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FL inverters
By RobC, Section Light Posted on Mon Feb 21, 2005 at 05:13:51 AM MST
12V Fluorescent Light experiments

I just built 3 of the 12volt conversions for the 40w tubes. These are the ones Bt Humble was talking about. They seem to work well enough. I got to thinking, I really want inverters for 8ft bulbs. In my storage box I had a 555 timer circut connected to a irf640n mosfet that I'm using for various experiments. I took the circut changed it to 18Khz @ 20% duty cycle approx and hooked it up to a modifyed ferrite switching transformer from I think an old tv. Next I hooked up an 8ft bulb applied power and I have a nice soft white light. I don't remember what the turn ratio on the transformer was but I will try to figure it out. I think this setup is as easy to build as the other and mosfets will keep going long after a transistor has died. 2 2n3055s died in the first attempt to get the 40watt units going somthing about the ferrite transformers was out of whack. I think this is a good circut idea but could probably use some input from sombody who knows more about designing circuts than I do.RobC

FL inverters | 9 comments (9 topical)

Re: FL inverters (3.00 / 0) (#1)
by BT Humble on Sun Feb 20, 2005 at 10:24:03 PM MST

I just built 3 of the 12volt conversions for the 40w tubes. These are the ones Bt Humble was talking about. They seem to work well enough. I got to thinking, I really want inverters for 8ft bulbs. In my storage box I had a 555 timer circut connected to a irf640n mosfet that I'm using for various experiments. I took the circut changed it to 18Khz @ 20% duty cycle approx and hooked it up to a modifyed ferrite switching transformer from I think an old tv. Next I hooked up an 8ft bulb applied power and I have a nice soft white light. I don't remember what the turn ratio on the transformer was but I will try to figure it out. I think this setup is as easy to build as the other and mosfets will keep going long after a transistor has died.

Cool! I've got vast numbers of ferrite transformers from old PC power supplies, but the windings are all wrong for what I'm trying to do with them.

2 2n3055s died in the first attempt to get the 40watt units going somthing about the ferrite transformers was out of whack. I think this is a good circut idea but could probably use some input from sombody who knows more about designing circuts than I do.

The trick is in the "feedback" winding. If it doesn't light immediately when you connect the power, you need to reverse the way you've connected it to your circuit. You also need some good heatsinking on the transistors, or they'll suffer badly.

I've since discovered that the TIP31C I was using on the 15W versions doesn't work for the 40W ones. I've now got a pair of 40W tubes lighting my shed, using some unknown transistors salvaged from a PC power supply. They're only drawing 2A, but they get pretty hot.

Thanks for the news, I'm glad that my work was of some use! ;-)

BTH

Re: FL inverters (3.00 / 0) (#2)
by Trivo on Mon Feb 21, 2005 at 04:23:15 AM MST

Hi BTH
The first transformer i tried to your formular on the TIP31c did not work so i
changed the thickness of the feedback wire to the same as the secondery wire and 14 turns worked fine on 40w tube can run two in series but loose a bit of brightness
Thanks for the info and pcb layout
Trivo

[ Parent ]

Re: FL inverters (3.00 / 0) (#3)
by deerslayer660 on Mon Feb 21, 2005 at 03:11:12 PM MST

I to am working on one but the .6mm trans wire was next to impossible to get here
i got close with the secoundary and tried using 1mm for primary and feedback the problem was the primary would not fit the core so i split it in half and made 2 layers think this will work? i still need to get a .47 cap so i can finish the
curcuit i am going to use a 14w tube think that cap will be ok? hopefully i can get the cap tommorow george

[ Parent ]

Re: FL inverters (3.00 / 0) (#4)
by Trivo on Mon Feb 21, 2005 at 04:26:56 PM MST

The wire size will be ok i made one with.9mm x 6 layers 450 odd turns then 1.6mm x 54 winds then 14 winds of .9mm and it worked fine
Trivo

[ Parent ]

Re: FL inverters (3.00 / 0) (#5)
by BT Humble on Mon Feb 21, 2005 at 04:54:02 PM MST

It should be fine, and the circuit isn't terribly fussy about having exactly 450/50/14 turns either.

If you want a cheap source for all of the parts except the ferrite then get yourself an old small TV or CRT computer monitor. The degaussing coil will give you enough enamelled wire for 2 or 3 transformers, and if you're a patient chap then the yoke coils on the "stem" of the picture tube can be unravelled for lots of thin wire. You'll get a couple of good power transistors and whatever capacitors you need, and probably the 2 resistors as well.

...and if you're really determined, you can cut up a section of the PC board and wire up the circuit point-to-point on the back side! ;-)

BTH

[ Parent ]

Re: FL inverters (3.00 / 0) (#6)
by nothing to lose on Tue Feb 22, 2005 at 06:07:40 AM MST

I knew there was a reason I never tossed out those 5 old monitors that don't work :)
And 2 small Black and white tvs too.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.
[ Parent ]

Re: FL inverters (3.00 / 0) (#7)
by RobC on Tue Feb 22, 2005 at 08:22:04 AM MST

I pull the circut boards out of them and turn them upside down. Next I light up my torch hit the oxygen and bring it just close enough to the board to melt the solder.
Then all you have to do is gather up the componets off the floor as the solder is blown not burnt away.RobC

[ Parent ]

Re: FL inverters (3.00 / 0) (#9)
by nothing to lose on Tue Feb 22, 2005 at 11:17:51 PM MST

Thanks Rob for the tip, I was going to do it all the hard way some day with a soldering iron. Thought about the propane torch but worried I'd burn em out with to much heat. Cutting torch is better idea for me and it's connected ready to go :)
.
nothing to lose

Spelin and tpying are my strong points, not electronics.
[ Parent ]

Re: FL inverters (3.00 / 0) (#8)
by deerslayer660 on Tue Feb 22, 2005 at 02:23:04 PM MST

the ckt works fine with 2 layers as primary going to make one with 6 volt trans and 555 next thanks george

[ Parent ]

FL inverters | 9 comments (9 topical)

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