why do I need a ballast resistor?

[backyardbill]

Fiatistas:

The ballast resistor block was on the car when I bought it last year. It gets pretty hot.

http://www.glocktech.net/fiat/a.jpg

I see other Fiat spiders with electronic ignition like mine without it. Why so

Update: the coil is a D-511/D-512 as shown here:
http://cgi.ebay.com/ebaymotors/D511-D51 ... ccessories

Plus, I just recently realized that my tach is registering about 300 rpm more that my standalone Sunpro tach/dwell meter.

Thanks

[kmead]

Tachometers are notorious for reading high, its part of the means of ensuring we don't over rev too much.

The ballast resister is related to the type of coil you have. If you have a factory electronic ignition you don't have a ballast resister type coil.

A ballast resister may be needed if the coil has the wrong resistance. It would appear you have the correct coil (the ignition module is a GM part) so I doubt you need the ballast resister.

Seems like some good info here:

http://www.hot-spark.com/Coil.htm

[manoa matt]

Bill,

The ballast resistors are only needed on points style ignition systems, purpose is to keep the points from burning up to quickly. Ballast resistor is not needed for the electronic breakerless system.

Not sure on the specifications for that coil, however the electronic ignition coil has different primary and secondary resistances than the points coil.

This is the coil I'm running with my stock electronic ignition system, it has the same primary and secondary resistances as the original coil with a bit more output: http://www.summitracing.com/parts/ACC-8145/

Mark found the stock tachs run a bit high during their dyno day, from memory it was around 100rpm. Maybe Fiat intentionally set them high so owners would have a safe margin against over revving.

Testing primary and secondary resistances: http://www.international-auto.com/fiat- ... n-coil.cfm

[backyardbill]

I assume that I don not connect the ballast resistor when bench testing the coil.

This is what I get:
primary = 2.2 - 2.7 ohms
secondary = 7,230 ohms
the ballast resistor is 1.9 - 2.0 ohms

This is in spec according to the Fiat service manual, section 55, Page 55-1, for either the BES200A or the G-37-SU coils up to 1978. But is out of wack for the AE1200A which is the right one for the 1979 and on model year.

According to http://www.hot-spark.com/Coil.htm I should use the ballast resister because my primary in less than 3.2 ohms.

So, do you think I can run this D-511/D-512 (older type) coil without the resistor?????

[manoa matt]

Those primary and secondary readings indicate that coil is for a points style ignition (up to 78). Need to get a coil with the proper resistances to run the electronic setup(79 and later). Should be 0.7 ohms primary, and 10.8K ohms secondary.

Forget the hot spark link. That is a entirely different system( VW/Porsche aftermarket system)

[backyardbill]

Yeah. Thanks for the info. I am shoping for one right now.

Does that ACCEL 8145 - ACCEL SuperStock Ignition Coils fit in the original aluminum holder?

[manoa matt]

Bill,

Summit is an excellent site because they list the specifications for the coils unlike other sites. Once you find one with the correct readings you can cross reference the part numbers to other sites/vendors/stores to find a better deal. I think a MSD blaster 2 coil might work, maybe one of the pertronix too. I picked the Accel coil because it had the closest readings to stock specs and was cheap.

The accel coil is a tad slimmer in the waist. I re-made the holding strap from aluminum, but you could wrap it with string like your girlfriend did with your class ring.

[kmead]

snip

I re-made the holding strap from aluminum, but you could wrap it with string like your girlfriend did with your class ring.

That is pretty funny.

I included the link as it had information about ballast resisters and their use, not to suggest that

Odd that whoever did the changeover used their old (or a old) coil and its associated ballast resister.

[backyardbill]

Yep, the whole electrical system was screwed up. The wrong coil was just another chapter in unraveling a mess. But, I think it is under control now. This should be the last remaining issue. Thanks for the help.

[ga.spyder]

I am using that same Accel coil,except the chrome one(I am a blinger ).I cut a peice of old heater hose and split it,and wrapped the band that holds the coil.Fits tight,and you cant see it.

[backyardbill]

Good idea. I ordered the yellow coil from Summit Racing.

Another concern: My tach reads about 300 rpms high. Is it possible to add something like an inline resistor to correct this?

I will first recheck the error once I install the new Accel coil (and remove the ballast resistor).

[backyardbill]

Update for those interested:

I received and installed the new Accel 8145 coil. No external resistor. No capacitor. The Fiat started right up. Warmed it up. Set the timing to 12 degrees BTDC (I locked down the vacuum advance in the dizzy for now, because its broke). Bingo. It idles at 850-900 for the first time since I got the car running last year. Even the dash tachometer reads correct now.

[ga.spyder]

Glad to hear that did the trick!!