My best scrap yard/dumpster finds. - Page 1
Forum section: electronics / general

author: Bendba
author_rank: Regular Contributor
timestamp: June 09, 2017, 04:39:00 am
content: Hi,I just wanted to share my last find at the scrap metal yards today. They not long started collecting "e-Waste" so every now and then I go dig through the piles and sometimes find some really good stuff, not free but for scrap price.What about a "little" power supply?It's got a very nice main to 24V 40A transformer and another 230/115V to 115V 1400VA transformer. Just a shame the the two sets of 3 output taps are connected together and not separate winding, would have made a nice isolation transformer. Three 100,000 microfards 40V capacitors but I don't know how healthy they are.I plugged it in to see if it works and measured something rather odd. The output of the transformer is 26Vrms (no load) but after rectification (full wave rectifier), there is only 24.6 VWhat happens to the ( Vrms x 2^(1/2) ) - ( 2 x Diode drop)?Shouldn't I measure around 35V?I took the leads of the rectifier and measures .47V drop through each diode, no short or open failure.

author: Vgkid
author_rank: Super Contributor
timestamp: June 09, 2017, 05:21:38 am
content: If that 24.6v is the output(which seems to be correct, it appears to be a custom telecom supply), then you have a rather good supply. If you cannot use it, someone would love to have it.

author: bktemp
author_rank: Super Contributor
timestamp: June 09, 2017, 05:40:23 am
content: The transformer has unusual specs: The label does not say 24V 40A, but for 24VDC 40A, so it is probably rated for at least 50-60A AC but maybe at a slightly lower voltage.I have no idea why you are getting only 24.6Vdc with 26Vrms input voltage. What happens if you put a load on it? Are the 24.6V reasonably constant? If there is something wrong, the voltage should drop significantly with a load connected.The cables going to the rectifier also have some strange labeling:9-50Hz12-50/60Hz10-60HzWhat is the output voltage of the unused cable?Based on the 43/03 and 0311 markings the device was probably build in late 2003.Based on the connectors labeled FLUID, ANALYSER and COOLING it doesn't look like telecom to me.

author: VulcanBB18
author_rank: Contributor
timestamp: June 09, 2017, 06:39:57 am
content: Where I work (tertiary education), they often have cleanouts, and in some cases it is ok to scrounge.Lately, a lab has been having a clean out. Apart from all sorts of sundry nice lengths of copper cable, there have been all manner of interesting electronic stuff, including a valve-based-on-PCB high voltage control for an electron microscope beam.Just today I swung past and out with the "good stuff" (they have a "take if you want" sign out, the "not so good stuff" goes in the skip, but still free for the taking) and there were three vacuum pumps out!I grabbed this one - heavy bugger - I just couldn't pass it up! Score!cheers,

author: Bendba
author_rank: Regular Contributor
timestamp: June 09, 2017, 06:47:38 am
content: Hi,It comes out of what seems to be an automated light absorption spectrometer. I pulled out a few nice little motors with optical encoders, toothed belts, pulleys and rods, going back Tuesday for more, I should be able to get enough out of it to build a CNC engraver frame. But that off topic for the moment.That's the main power supply for the machine.The "Fluid", "Analyzer" and "Cooling" connectors are 120V ac outputs.I get about 21V between the "12 - 50/60 Hz" lead and the "10 - 60Hz" which would make sense, having 26V between the two 50Hz leads.I did notice the 24VAC making too, so I expected something around 17~18V on the output of the transformer.I'll have to find a load for it and try again. I'll have to go some digging to find a significant 24V load for a close to 1kW power supply.Quote from: Vgkid on June 09, 2017, 05:21:38 amDon't worry, I'll put it to use, I have a lot of high power projects waiting for a power supply as the best I have at the moment are computer "ATX" power supplies.

author: Brumby
author_rank: Unknown
timestamp: June 09, 2017, 07:50:50 am
content: Quote from: Bendba on June 09, 2017, 06:47:38 amTalk about a quantum leap!Nice score.

author: Bendba
author_rank: Regular Contributor
timestamp: June 09, 2017, 08:03:17 am
content: Quote from: Brumby on June 09, 2017, 07:50:50 amFeels good to go from struggling to find a supply big enough for the project to struggling to find a load big enough for the supply.Quote from: VulcanBB18 on June 09, 2017, 06:39:57 amNice pump you got there.

author: ICR9000
author_rank: Contributor
timestamp: June 10, 2017, 12:49:02 pm
content: Enough cap's n gear there to jump start a jumbo jet son.

