Home brew TCI

[Big Beadle]

HI all, so i just got home from my vacation from hell, around mile 150 of 780trip and the black box **** the bed,my gm ho coils melted the solder off the joints. i re-soldered and made it the 300 miles to my hotel room in northern Maine, i was able to move it to the right side cover and left the lid off it to keep it cool.........I made it home so its time to put on the home brew black box (TCI) is there anything needing to be done on 79 special to make it work rite i am assuming its a direct replacement its already built ready to go Thanks in advanced

[CatatonicBug]

Maybe I missed this tech tip... What's a "home brew" TCI?

[Douglas Money]

All you really need is two gm ignition modules that get their trigger from the pickup coils and they can fire about any ignition coil that you hook up. Very simple easy to make and repair. Just remember a heat sink for the modules as well as heat transfer compound.

[cywelchjr]

Aren't the GM coils like less than one ohm? TCI systems are designed to work with higher resistance coils than CDI type systems (which is what almost ALL auto systems are these days) as the principle of operation is quite different. TCI type systems run a current through the coil normally at all time until ready to fire the coil, then cuts the current to generate the spark, where a CDI system does NOT supply a current until ready to fire the spark but supplies a much higher voltage pulse of short duration at the coil. I'm not sure you wouldn't burn out CDI type coils after a while trying to run them in a TCI type mode even if you managed to setup a TCI system that could source the current.

I mean, I could be wrong here, but it sounds to me like two incompatible technologies are being mixed here, which would give me pause, and I'm not surprised that it cause problems, HO coils designed for a TCI system should NOT draw significantly more current than the stock coils. HO coils don't do more current, it's more voltage, and it's done by a higher ratio of primary to secondary winding (OK, secondary to primary, but you know what I mean).

I understand that the GM trigger units are supposed to be able to drive most anything, but you still have the issue of the type of driver system your talking about. TCI acts like the old points systems, and opens the circuit for just a moment to fire the plug, this requires a certain amount of resistance in the coil to prevent the coil burning up from the current flow through it. CDI doesn't do this, it sends a high voltage pulse through the coil for a short burts, and uses a VERY low resistance coil. You cannot mix the two, you will burn up components if you try. The magic of the systems like megasquirt for fuel injection is that one of the things you can do with them is switch to CDI ignition as part of the EFI conversion, as the computer can handle TCI or CDI type ignition type coils, and wasted spark or individual coils as well.

[DAVINCI]

Our coils, 3 ohm, and the GM ignition module from the 70'-80's work together fine. The old GM coil-in-cap modules, IIRC, they called it HEI?? One of the members did a write-up here a few years back, do a search it should still be here.

[cywelchjr]

Our coils and the GM modules sure, IIRC the GM coils from that ERA were 3 ohm, but the newer coil packs for the HO coils IIRC are CDI coils with a much lower resistance, which is a different story, and the OP talks about the stock TCI with GM HO coils, which I'm not sure will work in either case. TCI systems need TCI type coils and CDI systems need CDI type coils, totally different resistances, with CDI coils designed for MUCH higher current flow for very brief periods of time vs TCI type coils that flow most of the time and spark by cutting off the current.

[Douglas Money]

OP Asked about a "home brew TCI Black Box". I simply stated that it was just as easy to use the GM parts with our pickup coils. That's all I said.

[cywelchjr]

OP Asked about a "home brew TCI Black Box". I simply stated that it was just as easy to use the GM parts with our pickup coils. That's all I said.

He mentioned that he had already built it, and IIRC that "homebrew box" is build using the GM parts. But they still can't drive CDI coils running TCI signals, even if THEY will handle the current (which I doubt, they were designed for 3 ohm coils too) the coils will burn out after a while, cause those lose resistance (less than an ohm IIRC) coils will draw way more current than they were designed for.

I've worked in electronics and technical support almost all my adult life, and I've learned to try and not let someone do something they shouldn't if I can give them advice that will keep them from doing something wrong. If they go in with their eye's open, then it's their call. If I know information that suggests they might be doing something that might cause damage to their bike, that would at least by omission give me some level of responsibility morally.

Notice I have said I believe this to be the case, so he can check it out. But you shouldn't run either the stock TCI, or the GM generic TCI setup with anything but 3 ohm coils (or 1.5 ohm with ballast resistor), both they and the coils if they are less than 1 ohm are not designed to work that way.

BTW, you CAN run a TCI type coil in a CDI system, it won't be as efficient but generally won't toast anything, but the opposite is generally not true, as the CDI type coil will just act as a short on the ignition system, melting solder joints and such (much like the OP ran into on his trip).

So, to the OP, measure the resistance of those coils, if it's not 3 ohms, it won't work with our bikes without a complete replacement of the ignition system with a CDI type system, and that homebrew system is NOT a CDI type system, it's just another TCI, albeit a little bit beefier and able to be built from off the shelf parts. As a matter of fact, I may well built one from my engine frame to run up my spare engine with, just so I can say I did.

[Big Beadle]

homebrew tci

Well guys I am assuming what i thought was a coil is a coil is as not true i was not aware of the different types of coils cdi vs tci. I just got done with a test run and it ran fine the 3k rpm and below dead spot is gone but go figure it wont run for long like this. I don't wanna burn up this home-brew tci because all parts were bought new, not that it was much $50 but anyway, can i get the ignition module that goes along with these coils and wire that in or do i have to put in a crank trigger sensor and reluctor wheel?? to make that work with these coils. I guess i can put the coils on the shelf until the FI comes into play witch i hope will be this winter, I can put the stock coils on if i have to but i don't want to. I was looking for more fire in the hole to get this ole girl woke up a little, and as far as the heat sink I made one out of a piece of 1.5" copper tubing cut 8"long sliced down the center lengthwise and beat out with a hammer, then i drilled many,many holes in it to disperse the heat. Copper has a good exchange rate with heat so i figured it would work well as a heat sink.
So what should i do ditch the coils or get the ignition module that belongs with them and add the crank trigger??

[cywelchjr]

Check the resistance of the primary side of the coils. If it's 3 ohms then your ok, but if not, then you need a complete ignition system compatible with them or you WILL burn up the ignition system and/or the coils.

I don't know what other system you can use other than something like the megasquirt. So if the coils are low resistance, you need to do the whole conversion or stick with the stock coils or compatible coils (there are compatible coils that provide much hotter spark, probably at least as hot as the GM coils do with the their proper setup).