AC circuit and PCB design questions

[sgraves66]

I'd like to incorporate this SSR (PF240D25http://www.mouser.com/ds/2/93/p_f-16841.pdf) into a custom PCB, protect it using an 15A fuse and provide in/out terminal blocks for connectivity/pass-through (load/neutral/ground). This is part of a home automation project and my first entry into AC circuit design. I'm essentially creating a WiFi-enabled motion detection faceplate to control lights throughout the house (120v/60Hz).

My initial research indicates that I would probably need 4oz copper thickness with ~6+mm trace between 'terminal block->fuse->SSR load' if I were to provide routes on a PCB that could sustain a 15A load. Not feasible for my purposes and price range. I plan to use stranded copper cable to complete the connections. Am I correct in this conclusion and is this the safest way to handle high current on a PCB? Should additional copper be available surrounding the pads on the PCB (planning on 0.06" outer/.04 inner) to support higher current or will standard dimensions work assuming the pads are sized appropriately for the through-hole AC components?

The max amount of current through the SSR should be on par with a single 100w bulb (~0.83A) and no more than ~2A for multi-bulb fixtures. Based on the datasheet for the SSR, temperatures seem to be pretty high for mounting it in a single/double gang box. Would an SPST relay be more appropriate in this situation? Although more expensive, I'd prefer the SSR for it's simplicity and decoupling nature.

For clarification, the PCB for AC is on a standalone PCB. Shielded cabling is used to connect it to a DC control board / MCU.

 

[Fish4Fun]

For turning lights on/off this SSR module is WAY overkill...it is designed to turn things like your STOVE on/off.....I honestly would press the "EASY BUTTON"....==> http://www.ebay.com/itm/8-Channels-...98?pt=US_Security_Cameras&hash=item3a974a78e6

Fish

 

[sgraves66]

Thanks for the feedback.

It's definitely a beefy SSR and I haven't ruled out general purpose relays in the 8-10A range. Aside from lights, eventually I will be controlling some other devices that can draw up to ~13A and wanted a single design for all - fusing will be used to limit the maximum allowed current for the specific application.

Based on another suggestion, it would be better to use a 5A fuse for light control if I do want to use PCB traces over stranded wire. It was also recommended to place traces on both sides of the PCB to double the capacity and halve the required width of each trace.

 

[dablakh0l]

15A on a 2oz external layer 1" long trace, 10° C temperature rise is about 6.4mm (single sided). Use 2 sides, you can go 4mm each side if you are limited for space. Remember, however that you need at least 1.5mm spacing between traces.

 

[Fish4Fun]

sgraves66,

I think relays for turning lights on/off and one or two "special purpose high-current" SSRs might make more sense than building 10 high current SSRs to handle X * < 1A loads and only using one or two for >10A loads...but that's just me....Unless you are driving inductive loads, I don't see any reason you would need SSRs @ all, why not simply use Triacs and Opto-Couplers?

As far as your PCB traces go...are you planning on having these boards done @ a PCB house, or are you planning to DIY? If you are planning to DIY it is easy enough to get 2oz/3oz/4oz material off ebay surplus merchants...typically for only pennies more than 1/2oz or 1oz....You could also consider "jumpers" placed close to the I/O holes so that you would effectively have "dual traces" w/o going to a multi-layer PCB...these are just some random thoughts....I typically make my PCBs on my little desk-top cnc router, so I tend to view PCBs as primarily a cost of surplus copper-clad board....If you are planning on having a PCB house do the boards then the heavier copper material can be a pretty big "up charge" from their "teaser pricing".

Anyway, Good Luck!

Fish

 

[sgraves66]

I think relays for turning lights on/off and one or two "special purpose high-current" SSRs might make more sense than building 10 high current SSRs to handle X * < 1A loads and only using one or two for >10A loads...but that's just me....Unless you are driving inductive loads, I don't see any reason you would need SSRs @ all, why not simply use Triacs and Opto-Couplers?
Fish

That's pretty much the conclusion I've come to now as well. The AC control board is modular by design, so it would be easy enough to create high current SSR modules when necessary and stick to relays instead for light control / low current applications. The triac/optoisolator solution seems appealing. I came across a few examples that can handle inductive loads as well. Thanks for the tip. I'm gun shy around AC - haven't spent a sufficient amount of time reading about AC principles and try not to introduce components I don't fully understand. Great hobby, but have little to no interest in burning the house down

I typically make my PCBs on my little desk-top cnc router, so I tend to view PCBs as primarily a cost of surplus copper-clad board....If you are planning on having a PCB house do the boards then the heavier copper material can be a pretty big "up charge" from their "teaser pricing".
Fish

PCB manufacturer or protoboard. I have been researching CNC solutions to save on costs, but not a possibility today. I'm more interested in 3d printers, atm.

 

[sgraves66]

15A on a 2oz external layer 1" long trace, 10° C temperature rise is about 6.4mm (single sided). Use 2 sides, you can go 4mm each side if you are limited for space. Remember, however that you need at least 1.5mm spacing between traces.

Using some online trace width calculators there seems to be a difference in trace width for internal vs external layers. For my purposes, traces would be external but are there any caveats (i.e. power dissipation) to applying a solder mask over these traces for AC?