DOUG,
COULD YOU RUN US OFF COPIES OF THIS INFO? WE'VE BEEN USING
IPC-D-275 FOR FIGURING CURRENT CAPACITY.
ROB
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Subject: Re: des re: hot trace width
Author: [log in to unmask] at internet-mail
Date: 4/9/96 9:49 AM
There are TWO issues here. One - current carrying ability over a long
period of time, two - current carrying ability over a short period of
time.
For extended use, basic good engineering practices say, the trace has
to be able to carry the current for which it's fused. As if it were
solid wire. Look up AMAPACITY in the Electrical Engineer's Handbook.
Find the current you need at the max. temp you'll experience in the
Underwriter's Laboratories column. Cross over to the gauge wire for
it. Look up the SQUARE MILS of the wire. From your known trace
thickness calculate your width.
Short time stressing for wires should be under a second. Fuses
typically react well under a second.
Be careful if you are doing trace calculations for Primary voltage
carrying traces.
Doug McKean
ADC Video Systems
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Subject: des re: hot trace width
Author: [log in to unmask] at internet-mail
Date: 4/8/96 4:10 PM
Andy Pedersen asked about trace with to current capacity requirements.
In addition to Kevin L. Seaman's variables (conductor width, thickness
and current) the board layout has an impact also, in a flex design,
The test folks caused a short (get to blame them _this_ time ;) )
that put 4 amps on a .013 trace. Where the trace was near other
copper, the board survived, but de-laminated in more open areas.
(and we still don't realy know how _long_ it was shorted)
(The trace is still connected & not shorted to any near by traces)
In "Electromechanical Design" by Ronald A Walsh, pg 255, 6.6.10
"Fusing Time-current for copper connections" he quotes an equation
by I.M. Onderdonk:
(let's see if I get this right..)
33(I/A)**2 * S = log10(((Tm-Ta)/234+Ta)+1)
I=A * ((log(((Tm-Ta)/234+Ta)+1))/(33 * S)) **.5
I=current, Ampers, A=conductor area, cir mils, S=time current applied,
seconds, Tm=melting point of copper in dec C, Ta= ambient Temp in deg C.
Has any one used this? I haven't tested it out ( we try to keep the
smoke _in_ the parts don't you know ;) ).
Bill Gaines
AeroJet (for $) IHPVA (for speed & fun)
IEPS (for info) SCCA (for trophys)
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