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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi guys, I little bit tuned the driving circuit and increased the power significantly… I’m still using the Jacob’s ladder as read out. According to the power meter I’m sucking over 500W from the wall. The heat sinks stay cold and the heating of the coils is very decent...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hi lads, when I've got my current work-load out of the way, I'll see what rectified voltage and current I can get from a few ignition coils I have to hand. I shan't be pushing them to destruction, but will see what they can do 24/7, which is far more useful for the applications in which I'm interested.
Isn't it strange that such simple measurements seem never to have been taken on this forum?
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Harry wrote ...
Hi lads, when I've got my current work-load out of the way, I'll see what rectified voltage and current I can get from a few ignition coils I have to hand. I shan't be pushing them to destruction, but will see what they can do 24/7, which is far more useful for the applications in which I'm interested.
Isn't it strange that such simple measurements seem never to have been taken on this forum?
Hi Harry, It would be great to have you on the iggy board…
Regarding the measurements, I‘ve got an idea for simple HV current measurements, but I need someone educated to help me with the math behind...
What if I take spark gap with defined gap size (let’s say 1cm) and a HV cap with known capacity. By using rectified output from the coils (I’m finishing 100KV oil dipped bridge right now) the frequency of sparks in the spark gap can be easily scoped. It should give us more or less rough idea about the current or not?
Any idea how to calculate from three known variables (spark gap size, cap capacity, frequency of sparks) the loading current?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Mates wrote ...
Harry wrote ...
Hi lads, when I've got my current work-load out of the way, I'll see what rectified voltage and current I can get from a few ignition coils I have to hand. I shan't be pushing them to destruction, but will see what they can do 24/7, which is far more useful for the applications in which I'm interested.
Isn't it strange that such simple measurements seem never to have been taken on this forum?
Hi Harry, It would be great to have you on the iggy board…
Regarding the measurements, I‘ve got an idea for simple HV current measurements, but I need someone educated to help me with the math behind...
What if I take spark gap with defined gap size (let’s say 1cm) and a HV cap with known capacity. By using rectified output from the coils (I’m finishing 100KV oil dipped bridge right now) the frequency of sparks in the spark gap can be easily scoped. It should give us more or less rough idea about the current or not?
Any idea how to calculate from three known variables (spark gap size, cap capacity, frequency of sparks) the loading current?
I think the potential uses of iggies have been very much overlooked - in some ways I think folk think of them as a sort of beginner's project, which is quickly put aside in favour of ZVS flybacks, instead of finding out what they can really do.
My own idea for measurements is extremely simple: nothing more than a half-wave rectifier charging a capacitor to discover the peak voltage. Then in steps a variable load is applied by means of high voltage resistors, or strings of lower voltage types. As the load is increased (i.e. by switching to a lower resistance) the voltage across the capacitor will start to fall from its peak value. I am very old fashioned, and would plot this fall on a sheet of graph paper, but I am sure there are much more modern methods. There will come a point where the voltage fall becomes unacceptable, and so using nothing but I = V/R you can get a faily good idea of voltage and current outut. Alternatively, you can just put a zener-protected moving coil milliameter in series with your load resistor, and measure the current available directly,
A four cylinder engine running at 6000 RPM generates 200 sparks/sec, so the full spark cycle lasts just 5 milliseconds.The time when the points are closed for a common or garden Lucas-type distributor is 60 deg. out of every 90 deg. rotation of the distributor shaft, so the points are open only one third of that time, or 1.67 millisecs.
In a mechanical interruptor distribution system, a capacitor is charged by inductive kick back through the primary to about 300V, and this is then discharged back through the primary to magnetize the core. So far as I can see, to imitate this electronically, one needs a rectangular drive wave of 300V, with Vhigh 3.33millisecs, and VLow 1.67millisec at between 4 and 6 amperes, depending on the model of iggy.
The multiplication factor in standard iggies is generally 100:1, so the 300V primary voltage induces a voltage of 30kV in the secondary, which once rectified, should give a voltage of ~42kV across the unloaded smoothing capacitor.
I have seen 30kV @ 20mA cited in a technical paper on iggies, which, if it is true, would correspond to 600W. If the input is 300V @ 4A, that would make the transformer efficiency 50%, which sounds believable. If it really can deliver such a current, then it has obvious applications for radiography and charging Marx stages.
In the EC, the most obvious source of ~300V DC at 4A or 5A is direct rectification of the mains - preferably via an isolation transformer if you have one. The input voltage could be varied with a ''variac' if you've got one. Then you just switch it on and off with a high power low Rds high voltage MOSFET very thoroughly protected against spike and negative swing damage. Nothing more than a 555 timer and a MOSFET driver would be needed beyond the MOSFET itself. On for 3.3millisec, and off for 1.67millisec. for a Lucas-type coil. It's completely reasonable to believe that the coil design team struggled to make it as efficient as possible, so PRFs much different to these are likely only to result in diminished performance.
I am no great theorist, so it's possible that my analysis has gone wrong somewhere, but I'm sure to be corrected soon if I've blundered!
Anyway, my approach is empirical - simply to measure the available output voltage and current - and see how closely this approaches theory.
Not such a big deal to find out what iggies can really do.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi Harry, I think I’ve already made enough iggy experiments to somehow “correct†your theoretical proposals.
