i put a 33 ohm resister on the gate and ground to earth and it still goes hunting......silly SCR

even when i ground the SCR gate to earth it does not stop the hunting ***

i changed SCR, no difference

brett

Some basic electronics.

U = I x R (Voltage = current x resistant)

U = ~300 Volt from flyback transformer
I = ?
R = 0.7 Ohm

I = U / R
I = 300 / 0.7 = 428 Ampere......I think the scr can't handle this current (?)

OK so i need an old points coil to test ....... with about 4 ohms,

i try tomorrow....its late now and all this testing R&D is tiring


If i reduce the input voltage down to 3 volts it sparks every 2 -3 seconds and i can then also trigger the gate from the positive pulse in between

brett

This are the specs of a HV-coil.
Prim-coil 58 mOhm (megaOhm)

Those Coil specs have a Ratio of 3,866,666:1

and my is .7 ohms primary and 13000 Ohms Secconary thats 18571:1

why is your coil have the primary/sec turns back to front ?

As normaly you have the low resistance on the primary and hi on the seccondary

brett

I think they make a mistake into the name, mOhm can also so be milli-Ohm.
But then the resistant of the coil is far to low.
Calculate the coilresistant by Voltage, 28,000 Volt : 400 Volt = 70 : 1
The resistant sec = 125 Ohm, prim = 125 / 70 = 1.8 Ohm

I don't know th resistant of the prim-coil, the coil I have is broken.

I'll email Roy wat resistant the coil must have.

Hi kermet,

Check the voltage at the HV cap. If is extreme then the cap will discharge. I ran into this problem too. Also with the "loud " transformer I think you may need to change some RC values to slow down the oscillations of the transformer. Or rewind the transformer. I have ran into all before many times.

There must be between the two ferrit parts of the transformer a gap of 0.5 / 1 mm

Hi Rob,

Why a gap? all the ferrite transformers I have seen have no gap. If you look at a psu from old computers that have one, there is no gap.

I think it lookslike there is no gap, but between the two parts is a thin layer of wax/glue.
All the HV-flyback tranformers I buy, see pics on the website, have a gap.
Why ?
You don't want a perfect transformer for this project, it has to be the worst transformer you can find.
A perfect trasformer can't / don't want oscilate, the frequentie you put into the transformer you want to get out (50Hz)
This transformer must be oscilate becourse otherwise the transformer can't sweep the voltage up enough.

Charlie, I see they erase my question about your emailaddress

Charlie one
http://www.rcuniverse.com/community/...1&memid=109693

Charlie two
http://www.rcuniverse.com/community/...1&memid=479794

Hi Rob,

Both of those are me. I moved from Laramie to rock springs. I forgot my login info and created a new account. I will have to experiment with the gap and see if it makes any difference.

The gap in toroids is to prevent saturation of the core. It is fairly common in power applications and is not always obvious from external appearance. Sometimes the construction is such that there is an inherent gap. Other times, there is a very small gap, but it is hidden by the enamel coating. This link describes it. See page 3 (Introduction): http://www.ferroxcube.com/appl/info/gaptoroids.pdf

There is similar literature available from most of the other manufacturers as well, e.g., Magnetics and Arnold.

John

You safe my ass again thx John

Great i will try a small gap.... But my other project say's not to leave a gap as it will over heat the transformer

But i will try and report back

brett

Intresting http://www.sportdevices.com/ignition/inverter.htm

Befor you ask me, why don't you build this one......I can't get the UC3845.

Ok i tried a .75 peice of plastic between the mullard former and that makes the transformer very quite.....but still self runs,

Charlie i tried changing the RC value to 1 k it slowed down the trigger, then 2.4k that stoped the circuit runing and overheated the BD242 (tip125)

I dont think my isses is on the RC side of the circuit, Charlie what did you do to fix your problem ( HV cap is 630 volts)

the more volts i use the faster the spark self runs,

brett

ps.Rob those chips are cheap over here

http://newzealand.rs-online.com/web/...&R=5165174

Hi Brett,

I ended up rewinding the transformer with different number of turns on the feedback and primary.

I blow the TIP162 when a wire get lose.

@Brett, I think you have to much Voltage from your flyback transformer.
It's hard to findout wat Voltage the transformer make, it's not a nice wave.
We have also a RS-electronics, but I can't buy there - only stores can buy.
The price is right, 0.41 euro = 1NZ$
http://nl.rs-online.com/web/search/s...rchTerm=uc3845

Rob,

You can program a pic to what the UC3845 does. its not that hard.

Hey Guys,

I am putting the final touches on a ignition tester.All it is,is a pic that will very the pulse from 8.9 hz to 222 hz. its to test the igition board and timing board with out a engine. I can post it all when I am done.

Sounds good Charlie.........

I have my power board working on the test bench

i used part of "sportsDevices" circuit and bigboats

triggers fine, but over 3.7 volts the tip125 gets hot, i chose the tip125 because its a 5 amp device



brett

Hi brett,

I also ran into that problem with the transistor getting hot. Do you have a base resistor in the circuit? I have found that a 100 ohm is a good value. I found that in my experiments that if the transistor gets hot I Needed to reduce the amount of turns on the feedback windings.

that was not nice having the site down......i felt alone haha

I have found if you current limit the input voltage the compontents run alot cooler

i just fitted a 10 Ohm 10 watt resister in front of my 7 volt pack, have now stolen couple fast recorery diodes from a TV in place of my IN5408

seem's nice now

brett


yes base resister is there,

circuit runs at 180 ma's and triger is about 250 ma's ( very hard to read triger)

My current transformer has 245 on the secondary,20 on the primary and 3 on the feedback. I get 408 volts out the rectifier.