AC mains on a PCB ?

I'm in a hurry, late for Shoe Fest.  You might want to throw a (sb) fuse in.  You seem to be using a chassis ground symbol for signal ground.

Thanks Mate. New to schematic design as well . Will change that.

So guys what about the ac routing and the how thick should the copper be on the board.

Ooops - looks like I accidentally hit the wrong reply button before...

On 03/09/16 14:57, George Thomas wrote:

A total newbie to eagle design and PCB fab. So plase bear with on my

silly questions, trying to learn.

 

I have pcb that is schematically completed with the layout. Before i

start the fabrication process i need some expert advise if the

components placed and the wires routed are ok for the ac mains and the

others. The load here will be a transformer. The ac mains are 240VAC and

all works well as designed in the schematic on a bread broad except for

the load for which MOC3023 is yet to arrive from where i've ordered.

You have a lot of traces running unnecessarily close to each other and

to pads. That's fine to low voltage stuff but undesirable when high

voltages are present.

Your placement of parts results in quite a few traces being quite long.

That's undesirable in all domains. I particularly note that the trace

from C7 to R20/21 goes all around the houses, when a simple rotation of

C7 could reduce it to nothing.

I don't know how much current that BTA08 is expected to drive, but the

text describing the board as a "spot welder microcontroller" hints that

you might be looking at several amps. If so, your traces look rather

thin to me, especially given how long they are.

Thanks a lot to take the effort to correct me.

I've removed C7 and R21 which are actually used to protect the optocoupler but i don't see they being necessary here and i have rearranged the the remaining too.

On 04/09/16 00:19, George Thomas wrote:

Thanks a lot to take the effort to correct me.

 

I've removed C7 and R21 which are actually used to protect the optocoupler but i don't see they being necessary here and i have rearranged the the remaining too.

 

Definitely better... but I still think you want more "meat" on the

important tracks.

So, thinking about your design, it seems to me that the crucial part -

the bit you need to worry about - is the path through the triac and

between the connectors. That's where ALL the current is flowing - the

rest is negligible. So, if it were my design, I'd start by placing

those three components close together for optimal (i.e. very short)

tracks. Then I'd make those tracks as wide as I could reasonably

achieve. The rest can then fit around that.

Also, the track from IC5 to R20 may be a low current track but it's at

mains voltage. I'd rotate R20 to keep that track away from the low

voltage ground plane.

Would I be right in thinking you're using the triac as a pure switch?

That is, you're either triggering it as early in the cycle as possible

or not at all? I only mention it because I have some experience of

driving a transformer in "light dimmer" mode (PWM of the mains cycle)

and it's... tricky.

Thanks a lot mate ! Appreciate it.

Yes your correct on assuming that the TRIAC is just a basic switch. It switches on at for predefined time set by the pot (R12). The time ranges from 100ms to 450ms. The load is a Microwave oven transformer - rewound the secondary to 3 turns 3AWG wire. The current is quite high at open circuit but with 222Ohm 100W resistor in series with the MOT, it delivers about 300 - 600A. Now at 100ms or 450ms the amps would be far too low (assumption).

Now about placing the components, will keep the AC components as close as possible with the widest copper. The space between the pins is short so that would limit the copper size there would that be a problem ? I mean the route to the TRIAC would be. I've rearranged the AC components closer. how are the track size for the other components looking ?

On 04/09/16 19:23, George Thomas wrote:

 

Now about placing the components, will keep the AC components as close as possible with the widest copper. The space between the pins is short so that would limit the copper size there would that be a problem ? I mean the route to the TRIAC would be. I've rearranged the AC components closer. how are the track size for the other components looking ?

 

The shorter those tracks are, the less it matters if they're not as wide

as you'd like. Basically, the copper track acts as a (low value)

resistor, where R = k.l/w (give or take). Short and fat is the lowest

resistance and hence gets least hot.

It looks like you've changed to a different triac in a wider (TO3-P)

package, which will help with wide tracks! If it were my design, I would

move the small transformer to the right a fraction and put the triac

between it and the connectors. That would, I think, allow the shortest

track from the "AC" connector to the middle pin of the triac. Well,

other than placing the triac between the connectors and swapping the

connectors so that AC is towards the top.

Thanks for your help Robert.

Yes I did change them, the earlier pin spacing was a close. I've changed the locations of the Transformer and reduced the track size of the other components (would that be ideal here as there is not current flowing through them). I've also removed the set of resistors and replaced it with just one and connected to ground such that all the LEDs are grounded via this resistor. No two LEDs would light up simultaneously, tested on the breadboard and that worked well. Hoping this would be a better layout.

On 05/09/16 11:56, George Thomas wrote:

Thanks for your help Robert.

 

Yes I did change them, the earlier pin spacing was a close. I've changed the locations of the Transformer and reduced the track size of the other components (would that be ideal here as there is not current flowing through them). I've also removed the set of resistors and replaced it with just one and connected to ground such that all the LEDs are grounded via this resistor. No two LEDs would light up simultaneously, tested on the breadboard and that worked well. Hoping this would be a better layout.

 

Looks good from the mains side. I can see quite a few opportunities for

improving the low voltage routing and I would probably put all

components at a multiple of 90 degrees rotation (i.e. not like R23 and

IC4) but those are not critical matters. You might want to position IC5

and R20 for maximal clearance between tracks, particularly the T1 gate

track and the one from R19.

Well, after a while, i've managed to move IC5 away from R20, i've also changed the angle for the R23 and IC5 making them more routable during Auto tracking

.