Harry wrote ...
In the EC, the most obvious source of ~300V DC at 4A or 5A is direct rectification of the mains - preferably via an isolation transformer if you have one. The input voltage could be varied with a ''variac' if you've got one. Then you just switch it on and off with a high power low Rds high voltage MOSFET very thoroughly protected against spike and negative swing damage. Nothing more than a 555 timer and a MOSFET driver would be needed beyond the MOSFET itself. On for 3.3millisec, and off for 1.67millisec. for a Lucas-type coil. It's completely reasonable to believe that the coil design team struggled to make it as efficient as possible, so PRFs much different to these are likely only to result in diminished performance.
First of all, using a single switch design like you suggest, without any resonant capacitor, will result in a very poor performance. So you should definitely think about half-bridge design, or some class E design with a resonant cap in parallel with the iggy primary. Also, switching 300V into primary of an iggy will induce giant voltage peak (my rough estimation is above 1500V). So either you own really special transistor or super powerfull transils or you simply destroy the switch…
Harry wrote ...
A four cylinder engine running at 6000 RPM generates 200 sparks/sec, so the full spark cycle lasts just 5 milliseconds.The time when the points are closed for a common or garden Lucas-type distributor is 60 deg. out of every 90 deg. rotation of the distributor shaft, so the points are open only one third of that time, or 1.67 millisecs.
In a mechanical interruptor distribution system, a capacitor is charged by inductive kick back through the primary to about 300V, and this is then discharged back through the primary to magnetize the core. So far as I can see, to imitate this electronically, one needs a rectangular drive wave of 300V, with Vhigh 3.33millisecs, and VLow 1.67millisec at between 4 and 6 amperes, depending on the model of iggy.
I don’t think the operation frequency you suggest (based on the four stoke engine calculation) is very practical. Also the calculation sounds quite funny to me, because I personally use iggy’s from a two stroke engine (from old DDR cars Trabant and Wartburg) where each cylinder has its own coil. According to your receipt I would end up in completely different freq. optimum. I think much more realistic ideal freq. estimation would be based on the core material. Of course it is not easy to find out, but at least I know from the basic experiments that iggy performance goes very rapidly down at freq. around 10KHz. The same empirical approach tells me that highest tolerable freq. optimum is close to the 3KHz (rather a bit below).
Harry wrote ...
I think the potential uses of iggies have been very much overlooked - in some ways I think folk think of them as a sort of beginner's project, which is quickly put aside in favour of ZVS flybacks, instead of finding out what they can really do.
I have seen 30kV @ 20mA cited in a technical paper on iggies, which, if it is true, would correspond to 600W. If the input is 300V @ 4A, that would make the transformer efficiency 50%, which sounds believable. If it really can deliver such a current, then it has obvious applications for radiography and charging Marx stages.
You suggest some practical use for the iggy in some HV applications, but with such a low frequency you plan to drive it the whole world of CW multipliers is lost for you… According to my opinion using iggy for multipliers makes these “girls†so special and much more interesting than fly-backs.
Harry wrote ...
that would make the transformer efficiency 50%, which sounds believable
I doubt about the maximum efficiency you calculated to 50%. That would be in my case minimum 125W dissipating from each iggy (in case my driving circuit would be optimal - which I doubt) and I’m sure that’s not true. I know how much heat dissipates 100W bulb despite it is illegal device in EU
Harry wrote ...
Not such a big deal to find out what iggies can really do.
Let's see...
Good luck in your iggy adventure I’m pretty curios where you end up. And as I said it is great to have you on board...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
[quote] Hi Harry, I think I’ve already made enough iggy experiments to somehow “correct†your theoretical proposals. And as I said it is great to have you on board...
/quote1252350925]
I suspected I might have got it all wrong, Mates, but one has to start somewhere when thinking about things on one's own for the first time. I'd love to join your iggy group, if you think I might have something useful to offer.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Small update… I finished 100KV bridge rectifier based on 1N4007 diodes dipped in oil and hooked it to the ignition coils (you can see it on the lower picture). Probably the best way to show the performance now is via my old SGTC, so I’m sending photos. Surprisingly, despite I played with the setup for quite a long time the coils were only very slightly warm
BTW: It’s pity that these spark gap based coils are so loud, because otherwise the sparks are beautiful. In a complete darkness I could watch them for hours…
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
lpfthings wrote ...
How do you run your ignition coils at such high frequencies?? Mine just tend to squeal and have a tiny arc when I take them into the Khz ??
There might be following reasons for your poor high freq. iggy performance. - Insufficient power supply - Bad driver, bad switching transistor - Difference in the core material between mine and yours ignition coils
In case your power supply is strong enough, you can post the schematics of the driver you use. In case it is only single switch you can have problem with the fact that the core does not de-saturate completely in higher frequencies. In other words pulsed DC is not very good for driving ignition coils (actually it is not good for any transformer). That can be partially solved either by implementing resonant cap over the coil primary or rather choose half bridge design which produces AC pulses.
Registered Member #1361
Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305
I bought the circuit as a kit, and I suck badly at drawing diagrams, but basically it uses a 555 and a MJ10012 transistor, which makes me think they are running pulsed DC ...
I have a 0-16V 30A bench PSU, so power shouldn't be that big of a problem.
The iggy coils are "GT40's" or something like that.
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