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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
from memory, there's quite a bit on this topic in the old Pupman archives, (previous millennium) search for HEI. EDIT: I just had a quick look, a good start may be here Terry's GM HEI Coil Update
Ignition coils have an open magnetic system - good for energy storage / poor as a transformer. .... lots of leakage inductance.
Also, the laminations aren't very thin so eddy current losses become a problem at higher frequencies.
For RELIABLE operation in flyback mode 50W is easy.
For a newbSGTC 50W can be quite exciting using exactly the components/values as if for an NSTsgtc etc (c10nF etc.) the spark rate is low ... but the arcs can be longer than a 450VA NST sgtc IF the primary capacitor can take the higher voltage. e.g. 30 kV from a flyback instead of 20 kV using NST
Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
From an ignition coil I disassembled, it had the core and windings potted in some kind of tar and on top of that there's a few layers of sheet steel, followed by the aluminium case.
I think the most eddy current loss is in the steel sheeting, but to avoid internal arcing I think getting the tar out for oil immersion may be troublesome, although there maybe oil filled ignition coils that I haven't come across.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi kiat,
well judging from sounds my ignition coils make when shaken I'm pretty convinced there's some kind of oil inside them - I'm not sure what kind it is nor how toxic it might be.
For the fun's sake I tried running a smaller IC (the one visible in background of my last video) from a H-bridge, but I didn't even reach half the input voltage and it died internally. I suspect it's internal construction might have been faulty and perhaps it arced over along the output connections which might not be completely submerged in oil, as output is practically 0V now.
I know many people push their ignition coils to arc over externally very easily, and easily get arcs that start at 5cm or more... mine only started at like 2 at most, so I probably shouldn't take this coil as a reference. I didn't dare to run my other coils to external arcover without oil (which would ruin them instantly) as significant corona was already showing on the terminals.
After I get some more coils I might pick out some for special H bridge punishment and see what can I get out of them...
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
I had some very good results with a Bosch coil , from a VW car but using it for a completely different purpose, my electric fence HV generator: Not the same performance with a Dacia (local car manufacturer) coil , so when you say people get better results it might be due to better coils. The Bosch put out a 2 cm spark with my pulse driver, while the Dacia coil would work up to 1cm the most, for the same input parameters. I know that the Dacia uses oil for insulation, not sure about the Bosch one.
I don't think pushing coils to failure levels is a good idea, instead a very reliable driver might be a useful project.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi radhoo,
150V drive from a half-bridge seems like a fairly sweet spot for driving an ignition coil for power supply use. Full bridge would be rather pushing it but would surely produce some fun looking sparks but I'm not sure how long would it last this way.
What about those HEI ignition coils, what are their voltage standoff characteristics compared to usual can style coils?
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half bridge ignition coil driver - power your SGTC cheaply.
