AC mains on a PCB ?

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.

yea ! your right. That was un-ticked all the while. Ticking it would pour more copper in those empty spaces under IC1.

you mean pinswap, right ? well that would again make the other trace longer, wouldn't it.

George Thomas wrote:

 

you mean pinswap, right ? well that would again make the other trace longer, wouldn't it.

I believe that's what was meant. It will lengthen the shorter trace slightly but shorten the other a lot more and stop it having to run around and under the transformer to get to the desired pin. You also need to make more space to get clearance between the two traces, you really don't have enough around the connectors. What is the pin pitch of your mains connectors, is it sufficient or do they need changing? Looking at the input on a typical 240V PSU I have here, the pitch on the input connector is 3.96mm. If you look at the clearance between the pads with connectors of this pitch you'll see that it's several mm. You should use this as a guide as to the minimum clearance between mains conductors and also their clearance to anything else. The advice Joern gave for moving parts and rerouting traces above is all valid and is what I would also suggest.

Best regards,

Rachael

Well i hope this layout is what you guys suggested. When you said pitch is it the distance between the two terminals of the connector ? well on the physical connector it is 4.6mm

Hi George,

You've made some improvements in clearance and routing to the transformer but in the process you've changed a lot of other things in a very different way to what was suggested and now it appears the nice clearly defined isolation barrier you had between the AC side and DC side is gone. Your opto-coupler now has all sorts running underneath it again and doesn't sit across a clear isolation barrier. I suggest you take a step back to the previous layout and have another go. Draw some guides on tDocu or something to show the AC side and the DC side and lines to show the minimum isolation gap to help you place your AC side components and DC side components. Then don't route anything from the AC side or the DC side across the isolation barrier.

Another thing to note, you shouldn't run traces underneath the transformer as you'll likely end up coupling 50Hz mains noise onto them and taking this into the rest of your circuitry.

Best Regards,

Rachael

Hmmmm knew there was something wrong when autorouting was completing at 100% for all the efforts . So is there any option to avoid traces under or near IC's and opto-couplers and where else should i avoid traces, caps ?

On 06.09.2016 22:43, George Thomas wrote:

yea ! your right. That was un-ticked all the while. Ticking it would pour more copper in those empty spaces under IC1.

Dont forget those shielded holes in the corner.. I suppose you do want

to put this pcb down in a box? Maybe even shielded metal box?

Interesting project. Without reading it all, I hope you have dimensioned

the AC-LOAD wires for those high currents.

Also, even if this is out of my experience field, I would take an extra

look at this high current current loop. You don't want an EMP generator

For example, I would route the pulsed load pin direct to the AC

input, not passing the transformer first. This will narrow the loop, and

also avoid spikes at the transformer due to voltage loss during current

pulses.

Also, make sure its fire- and explosion-proof in case something should

short circuit, or you get struck by lightning at the AC. I saw someone

mentioning fuse, and I assume you have one at the AC inlet, prior to

entering the pcb.

George Thomas wrote:

 

Hmmmm knew there was something wrong when autorouting was completing at 100% for all the efforts . So is there any option to avoid traces under or near IC's and opto-couplers and where else should i avoid traces, caps ?

Yes, you can use the restrict layers to specify where traces are not allowed to go. Take a look at this article for a quick guide on how to do this: http://dangerousprototypes.com/blog/2012/08/08/how-to-eagle-keepout-and-restrict-layers/

In general however, a lot of auto-router issues stem from deficiencies in the initial placement. With any routing job, manual or auto, but especially with auto routing, the placement will make or break the layout. Your latest placement has a number of issues, a few of which I highlighted in my previous post. You need to take a step back and think about how the circuit "flows" and try and place things to keep the flow simple.

If I were you I would consider doing at least some of the more critical routing manually and leave the auto router for the less critical stuff. Also, don't just hit the autoroute button and let it do it's thing in one go, tell it to route specific smaller groups of more important signals first, inspect them and manually tweak if needed and then move on to the next. Breaking it down in this way and keeping an eye on how it is doing will give you a better chance of success.

Jorge Garcia wrote a good blog post on the auto router a while back which is worth a read: https://www.element14.com/community/community/cadsoft_eagle/blog/2015/06/17/are-you-better-than-the-autorouter

Best Regards,

Rachael

Morten Leikvoll wrote:

 

Also, make sure its fire- and explosion-proof in case something should short circuit, or you get struck by lightning at the AC. I saw someone mentioning fuse, and I assume you have one at the AC inlet, prior to entering the pcb.

Yes absolutely! The fuse in the mains plug probably isn't enough to protect the circuit though as it may be over rated and won't necessarily blow quickly enough. I'd consider adding a PTC and MOV's and/or TVS diodes as surge protection if this were my design. I'd also add some EMI filtering and have the earth connected in too.

Best Regards,

Rachael

On 07.09.2016 10:53, rachaelp wrote:

Morten Leikvoll wrote:

 

Also, make sure its fire- and explosion-proof in case something should short circuit, or you get struck by lightning at the AC. I saw someone mentioning fuse, and I assume you have one at the AC inlet, prior to entering the pcb.

Yes absolutely! The fuse in the mains plug probably isn't enough to protect the circuit though as it may be over rated and won't necessarily blow quickly enough. I'd consider adding a PTC and MOV's and/or TVS diodes as surge protection if this were my design. I'd also add some EMI filtering and have the earth connected in too.

 

Best Regards,

 

Rachael

Fuse in the mains plug? That is UK-specific I guess. Either use IEC

power inlet with embedded fuse (like farnell 1516059), or make sure the

first thing the power line meets, is a fuse. (And ground meets the metal

box).

On 07.09.2016 10:53, rachaelp wrote:

Morten Leikvoll wrote:

 

Also, make sure its fire- and explosion-proof in case something should short circuit, or you get struck by lightning at the AC. I saw someone mentioning fuse, and I assume you have one at the AC inlet, prior to entering the pcb.

Yes absolutely! The fuse in the mains plug probably isn't enough to protect the circuit though as it may be over rated and won't necessarily blow quickly enough. I'd consider adding a PTC and MOV's and/or TVS diodes as surge protection if this were my design. I'd also add some EMI filtering and have the earth connected in too.

 

Best Regards,

 

Rachael

Fuse in the mains plug? That is UK-specific I guess. Either use IEC

power inlet with embedded fuse (like farnell 1516059), or make sure the

first thing the power line meets, is a fuse. (And ground meets the metal

box).