Stepping down mains cheaply/ BFM question - Page 1
Forum section: electronics / projects

author: willie_phistterbut
author_rank: Newbie
timestamp: May 31, 2017, 07:23:55 pm
content: I'm trying to get some funding to go back to school with so I'm going to design and build some desktop electronic toy/gizmo via crowd funding. I need to step down and rectify 110v to get a 15v supply dc. I'd rather not have to source a bunch of unknown wall warts from the Wun hung lo factory if I can include a small transformer and full bridge rectifier myself. A short review of digikey lends me to find such transformers for 18$ a piece though at least. What would be more cost effective/safe in the long run? A cheap wall wart of unknown quality or making sure peoples houses don't burn down prematurely, thwarting my further attempts to gain decent reputation and funding? I'd be looking at making about 50-150 of these devices at about 100$ per unit minimum. Stay tuned for a poll related to that subject. Thanks everyone.

author: DBecker
author_rank: Frequent Contributor
timestamp: May 31, 2017, 08:03:11 pm
content: At those quantities it's really difficult to make anything that is both cheap and safe.You'll be paying far more than an Asian factory for either safety rated input components or any transformer. Of course you'll be paying quite a bit more than wholesale for a wall brick, but at least it avoids paying a big premium for both the power supply and board area.Have you considered USB power input, with a boost converter if you need higher voltages?Otherwise look at enclosed power modules.

author: jbb
author_rank: Super Contributor
timestamp: May 31, 2017, 08:38:40 pm
content: There is a reason most consumer electronics uses a wall wart: safety certification. For commercial sale of an interim which has the mains plugged straight in, you'll need toofficially meetsafety standards. This means lots of design effort and several thousand dollars worth of testing. Just buying the standards can be expensive to begin with.While certain people have been known to wink at Electromagnetic Compatibility standards (i.e. RF noise) and largely get away with it, fudging a safety certification could land you in very hot water if someone gets injuredor worse, dies.I suggest you re-purpose the thread to: 'can people recommend some OK manufacturers of wall warts?'You absolutely can get quality goods out of China, the trick is to find the good manufacturers who give a damn. (If you pay rock-bottom prices, you'll have a high risk of getting dangerous crap. Some really shady places send you an OK units for samples, and then send dangerous #### units for production. )If you don't want to mess about and are willing to pay a bit (or a lot!) more, DigiKey (and Mouser, Element14 etc.) has a selection of adapters with datasheets and known manufacturers available.

author: thm_w
author_rank: Super Contributor
timestamp: May 31, 2017, 11:01:54 pm
content: Quote from: willie_phistterbut on May 31, 2017, 07:23:55 pmYou haven't specified a current. It is certainly not going to make sense to purchase a transformer and design a bridge rectifier/power supply yourself. Unless its for a learning experience.Digikey sells wall adapters, here is a 15V 8W one for $7:https://www.digikey.com/product-detail/en/triad-magnetics/WSU150-0560-13/237-2237-ND/6600171I have a lot of quality surplus 12V 1A and 9V 1.7A supplies. I'm sure others out there do as well, that you could pick up for next to nothing. I would try to design around 12V if that is possible.