author: Bendba
author_rank: Regular Contributor
timestamp: June 11, 2017, 03:51:28 pm
content: Quote from: ICR9000 on June 10, 2017, 12:49:02 pmI better go back to the scrap years and look for one then.Not sure about the health of the caps. They seem self discharge awfully quick. (Down from 24V to 12V in less than 60 seconds) and I hadn't got any test equipment to measure that.I ended up striping all the control circuitry, the power supply shuts itself of after 5 minutes. Even with q load. I'm guessing the control circuit is expecting some communication from the machine.So back to simply a transformer and bridge rectifier. Though I stuffed up and list the photos I took when dewiring it, they got compromised, thank you sd card, so I'm not sure I reconnected the transformer the way it is intended to be. Though I now have readings that make more sense, 18.5V rms at the transformer output and 25V once rectified. Could it be that because of all the extra circuitry, the output of the transformer was distorted and giving me a false reading?The transformer is a bit unusual, here is a very crude drawing of itThere is an input winding, blue on the sewing (actually multiple windings to accommodate for different main voltages) separated from the other winding by a magnetic shunt like in a microwave transformer. Then on the other side of the shunt, is one winding, the green one, with an offset "center" tap that outputs about 300v (240 and 60 between ends and tap) that was somehow connected to two 20 microfarads 400V capacitors. I couldn't remember how that was connected.And the dawns red winding outputs the 18.5V (with two tap, depending on the main frequency)In didn't load the transformer again as I have first to work out what that capacitor is supposed to do.Does that configuration have a specific name that I can search to read more about it.Could I have drawn out wrong and it would be more like this: and the green winding would magnetize the shunt more or less to regulate the transformer?Edit:I think I found it. It matches the description of what is called a ferroresonant transformer. I have to read more about it but I'm assuming that the taps on the middle winding are to connect the capacitor on one or the other depending on the main frequency.

author: Bendba
author_rank: Regular Contributor
timestamp: June 12, 2017, 08:29:56 am
content: I think I worked it out. I wouldn't mind if someone can confirm I worked it out right.This is the winding diagram.The main at the input of the transformer while in operation.That's the output when no capacitor is connectedThe output with capacitor connected from 16 to 14Output with capacitor connected from 16 to 15Is it normal to have that square-ish output waveform? Or would the distortion be coming from the probes / scope?I loaded it a bit but the best I could do was pulling 5A, not much for a 40A output.The other thing is that the transformer is pulling 3.8A on the main even when unloaded. It's not getting warm thoughNote: Anything more complex then 1 input / 1 output is a bit like black magic to me. I still struggle keeping up with fluxes, fields, ...

author: TerraHertz
author_rank: Super Contributor
timestamp: June 12, 2017, 10:02:51 pm
content: Your first drawing is more correct, but you left out the caps (on the green winding.)This is a basic constant voltage output transformer. A kind of regulator that uses only magnetics.Don't feel bad about not understanding it, at the moment I don't really either. I think I did in the past, but have forgotten the details. Hopefully someone here can give a comprehensible explanation. (And this time maybe I'll remember it.)I know the output waveforms are non-sine due to saturation of parts of the iron core - which is deliberate and an element of the voltage regulation process.

author: bktemp
author_rank: Super Contributor
timestamp: June 13, 2017, 04:41:42 am
content: A constant voltage transformer explains the unusual names on the output connections. In addition to changing the capacitor connection you also need to adjust the output winding when switching frequency (connection 9+10).Wkipedia has some information about constant voltage transformers:https://en.wikipedia.org/wiki/Voltage_regulator#Constant-voltage_transformerIt basically acts as a limiter by saturating the core, followed by an LC resonant circuit to recreate the sinewave.

author: Bendba
author_rank: Regular Contributor
timestamp: June 16, 2017, 04:51:16 am
content: Quote from: TerraHertz on June 12, 2017, 10:02:51 pmThat's reassuring. I get the idea but the needy-greedy details are a bit muddy. But I'll get there.______________________________________________It's party time!!!Bulky household waste collection week in my council. Well, next week but people already put stuff outside.I went for a half hour drive and picked up 4 CRT tv's, one with built in VCR, 3 microwaves, an 32" lcd tv, and a couple of radios and printers.I'll be doing some scraping this weekend and I can put the gutted carcasses outside before they do the pickup.I just wish people would throw out oscilloscopes and other tools.

author: Bendba
author_rank: Regular Contributor
timestamp: June 19, 2017, 03:45:36 am
content: Just gotta love people throwing out perfectly working stuff.Today on the side of the road, a 27" Sony CRT (4 composite inputs, one component input and antenna input).I needed a good screen for my Commodore 64 anywayGot it home, plugged it in and that's it. (Could do with some fine tuning)

author: Bendba
author_rank: Regular Contributor
timestamp: July 01, 2017, 06:08:09 am
content: Hi there,The council pickup is all over. There is the tally. Most of it has already been scraped and taken apart to save space.7 CRT tv's, one has a built in VHS recorder in it (keeping that one, as well as the 27" Sony)1 CRT computer monitor (VGA)8 microwave ovens4 large LCD tv's, one was a LED back lit (that'll give me some bench lighting for the day I build a lab)3 VHS2 DVD players1 steam clothes iron (I'm thinking about modifying the boiler's fittings for a model steam engine)2 cordless drills and chargers1 bashed up UPS full of nippon chemi-con caps (hence the photo)5 car lead acid batteries to trade at the scrap metal yards2 cheap "hi-fi" radio-cd-cassette players5 inkjet printerSo I'm all stocked up in transformers, caps, switches, connectors, leads, motors, opto's, screws, power transistors ,... I kept one of the tv's SMPS (+-5, +-12, +24, +32V output.) Stocked up on VFD's too.And I got a big bin of boards to salvage parts out of.

