:
>
>I = k * T^0.44 * A^0.725
>where is:
>I = max. trace current
>k = derating constant (.024 for inner layer, 0.48 for outer)
>T = maximum temperature rise above ambient (in deg. C)
>A = cross sectional area in square mils
> as a product TW*CW where TW is trace width in mils
> and CW is coper wight in oz. (1oz = 1.44 mils)

I came across this piece in Radio Communication (at section 17.21):

"Avoid high current density points. Rapid changes of line width should
be avoided, particularly in circuits carrying several amps. The
recommended current density "I" in amps is:

I = 3(cube root of w^2)

where "w" is the width of the copper track in mm.
Circuit board tracks make excellent fuses if poorly designed."
HTH.
--

"What is now proved was once only imagin'd"
- William Blake, 1793

0 new messages