Real Fiero Tech

Mach10 wrote:Stock ignition is fused to 10a...

That's 10a @ 12v, though... It'll be a little less at 20

thats not your coil, thats your ignition switch.

Without checking it out yet, I figure that it's probably just a DC-DC convertor - 12V in 20V out. Probably need an oscillator stage to convert 12VDC to high frequency AC, then feed it into a step up stage (transformer? diode/cap ladder with caps big enough to give the higher current output?) They probably do double the 12-14.7V to 24-30V then regulate it down to 20V with a regulator of some form. I'm no EE, so that's just my best guess.

As an almost off topic tangent, I once had an ignition problem on my 79' mercury 90HP outboard - 6 cyl inline, with CD ignition, and distributor (bear with me here). I had replaced the OEM ignition system when an accident burnt it out (my bad). The problem was, I kept burning out brand new coils with this new system when I ran the motor up and let it cruise at any significant RPM. It turns out that my charge system is unregulated - just a flywheel/stator charge system. With new car batteries once charged up the voltage will climb and climb, and the increased voltage on the primary side of the coil eventually smoked it - I was getting like 18 volts at WOT. It turns out that the old school type batteries start losing water instead (could they not just install a regulator?), but keep the voltage limited to no more than 14 or 15V and as soon as I changed it out, the problem never came back. The relevance: Are you coils gonna be cool with that? Mind you running a 6 cylinder 2 stroke at 5600 RPM is like running a 4 stroke 6 cylinder at 11,200 RPM off of one coil so... Also, you have COP and shit, so it probably doesn't apply.

On the other side of the durability spectrum, I have done experiments with charging arrays of disposable camera flash capacitors in arrays of 4, 8 or 12V and discharging them into an automotive ignition coil - the one I used was an oil filled one from an Audi - dumping 4 cap array charged to 480 volts through a 4 stage stepup ladder from the AC mains into the primary resulted in a FOOT long arc (I had to make an insulated tower to get the hot terminal far enough way from ground). Also: make sure you don't have one hand close to ground, and one hand close to the terminal when it fires, or you could be severely electrocuted. You don't want to know...

/ADD tangent

Mach10 wrote:So, a few caps here, some MOSFETs there... No problemo...

All you need is to build a switching power supply that can handle 10a of surge load, and provide a nice stable 20v output.

But more voltage means more heat, and it has to do all this under the worst possible conditions.

The circuit would be easy. Keeping it from self-destructing (and the coil) would be a little harder.

More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

Starlite528 wrote: More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

actually less amperage means less heat for the same wattage.

Kohburn wrote:

Starlite528 wrote: More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

actually less amperage means less heat for the same wattage.

Yeah, I guess what I said was a bit incomplete.

Starlite528 wrote: More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

AC principles aren't really applicable to DC circuits

Starlite528 wrote:
More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

Ohms law, man.

I = v/R

12v / 0.45 (primary, GM) = 26.67 amp peak

20v / 0.45 = 44.44 amp peak

Coils usually have a ballast resistor in-line to bring this down. IIRC, it's around 1-3ohms.

12v / 3.45 = 3.49a
20v / 3.45 = 5.73a

the primary is only .45 ohms I had it at 500 for my calcs. Whoops.

Blue Shift wrote:\The relevance: Are you coils gonna be cool with that? Mind you running a 6 cylinder 2 stroke at 5600 RPM is like running a 4 stroke 6 cylinder at 11,200 RPM off of one coil so... Also, you have COP and shit, so it probably doesn't apply.

N/A

If they sell a unit to do it, and get good results then his coils will be fine with it.

Secondary coil is higher, I've seen from 2k through to 5k... The primary is usually pretty low resistance, though.

I'm pretty sure the ignition coil is fused 10a. The ignition switch is fused 3amp to the starter for shizzle.... I gotta get my wiring diagrams out to check, though.

Mach10 wrote:

Starlite528 wrote:
More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

Ohms law, man.

Off topic,

but he's saying to transmit AC power, you can either have a high voltage and low current, or a low voltage and high current.

Heat (P) = I^2R

Low current wins in AC transmission lines. A lot cheaper than lowering the resistance of the lines. So you have half a million volt transmission lines

Is 0.45 ohms something somebody measured?

It's what's listed as a measurement for a GM HEI coil... *shrug*

There will be some variation depending on a bunch of things such as design, heat, age, condition etc.

It's a good starting point; I can't see +/- 1 or 2 ohms making that much of a functional difference.

whipped wrote:

Mach10 wrote:

Starlite528 wrote:
More voltage actually means less heat. That's why grid power runs at 13-14kv or more. They step it down to 4800volt for local distribution.

Ohms law, man.

Off topic,

but he's saying to transmit AC power, you can either have a high voltage and low current, or a low voltage and high current.

Heat (P) = I^2R

Low current wins in AC transmission lines. A lot cheaper than lowering the resistance of the lines. So you have half a million volt transmission lines

submarines use 400hz power because it enables smaler diameter wire. Space is a commodity on a sub.

Power does equal I^2*R but it is also P=V*I

power does not equal heat though. transformer design and materials has more to do with it than total power. There is a linear relationship, but you must respect the integrity of the equals sign.

Stupid equals sign :cussing:

p8ntman442 wrote: submarines use 400hz power because it enables smaller diameter wire. Space is a commodity on a sub.

What does the frequency change?

400hz ac is close to dc, atleast closer than 60hz. Therefore you can run less current and produce more power. You take the integral of the sinewave and multiply it by the integral of the current sine wave and get your power. Bigger value for voltage, less you need in current.

Not sure if it applies in transmission of power, but in RF, the apparant resistance of a wire changes depending on the shape and composition of the wire, and the frequency of trasmission--not just the size and length. RF only uses the exterior of the wire (for all I know this may be true of DC, also), which is why a lot of solid RF "copper" cable is just copper plated with an alloy core.

:scratch:

That's a function of the frequency. The higher your frequency the farther from the wire's core the electrons travel. In other words, a copper pipe will have as much current carrying capacity as a solid copper wire of the same diameter when operating at high frequency. DC uses the whole cross section of the conductor. Frequencies in the range we're discussing can also be considered to use the whole thing.

Trot, the gray, fox...

Mach10 wrote:Not sure if it applies in transmission of power, but in RF, the apparant resistance of a wire changes depending on the shape and composition of the wire, and the frequency of trasmission--not just the size and length. RF only uses the exterior of the wire (for all I know this may be true of DC, also), which is why a lot of solid RF "copper" cable is just copper plated with an alloy core.

:scratch:

I also know that resonance plays a factor somehow, and that each conductor has a "sweet spot" that provides very efficient transmission.

And then we start getting into pass-bands, capacitance, and all kinds of other crap.

12 volts of DC, it's good enough for meeee!