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Flybacks- Big & Small; Performance Analysis

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Nikhil

Sat Jan 10 2009, 03:41PM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

I've been using flybacks with small cores for all my activities. Recently i came across way big flybacks in a local junkyard. Most of em had a huge case and a big core. I suppose the o/p of fbts are at the mercy of internal arcover or melting which has nothing to do with the 'case' size. Why not vary the size of the core alone keeping the case size constant, whats the purpose of a big case? Definitly more energy must be involved with the bigger cores but is'nt this a clash b/w power and insulation!! Do bigger flybacks have better insulation/ higher voltage ratings, r they more reliable than the smaller ones? Could you plz help me understand the difference in performance btwn the big n small flybacks- How does SIZE matter?

Dr. Dark Current

Sat Jan 10 2009, 03:55PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Nikhil wrote ...

Why not vary the size of the core alone keeping the case size constant, whats the purpose of a big case?

With bigger case you can use thicker wire and more powerful diodes -> less heating.

Nikhil wrote ...

So whats the use of a big core when the insulation is inadequate? Could you plz help me understand the difference in performance btwn the big n small flybacks- How does SIZE matter?

The insulation is always adequate, otherwise the transformer could not sustain full voltage. For small power, use a small transformer. For higher power, use a big transformer. Does make sense?

You don't want to use a big transformer in a small TV because the manufacturer would be paying for extra power which would never be used.

Littlew

Sat Jan 10 2009, 04:47PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating. If you got old style flyback transformer you can use primary coils to draw arcs(approximately 800 turns of 0.20-0.50mm wire), and if you are lucky you can find flyback that produce 25kV AC.

Nikhil

Sun Jan 11 2009, 02:13AM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Littlew wrote ...

Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.

ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?

Littlew

Sun Jan 11 2009, 04:08PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

Nikhil wrote ...

Littlew wrote ...

Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.

ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?

In most CRT tvs >20-40W, but it can pump more power.
But you can find TVs where flyback transformer used to power whole TV, so there is 100w or more

Dr. Dark Current

Sun Jan 11 2009, 04:40PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Nikhil wrote ...

ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?

I think its around 50W usually.
Surely, they will run at 300W but just for a few minutes before getting extremely hot (there are rare exceptions). Most of them may run at 100W continuously but their lifetime can be much shorter.

Most designers design the parts for reliability, this also means overrating them. If they can just supply the needed power, they might well fail after 2 years, but if designed propery, can operate for e.g. 30 years or more. It's just that some designers (and manufacturers) overrate their parts more and others less or not at all (china).

Kolas

Wed Jan 14 2009, 03:11PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas

Dr. Dark Current

Wed Jan 14 2009, 04:28PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Kolas wrote ...

Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas

I'm pretty sure the diodes go first. In my experience the core is not the limit, but the heating of the diodes and secondary winding.

I had good experience with Sony Trinitron flybacks, some have a ~5cm plastic "tower" sticking out of the top to which the HV lead is attached. Such as this one, producing god-knows-how-much kV, and it is still perfectly fine by today:

it could do more but I just used halfwave rectification for oh-cool 50hz buzz

Kolas

Wed Jan 14 2009, 04:45PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

haha that looks alot like my work bench. Cool looking flyback though. My best preforming flyback was a similar looking unit but it was white and massive, as is that one.

GeordieBoy

Wed Jan 14 2009, 04:50PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> I'm pretty sure the diodes go first...

Also, remember that the stack of series connected diodes in a TV flyback transformer only needs to be rated for slightly more than the DC voltage that it puts on the picture tube's anode. The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?

-Richie,

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