Unknown Transformer and Multi Power Supply Help? - Page 1
Forum section: electronics / projects

author: PhynixViking
author_rank: Regular Contributor
timestamp: January 08, 2013, 05:03:10 am
content: Ok so! I made a while ago a very simple 12v and 5v bench power supply that has about 1 amp at 11.90 volts and 2 amps at 4.99 volts. WELL I've been using it and it seems to over heat ALL the time and very often!I could use some help with "version 2" lolFirst can someone find specs or data sheet on this transformer? I got it from a APC Battery Back Up (110v ac and 12v dc battery) and after some testing I found the following:(NOTE: there is a white on both sides. The white is different.)Using BLACK and WHITE as AC Mains In I get:White + Purple = 8.5VWhite + Yellow = 17.11VIt says on it:430-2002.11CLASS 130(B) Z150HLEI-4 E154515__________ 0129Nothing else... it has 2 wires (black/white) on one side and 3 (White, Purple, Yellow) on the other.I'm hoping it is some where 10 amps range *fingers crossed* or more.SO! I plan to use this as a multi select 15V, 12V, 9V, 6V, 5V, 3V and a Variable (LM317)Just to make sure all of the 78XX's can be used parallel to increase amp handling correct?And the LM317 can too?I'm thinking that I'll "align" them as follows:8.5 volt setting holds: Variable (LM317), 3v, 5v, and 6v17 volt setting holds: 9v, 12v, and 15vI haven't played around much with "Negitive voltage regulators" can I or "should I" use a positive one WITH a negative one (of course each on its own separate circuit layout) would that be "better" then just putting two positive in parallel?And can they then be parallel (2 neg's parallel with 2 pos parallel)And is there such a thing as "too many parallel regulators"? (Example 5 or more?)Anyone have recommendation for Filter Capacitor size?My old version I had a small filter cap on each regulator then I had a "larger one" right before the out-put. Good idea or bad?And any way to make it able to handle stress? (Example: shorts or even reverse voltage.)I know I'm asking a lot here, LOL thank you everyone for any advice you can give! I'd like to make something simple but also very safe!I've been mostly on the "repair side" of things and heavy into computers. Recently been getting more into electronic design. (More fun to build something from nothing then fix something someone else made. LOL)Again thanks! ^__^

author: mariush
author_rank: Super Contributor
timestamp: January 08, 2013, 05:45:03 am
content: So that transformer has a primary of 110-120v and two secondaries each of about 8v. White and purple is a secondary, purple and yellow is the second secondary.Keep in mind when under load, the AC voltage will drop by 1-2v so your transformer is probably 15-16v, just enough to charge a 12v battery.I think that if you short the white and yellow wires, you basically get 8v or so and double the current, but don't quote me on that.You can use the transformer as split power supply + 8v ---- 0v ----- -8v and go from there with a bridge rectifier and so on, or you could just use white and yellow to get a simple 16v DC output. This would also make it easy for you to get the negative feedback at the regulators so that you'd go as low as 0v at the output, otherwise you'd get a minimum of 1.25v or so. You have -8/-9v from a secondary so you can use something like a 7905 to get -5v out of that, which you can then use for negative feedback.Yes, you can use two linear regulators in parallel for more current, but you'd need to make sure they're balanced and not just one regulator being overloaded.Read this when you can, shows how to use resistors and opamp to make two regulators behave properly :http://electronicdesign.com/article/power/double-your-output-current-with-parallel-voltage-r-9270Or you could use something a bit more expensive like LT1083 (7.5A) , LT1084 (5A) , LT1085 (3A) :http://cds.linear.com/docs/Datasheet/108345fg.pdfThey're not cheap, at about 8$ a piece but they're quite nice. The datasheet even has example circuit showing how to parallel them with just a bit of thicker wire (to act as a resistor and balance the regulators).Either way, you'll need serious heatsinks if you think you're gonna get some voltage at 5-10A from 15-17v input. (Vin - Vout) x current = power wasted as heat ... for 5v and 0.5a you have (16v - 5v) x 0.5 = 11*0.5 =5.5 watts. You'd need a large heatsink to dissipate that much heat.Depending how you make the power supply you could use a relay of some sort or switch to short the white and yellow wires to switch between 8 and 16v so that the voltage drop on regulators is lower - these regulators need about 1.5-2v above the desired voltage to output stable voltage, so when you want about 6v or less, you can just switch to single 8v input and do the job and not overheat the regulators.

author: PhynixViking
author_rank: Regular Contributor
timestamp: January 08, 2013, 07:53:54 am
content: mariush - I was going to wait for a few more replies but KICK A** Advice!! Thanks!!! ^_^I love relays.. and I'm ashamed at myself for not thinking of using them how you explained!!!Most of my "work" is from scrapped "recycled" electronics. 7.5 amps is a big difference to refuse. hmm... I might have to just put some money into this project.I'm planning on having it made that all the Regulators are on a shared copper plate with a HUGE copper (with heat pipes) heat sink or two... (talking over a pound of copper) and a couple 120mm fans (and/or liquid cooled. I'm currently working on a audio amp project that I'm experimenting with liquid cooling system.)

author: N2CUA
author_rank: Newbie
timestamp: February 20, 2016, 04:57:37 pm
content: What about just wiring up a full wave bridge and capacitor and feed it to a :http://www.ebay.com/itm/271970055485orhttp://www.ebay.com/itm/262196407044With :http://www.ebay.com/itm/400969599170And let the converter do the regulating ..