awalker@topaz.ARPA (*Hobbit*) (01/11/85)
Want your points to last forever? It is real easy to upgrade a ''standard'' points-capacitor-coil ignition to an electronic version that will deliver close to twice the spark power of the stock ignition. I put one in my 4-by project and it's been kicking out the EMF ever since. Basically you place a two-transistor amplifier between the points and the coil. However this involves moving the capacitor so that it is in parallel with the coil rather than the points. This allows you to use the points as a low-signal switch, and the coil/capacitor circuit to resonate when the points open. It's this resonance that actually generates the spark. Since the fall time of a transistor is so much faster than a pair of points, you get a bigger bang from the business end of the coil. At this point, the question about eliminating distributors becomes academic. The problem with stock ignitions arises just when the points open. At the exact time when they start to separate, coil current falls. The coil, as most coils will, tries to compensate for this current drop by generating a 300 or so volt backlash, which the secondary picks up and turns into your 15 or so KV. But as the points open wider, the voltage across them increases at the same time, so you get a spark. This makes a raggedy falling-edge situation at the coil, and tends to reduce the output voltage. Since the transistor unquestionably turns *off* when the points open at all in the amplifier circuit, you get a nice clean falling edge and the coil generates its backlash against the resulting *zero* voltage instead of whatever's left around from the sparking. So you get a much heftier kick at the secondary. You have to find a transistor whose VCE is close to 400 volts, or the backlash will kill it. You could even replace your points with an inductive or IR pickup, but I didn't bother with that, because just in case the amp *does* die at 3 in the morning and I don't have an extra transistor with me, I can switch back to regular ignition mode and get home. I haven't had to do this yet... _H* [here, just hold this wire for a sec]
phil@amdcad.UUCP (Phil Ngai) (01/12/85)
> Want your points to last forever? ... > the fall time of a transistor is so much faster than a pair of points, you > get a bigger bang from the business end of the coil. At this point, the > question about eliminating distributors becomes academic. I think you're confusing points with distributors. I have an electronic ignition with an optical sensor. I do not worry about my points failing because they have been replaced with a beam of light which will never wear out. The problem my car had was due to a wet distributor cap which shorted out the spark before it got to the spark plugs. Also the rotor was pretty worn so I replaced it at the same time. These are the issues I was trying to address by talking about eliminating distributors. -- AMD assumes no responsibility for anything I may say here. Phil Ngai (408) 749-5790 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.ARPA
mikey@trsvax.UUCP (01/14/85)
All you did was eliminate contact wear due to arcing. The points will STILL need adjusted periodically as the fibre pad that contacts the shaft will still wear. A side benefit is that if you set your circuit to shut down fast, it will increase effective dwell. mikey at trsvax