author: JPortici
author_rank: Super Contributor
timestamp: July 01, 2017, 06:46:35 am
content: For the joy of dave, i found some (WORKING!) amstrad CPC computersi remember he saying he really wants to do a teardown of those but i sold them all but one years agoand the one left is the very first computer my family had, older than me, can't give it away

author: Bendba
author_rank: Regular Contributor
timestamp: July 02, 2017, 12:38:07 am
content: I wish I'd find that sort of things one day. The best stuff I found so far was a portable tv-radio-cassette player.Hope your CPC is still working.

author: VK3DRB
author_rank: Super Contributor
timestamp: July 02, 2017, 08:57:46 am
content: Best I found was a drive-in speaker at the side of the road on the annual rubbish dump day. In its day, you hooked the speaker on your window and the wire wound pot usually crackled the sound as you turned the pot. The sound was definitely lo-fi, but they were what they were and drive-ins were fun. I never hooked up the speaker but a few years alter, a bloke was selling a Gottleib pioneer pinball machine. He wanted $1500 for it. As he was a collector of memorabilia like petrol station signs, I asked if he would negotiate the price if I offered him the drive-in speaker. He REALLY wanted that speaker. He let me have the pinball machine for $700 plus the drive-in speaker. So that speaker was worth $800 to me.There are drive-ins still in Melbourne.

author: JPortici
author_rank: Super Contributor
timestamp: July 02, 2017, 09:12:56 am
content: Quote from: Bendba on July 02, 2017, 12:38:07 amit is31 years old and counting

author: H.O
author_rank: Frequent Contributor
timestamp: July 05, 2017, 04:34:30 pm
content: This is probably the best dumpster dive score I've ever done.The other day I found this EWM Tetrix 180 TIG/MMA machine in the dumpster (well, the recycling bin for electronics to be accurate). At first try it looked to be working but I quickly realised it had no control of the current, it was 100% all the time. I obviously suspected the hall sensor or measuring circuitry and I was correct but I could barely believe what the actual fault was. Nope, I'm not kidding.

author: calexanian
author_rank: Super Contributor
timestamp: July 05, 2017, 05:09:32 pm
content: Somebody totally wasted that welder, and never opened it up. Sad. Oh well, great for you!

author: Cyberdragon
author_rank: Super Contributor
timestamp: July 05, 2017, 11:12:59 pm
content: Wait, if it was defective like that from the factory, why didn't the bloody idiot get it repaired under warranty?!

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: July 05, 2017, 11:41:46 pm
content: Ohh sweet..its unplugged! Winning!

author: TerraHertz
author_rank: Super Contributor
timestamp: July 06, 2017, 12:13:30 am
content: Niiiice!Did you take that photo before or after noticing the unplugged connector? If after, I like how you put it at the frame corner, so it's not obvious at first glance. More fun that way.

author: H.O
author_rank: Frequent Contributor
timestamp: July 06, 2017, 05:24:24 am
content: It was not from the factory, the machine has clearly been in use for some time, several stickers on it (which I removed), dust and dirt (which I cleaned up) and wear & tear on the front panel etc. My guess is the connector wasn't latched properly, either from the factory or from a previous service/repair and had come disconnected due to vibrations while transporting it.I took the photo after noticing it was unplugged, the hall sensor was the first thing I looked for when opening it.It's lacking the (optional) water cooler but for occasional garage use a self-cooled torch will be fine - and of course, for MMA it's not a problem.

author: calexanian
author_rank: Super Contributor
timestamp: July 06, 2017, 06:02:58 pm
content: I wonder if somebody "Broke" It with the intent of the company having to buy them a new one.

author: aargee
author_rank: Frequent Contributor
timestamp: July 07, 2017, 02:18:47 am
content: Or broke it, hoping to intercept it at the dumpster but H.O beat them to it.I have seen this before. The connector is not pushed until the capture mechanism clicks. It works for years until the plastic shrinks a little or the hot/cold cycles and the cable tension makes the connector let go.

author: westfw
author_rank: Super Contributor
timestamp: November 13, 2020, 10:12:36 am
content: QuoteWe stayed at a motel once that had apparently been replacing their in-room TVs with modern flat-screens.They had about 20 pretty-large-screen CRTs piled in their parking area.It was very tempting. But I already have too many screens, and big CRTs are ... big.