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Transistors & Flybacks

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Evilren

Tue Apr 08 2008, 08:50PM

Registered Member #1392 Joined: Sun Mar 16 2008, 05:00AM
Location:
Posts: 4

Yup it's easy to wind a good flyback, but harder to insulate. peak turn off voltage on the primary times the turns ratio is a good approximation of the voltage you'll get out. (leakage inductance changes that just a little.)

quicksilver

Wed Apr 09 2008, 03:46PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I have noticed that several transistors are (sold as) audio oriented in their construction (2N3773) while others (MJE13009,7) are the smaller variety. With a good heat sink should there be any functionality issues?

Monitors have been free sources for the MJE-chip type but high voltage transistors exist in monitors & TV's rather sparsely. Just my opinion, but the sourcing of components is an important issue for the hobby in general. I am always looking for HV components now as I believe that we will see less and less of them as time goes on.

The use & enhancement of flybacks can be very important as many folks simply don't have access to NST's where they live (or can't afford them, etc). Is there any specific technique to pulling the core from a flyback? It seems that the potting polymer has them well glued in!

...

Wed Apr 09 2008, 04:00PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The 'standard' way is to soak it in boiling water for a while, which softends the glue

Seems to work pretty well

Wolfram

Wed Apr 09 2008, 04:57PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

quicksilver wrote ...

Just my opinion, but the sourcing of components is an important issue for the hobby in general.

I couldn't agree less

The way things are developing, we are most likely going to see more usable components in electronic trash. A few examples.

Normal electric stoves are getting replaced by induction stoves. These usually contain at least 8 600V IGBTs that should be good for moderately powerful DRSSTCs. They also contain some nice high-current capacitors that could be good for DRSSTC tank caps. The heating coils consist of litz wire, which is also useful.

CRT monitors and TVs are replaced by plasma and LCD displays. LCD displays contain lots of small transformers capable of a couple of kilovolts in the inverter. The power supplies for bigger LCD TVs also contain some nice FETs. Plasma TVs are even better. You would not believe the amount of semiconductors in these. The power supply contains some (up to 6 or more) (often IRFP460 league) MOSFETs. The rest of the boards often contain lots of MOSFETs, I've seen up to 100 TO220-devices in some older plasma sets. Some plasma sets contain 5 65A 200V FETs and 5 50A 250V FETs. Expect lots of other useful components as well.

Air conditioners are starting to use frequency converters to take care of motor speed control. I've found many nice electrolytics, IGBTs and power modules in these.

MOTs in microwave ovens are starting to be replaced by inverter MOTs. These are harder to use, but for the solid-state experimenters, these are a real goldmine. A couple of big IGBTs and a nice ferrite core with bobbin can be found in these. They are also feasible to rewind for higher voltage, as there are relatively few windings on the secondary. Could work nice for driving CW-multipliers, particularly due to the high frequency operation.

But sadly, these new items are mostly using SMDs, so getting standard resistors and caps from them can be a challenge. Luckily, CRT monitors and TVs are being thrown out at an extreme rate at the moment, and they will continue to be thrown out for years to come as the last of them are being replaced. Electronics scavengers have never had as good times as now.

Experimentonomen

Wed Apr 09 2008, 06:41PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

I think i can get hold of whole rolls of mylar insulation @ work, there are some of it in the basement there that should have been thrown out long ago.

quicksilver

Thu Apr 10 2008, 02:19PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Anders M. wrote ...

The way things are developing, we are most likely going to see more usable components in electronic trash.

True, the window of opportunity is strong at this time. But what I am describing is a pattern which (only my opinion of course) will result in a shortage in some time in the future (Eventually those monitors will be exhausted)....perhaps. What you describe is VERY valuable. Obviously your knowledge base exceeds my own by quite a bit! ....And this is exactly the contribution I prize.

Frankly I hope I'm wrong. I asked for the "used disposable cameras" yesterday at a pharmacy. I received a boat-load! I salvaged nearly 50 quality caps and similar number of AA batteries from those cameras: enough to make a damn fine cap-bank! I just can't see that wastage of electronics continuing.....maybe it's just me but those caps sell for about $3 each, etc. Can these manufacturers continue to throw away that resource?

The experienced members here are seeing what I do not. From my perspective items that utilize greater energy compete with a growing population base for finite energy resources. Copper is increasing in cost: we are seeing design differences in NST's, perhaps because of this. I appreciate more than you may know the observations of useful materials. Without the engineering background I would never have even thought about the stoves, etc. I actually 'cut & pasted" the post you made as I consider that a resource worthy of keeping. Observations like yours helps me gather materials: I simply don't have the expertise to see the forest before the trees.

Proud Mary

Thu Apr 10 2008, 03:05PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

When I first started this hobby years ago, there was very little that could NOT be salvaged from a 1950s TV set or wireless. Everything from valve sockets, valve screening cans, the valves themselves, tag strips, Rs and Cs with long leads and clearly marked values, mains transformers and HT chokes with flying leads, huge ceramic dropper resistors, full size variable resistors, IF and RF transformers in aluminium screening cans which were made to hold down with screws, the metal chassis itself and all those useful metal angle pieces and support straps held together with real nuts and bolts,

Backyard Skunkworks

Wed Apr 16 2008, 05:58PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

I just got the flyback effect to work with an MOT, I think. I discharged a 15uF motor cap at 300VDC into the primary and I could get as much as a 5mm long spark out of the secondary before the insulation started to break down. Wouldnt the spark on one of these normally be around 2mm when you have 340v peak to peak from 120VAC? Its rated at 2.1kV output (same peak input voltage as 120VAC) which should make about a 2mm spark, so I guess this is the flyback effect in action?

quicksilver

Wed Apr 16 2008, 10:06PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Flyback transformer observations:
I tested quite a few flyback transformers using a power source from which I could control current as well as voltage. Moving to 15Vdc from
12 does not have as great an impact as making a 12Vdc input reach 3 from 2.5 amps. The source does not go beyond 15v so that was where
I had to stop.

The 2N3773 transistor is a great little item. The 2N3055 appears to "lock-up", overheat and generally does not preform well
in most circumstances with the standard little circuit that many folks are using. Perhaps in a circuit with two 2N3055's
the transistor would preform better(?). I have not tried the MJE13009 yet however. It is of the smaller type, yet heat sinking
it seems little problem.
I think it's becoming very obvious that this circuit is the better way to go....

However the original author appears to think it needs some work. I don't have the experience to judge.

The 2N3773 does NOT get as hot as the 2N3055 (which makes sense as per it's rating).
The winding or both the feedback and the primary coils appear to be a "crap shoot" as they appear contingent on elements that
are difficult to determine such as the amount or secondary windings and thickness of that wire. In addition the core appears to be
an influencing factor as the larger ones - even on transformers that do not appear larger in their secondary windings, preform
stronger. One factor that does appear controllable is the 'evenness of the coil. If a coil is laid down in a sloppy fashion,
it will not preform as strongly as one with even spacings to the winding. Therefore it appears that insulated wire often works
better than varnished wire, in that the insulation provides consistent coil spacing.
The adjustments of the rectifier on some flybacks influence the arc, while others do not appear to have any impact. I don't assume anything
but perhaps that portion of the transformer is ruined or the design may differ....
These experiments are getting to be as much fun as when I was a young man. I just wish I had more time.

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