Ultrasonic Acoustic Levitation Device Help - Page 1
Forum section: electronics / projects

author: azarak
author_rank: Newbie
timestamp: August 04, 2015, 04:14:35 pm
content: Hi all,I'm new to the forum and relatively new to electronics so forgive me if I'm doing something fundamentally wrong ! I'm trying to build anultrasonic acoustic levitation device. I'm following Mike's build from his channel mikeselectricstuff.My first problem was finding a transformer. I got one in the end from an old DELL PSU.Power Supply StickerTransformerI connected it all up to the driver circuithttp://electricstuff.co.uk/levit.htmland the transducer. When powered on the transducer starts making sounds, either a tone or white noise depending on how its tuned. Great ! I now set up my multi meter in the circuit so I can read the current draw but no matter how I tune it I can never get it to draw more than 0.04A. Mike said in the video that I should be able to play with the pot to tune it to the transducer's natural frequency where it will draw about 2 Amps or more. No matter how I tune it I can't get it to draw that much !What am I doing wrong ? Have I got the wrong type of transformer ?Thanks guys

author: mikerj
author_rank: Super Contributor
timestamp: August 04, 2015, 05:59:11 pm
content: Have you wired up the transformer the correct way around (i.e. backwards to normal use)? What voltage are you getting on the secondary side?

author: azarak
author_rank: Newbie
timestamp: August 04, 2015, 07:52:55 pm
content: I think the transformer is wired up correctly. I don't have a data sheet or anything to indicate which wires are primary and which are secondary. There is nothing on the transformer to indicate which is which other than arbitrarily (I think) coloured wires coming out of it. I figured out the pairs of wires that match to a coil by doing a continuity test with a multimeter. I've only just tested to see the voltage on each coil. Applying 5.29v to the primary gives 2.7v out on the secondary. Ok so that's stepping down. Maybe I have just got them the wrong way round ? However, if I excite the secondary coil instead of the primary coil we still have 5.29v applied to it and 2.7v coming out. Is this normal ?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 04, 2015, 07:58:17 pm
content: That doesn't look like an SMPS transformer to me. More like a normal mains transformer (standby supply?)

author: bktemp
author_rank: Super Contributor
timestamp: August 04, 2015, 08:18:19 pm
content: It could be the passive PFC inductor (marking: PFC48V). Early power supplies used large and heavy iron core inductors in front of the bridge rectifier for PFC instead of the better active PFC. Then this could be 2 loosely coupled inductors.

author: DanielS
author_rank: Frequent Contributor
timestamp: August 04, 2015, 11:42:52 pm
content: This transformer is definitely not any sort of switching-oriented device: switching transformers need very short leads to minimize EMI and stray inductance. Long leads like these only make sense for either passive PFC or bridge-less APFC inductors.The main output transformer in a desktop PC supply would have at least two terminals for the primary (possibly four if there is a recovery winding, possibly one more extra terminal for a shield if present) and at least four terminals for the secondary: 0V, 3.3V, 5V and 12V.The transformer you are looking for should be similar to the attached picture.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 05, 2015, 08:08:46 am
content: I remember my first PSU was a dell atx and when it died i connected up the transformer (yes i did connect it the correct way) and it kept on shorting out (the cause of failure in the psu was a dead transistor and the transformer tested fine when i pulled it out) so maybe try a different transformer.This might or might not be very helpful at all but that is just my experience with a dell transformerHope this helpsSent from my iPhone using Tapatalk

author: azarak
author_rank: Newbie
timestamp: August 05, 2015, 10:02:14 am
content: Ok thanks guys. I did find another transformer from the same DELL board. I've attached some pictures. Do you guys think this will do the trick ? It doesn't have any common connectors unlike DanielS's picture. If so how can I tell which pins correspond to which coils ?Thanks Again

author: DanielS
author_rank: Frequent Contributor
timestamp: August 05, 2015, 07:57:02 pm
content: If you have a signal generator, put a 50kHz 2Vpp sine wave on the primary and use an oscilloscope to find a pair of output terminals that have the transformer ratio you are looking for.

author: azarak
author_rank: Newbie
timestamp: August 05, 2015, 10:14:02 pm
content: Thanks DanielS. I don't have a sine wave generator. To drive the transducer I'm just using a square wave as shown from the schematic. I tried this second transformer but I had no success. This is driving me crazy. I tried every combination of pins acting as either primary or the secondary. I tested it by connecting it to my square wave and measuring the voltage on the other side and I'm not getting anymore than 4v. Weird I don't know what I am doing wrong. Is it feasible to just wind my own ? or find some where that will sell something I can use. I have had a browse on the internet but I can't find anything that is going to step up that high.

author: DanielS
author_rank: Frequent Contributor
timestamp: August 06, 2015, 01:02:35 am
content: Follow the PCB traces and it should be quite obvious which winding belongs with which input/output.Since you want to step up from something like 12VDCto 400VPk, you will probably want to use the 5V winding as your new primary.The transformer's high voltage winding should be quite easy to find since one of its leg will usually be connected to the primary-side switch and the other connected to the positive terminal of the input filter capacitor with fairly thick traces or copper pours.