Minimalist Rube Goldberg power supply. - Page 1
Forum section: electronics / beginners

author: HardBoot
author_rank: Regular Contributor
timestamp: October 09, 2012, 01:19:27 am
content: I need a 150V DC 80W supply for something and I'm in 120v-land.I can't find any cheap PSUs which can do this, especially at 80W, so I guess I'll make this myself.I'd like the parts cost to stay under $10, and I don't care much for efficiency, it just has to be reasonable.I don't have any transformers sitting around capable of that power... a lot of inductorss though.So with the parts I currently have, hooray, this may actually work.That's $5 of parts so far(even with high-end caps rated for 250v 105c)... although the inductors are scrap...Regulating that to 150v should be super easy... but... I want to do it for dirt cheap.Any recommendations?

author: Psi
author_rank: Super Contributor
timestamp: October 09, 2012, 01:38:56 am
content: Are you sure a non-isolated supply is suitable for your intended application?Also, that doesn't look right.

author: HardBoot
author_rank: Regular Contributor
timestamp: October 09, 2012, 01:43:12 am
content: Quote from: Psi on October 09, 2012, 01:38:56 amMy workshop mains is isolated and I'll be fusing L/N.Although... I could replace my scrap inductors with a scrap transformer... if I can find a 1:1 or 1:2.

author: ptricks
author_rank: Frequent Contributor
timestamp: October 09, 2012, 02:06:12 am
content: Quote from: HardBoot on October 09, 2012, 01:43:12 amNEVER fuse the neutral of an AC system, always fuse the hot side. If you lose neutral connection and contact a device connected to the hot you can still be shocked, where as a blown hot fuse and contacting the device you cannot be shocked.When you say the workshop is isolated ? how is it isolated, unless you have an isolation transformer powering the entire shop it isn't isolated, and NEC codes don't allow for structures to have floating grounds for good reason, it is dangerous.I would find a transformer that is close to what you need and take it apart and re-wind it to match what you need. The design that you posted would likely trip a breaker because it is going to have a huge inrush of current when it is plugged in or unplugged.There are plenty of times to hack a power supply together but directly powered from mains with no isolation isn't one of them.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 09, 2012, 02:22:09 am
content: Quote from: HardBoot on October 09, 2012, 01:43:12 amour electrical grid is isolated from the moonhow good is your lab isolation if it still can kill you?

author: HardBoot
author_rank: Regular Contributor
timestamp: October 09, 2012, 02:25:53 am
content: Live fused, neutral fused, ground to neutral, the GFI will go SCREEEEEEEE and disconnect L/N if something fails but keeps ground.Ground is regular ground, the N is floaty since it's on the transformer.Ya I have a small isolation transformer, I just use it for my electronics, the beefy stuff like blower, band saw, table saw all go their own breaker.I'm still digging for a transformer though, because then I can do stupid things with those inductors.Edit: I give up, I only have teeny tiny things that are 1:1 and 1:2, all of my higher wattage buggers are from 1:10 to 1:Tesla

author: T4P
author_rank: Super Contributor
timestamp: October 09, 2012, 07:56:02 am
content: Looks dangerous to me... if you saw before that Flunze idiot a while back made a AC mains power'd supply and claimed it is safeThis looks to me like it's on the same levelisolated or not.Touch any of those terminals even if it's isolated can get you killed tooDon't put complacency on GFCIs, they aren't magic things that save human lifes and i only trust them until i get myself shocked .... My GFCI did not work a few times

author: Psi
author_rank: Super Contributor
timestamp: October 09, 2012, 11:21:06 am
content: There's nothing wrong with capacitor/inductor floating/nonisolated power supplies per se, they do have their uses.You just have to be sure it's the right type of supply for your application and for the vast majority of applications they aren't.They're good for small devices which little or no outputs.Like maybe a mainstimer module, it has only one output (it's relay contacts) which are isolated by design. And the only input is mechanical by means of a pot.So it can be isolated by a plastic case quite easy.