Cheap plastic enclosures for electronics? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: August 11, 2021, 02:16:35 pm
content: Hi,I need to find a plastic box in which to mount an autotransformer , a mains transformer, and a mains fan in.Autotransformer = RS 890 2765 (200VA)Mains transformer = 503950 (200VA)Mains fan = RS 544 0683 (13W)The cheapest i can find is Farnell 3375957 at £33.This is way too expensive, as this is just for a production test rig up, not for sale to a customer.Where do you get cheap plastic enclosures for electronics, of size roughly 300mm by 150mm by 150mm?I reckon even Walmart or Tesco's may have something?

author: dietert1
author_rank: Super Contributor
timestamp: August 11, 2021, 03:28:00 pm
content: Don't build, buy one at ebay:https://www.ebay.de/itm/203549724930?hash=item2f64825102:g:fQkAAOSwCMhhC6psIt does 400 VA.Regards, Dieter

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2021, 03:48:19 pm
content: As discussed in yourotherthread on fixing your autotransformer into a plastic enclosure...https://www.eevblog.com/forum/manufacture/how-to-mount-autotransformer-in-plastic-box-for-test-jig/You need a case suitable for supporting the weight of the 1 - 1.4kg autotransformer on it's two mounting screws, and also take the weight of the 2.8kg mains transformer. You will probably find a sheet metal enclosure stronger and more economical at those sorts of dimensions rather than a moulded plastic one.Also note the cautions in your other thread about whether you need to provide an additional support plate to support the autotransformer on the case panel, this probably applies to athinsheet meta as it does a cheap plastic case.

author: nali
author_rank: Frequent Contributor
timestamp: August 11, 2021, 03:54:50 pm
content: I'm quite suprised that aone offcost of £33 is such an issue for a test fixture?? After all, how much have you invested in time looking?Anyway if you can go larger 300x300x150 you can get metal electrical conduit boxes for less than that.

author: Faringdon
author_rank: Super Contributor
timestamp: August 12, 2021, 05:06:58 am
content: Thanks, we cant use metal as we'd have to be sure of earthing it to be safe, and in the production facility, we cant be sure of that.

author: Monkeh
author_rank: Super Contributor
timestamp: August 12, 2021, 05:09:17 am
content: Quote from: Faringdon on August 12, 2021, 05:06:58 amWhat absolute rubbish.

author: Faringdon
author_rank: Super Contributor
timestamp: August 12, 2021, 05:20:36 am
content: thanks, i mean say if it was in metal encl..and some live part touched the metal enclosure, and it wasnt earthed....

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2021, 08:48:44 am
content: What are you going to do with all of the metal fixing screws for the transformer, fan grill, variac, etc.? These items are too heavy to use Nylon fixing hardware and any metal fixing on a mains powered plastic cased item need to be earthed.You either go full Class-II or you provide it with a proper reliable Earth connection. The apertures in a standard welded wire fan grill are also too large for Class-II.There's no way it should be possible for any loose live parts to be coming into contact with the enclosure in the test setup, otherwise they are probably just as likely to come into contact with the operator who is adjusting the variac.Stop being a cowboy and do it right.

author: Faringdon
author_rank: Super Contributor
timestamp: August 12, 2021, 12:12:03 pm
content: Thanks, but I initially suggested a metal box, but was told to do it in plastic.Its only for a test jig on production. Ill put a sign on it saying dont tip upside down or move roughly.I will just have to fix the heavy stuff in place as best i can and use loads of bodger blu tak lumps to stop heavy stuff coming loose and moving about.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2021, 05:27:58 pm
content: Yeah, that's going to work well when they warm up! If it's being used by lower skilled production line staff then they deserve proper care towards their safety, not just a label.I take it you're working for yet another crappy company? I guess statistically you must be, but it beats me how you keep finding them.P.S. Why not put it in a properly earthed metal cabinet and just put a plastic safety shield over it?

author: Ian.M
author_rank: Super Contributor
timestamp: August 12, 2021, 06:11:41 pm
content: For %DEITY%'s sake, even a wooden box would be better than plastic. At my old job the shop Variac was in a wooden case.6mm hardwood WBP plywood screwed and glued to an interior batten at each edge would do the job nicely. It would still need something to spread the load of that panel mount Variac, but I reckon you could get away with a M10 x 50mm 'penny' washer (or better 60mm) drilled for the Variac's fixing screws. It would be hidden behind the knob so no exposed metalwork. However you should still ground the Variac shaft and frame.The other transformer could also be mounted to hardwood blocks screwed and glued to the plywood base, so its mounting screws don't penetrate the base. Drill the hardwood block for countersunk machine screws from the bottom up, and epoxy them in place to provide studs for mounting the transformer. Hint: Before assembly solvent clean the screws, so epoxy can bond to their threads and dip the portion of the thread that will be exposed as a stud in molten candle wax to allow any excess epoxy to easily be removed leaving a clean thread. Seehttps://www.westsystem.com/instruction-2/epoxy-basics/bonding-fasteners-hardware/

author: Monkeh
author_rank: Super Contributor
timestamp: August 12, 2021, 06:24:49 pm
content: Quote from: Gyro on August 12, 2021, 05:27:58 pmI was hoping he'd gone and got a suitable job at Tesco, but it seems not.

author: floobydust
author_rank: Super Contributor
timestamp: August 12, 2021, 11:00:41 pm
content: Test fixtures need to meet OSH and electrical safety standards. People of all walks of life use these fixtures and they need to be proper, as most people don't like electrocuted employees.At treez corp. the "responsible member" is whom?Professional engineers cannot enable or support such an unsafe project as this.We have a Code of Ethics and when the boss says "it must be plastic" and Horace Wimp agrees, it makes for a disaster."£33...This is way too expensive""we cant use metal as we'd have to be sure of earthing it to be safe""but was told to do it in plastic"Other forums forbid and lock threads such as this, where OP is clearly out of their ability in a build that affects safety of the public, such as a production environment.