Transformer substitution - Sanyo DP42849-01

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I'd guess the quality of the litz wire is probably not even close to that of my datasheets. So that may be a factor.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

Well, that litz wire I ordered was too small so I decided to try my luck at making my own. I made a jig which involves me stretching the wire from a hook in my living room wall, to another hook in my shop doorway, about 20 feet away. That hook can be spun with a screw gun equipped with a phillips bit. It's 25 strands of 39AWG magnet wire I got from Ebay. First attempt, I'll call fair. I'd say it went well, but as soon as I released tension, it unwound quite a bit. I wrapped 1 primary bobbin with it and my resistance is .84Ω. That's right on target with what I was expecting the original windings should have been. The two issues I came across were, 1, that it didn't stay twisted as tightly as I wanted it. And 2, that each strand wasn't equally tensioned so I noticed in a few areas that I had individual strands with a bit of slack. So I'm not going to use this first one. My next attempt, I'm going to try to maintain equal tension between strands, and I'm going to coat the wire with insulating varnish before I release the tension.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

If you ever plan on making litz wire, make certain you have a lot of patience. I wasted at least 800 feet of wire before finding a way that works. This stuff is just way too fine to work with 1 strand at a time. I had originally planned on trying to make some complex jig which would twist and wrap this stuff onto a spool, but then I found a YouTube video where some guy was doing it the way I'm now doing it, but he was working with much bigger wire. Well anyway, I had bought 50 plastic sewing machine bobbins for that project. So, what I just did that worked, is I wound 5 bobbins with the wire, put them all on a screwdriver, soldered the ends together, and then I was able to work with 5 wires at a time. And, before I twisted them, and after, I coated them with insulating varnish so they will not unwrap. So far, so good. I'm waiting on the first one to dry now.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

Failed again. It does come on, and the temp is much lower, but once you turn it off it wont come back on until it cools. Inductance is very low on the new primaries. All I can think of is that the ferrites must be damaged from overheating. I guess I'm going back to the original plan, trying to find a suitable substitute and making an adapter board.

[Agent24]

Re: Transformer substitution - Sanyo DP42849-01

Bummer... assuming everything else is the same, including the winding technique, you may be right about the ferrite being overheated or damaged in some way. It's the only other thing I can think of that would affect inductance too.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I don't like to give up, as we can see from how long I've been working on this project. I've been doing a lot of research on ferrites and I can find a lot of references to them being permanently damaged from overheating, but these are not even getting half the temp that permanent damage would occur. So, I'm led to believe it is something I'm doing wrong. And, I actually think I've figured it out. In the ones I've rebuilt, the ferrites aren't touching each other. There is a very thin layer of adhesive which separates them. I had originally believed this was plastic, part of the primary bobbin. Then I pushed through one with a screwdriver because I had no other way of getting a broken ferrite out. What I found, is that this layer broke out way too clean to be part of the bobbin. If it is part of the bobbin, it must be a defect because it significantly affects the transformer's inductance. I experimented a bit and found that separating the primary and secondary ferrites by as little as 1mm reduces their inductance by almost 40%. I'd bet there's at least that space between the ones I've rebuilt because I've added my own adhesive on top of that. The piece I broke out of one was .52mm thick. I have the last 2 I rebuilt soaking in acetone to loosen the epoxy. I'll try one more time when I get them apart. Probably have to soak them at least 24-36 hours.

I have not failed, I have simply learned several ways not to rebuild a transformer. And, what I lack in success, I have gained in knowledge.

[budm]

Re: Transformer substitution - Sanyo DP42849-01

I did not have a chance to read through them yet.

http://powerelectronics.com/content/why-have-air-gap
http://info.ee.surrey.ac.uk/Workshop/advice/coils/gap/

[Agent24]

Re: Transformer substitution - Sanyo DP42849-01

Of course! I was told about the core gap and effect on inductance a while back but had forgotten: https://www.badcaps.net/forum/showthread.php?t=36874

I guess when cool the inductance is enough for the circuit to work, but after heating up it drops just enough to prevent it from restarting again. Or perhaps the transformer drive circuitry is also being overworked in some way and ends up needing a rest before it can start again.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I guess when cool the inductance is enough for the circuit to work, but after heating up it drops just enough to prevent it from restarting again. Or perhaps the transformer drive circuitry is also being overworked in some way and ends up needing a rest before it can start again.

Also, the resistance on the wire increases as the temperature rises. Both probably play a role.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I just put a caliper on a good transformer, and the last one I rebuilt. Good transformer, 57mm. Transformer I rebuilt, 58.24mm. That's from the back of the primary ferrite to the back of the secondary ferrite.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

After reading up on the purpose of an air gap (thanks Budm), I can be led to believe that maybe there is supposed to be a gap, but if so, I need to determine exactly what that gap needs to be. What's clear is that my last attempt is 1.24mm more gap than what it should be.

[Agent24]

Re: Transformer substitution - Sanyo DP42849-01

maybe there is supposed to be a gap, but if so, I need to determine exactly what that gap needs to be.

