Hi. I am putting a number of PCB’s and other components in a 1/8" plastic outdoor electrical box. This is going to be a brewing controller so the fewer holes I drill in it the better.
How can I mount things like PCB’s to the plastic?
This sounds simple but I have not found a reliable way to do it. I could drill a hole, then use standoffs and a nut and bolt through the box… but I really want to stay away from drilling holes through the box. I had a few plastic terminal strips so I tried PVC cement figuring it would chemically bond the two plastic pieces together. This worked at first but one of six did not hold so I assume the others are going to fall eventually.
I have used epoxy in the past with standoffs and with flat head bolts upside down. The real issue here is that whatever I glue to the surface can snap off due to the flex in the plastic box. The smooth surface does not help things stick well either.
Does anyone have any ideas what to do? I really feel like someone else has solved this problem before. I need this to be rock solid so I dont have 120vac falling into 5vdc and shorting things out.
Why do want to use plastic? It’s not really suitable for that sort of thing. I’d find a local metalworking shop and get them to fold a couple of pieces of aluminium sheet.
leon_heller:
Why do want to use plastic? It’s not really suitable for that sort of thing. I’d find a local metalworking shop and get them to fold a couple of pieces of aluminium sheet.
I tried that a few years ago when building a custom HTPC and they wanted $100 just for a simple 2 piece, 2 fold, 3 sides each, box. Metal is much more difficult to cut and left me with the same issue of mounting things. I used JB metal weld and glued bolts upside down. They all eventually snapped off. Again, smooth metal + glue doesnt work well. Not that I am going to use metal but I dont see a good way to attach standoffs without drilling or welding…
I’m using plastic because its a waterproof outdoor box. I will have 120vAC, 24vAC, 12vDC, and 5vDC all in the same box and having metal connectors means I can easily short out connectors etc. Plastic is much easier to cut into etc too.
pcmofo:
OK so find me a 12"x12" plastic enclosure that can hold various PCB’s, transformers, etc.
They dont exist to my knowledge…
Here’s a list of manufacturers that make industrial & commercial electronic enclosures. I don’t know specifically what you are looking for,but one of these may have what you want:
They are self adhesive, and clip into 4mm mounting holes on your PCB. To release the PCB you push in a little tab that clicks over the PCB when it is locked in.
They come in a range of different heights. Another good thing is that they allow for inaccuracy in the mounting location, because you can clip them into the PCB, then push them down onto the mounting surface to get it exactly where you need it.
Those look awesome but are they going to stick well? I need to mount a standard PSU PCB from a computer PSU. I also have a metal transformer thats a bit on the heavy side.
The more you use the stronger they are They aren’t that long, so the moment generated by the mass of the PCB would be fairly small. The surface area of the mounting surface is large.
They have the standard double sided foam tape stuff on the underside - proper 3M scotch brand I think on mine, obviously if you get them somewhere else they may be different. They stick very very well. The foam allow you to cut though with a knife if you ever want to remove it.
If you were really worried you could remove the adhesive that comes with it and epoxy them down yourself
basically a 3/8" Nylon standoff with one male and one female end both with #6 threading. So I am hoping to drill and tap a #6 hole in the box itself and then put glue of some kind in it and thread in the Nylon standoff and cut off the excess. Hopefully the plastic on the box and standoff will be bonded by the glue and be a rather permanent connection for things.
leon_heller:
Get a proper enclosure. It’ll be much easier to mount the PCB as well as providing better protection and EMC performance.
OK so find me a 12"x12" plastic enclosure that can hold various PCB’s, transformers, etc.
They dont exist to my knowledge…
Back when I needed something like this I found a sprinkler timer box (rain-bird, I think) at the local hardware store. The good thing about this was that it was a removable panel inside with a grid of holes drilled in it (there’s more space behind the removable panel where you can hide even more components). The whole thing is water-tight with a gasket. I don’t think it’s quite 12x12, but it’s not far off.
Here’s a picture – It’s housing a fuel injection computer on my sandrail.
There is an easier way to get a metal box if you do require it. Check out www.protocasedesigner.com - they have free CAD software that allows you to design enclosures with standoffs built in, powdercoats, silkscreens, etc and have a 2-3 day turnaround. Still costs money but more 21st century than the average metalshop.
Check out my blog entry on putting an Olimex STM32 P103 prototyping board in a custom enclosure from Protocase:
They aren’t that long, so the moment generated by the mass of the PCB would be fairly small. The surface area of the mounting surface is large.
