What current do i need to drive flyback transf. from CRT monitor? - Page 1
Forum section: electronics / beginners

author: Vancata
author_rank: Contributor
timestamp: March 31, 2014, 07:29:13 am
content: Hey there, i got a flyback transformer from old 15'' CRT monitor and I want to make Jacob electricity ladder for fun.-In the schematic for the ladder (uploaded one) i use 220ohm 5w instead 240ohm resistor and the horizontal driver transistor (TO220 + heatsink) that i took from the CRT monitor instead 2n3055.Anyway in the added photo the same colored pins have connection ONLY between each other and no connection to any others. So 3 groups of x3pins and 1 HV 0.I did some Ohm mesurments and i found the highest resistance between 5 and 7, so this should be the prime coil.Found the High voltage zero by inputting some voltage on the High Voltage Input.So now i'm not sure which one should be my feedback coil but i did some tests et.c They all got like the same resistance between them ~0.8Ohms.Anyway my main question is what current should i need to drive this flyback transformer and have decent little spark to make the "Jacob ladder"? I have calculated that i need like 0.5A but I'm not really sure in my calculations.My power supply give only like 1.5A at 12V and no matter how i set up this bast*rd i keep getting my overload current protection switching ON. (The power supply is the cheapest chines liner one anyway so i can try with ATX psu from pc that have like 18A on the 12V rail).Any advice's will feet nice!

author: Vulnavia
author_rank: Newbie
timestamp: March 31, 2014, 08:55:27 am
content: RE: Half-Royer design --- ATTN:VancataPlease be advised that (full Royer)ZVSor PWM topologies offer superior results for the described application…That said, if you indeed wish to implement the half-Royer design (shown in the schematic), desirable operation will demand installation of ‘your own’ primary and feedback windings (4-to-5 and 2-to-3 turns respectively) -- Your low EMF supply should be capable of at least 25 Volts at 10 Amperes. Moreover please note that deflection BJTs while offering significantly greater collector to emitter breakdown figures exhibitdismalhfe...Best of luck

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 31, 2014, 10:33:54 am
content: Not really enough power to do anything with, those transformers are worth about 30-50W in normal operation as is.The high voltage output has diodes built in, so you probably aren't going to get very good performance in a ladder. They tend to spark rather than arc.If you can find a really old one without integral diode, you'll have better luck; but the arc still won't be very thick and hot for the purpose. Something like an ignition coil would be best.Tim

author: Vancata
author_rank: Contributor
timestamp: March 31, 2014, 01:30:07 pm
content: Pf, i'm kinda sad. Now i need to look for old model car coil or something...Anyway found one old fat transformer from a friend. Just tested it and it have 18V and 35V AC on two of the secondary coils. Hope he can deliver some nasty Amps there too or i will just fry it. So now will check my goodies for 4 powerful enough diodes for the Bridge Rectifier, and one big output cap capable of 40V.

author: N2IXK
author_rank: Frequent Contributor
timestamp: March 31, 2014, 01:44:40 pm
content: Typically, the primary winding in these is fed from ~+130V or so, and switched in the grounded side by the horizontal output transistor, a big beefy NPN BJT, usually with an integrated damper diode across C-E.

author: Fank1
author_rank: Regular Contributor
timestamp: April 01, 2014, 12:41:28 am
content: The quickest way to make a Jacobs Ladder is to get an old neon sign transformer.

author: Vulnavia
author_rank: Newbie
timestamp: April 01, 2014, 01:24:48 am
content: Impressive results (>50KV) may be obtained via use of an asymmetric PWM driver/snubber arrangement in conjunction with a flyback transformer incorporating internal rectifiers (DST or single ---Not E-multiplier, however - inasmuch as the caps will fail and short the secondary!). Of course the phasing (i.e. ‘polarity’) of the primary must be such that the high magnitude ‘side’ of the induced secondary pulses forward bias the rectifiers. Note that, owing to asymmetry, the above described arrangement functions reliably atoutputEMFs well in excess of the reverse breakdown figures of the rectifiers, hence obviating ‘risky’ methods such as electrically destroying same in an attempt to establish symmetrical ‘conductors’.FWIW your transformer is probably of the DST design (assuming the monitor was manufactured within the last fifteen to twenty years).Best of luck!