Didn't you say you measured the original glue at 0.52mm? I guess the correct gap would be that much? Or maybe I missed something.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

Didn't you say you measured the original glue at 0.52mm? I guess the correct gap would be that much? Or maybe I missed something.

I thought that too. But, it wasn't even. That was the thickest point on the piece I broke out. On a working stock transformer, I measure 57mm from the back of one ferrite, to the back of the other. I currently only have 1 loose ferrite to measure and it is 28.125mm. Double that and you get 56.25mm. Subtract that from 57mm and you are left with .75mm. So, I'd say .75mm is what it should be. But, that's assuming they are all precisely the same size. I prefer having more than 1 so I can get an average. And then too, I have never disassembled a working transformer so I don't know that the failed ones don't have some physical defect, such as the ferrites each being .375mm too short. I've also never measured one before disassembly. I must admit, I never had a clue there was this much involved in building/rebuilding a transformer.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I finally got time to work on this a little more and I believe I got it beat. It was the inductance all along. Or rather, the air gap. I found that the inductance was as high as 6mh when the ferrites touched, and separating them by no more than a millimeter reduces that to around 1mh. I decided that it would be better to try to tune them with my LCR meter rather than chance that separating them a certain distance would be accurate. So, I pulled a good transformer and checked the inductance. I got about 1.75mh on the primary side and 40mh on the secondaries. On this attempt, I cemented the secondaries in place first and once the epoxy cured, I adjusted the primary side ferrite until I got a reading of exactly 1.80mh on both sides. Epoxying them without them moving wasn't easy. I decided the best way was to just drip some on each side without actually touching them, just to tack them in place, then, once that cured, I put more on. 3 1/2 months, 3 failed attempts and about $325 invested (about $80 of that was new shop equipment though), and I'm pretty confident I got it right this time.

So here's the numbers:

Startup current draw: Rebuilt about 1.5A. Stock about 1.6A (last board was 1.48A).
Current draw after ten minute warm up: Rebuilt 1.24A. Stock 1.23A.
Temperature (left side, right side): Rebuilt 170°, 160°. Stock 177°, 163°.
Inductance: Rebuilt 1.80mh. Stock 1.75mh.

According to the label on the back of the tv, it is rated at 216 watts. I dont know what the power factor should be but, with a power factor of 1, that would be 1.8 amps.

[Agent24]

Re: Transformer substitution - Sanyo DP42849-01

Congratulations! Just goes to show the old saying is right. Don't give up, you never know how close success is.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I don't give up easily. I do have to step away sometimes though. I couldn't have done this without the insights and suggestions from everyone, particularly Budm. So, thanks everyone.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I think I'm going to play around a little with the next one. I'd like to try and reduce the temp a little beyond what the stock ones are. Maybe a 5% increase in inductance, or a larger secondary conductor. I think that, since it's the secondaries which get hot, then maybe I'll try a larger gauge conductor first. If I reduce the current by increasing inductance, it may cause it to be too little current and cause premature lamp failure. Or, maybe even cause sets with older lamps to not work at all.

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

On second thought, I think I'm going to stick with 34AWG. I got thinking about it and, although there is a very high rate of failure among these transformers, these TVs were made in 2009-2010. That said, it would seem that they do last 4+ years. I think now I need to focus on better methods of disassembling them. I've broken 6 so far, but three were ones I had to take back apart a second time. I've tried various solvents (Cyclohexanone, Methyl Ethyl Ketone, Acetone, and PVC pipe cleaner), all of which are extremely hazardous. The pipe cleaner seems to be the most effective, but very slow. They are made of polystyrene, which is acid resistant, so I think I'm going to try sulfuric and muriatic acids next. It shouldn't take more than a few drops. I have no issues removing the epoxy on the outside of them. My heat wand and a razor make quick work of that. It's the stuff on the inside of the secondaries that gives me a hard time. I have found that it's best to remove both secondaries together and worry about the ferrite after they're out. Pushing the ferrites out from the bottom, after scraping the adhesive from around them, works better. I'm thinking the acids may corrode the pins, so I'll test on some broken pieces first. Another option may be to somehow heat the ferrites. I tried with my soldering iron before, but I couldn't get them hot enough. I'm wondering if I could heat them with inductance.

[Agent24]

Re: Transformer substitution - Sanyo DP42849-01

Trying to heat them via inductance is probably more likely to cause overheating damage to the ferrite, I would guess, but I don't know.

How about http://shaddack.twibright.com/projec...ferrite_cores/ or http://www.imajeenyus.com/electronic...er/index.shtml

[lookimback]

Re: Transformer substitution - Sanyo DP42849-01

I had actually tried putting one in the oven last year. 45 minutes at 350°. Tried boiling too. But I think too much time elapsed between removal from the oven and my extraction attempt. I have an old tcon cover I fashioned into a pulling jig. The lip on it slides behind the lip on the ferrite allowing you to pull evenly without gripping the ferrite with pliers. I may revisit the oven technique because I didn't have that the last time.